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Matching twist rate and bullet weight in rifles.

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The are many benefits to understanding and matching the twist rate of your barrel with the projectile weight you are using. Primarily, accuracy. This article is a high-level overview of the subject, and as such, a few concepts and terms are simplified. If you want a truly in-depth study of the subject – get Brian Litz’s series of books from Applied Ballistics. If you want functional information, read on.

Too fast a twist rate and the projectile can potentially damage the projectile jacket as the excessive force separates the jacket from the core. As we get faster and faster twist rates – this is becoming more of an issue. I personally know a few guys with 1:7.5 Creedmoors that are having the Hornady Match projectiles spinning their jackets off on them mid-air.

Twist rates and bullet weight are often MISUNDERstood, but there are some simple and practical guidelines.

But first, a little background.

TWIST RATE

You can read an expanded article on twist rate over here – but in summary, a twist rate is the number of times your rifling (the groove in your firearm barrel) makes a full revolution over a set distance – this is generally expressed in inches – so a “1 in 10” makes one revolution of rifling every ten inches of barrel length.

BULLET WEIGHT

Bullet weight has increased as we are reached out further and further with our rifles.

A heavier projectile (more grains) will often come with a better (higher BC) – that is, the ability of the projectile to buck wind – they fly truer, for longer.

bullet weight, Matching twist rate and bullet weight in rifles.

However, it’s not just as simple as putting the heaviest bullet you can down the barrel. More weight requires more powder to move – and speed is still a priority as a slow-moving bullet spends more time in the air, has more time to be affected by the wind, and in the understanding that everything drops at the same speed (thanks, gravity!) the faster it moves, the further it can reach with less ballistic drop.

MATCHING TWIST RATES AND BULLET WEIGHT

So, in very simple terms, the heavier the projectile (it is actually a function of bullet length and sectional density, but we are simplifying things here), the faster (lower number) twist rate you are likely to want to utilise.

I know, I know, just tell us already – what do I put in my rifle?

Well – here is a very basic chart that will set you off on the right foot. Like all things reloading, there are always exceptions.

Twist RateProjectile Weight
.224 / 5.56 (your .223 Ar)
1:16Up to 55 grains, 4300 fps or more
1:15Up to 55 grains, 4100 to 4300 fps
1:14Up to 55 grains, less than 4100 fps
1:1255-63 grains
1:963-70 grains
1:870 grains or more
6.5mm
1:9Up to 130 grains
1:8130 grains or more
.308
1:15up to 150 grains
1:14150 to 168 grains
1:12168 to 170 grains
1:10170 to 220 grains
1:8220 grains or more

This is just a quick list to give you an idea.

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OVERSTABILISING THE ELD-M PROJECTILE.

I recently have had a good mate who has been destroying ELD-M’s with abondon.

It’s a 1:7.5 Twist, chambered for 6.5 PRC and he is getting projectiles disintegrating mid-flight. Too be fair – he is running right at the ragged edge of velocity/pressure/speed and the resulting twist these things are undergoing – but – it’s not super crazy what he is doing.

If you have a projectile that just seems to be going a little crazy – or – even missing rounds on target – it might be worth considering if we have managed to out twist some of the options on the market.

Delta Stryker 4.5-30×56 first thoughts.

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I was sent up one of the Delta Strykers for a review/overview/play. Initial thoughts and a couple of comments.

It’s a very nice scope – and going to be hard to beat for the price. Is it truly top tier though?

First Thoughts – Sabre Tactical Ammo Wallet

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I have gone through all manner of ammo carry methods – MTM Boxes, TACPac Cases, differing wallets of folders – so when one of the Sabre Tactical Ammo Wallets turned up with a clients rifle – I was keen to check it out.

I have met Carl (the owner) a couple of times at shooting competitions now, and he has become an active part of the community (probably more than me at this point!) – with a background in military shooter work (combat shooting team and sniper instructor) he is obviously well qualified to be putting out shooter equipment.

