AR308 FTF after 5 rounds.

hv55maxx

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Adjustable gas block. DRD Tactical upper/lower set to take PTR91 mags. Surplus 20 rd mags. I have already adjusted gas block (cases that eject land 2-3oclock), Dremeled feed ramps and polished, and took the Dremel to the front of a few mags and also bent feed lips up slightly after grinding and polishing mags to help with feeding. Seems like the tension on mag springs are not sufficient to boost 6th+ round up high enough (also possibly mags don't sit high enough). Bolt grinds along top of 6th+ casing leaving stripe. There is also some FTE occurring same time as FTF.

Hand loads pass LE Wilson case gauge and are Federal GMM recipe. Fire in my friends Windham with no problems.

Definitely 308 carbine buffer and spring. Not AR15 equipment.

What else am I missing NES?


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My friends brand new .308 did this for 40 rounds until he read the manual that came with it. It was said to run the bolt carrier group generously lubed for the first 200 rounds of break in. We soaked it, literally dripping and it ran like a champ for the next 140 round we put into it that day.
 
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Fixxah

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I use the Dillon case gauges. Wilson isn't a carbon copy of the case as it should be. Doubt it has anything to do with your issue. Just a suggestion on my part.
 
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KMM696

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Not short stroking. Not grabbing the next round. Unfortunately the more I shoot it I think it's a mag fitment issue with the receiver. I definitely need to try springs before anything else at this point.


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I believe you're on the right track with looking at the magazine fit in the receiver.

CMMG tried the G3 mag AR10 before, too. They no longer sell it, wasn't reliable enough. I couldn't find a G3 mag lower or rifle listed on DRD Tactical's site, either. Myself and exodius each had one of the CMMG efforts. His never ran reliably. Mine was great for the first 400 through it, and then went in the toilet, with the bolt overriding cartridges after a few shots. If you search for either of our usernames and G3, you should find the threads we were talking about them. CMMG sold quite a few of these, and I'm not sure if there were ones that worked and we just got unlucky, or if no one wants to talk about their build not working. CMMG also managed to not quite hit the right spot on the hole for the buffer retaining pin, so I'm not sure what their idea of acceptable tolerances was.

My suspicions also were focused on the mag, mostly the mag catch. The engagement pad on a standard AR mag catch is much smaller than the hole in the side of a G3 magazine. There are a couple things you can try. Armalite makes a mag catch specifically for their 308 ARs. There's a short writeup on that here. Might help. Also, SI Defense (who also tried this concept, and stopped) published instructions on modifying G3 magazines that allow the cartridges to sit up a bit higher in the mag. I've done a couple of these, with promising initial testing. Not convinced it's completely fixed yet, though.

I think the companies who've tried this made a mistake by not designing a mag catch (and the receiver to fit it) specifically for G3 mags. Worst case, I'm going to a standard magazine lower. Just before I do that, my plan is to make a mag catch that actually fits a G3 mag, modify the lower so it fits and give that a try. Low priority projects right now.
 
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How do you know its not short stroking? kinda sounds like it is considering you're having FTE and FTF and have an adjustable gas block. Id adjust it for max flow to rule it out.
 

hv55maxx

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How do you know its not short stroking? kinda sounds like it is considering you're having FTE and FTF and have an adjustable gas block. Id adjust it for max flow to rule it out.


because i mentioned i adjusted it already (played with it open and closed it) in OP and it didnt change the problem. When i cycle by hand pulling all the way back it still does not grab a round after a few rounds from the mag
 
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