We chose the excellent 168 grain TAP rounds from Hornady.
First test was to try the difference between standard factory supersonic ammunition. We compared to the original Accuracy International barrel in 308 that was a 1-in 12 twist and 24 in long to the new fast twist 16. So testing the rifle, we started with factory supersonic rounds just to check all was well and it worked with these as a benchmark. We have also designed the barrel so that we can put an integrated suppressor on it in the future, hence the shoulder at the back.
As we were building this primarily as a subsonic barrel, we saw no reason in having a longer barrel than necessary as we are not looking for extra velocity. The second consideration is length, and we went for a 16-inch barrel. This allows us to stabilize any bullet up to about 250g and will easily stabilize the current factory subsonic expanding bullets which are either 190 to 220 grains. So rather than try and use a factory rifle I thought we would attempt to make the perfect 308 barrel for the 1996 Accuracy International we have.Ĭlearly the primary consideration is twist rate, and we went for a 1-in 8. This sees most existing factory 308 with a 1-in 12 or 1 in 13 unable or struggling to stabilize these bullets. But this means great news for 308 owners, or does it?īoth Hornady, Nosler and Federal make some superb 308 bullets designed for expansion at subsonic velocities however both really need a twist rate of better than 1 in 11. This is primarily due to the 300 blackout. Now, however, bullet manufacturers are making some subsonic bullets that are designed to expand at subsonic velocity. They work well but do not expand at these velocities. Remember we cannot get extra energy from velocity as we are always just below the speed of sound, so velocity remains constant. Its extra weight helped with energy as well. 308 220 gr InterLock® RN from Hornady perfect. So in the early days of experimenting, I found the. The ideal shap for stabilising would be a flat topped and bottom cylinder, the worst shape to stabilise would be a pointy bullet with a boat tail. To get a bullet to stabilise where the twist rate is marginal, like a 1:12 308 barrel shooting subs, you can overcome it with the shortest fattest bullet you can find. Infact with the Lapua Subsonic bullets I would have done well to hit a barn. But one of those things I’ve never succeeded very well with is getting subsonic rounds to hit the target with any accuracy. The 308 is one of those rounds that just does so many things. The 308 and it’s use with subsonic and supersonic ammunition utilising a faster twist barrel.
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