The ammo wallet is a solidly built, well thought out method for carrying either 40 rounds of short action ammo or 20 rounds of long action ammo (depending on the wallet you get). The one that turned up had 6.5 Creedmoor in it – but it’s clear it’s going to fit the vast majority of cartridges.

It is what I would call semi-rigid – it’s going to hold its shape well, but still soft-touch enough that it’s not going to clank around in your bag. Realistically, for a competition – you are going to be carrying two, if not potentially three of these in a pack – so it could get a little bulky – but being most of us are carrying around a backpack, not too much of an issue.

A simple magnetic clasp holds the folder shut when closed, which, in my brief play with the wallet, worked well.

The one thing I personally would change, is the insert – to me, having my reloading information in the field is fairly pointless – when I am on the line, the charge weight or the amount of times I have reloaded the brass is useless to me.

So. Here is my version! Print it out, trim to lines and I personally would then laminate it to serve double duty as an insert of general data/reference card.

The gun got a paint job!

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Black guns are boring. I knew, even before getting it, that I wanted to give the KRG Whiskey-3 chassis a paint job at some point. After watching a phenomenal video from Caylen @ Modern Day Sniper many moons ago, I had the methodology in mind, and started putting together the components I needed to do the job.

The paint was easy enough. You essentially need matt or satin (or gloss, up to you) paint that is suitable for metal and plastic. The Rust-Oleum was freely available from the local Bunnings, so I grabbed a couple of cans.

I have long had a wallpaper on my computer desktop from Altus Shooting Supplies which features a bit of red in it – this is my competition rifle – so it didn’t need to be in ‘full camo’ – I wanted something a little different.

As per the above video – I wanted to use the sponge method – do you think I could find any though! For a couple of months I have been checking out hardware and craft stores – and in the end, ordered them online and waited for them to come in. Apparently, talking to a few people, the raw sponge has been a little hard to come by recently. Blame COVID!

Prep Work

After pulling the scope off the rifle, I took the action out of the chassis and removed anything I didn’t want painted from the rifle – in my case – this was basically the buttstock and cheek riser pads. I gave the whole rig a clean down with some carb cleaner (any degreaser would work). As I skipped the base spray, I didn’t need to mask anything off. I was going to hand apply all the paint, so just avoided anywhere I didn’t want it to go.

I liked the idea of some of the paint over the steel barrel – rather than laying down a coat of black first. Again – up to you.

Painting

I grabbed some card to work as a bit of a pallet (actually target board) and sprayed the paint onto the board, before loading up the sponges and setting to work.

I would suggest starting with the lightest colour first, then working through to the darkest. You can always (as I did) add more paint on top of the lower coasts – so start sparingly, paint a bit, step back, observe, paint a bit more and so on. I think this really is a case of less is more – though it totally depends on the look you are after.

In the video Caylens finishes off the job with a matt overcoat. To be blunt, I also like the worn look – so don’t mind if the paint gets a rough time.

Results!

I am certainly happy with the results. The gun still smells a little of the paint solvents – but I am sure that will dissipate fairly quickly – and it’s not really a concern for a comp gun anyhow. The paint also feels a little tacky on the grip – so will be interesting to see if that disappears as it cures over a couple of days.

Regardless, the gun turned out how I hoped it would, so it was simply a case of reassembly everything and taking out to shoot.

I am sad to say the paint job didn’t improve the tripod shooting! 😉

MOA – Minute of Angle & MilRAD

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A minute of arc (MOA)1, arcminute, or minute arc, is a unit of angular measurement equal to 1/60 of one degree.

MOA – Minute of Angle

In shooting circles, Minute of Angle, or MOA represents approximately one inch at 100 yards.2

Many modern rifle scopes are set up to adjust in half or quarter MOA increments, also know as ‘clicks’. Therefore, if you know the distance of the target (100 yards) and your point of impact is 3″ high and 1.5″ of where you intended the shot to go, then you need to adjust your scope 3 MOA down, and 1.5 MOA right. This makes adjustments on the scope easy, enabling you to dial quickly in the scope to your intended point of impact.

