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Old December 14, 2019, 06:22 PM   #12
Join Date: March 4, 2005
Location: Ohio
Posts: 17,027
The 5.56 and .308 barrel life is similar. In the late '90s, Precison Shooting published an article by then Sierra ballistics technician Kevin Thomas, who shot out several chrome moly and stainless match grade barrels in .308 firing their standard test load for the 168-grain SMK from a machine rest using a special lot of bullets that were set aside by Sierra for reference work because they turned out to be extra-accurate. The chrome-moly went down at 3,000 rounds and the stainless lasted 3500 rounds. The stainless went to 4,000 rounds when it was cryo-treated, so you could maximize your match barrel life by doing that to it. Thomas reported that he declared a barrel shot out when the first flier appeared.

That matches how I've seen them go down. I've not had one go suddenly, the way Jim Watson described, though that is perfectly possible depending on exactly how the throat broke down and how much muzzle funneling there is. The mode that I've seen is that all is well and then suddenly you get an uncalled flier. Over a relatively short time (100-200 rounds), those fliers become more and more frequent. When I shot out my first M1A barrel, I was shooting well enough in the local reduced range matches to regularly clean the 100-yard reduced prone slow fire targets. So, I'm in the middle of what I expect to become another 20 tens and Xs one afternoon when an uncalled 9 at about 10:30 appears. By the time another 50 rounds went through it I was getting 2 in 20, all 9s in that upper left quadrant of the target. After another 50, it was 4 in 20. At that point I finally wised up to what was happening and stopped blaming myself and got another barrel.

If I'd kept that barrel, fliers would eventually fly even wider and the spread would have been greater. My main point is, the first flier was wide enough that it had immediately become impossible for the gun to clean slow fire targets at any distance. I suppose it would have cleaned the standing slow and the rapid fire targets because the number of moa in their 10-rings is bigger, but I'd have to be shooting better than before to keep it there. The barrel was just gone as far as being an over-the-course barrel. There was no change in acceptable range. It was bad for all of them all at once. It is possible that by 600 yards, given that moa spread out over distance, it might have given me 8's instead of nines.
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