Re: 1 in 7 twist 3 groove 7mm barrel no issues
I had to rebarrel 16, 7mm Allen Magnum rifles on my dime for just this reason. They were the original batch of rifles designed to shoot the 200 gr ULD RBBT wildcat bullets.
Every one of them shot amazingly well until they hit from 200-300 rounds down the barrel. Then it was like a switch was flipped and the rifles went from 1/4 to 1/3 moa rifles to having 50 to 100% of the bullets coming apart in flight.
That said, these were being loaded to a velocity of 3200-3350 fps with the 200 gr ULD RBBT bullets. After this occured, nearly every rifle still shot very well the 160 gr Accubond bullets loaded from 3400-3550 fps.
Obviously this is higher velocity levels then you will be dealing with so that may help you dramatically.
Also, I have found that the 180 gr Berger will take slightly more abuse then the 200 gr ULD RBBT. The reason is because the 200 gr bullets were made on 30 cal J-4 jackets that were reduced in diameter to work with the 7mm bore size. This certainly work hardened the jacket and this may also be the reason for the bullet failures once the barrels got 200-300 rounds down the barrel.
I will say that in my testing, the Berger 180 gr VLDs shot very well in most of these barrels as long as they were shot at velocities under 3300 fps on average..
That said, with the VERY fast twist which is much more then needed for either of these bullets, once the barrels get some wear on them and the throat roughens up, you may start seeing some issues but I suspect at the velocity range you are at you will not see this nearly as soon as the 7mm AMs did.
The cure was pretty simple, go to a 1-9, 4 groove barrel or a thin land Rock 1-8.7 5R barrel which seem to solve all the problem.
I have a 7mm AM that has a Lilja 1-9, 6 groove and it was tearing 200 gr ULD RBBT apart and last weekend I tested the 180 gr Berger in it and they shot very well, at least for a barrel with the number of bullets this one has down it, roughly 800 rounds.
Again, I would suspect you will see problems MUCH farther down the road then we did and possibly you may never see a problem before the barrel is ready to be replaced.
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