It is worth noting; that scopes can be calibrated in true MOA, or in Shooters MOA (SMOA) – which is a true 1 inch at 100 yards. While this may not make a whole lot of difference at shorter ranges – at longer ranges the difference compounds – if adjusting over 20 MOA, this could add up to over an inch difference. Significant if you are looking for a first shot hit.

Firearm accuracy

MilRAD or MOA?

Manufacturers will often express the accuracy of their firearm in MOA. For example, a 1 MOA rifle should be capable, under ideal conditions, of shooting on average, 1-inch groups at 100 yards. This discounts shooter error – and often also defines a particular ammunition that needs to be used. It also often only refers to a group of 3 to 5 shots. It is often suggested that larger groups should be utilised to measure this. Many modern rifles are capable of ‘sub-moa grouping’ – it has become the defacto standard for marketing a precision rifle.

But we live in a metric world

True. Though many people have adapted to the MOA standard, another system, the MilRad lives in the metric world. A MilRad is equal to one 1000th of the target range. This is laid out in a circle around the shooters position, with the target range as the radius. Which means, 2 x π x 1000. Therefore 1 MOA = 0.2908 MilRad. Adjusting one Milrad up at 100 metres will result in an offset of 100 mm. The markings on a reticle that mark MilRads are called MilDots. Such a reticle is called a MilDot Reticle.

Mixed systems

What is most important is that no matter what system you decide to use is ensuring that the reticle measurements (if it has them) and your turret adjustments are the same. For example, if your reticle gives measurements in MOA, don’t get turrets with MilRad adjustments. You are just asking for confusion. If you are mathematically inclined, go for it – but converting from imperial to metric while estimating wind and range and hoping the animal doesn’t wander off could be a bit much. Why a manufacturer even allows you to purchase them this way I am not sure. But it is possible, so pay attention when buying.

MOA Reticles

What system should I use?

Depends. While MOA inherently has finer adjustments what MilRAD it makes sense to stick with what system you are already familiar with. I.e. if you were to estimate a distance to an object, would it be in metres or feet? What do your shooting buddies already shoot? It might make sense to keep it the same so you can easily communicate back and forth. Already own a rangefinder? What is it set up to return information in? By keeping the system the same you reduce the amount of conversion you have to do.


  1. known as minute of angle in shooting circles 

  2. it’s 1.047 inches, but screw that for calculating in your head 

WEZ, Error Budget and you – or, will it hit at one kilometer?

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A comment from a home-kill butcher/taxidermist I was having a chat too recently brought it home – he estimated that over 50% of the animals that were being brought into him to deal with had been shot in the rear half.

I would be interested to correlate this observation with distance shot at, but regardless, it would indicate that there is a lot of folks out there taking shots they shouldn’t be.

Often, I have folks purchasing rifle systems with the intent of stretching out their ‘effective hunting range’ – and I always make sure to have a decent conversation with them about expectation, reality, and ethics when it comes to long range hunting. I have seen animals wounded, badly, in situations where it simply shouldn’t have happened, by people that should have known better.

Wouldn’t it be useful to have a piece of software that would give us an impartial measure of our ability to shoot to distance? Well, it exists, in a couple of forms actually, and the results can often be sobering to both experienced and new shooters. This software is employed by a lot of folks already (i.e. military and police) as a method of impartially evaluating weapon systems and their deployment in situations where it’s important to be able to understand the big picture, before taking the shot.

At the moment I have two pieces of software that can be used to create a profile of hit probability, Applied Ballistics and Coldbore. This article is just a bit of an introduction to the systems and some of the concepts within, over the next couple of articles we are going to look into some specific factors that affect your hit probability, as well as run some specific examples to illustrate the point.

