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Sounds to me like a feed ramp issue. When the cartridge starts into the chamber, it angles upward and the bolt is only contacting a very small part of the case base to begine with, so as the cartridge angles upward to go into the chamber, the bolt looses it's grip on the case base and slides over the case, jamming the cartridge between the feed ramp and the throat dimpling the case and showing bolt marks on the brass. Cure is to polish the feed ramp and in extreme cases, machine the ramp itself. Another thing. If the rifle is chambered for 308, don't be loading NATO military ammunition. There are inherent case differences between consumer 308 and Nato rounds.

Finally, 2" at 25 feet is terrible. If I had any gun that printed that group, it would get sold. Even my lowly AK's that I offed years ago would print better than that with steel case Wolf. I happen to have in my shop, a 308 hunting rifle that is exhibiting the same issues. I'm going to modify the feed ramp slightly. While it's a bolt gun, the principle is exactly the same, the difference is the operator is loading and extracting the round and with a bolt gun, lockup in battery is much tighter and why a bolt gun will always shoot better than any gas blowback gun. All has to to with the the fit of the cartridge in relationship to the chambering and headspace as it relates to lockup in battery, but 2" at 25 feet plain sucks. I'd be embarased to tell anyone that.

SOP with me, with any new rifle, custom built or not, is a complete tear down and through cleaning and lubrication before the first round ever enters the chamber and not with motor oil either. Motor oil is for internal combustion engines, not firearms. Use a firearm compatible oil of your choice but take the motor oil crap and loose it.
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In as much as I don't own one and don't want one, I threw my opinion out without reviewing the manufacturers specs. However, don't ever assume all factory rounds are the same because they aren't by a long shot. Why, other than rimfire, I don't shoot any factory ammunition. Irregardless, it's a feed ramp issue, I can ascertain that from seeing the picture of the round cocked in the throat, the scrape marks on the brass case and the dents in the case below the shoulder datum. The cure is to polish the feed ramp or reduce the taper from the base to the feed end as you cannot easily adjust the bolt to case engagement dimension.

I do know that a 2" group at 25 feet is not hunting quality. Might be pray and spray quality however.
 

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Discussion Starter #24
Sounds to me like a feed ramp issue. When the cartridge starts into the chamber, it angles upward and the bolt is only contacting a very small part of the case base to begine with, so as the cartridge angles upward to go into the chamber, the bolt looses it's grip on the case base and slides over the case, jamming the cartridge between the feed ramp and the throat dimpling the case and showing bolt marks on the brass. Cure is to polish the feed ramp and in extreme cases, machine the ramp itself. Another thing. If the rifle is chambered for 308, don't be loading NATO military ammunition. There are inherent case differences between consumer 308 and Nato rounds.

Finally, 2" at 25 feet is terrible. If I had any gun that printed that group, it would get sold. Even my lowly AK's that I offed years ago would print better than that with steel case Wolf. I happen to have in my shop, a 308 hunting rifle that is exhibiting the same issues. I'm going to modify the feed ramp slightly. While it's a bolt gun, the principle is exactly the same, the difference is the operator is loading and extracting the round and with a bolt gun, lockup in battery is much tighter and why a bolt gun will always shoot better than any gas blowback gun. All has to to with the the fit of the cartridge in relationship to the chambering and headspace as it relates to lockup in battery, but 2" at 25 feet plain sucks. I'd be embarased to tell anyone that.

SOP with me, with any new rifle, custom built or not, is a complete tear down and through cleaning and lubrication before the first round ever enters the chamber and not with motor oil either. Motor oil is for internal combustion engines, not firearms. Use a firearm compatible oil of your choice but take the motor oil crap and loose it.
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1. It’s not a feed ramp problem. .308 WIN rounds (even Tula) feed perfectly. It’s most likely a short-stroking problem. The lower-powered 7.62 NATO rounds aren’t cycling the bolt back far enough.

2. As someone already addressed, 7.62 NATO is approved, as it is out of almost every rifle chambered in .308 WIN.

3. I said LESS THAN 2” at 25 YARDS if you read my post (so far I’m not real confident of that). Anyhow, this wasn’t a range session to see how small I could get my groups. It was the first time I’d fired the rifle.

4. Re: motor oil: On this one, you just plain have no idea what you’re talking about, and I’ll leave it at that. Synthetic motor oil - especially Mobil 1, through th years, has gained wide favor as a perfectly acceptable gun lubricant.

Again, when I get the chance to take the M&P 10 Sport back to th range, I’ll let y’all know th Deal.
 

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A little status on my M&P 10 Sport. Before I did some mods and on my first range session I was having issues with it firing 7.62 X 51 NATO Ammo. I would get overlapping failure to extracts. I then had a local gun smith install an Odin Works Free Float Rail and SLR Sentry S7 Adjustable Gas Block. I also installed a Lantac Dragon for 7.62 to tame the recoil. On the next range session I could not get the bCG to lock back and experienced a extreme failure where the buffer tube bent after the castle nut walked loose. I replaced the buffer tube with a Spike's Tactical Buffer Tube made for AR10s still using the factory buffer spring and buffer. After doing some research I found a post on a forum where a guy drilled open his gas block using a 5/64" drill bit. I tried not to make it a science project so I went ahead and bought a 5/64" drill bit and using my micro dremel opened the gas port using the 5/64" drill bit. I also polished the feed ramps and polished the chamber using a .45 Cal Mop and Mom's Polish. I did this because inwas getting some pretty bad scoring on rounds when ilI would try to cycle the rifle manually and also noticed the head of the round dented from bouncing on the feed ramps. Went to the range and was able to successful get the BCG to lock back on the adjustable gas block 8 setting as well as run 7.62 X 51 NATO through it successfully. It was o ly a range session of 100 rounds with a mix of 7.62X51 Nato, .308 150 GR Aguila, and Fusion .308 168 GR. I plan on trying to make it out to the outdoor shooting range to push it further and run more ammo through it. Also to add it wasn't a mag issue. I go same results feom using a 10 Round PMAG, 20 Round PMAG, and 20 Round DPMS Mag. Each would fail to lock back before opening up the gas port and successfully locked back after. Just thought I'd post to share .

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