daveblack

Tried a standard weight rifle buffer, plus my ground down bolt catch. It fed 4 rounds before failing to feed correctly again. Basically, the round is stuck halfway up the feed ramp and the bolt has slammed into it at a 45° angle. Put a nice dent in the round. Same as last time. Any other suggestions to save me from buying a new upper/lower?

Hah! Totally unpossible. You are right on - it was 5/64". 1/16" fit with a little room. As Cunuckgaucho pointed out that would make it at least 0.088" measured diagonally and <0.11". 5/16" made no sense, now that I think about it. Thanks for the expert analysis. So try with a standard weight rifle buffer? I'm trying to minimize recoil as much as possible. Would I step up weight, if it works?

Points for helping people here? I like that. Well the Aero bolt catch didn't completely fix the problem. Dimensions are about the same. It looks stronger. I filed down the top of the bolt catch. It helped. Also removed a hair off the back of the upper. Here is what that looks like: I "measured" with an allen wrench. A 5/16" allen wrench nearly fits. That would be alot more than the range you listed above. Not sure how that computes. Also took a picture. Does this look normal? Drew lines to make sure gas block was centered and tightened down more. It was blowing outside of the gas block. I may give it another shot at the range to see how those adjustments impacted things.

Thanks - that's good advice. I will give this a shot, if I still have problems. I think you may have helped me find the major problem. The Luth-AR 308 Bolt Catch seems to stick out too far/high. I took it out, put in the front takedown pin and everything almost perfectly lines up. The charging handle pulls back clean now. The upper was see sawing around that bolt catch when I had the front takedown pin in before. Ordered some Aero bolt catch replacements. Fingers crossed. I'll report back if this fixes the problem. That's not the only problem. The lower/upper mating is still a little off in the rear takedown pin. I'm going to have to either shave a hair off the front of the lower or rear lug of the upper.

Hmm... that makes sense. Not opposed to doing some machining on it - what do I have to lose? Looking at this again, it looks like the takedown holes are off - the rear looks like it should be centered. If I grind out about a millimeter on the left of the front/rear, it will lay flat, but it will leave a gap at the back. Someone else did this on another lower with fitment issues. Anyone think that is a good idea? Thanks - I will keep that in mind. Used a 5D Tactical rig to mill this. Went with Right to Bear Arms 80% lower, because wanted the durability of forged, but looks like that was a mistake. Thanks for the advice. I should have looked harder for a matched set. Wanted to go with an 80% lower, because of current political climate. Difficult to find 80% matched sets. Daytona Tactical only company that I can find that has anything right now, but their reviews are pretty abysmal. Might give them a shot anyway. 5.2" buffer. I don't know. Is there a way to measure? This is the barrel: https://www.ballisticadvantage.com/20-308-heavy-profile-rifle-length-ar-308-barrel-modern-series.html

First post here. A member here suggested I ask the knowledgeable members here about my build. I am not 100% sure what is going wrong with my build. Built a .308 with these parts: -Aero upper -Right to Bear Arms 80% lower -Faxon Firearms Low-Profile 0.750" Gas block (fixed) -Heavy Rifle Buffer (9oz) -Armalite Buffer Spring -Fixed rifle stock -Luth-AR 308 Bolt Catch -20" Ballistic Advantage barrel There is a gap when I connect the upper and lower. You can see where the Aero upper hole does not align with the rear takedown slot. I can get the rear takedown pin in only by hammering it in. Picture is with the front takedown pin only. When I fire it, the round ejects, but the bolt only goes back halfway and the next round doesn't feed right. Can pull bolt all the way back with the charging handle to reload manually. I have this same problem with an identical upper/lower combo. On that build, the bolt gets caught when I pull the handle all the way back. It slams forward when I hammer out the rear takedown pin. I have also tried a different upper and have the same fitment issue. It looks like the slope of the lower doesn't start early enough at the back. Any ideas how to fix this?