Allied Ballistics and WEZ

Some of you may already be familiar with Applied Ballistic (I would hope). Brian Litz and crew have been working hard to make calculating ballistic solutions more accurate, faster and easier for many, many, years and currently spearhead the developments in the ELR1 world as well.

Part of the Applied Ballistics Desktop suite is something called WEZ, Weapon Employment Zone Analysis.

This number crunching bit of software allows you to combine all the factors that can affect our probability of hit and targets of defined size and distance.

WEZ is somewhat the standard when it comes to understanding Probabilty of Hit in many military and LE applications.

Coldbore and Error Budget

The second piece of software I use, and my personal choice, is Coldbore.

Coldbore is the ‘old school’ of ballistic calculators – not as well known, potentially more powerful (in ways) and has a lot more inputs and control over the variables you can enter and test.

Coldbore is what I use to generate the data for the range cards I create for clients, as well as test out plenty of ‘what if’ scenarios.

Creating a shooting environment

What both of these systems hinge around, is entering in the firearm system data – ballistic coefficient, muzzle velocity, system accuracy, as well as the environmental data – wind, range, air pressure, and then adding in variables.

The reality is, we don’t shoot in a vacuum. We shoot in the real world, where not everything can be controlled or often, measured to the theoretic levels of accuracy that our ballistics software can calculate to. Hell, this is assuming that you are using a ballistics calculator in the first place!

It’s these variables that create the hit (or miss probability), that go way beyond the concept of your ‘one moa’ gun at 100 meters is a ‘one moa’ gun at 1000.

Sorry to break it to you, but things don’t work like that, at all.

Arguing with the Math

People like to assume things are linear. If I shoot a certain group size on paper at the range, the gun must just shoot the same, at any distance out until the projectile runs out of steam.

However, most of those people would also admit that wind blows a bullet around, most could also observe that estimating wind can be a bit of ‘a black art’ and, most would also understand that the wind isn’t a constant, as it increases and decreases constantly.

Now, also understand, that the velocity of the projectile isn’t a constant and varies from shot to shot.

Understand that the B.C. of your projectile also varies from shot to shot.

Rangefinders have variance in them.

So do Kestrels (at best) or your estimations of temperature, humidity and air pressure.

Was your scope mounted at exactly 5cm above bore, or was is closer to 4.8cm?

Cant. Slope. Azmuith.

All these factors (many, admittedly in tiny, tiny amounts) all add up to a variance in shot to shot.

Some of these, like range, and wind, to a certain extent, can be minimised in variance after the first shot, but for that first trigger pull, there is a lot more going on within the ‘system’ what just the size of the hole in the paper when you zeroed your rifle.

The further you go stretch out, the more effect these system and environmental factors play into your result.

No matter what you do, you will miss

You can’t deny physics. So, it’s important to understand, that at certain distances, no matter what you do, whether you nail the fundamentals, break that shot perfectly, follow through like a pro, you may still miss due to the firearm systems (this includes the environment) inherent error at distance.

Ever been shooting in a field shoot at a target and the rounds just seem to slip by the left, then the right, then the right, then a hit, then left and so on? That is what we are talking about, and that is what we are looking to quantify and understand, and potentially, just potentially, work to mitigate a bit.


  1. extreme long range 

Rusty from Impact Dynamics

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I have seriously enjoyed watching Rusty and his many projects grow and grow. From the Podcast to the huge amount of video content to the PRS Competitions – Rusty has been working his arse off growing the Precision Shooting community in Australia.

We have spoken before, and popped up on each others shows once or twice – so I thought it would be a good idea to catch up to discuss how shooting in Australia (and NZ) has been growing over the last year.

High Ground Gear HG-831 Modular Pack

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A quick intro to the High Ground Gear HG-831.

High Ground Gear are an American Company, based in Philadelphia, and they have a simple, but a very effective philosophy – reduce the amounts of steps required to achieve a task – that is, maximum efficiency for minimum effort. You have to love that as a concept.

