Workshop Cut and Shunt
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- Last updated: 24/04/2017
Primarily, people who fit a sound moderator to their rifles want to know how much barrel they can remove before the velocity is impaired. It also has legal implications for minimum velocities and energy figures for deer control, so it can be a costly mistake if done wrong.
It’s fine working it out on a ballistics program but there is nothing like using real barrels and bullets, to actually see what happens in real time. Some calibres, such as the .308, can have their barrels reduced a lot, as they are efficient performers, I use a 14.5 inch RPA barrel and it’s still deer legal. However, the smaller calibres, especially the faster shooting ones, can be less tolerant to barrel reductions and the .243 Win is one such case!
So to stay legal, I wanted to test a variety of factory ammo and reloads in a standard length .243 and then reduce the barrel one inch at a time. You might recall I did this with a 308 in the January 2017 issue and it proved very interesting.
The test rifle was a Tikka M55 Biathlon model with a 24” barrel from end of chamber to muzzle exactly. I shot 5-shots of each of the differing bullet weights at this length and then at subsequent reductions. I took an inch off at a time with a hacksaw and then to ensure the muzzle has no burrs, a carbide cutter is used to give it a re-crown. I used a Chrony F1 chronograph to measure velocities at sea level, 20° centigrade. Accuracy is of no concern for this test and would alter depending on your own rifle any way, so it’s just to show velocity loss and its consequences.
The 243 can be used not only for deer but also as a hard-hitting vermin/fox tool and so a varied range of bullet weights can be used. Lightweight 55-grain projectiles speed along at 3750 fps, whilst 70-80 grainers are dual-role fox and deer bullets, dependent on internal construction. Whilst 90-100 grainers are more commonly used for deer. Each perform better or worse given the rifling twist rate used. Light bullets work with older 1 in 12” twist barrels, whilst the heavier ones seem best in 1 in 8 to 1 in 10”.
Each weight is also more efficient at differing barrel lengths, this is important if you do not reload, as you have no way of changing the load as a reloader can, to compensate for barrel length reduction. Whereas a reloader can use a lighter bullet and a faster powder in a shorter barrel a factory load 100- grain user will be stuck with it. That’s why it’s important to see what barrel reduction actually does to differing bullet weights. I have tested many 20”, factory .243 Win rifles and come away with raised eyebrows!
Results for differing weight bullets Factory versus reloads: I used factory loads, as well as some reloads, to show how you can compensate for some velocity loss by reloading with differing powders and weights. I have also included a predicted table from Quickload ballistics program to see how accurate it was. In factory ammo I used Winchester’s 55-grain Supreme and 80-grain Soft Point and Federal, 100-grain Power Shok to reflect the broad range of .243 Win usage and weight options. Table 1 is factory load, Table 2 Reloads and Table 3 predicted results using Quickload
A lot of figures I grant you but very interesting none the less. Firstly, for vermin and fox control, there is no legal energy (ft/ lbs) requirement as there is with deer, so from a deer-legal point of view it’s two fold. The magic figures to remember for England and Wales are 1700 ft/lbs for large deer and just 1000 ft/lbs for small deer. In Scotland it’s 1750 ft/lbs and 2450 fps minimum and 100-grain bullet for larger species deer.
Looking at the factory loads, you can see that the 55-grain is the fastest but does no reach even 1700 ft/lbs but then again it’s a varmint bullet and not suitable for deer any way. It has a total loss of -440 fps from 24 to 16” but even at 16” it has enough energy for any fox and makes an effective short rifle. The 80-grain factory was much more like it, 1943 ft/lbs at 24” and only dipped below the 1700 ft/lbs energy level at 18” length. Total velocity loss was -396 fps.
However, 100-grains is Scotland’s minimum weight for larger species deer, so at 22” I was under at 1658 ft/lbs, which makes you think. Similar to the 55-grainer, it lost a total of -442 fps
Switching to reloads should help boost velocity/energy by tailoring the recipe to match the shortening barrel length. Now the 55-grain bullet with a load of 48-grains of RL7 powder gave a healthy 1827 ft/lbs and if you were to use it in England on deer, not recommended, as it would drop below the 1700 ft/lb mark at 20”.
Again, the 80-grain bullet with 49-grains of RL19 proved very efficient with 1968ft/ lbs energy and only dropped below the 1700 ft/lbs mark at 18”, 1672 ft/lbs in fact. After that, it plummeted like the other weight bullets. The 100-grain bullet with 43.5-grains of H 4350 shot a good 1926 ft/lbs and now drops below the 1750 ft/ lbs at 21”, with a total loss of 486 fps.
To me, the 80-grain bullet weight suits the .243 Winchester cartridge well. Giving a blend of good velocity/energy retention and efficient ballistics at shorter barrel lengths. I would not personally go below 20” on a .243 rifle and watch those heavier 100-grain bullets because they struggle to stay deer-legal at reduced barrel lengths.
It’s interesting that the Computer ballistics program Quickload accurately predicted the velocity loss and is therefore a great aid and reliable. What you must remember though is that these results are for this .243 barrel and older or newer, cleaner or differing twist rates and rifling grooves can all affect the velocity. From experience, I have had as much as 100-200 fps difference with the same load but in differing barrels. But what this hopefully does is give you an idea of how far you can shorten a .243 barrel for sound moderator fitment. If you do not fit a sound moderator and just want a short rifle, then even with the reloads there is a lot of muzzle blast when you get below a 20”, so be warned.
Also, the newer Hornady Superformance ammunition, particularly the 75-grain SST is pretty hot and so shopping around for decent factory ammunition can help maximise your short factory rifle if you do not reload. A good 75-80 grain bullet weight would seem ideal to me and cut a barrel to 20” with those 4” saved exchange that length for a sound moderator, so you get a quieter rifle but without increasing the overall length! But like I said, be careful, as individual examples will likely produce slightly different results!
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