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Posted: 11/26/2016 4:21:50 PM EDT
| Just finished a .308 build using a Faxon barrel, Tactical Machining receiver set and DPMS BCG. Checked headspace, ejects fine, bolts locks back, and everything else seems good including the feed ramps but it won't feed reliably from the right side of the magazine. I've tried slowly feeding rounds by hand using the charging handle and noticed that the bolt lug that strips the round from the right side of the magazine tends to slip over the top of the cartridge. The rounds from the left and right side are also traveling up the feed ramps at different angles. I've tried a couple different types of ammo and several different PMAGs with the same results. Anybody have any ideas as to what could be causing this? After searching online it doesn't seem to be a common problem at all. |
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Quoted:
Just finished a .308 build using a Faxon barrel, Tactical Machining receiver set and DPMS BCG. Checked headspace, ejects fine, bolts locks back, and everything else seems good including the feed ramps but it won't feed reliably from the right side of the magazine. I've tried slowly feeding rounds by hand using the charging handle and noticed that the bolt lug that strips the round from the right side of the magazine tends to slip over the top of the cartridge. The rounds from the left and right side are also traveling up the feed ramps at different angles. I've tried a couple different types of ammo and several different PMAGs with the same results. Anybody have any ideas as to what could be causing this? After searching online it doesn't seem to be a common problem at all. Congratulations! You are the recipient of the "Faxon has not heard of that one..." award. 
And to think, we thought we've encountered everything. Can you get up some photos of the installed barrel, with/without mag inserted, etc? Fun sarcasm aside, we'll be with you until resolved successfully. |
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First guess is the use of a potentially incorrect buffer/buffer tube.
How much of a gap from the back of the bolt catch to the bolt face when the weapon is fully to the rear? If its a short distance, the magazine does not have enough time to feed the round up causing the bolt-override malfunction you are seeing. |
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looks like the upper rcvr doesn't have the ubiquitous M4 feed ramps, however, the barrel does. normally that's not a show-stopper. but just wondering...
could be that as bullet tip slides off the front of the mag, encounters the receiver ledge, the tip goes up ramp, as it goes over the edge where the rcvr M4 feed ramp would be, since the cartridge in this transition state is still grasped by the curved mag feed lips, that the ramp tips the front of the cartridge up, and consequently the back-end tips down, and slides down off the bolt face? that receiver edge serving as a lever point, bullet tip encounters barrel extension feed ramp, tips bullet-tip up, back-end tips down? since the pic shows that the cartridge is initially stripped off the mag and starts to go up the ramp, that implies that the bolt face does indeed catch the base of the cartridge off the mag, for starters. but then somehow the back end of the cartridge tips back down into the mag just enough for the bolt face to slip off? just a wild-assed guess. probably not worth even 2 cents. you'd have to manually cycle it in slo-mo. |
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Two rules in my book:
Feed problems are mags - especially missing one side pickup, if it were me I'd try a metal nag or two, especially if those p-mags were from the same lot. Modern AR10s are over gassed- might be the buffer is bouncing. I would also try a carbine buffer as a test. |
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I've thought about the lack of M4 cuts but there doesn't seem to be any part of the cartridge hitting that area.
You can see where the bolt lugs first start to contact the rounds from each side which seems to be a lot "higher" than on my 5.56 guns. 
As far as magazines I've tried several 20 and 25 round PMAGs from 2013 to 2016 and they all behave the same. I did notice that the feed lips are not just thicker than the 5.56 mags but get thicker toward the back which may angle the rounds too much. I'll have to order some metal mags to see if the thinner lips make any difference. |
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Quoted:
First guess is the use of a potentially incorrect buffer/buffer tube. How much of a gap from the back of the bolt catch to the bolt face when the weapon is fully to the rear? If its a short distance, the magazine does not have enough time to feed the round up causing the bolt-override malfunction you are seeing. I was recently out sighting in my two LR308 builds, which used tactical machining 80% lowers, and I experienced exactly what you stated in your last paragraph. The DPMS 20 round mag, with its slick finish and strong spring, was able quickly feed the next round, even near an empty mag. Same for the 5 round c products mags. However, the brownells 20 round aluminum mag, with its rougher finish and weaker spring started to fail to feed at the last few rounds in the mag. Same with both my 10 and 20 round pmags failing to feed with only a few left in the mags. Bear in mind, all mags and both rifles are in virgin condition. Nothing is broken in. One rifle has a rifle length buffer system and the other had a carbine length buffer system. Symptoms were consistent between both rifles regarding the mags. The gap between the bolt face and the mag catch when fully retracted is about 1/4-3/8" on both rifles. I was feeding ZQI and prefecta brass 7.62 ammo. |
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Quoted:
I was recently out sighting in my two LR308 builds, which used tactical machining 80% lowers, and I experienced exactly what you stated in your last paragraph. The DPMS 20 round mag, with its slick finish and strong spring, was able quickly feed the next round, even near an empty mag. Same for the 5 round c products mags. However, the brownells 20 round aluminum mag, with its rougher finish and weaker spring started to fail to feed at the last few rounds in the mag. Same with both my 10 and 20 round pmags failing to feed with only a few left in the mags. Bear in mind, all mags and both rifles are in virgin condition. Nothing is broken in. One rifle has a rifle length buffer system and the other had a carbine length buffer system. Symptoms were consistent between both rifles regarding the mags. The gap between the bolt face and the mag catch when fully retracted is about 1/4-3/8" on both rifles. I was feeding ZQI and prefecta brass 7.62 ammo. Quoted:
Quoted:
First guess is the use of a potentially incorrect buffer/buffer tube. How much of a gap from the back of the bolt catch to the bolt face when the weapon is fully to the rear? If its a short distance, the magazine does not have enough time to feed the round up causing the bolt-override malfunction you are seeing. I was recently out sighting in my two LR308 builds, which used tactical machining 80% lowers, and I experienced exactly what you stated in your last paragraph. The DPMS 20 round mag, with its slick finish and strong spring, was able quickly feed the next round, even near an empty mag. Same for the 5 round c products mags. However, the brownells 20 round aluminum mag, with its rougher finish and weaker spring started to fail to feed at the last few rounds in the mag. Same with both my 10 and 20 round pmags failing to feed with only a few left in the mags. Bear in mind, all mags and both rifles are in virgin condition. Nothing is broken in. One rifle has a rifle length buffer system and the other had a carbine length buffer system. Symptoms were consistent between both rifles regarding the mags. The gap between the bolt face and the mag catch when fully retracted is about 1/4-3/8" on both rifles. I was feeding ZQI and prefecta brass 7.62 ammo. Try better ammo. Both of those are notoriously under powered and inconsistent. You get what you pay for applies here. I don't think you need match ammo or anything, just quality ammo. I've personally have yet to experience any problems from American Eagle 150g. Not the most accurate, but has been very reliable for me. Try some better surplus rounds maybe. |
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