Constant System Improvement

Those who have already read up my reviews on the Mystery Ranch Mountain Ruck and Crew Cab will know I have a thing for heavy duty modular pack systems. Certainly, the Crew Cab is awesome in that I can use it as a load hauler, then drop off the load cells and fold it up into a daypack. However, if I want to continue to carry the SLR Camera system, I need to also carry the Nice Frame – as the Hazard 4 SLR Pouches are mounted onto the hip belt. I wanted another layer of modularity. Enter the High Ground Gear HG-831.

I think I originally stumbled upon the HG-831 through Soldier Systems and their feature on the HG-830 System. The HG-831 is a combination of the HG-830 Modular Pack and the HG3D 3 Day Pack. I was originally looking at just the 830, but the addition of the 3 Day Pack saved me building something similar out of 3rd party packs anyhow.

Check out the links above to get a quick idea of what the basic kit comprises of – all the photo’s below include additional pouches I have added – I figure showing it off in context is going to make a bit more sense of my use.

The HG-831 synched in tight. It can go smaller, as in photo there is still a pile of gear underneath the pack (like a tripod).

Usage – Hunting and Photography

hg-831-1-of-180

First off – I am not military, never have been and likely now never will be. So my use is going to be a little different to what they original designers may have intended. From reading on the website, it sounds like High Ground works a lot with JTAC – those guys who get to carry around a massive amount of firepower in the ability to communicate with air and artillery assets, i.e. Radio Operators. As a result – common to most of HGG’s packs are aerial slots and cable routing systems. Not something I am likely to use, however, the modularity that is required from mission to mission is something I do intend to utilise a lot.

The pack has two main uses for me – Shooting (rifle) and Photography. Both usages assuming I am going to be out in the bush for 1 to 3 days as well – so apart from the camera gear / rifle I am going to need to carry sustainment gear – shelter, sleep systems and food.

The HG-831 Stretched Out. You could also another additional pouch onto the PALS webbing on the outside. At that point, though, I would probably be going for a heavier pack system again.

The 3 Day Pack

There is a hell of a lot going on with the High Ground Gear HG-831, so I will start from the top and work my way down. First – the pack itself. The main section has a zip top and bottom – so you can get in through the top, but still access the bottom of the load if you want to without having to empty out everything else.

The main section has dual aerial ports at the top,  again, not something I am likely to use – but for the intended military market – indispensable. HGG call the pack 2500 cubic inches. I live in a metric land – so that equates to just over 40 litres. Though, as always, the only way you can tell how much you are going to get into it is to load it up. In my case – I am easily able to get a couple of days worth of gear into it. That’s before I even think about the external pockets. Of which it has plenty.

External Pockets

The top pocket has enough space to carry all those things you like to access regularly during the day. All the zips are high quality and feature a material flap to help keep to water out. This pocket is – just – big enough to fit an iPad without a cover into. It’s a squeeze – but that gives you an idea of size.

The second external pocket is mounted onto a compression panel that also provides a great place to keep the rain jacket nice and handy. On top of the panel is a pile of PALS webbing – just incase you need to put some more storage on there.

The compression panel will open up quite a bit – not enough to stash a helmet into though. On each side of the pack are mesh sleeves – ideal for water bottles, gloves and other quick access items. With a bit of contortion, you can get to them while wearing the pack – but it’s a bit of a stretch and I wouldn’t want to try it while wearing heavy clothing or say, body armour.

Finally, the bottom of the pack contains a small pouch that holds a rain cover – double sided – one side to match the pack the other in blaze orange. As I plan on using this pack hunting, being able to quickly pull out a large panel of blaze is appealing to me. You don’t always want to remain unseen in the bush! Also, even though the pack is water resistant, and anything important will always be packed in a dry-bag – keeping the rest of the pack as dry as possible means you don’t end up carrying about dead weight in the form of water.

