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Posted: 9/14/2016 6:55:54 PM EDT
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I have a Hogan 308 18" (it's a piston rifle if that matters any). Latest load i did was 39.3 grains of H4895 with a 168 projectile. See primers below in pic. The starting load is 40.0 in manuals so I am nowhere near max. The oal is not too small. My chrono this week had the string avg at 2460 fps.
I have sent the rifle back twice. The first because of feeding issues and they said it was under gassed. I wonder because of that if they increased the gas port size on the barrel and screwed it up. The second time i sent it back because of pressure they replaced the bolt and he slightly reduced the length of the firing pin. I don't think it's my reloads, I haven't shot factory rounds in a while but they were having issues also. Any other ideas besides replacing the barrel? 
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40.0 grains of H4895 is a maximum load when using 168 grain Sierra Match Kings and Lake City brass. So you start load was .3 grain over maximum.
Nosler and Hornady 168's can be safely substituted for the SMK, foreign made 168's maybe not. Start around 39.0 grains using USA made 168 match bullets when using H4895. Watch for pressure signs and increase charge weights .5 grains at a time up to the 40.0 maximum. Your firing pin hole in the bolt face may oversized and may be contributing to the cratering. Loading 7.62x51mm brass is not covered in the standard reloading manuals. The standard rule of thumb is to drop your commercial brass load by 2.0 full grains of powder when loading Lake City or IMI brass. An old NRA article covers this in depth and is available online through used book stores. The book is called "Semi-Auto Rifles - Data & Comments". I scanned and posted several of the pages and they are archived in the reloading section of this sites "Armory" page. Good Luck. 2500 fps would be close to maximum when fired from a 22" M1A. Your maximum load velocity with 168's fired from an 18" barrel using Lake City brass is going to be around 2400 fps. |
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Can a piston system even be overgassed? Doesn't the piston assembly have a relief valve to vent out the excess gas?
The primers certainly look a bit malformed, but I'm not seeing ejector swipes which are an even worse sign of too much pressure. Is the chamber tight? If you chamber a live round and try to extract it with the charging handle, is it unbearably hard to do so? |
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