The whole of the High Ground Gear HG-831 has a ring of webbing around it – making lashing additional external items easy – think walking/tent poles, sleep systems of even a meat bag. The bottom of the pack has strapping to lock in a sleeping pad if you wish, though I think I will be keeping everything in the pack itself – a shooting mat maybe? The are plenty of compression straps to lock the pack down tight onto the frame. Each strap has a neat little velcro loop on it that makes shortening and tidying up excess strap easy.

A piggybacking pack – the frame

The pack itself has no frame – it is designed to clip onto what is essentially the 830 Frame.

The frame is what I guess you could call and ‘external frame’ – that is, the suspension and strap system is separate from the pack itself – much like the Mystery Ranch NICE frame. The straps and frame on the whole aren’t as heavily built as the NICE – but then, it’s also not designed to carry as much. What is unique about HGG’s offering though – is that once the daypack is removed – you essentially have a blank slate in the form of rows of PALS webbing, that you can then attach your selection of MOLLE gear to. Depending on what you are using the pack for, this could be a rifle scabbard, tripod, breacher tools – HGG even do pouches to hold the Carl Gustav Rounds. In my case – this is currently set up with an Eberlestock  Saddle Bag and two of HGG’s breacher tool holders – which also work as excellent tripod holders.

On the inside of the frame is a pouch for a three-litre hydration bottle and the shoulder straps feature zipped channels that are ideal for routing hydration tubes and in the case of radio operators, cabling down. Its a simple and neat system that works well.

The frame itself has a slight curve to it – designed so the pack fits over a military users body armour. Also, foam padding on each side locks the pack over armour and into the pack – Additionally, they serve to lift the pack away from the back – providing a bit of airflow.

I am experimenting with using the pack both with and without the padding – I am not wearing body armour while tramping, so may not need them. I will report back later with my eventual preference.

A sturdy handle sits on top of the frame – which also nicely tucks out of the way when not in use.

The waist belt features a ‘pull forward to tighten’ system – much easier to use than the traditional system, and the additional clips on the outside of those? Well – those are another of the pack’s unique aspects. Unclip both of those, pull the backpack from the rear, and the whole backpack comes off – leaving you with just the waistbelt on you – a battle belt, essentially.

More tricks up its sleeves

The High Ground Gear HG-831 backpack has two long stiff sections that slide up into sleeves on the belt – effectively transferring the weight of the pack to the belt itself. The beauty of this system is the fact that you can remove it very quickly, and still have any pouches that you have attached to the waist belt on your hip. In my case  – this is my camera gear. I now have just the essentials with me – and I can leave the pack at camp. I want to take a tripod and some extra gear with me? Easy – pop off the pack and I have my second layer of organisation ready to go.

High Ground Gear also offer a separate assault strap for the High Ground Gear HG-831 – this is essentially another row of PALS webbing that can be clipped to the belt – giving your more mounting points on in the small of your back. I currently have their horizontal compression pouch on there – but options are limitless.

Systems

hg-831-10-of-18

As I mentioned earlier – I intend on using this pack for two main ‘systems’ – a backcountry camera (SLR) system and a rifle system. This pack gives me the ability to walk some distance in, set up camp, drop my first layer (sustainment), head out the next day (daypack), then drop the pack when I am in locale or dropping down to take a shot. At all times, I can keep my essentials on me. It’s fantastic.

It is important when looking at a system like this, that you have some form of plan in mind. This isn’t the sort of pack you just pick up and use. You are going to need to think about it’s implementation, which to be fair, you should be doing when it comes to your equipment anyhow.

At this time, this is the only system I know like this. High Ground Gear have come up with a unique and awesome system that I am going to have lots of fun developing system off. I plan on a couple of follow up articles as a further refine mine.

OCW Testing take 2: OnTarget TDS

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After my previous testing out at the range, trying to determine OCW, I reloaded another set of rounds headed out to the range to shoot them off then came back and collated the information in OnTarget TDS.

OnTarget TDS

OnTarget Target Data System (TDS) is an extremely useful piece of software produced by Jeffrey Block. It is essentially the up-speced version of his OnTarget software, adding automatic target recognition, multiple target overlaying, OCW measuring and several other features.

I had been using his OnTarget software for a while – scanning in my targets and using the program to calculate things like MOA. It has also become a really nice way of cataloguing my shoots. I simply scan it in, identify my POA and shot holes, and can also note down things like load, conditions and other factors. Saving it as either it’s native format, PDF or JPG, I now have a digital record of all my targets – no need to store and retrieve the paper later.

Collating Data

Where TDS nicely steps up, is that it enables to to load in multiple targets and overlay them on one screen. The individual group information is still available, but it also lets you get an overview of a days shooting. For example – in the target below, we have a combination of 27 rounds, shot at multiple targets with no adjustments made on the scope.

TgtGfx

While some people would zero a scope of a 3 group shot, I now have data for a 27 round group that I can base my adjustment off. The reality is I wouldn’t for this particular example – as there is a variation in load going on (it’s my OCW test) – but once I have settled on a load – keeping this data means I can build up a true profile of the randomness inherant in what happens when you pull a trigger. In the end, it is going to be much closer to a true zero than firing of 3 shots and then adjusting.

TargetCombined

Automagically entering targets

If I wanted to, I could print off the internal targets and then scan them into the system and the software would identify and record all the shots for me. However, to do this, you need to be using one target per shot. You can print targets with multiple targets on it, and then cycle through the page, and while this is the plan eventually, but I will be honest when I say that I don’t have the personal accuracy right at this moment to pull that off. Soon though. Soon.

In the meantime, it doesn’t take me too much longer to enter them in. I also personally like the idea of printing off the targets in A3 size – which you can’t do within the program at the moment.

OCW Analysis

Another feature of the software, once you have loaded in a round robin of groups, is that the software will chart the OCW patterns for you – I use the example on his site because it is a lot clearer than mine –

TDS_Data4

If you understand OCW as a concept, then you can also see how this makes it a lot easier to identify where you want to be continuing to develop you loads. In my case I will happily admit its more my shooting that is causing the spread. However, it did have a very interesting result. According to the software, my smallest ADC or shift in POI between strings is also right where the group closed up. Now, this isn’t remotely how OCW is designed to work. It’s either fluke or coincidence. However, it’s also where I am planning on basing my nest set of loads around. I am actually going to pick a mid point on powder weight, then start playing with OCL to see what happens.

Of men and rests

I have also decided I really need to replace the bulls bag. While it is a great solid rest, it is also too low, and while I could drag along a big slab of granite to lift it up, I figure I might as well just get something like a Caldwell Rock BR and be done with it.

Shooting Units: Twist rates and your barrel

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A preface to twist: rifling

Before we talk too much about twist rates, we also need to talk about rifling – the mechanism that creates the twist.

Rifling refers to the groove in a barrel of a firearm which causes the bullet to spin as it leaves the firearm. Spin creates a gyroscopic force which in turn stabilises the projectile while in the air – it’s similar to the concept behind spinning a wheel and holding it by its axis – it naturally want’s to return to an up and down alignment – the spin is creating its own stability.

Twist – imperial strikes again!

Twist rate is the distance the rifling takes to complete one full revolution – expressed in inches – i.e. 1 in 10, 1 turn in 10 inches. Shorter is faster and imparts a faster spin rate.

Bigger Bullets, more spin required

Generally, the bigger (longer, which means heavier) the projectile, the more spin it is going to require to stabilise it. A 168 grain projectile is going to need a much short twist rate than a 60 grain.

When it comes to design considerations, manufacturers will often match a barrel and caliber so that the twist rate is going to be suitable to stabilise the majority of projectiles the owner is likely to want to shot through it.

To little twist rate and the bullet can start to tumble mid flight – the results in keyholing targets – where the bullet cuts rectangular shaped holes in the paper. Accuracy also goes out the window. Too high and you can start damaging the barrel and potentially cause the projectile to basically self destruct mid flight as the jacket starts to spin apart.

Bullets Twist 224

Did you know your bullet is actually bigger than your barrel?

It’s an interesting thought. When we pull the trigger, pressure quickly builds and results in the projectile heading at high speed down the throat towards the rifling. At this point it will have expanded slightly from the pressure and enters the rifling. The projectile now gets ‘engraved’ by the rifling – beginning the spin.

This is why some firearms have freebore – freebore helps keep the pressures low by having the gas expand before the projectile engraves. However, minimising this freebore can mean more accuracy – it reduces the potential for the projectile to distort before entering the rifling.

Getting the right twist rate

For most off the shelf rifles – twist rate is going to be already matched to common projectiles by the manufacturer. However, if you have a specific use in mind, which can lead to a specific bullet weight, then it won’t hurt to also check that the twist rate is going to be optimal.

These days there are plenty of online calculators (such as here) – the formula used is called The Greenhill Formula.

T=150(d/r), where T is the twist rate, d is the bullet diameter, and r is the bullet length to diameter ratio (bullet length divided by its diameter). For cartridges with a muzzle velocity of more than 2,800 fps, substitute 180 for 150.

Let’s use a common example – .308 168 grain Sierra Matchkings. That’s .308 diameter and 1.210 long. 3.929 ratio.

T =150 x (.308/3.929) = 150 x 0.078 =11.76

That’s an ideal twist rate of 1:11.76 – close to 1:12 – a common twist rate for .308 rifles.

That’s a match for my new Rem700 Varmint in .308 – also why I am going to start my reloads based on a 168 Sierra Projectile. It also means I likely won’t have much luck going any heavier in projectiles.

Common twist rates by calibre

.17 HMR = 1 in 9″
.22 Long Rifle = 1 in 16″
.222 Remington = 1 in 14″
.223 Remington = 1 in 12″
.22-250 Remington = 1 in 14″
.243 Winchester = 1 in 10″
6mm Remington = 1 in 9″
.240 Wby. Mag. = 1 in 10″
.25-06 Remington = 1 in 10″
.257 Wby. Mag. = 1 in 10″
6.5×55 Swedish Mauser = 1 in 7.5″
.260 Remington = 1 in 9″
.264 Win. Mag. = 1 in 9″
.270 Winchester = 1 in 10″
.270 WSM = 1 in 10″
.270 Wby. Mag. = 1 in 10″
7×57 Mauser = 1 in 9″
7mm-08 Remington = 1 in 9.25″
.280 Remington = 1 in 9.25″
7mm WSM = 1 in 9.5″
7mm Rem. Mag. = 1 in 9.25″
7mm Wby. Mag. = 1 in 10″
.30 Carbine = 1 in 16″
.30-30 Winchester = 1 in 12″
.308 Winchester = 1 in 12″
.30-06 Springfield = 1 in 10″
.300 WSM = 1 in 10″
.300 Win. Mag. = 1 in 10″
.300 Wby. Mag. = 1 in 10″
7.62×39 Soviet = 1 in 10″ (Ruger)
.303 British = 1 in 10″
.32 Win. Spec. = 1 in 16″
8×57 JS Mauser = 1 in 9.25″
.338 Win. Mag. = 1 in 10″
.340 Wby. Mag. = 1 in 10″
.357 Mag. = 1 in 16″
.35 Remington = 1 in 16″
.35 Whelen = 1 in 16″
.350 Rem. Mag. = 1 in 16″
.375 H&H Mag. = 1 in 12″
.378 Wby. Mag. = 1 in 12″
.416 Rem. Mag. = 1 in 14″
.416 Wby. Mag. = 1 in 14″
.44 Rem. Mag. = 1 in 20″
.444 Marlin = 1 in 20″
.45-70 Govt. (Marlin and Ruger rifles) = 1 in 20″
.450 Marlin = 1 in 20″
.458 Win. Mag. = 1 in 14″
.460 Wby. Mag. = 1 in 16″