First AR Problem

[Ralgha]

So I finally acquired the last parts for my first AR and finished assembling it. Problem now is that I usually can't rack the bolt, it appears to be hitting the bottom lip of the buffer tube. If I unlock the takedown pin and hold the upper and lower together by hand, then I can rack it, as it allows the upper to shift up just a hair. If I have the pin locked in, then I can sometimes rack it, with difficulty, if the castle nut on the buffer tube is just a little loose and I do a special dance.

The parts in question are an Aero enhanced upper, Aero gen 2 lower, PWS EBT Mod 2 buffer tube, and a Superlative Arms piston kit bolt carrier. I'm not ruling out an error in assembly, but it's pretty simple, I don't think I screwed anything up. I'm probably going to have to take it to a gun shop nearby to figure out what the problem part is since I don't have any other parts to swap around.

Is there a most likely culprit part that might be out of spec? Any common noob assembly mistakes I should check for?

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[308]

Photos?

 

[Ralgha]

Unfortunately I'm out of town and won't be able to get any pictures for a few days.

 

[edslhead]

Do you have the retainer in properly? The buffer tube should just cover enough to keep it in place.

 

[Boboclown]

Measure to see if something out of spec, check if the receiver extension is on straight, maybe a burr on the BCG. Could be a number of reasons.

 

[PiratePast40]

Do you have the retainer in properly? The buffer tube should just cover enough to keep it in place.

That's the first thing I would check. Someone I know did the same thing, but I'm not naming names!

BTW, don't forget that you can use the adjustment screw under the handgrip to tighten up the lower and upper. Just one of the advantages of the Aero Gen 2 lower. And the M4E1 upper/handguard is sweet. Love mine.

 

[Ralgha]

It's not the buffer retainer, I'll check for burrs when I get home. The upper and lower mate up tight, no play, even with the adjustment screw under the grip completely loose.

 

[OFADAN]

Adjustment screw? It's a piston gun not DI?

 

[bolus]

remove the buttstock, buffer tube, buffer and spring. reassemble the upper and lower and see how the bolt carrier looks from behind. You can also slowly pull the charging handle back and see how the bolt carrier would be moving into the buffer tube (which is removed)

 

[Ura-Ki]

I have seen several out Of Spec buffer tubes that were not in alignment due to machining offset or bent! Some of these "Millspec" buffer tubes are not actually Millspec! This can cause all sorts of headaches! I would look there after the buffer retainer pin is eliminated as a possible cause.

 

[Ralgha]

I'll try removing the buffer tube and cycling the action next, that's a good idea. I don't have another buffer tube to try though, so that'll require a shop's assistance or something.

The adjustment screw in question is part of the lower, you can use it to eliminate play between the upper and lower.

 

[Vorpalis]

Along with Bolus' suggestion, look for wear marks:
– at the outer edge of the rear end of the carrier;
– in the groove along the carrier's bottom where the buffer retainer passes;
– on the buffer retainer itself;
– and on the inside edge of the receiver extension (buffer tube).

If present, wear marks will tell you what the problem is. You could even try marking each in turn with small dab of paint or Whiteout, assemble and try to rack it, then disassemble and check where the paint transferred to (then clean the paint off before it dries – duh).

Also check that the charging handle isn't impinging on the stock. That can cause a similar issue, and it might also seem to go away when the castle nut is loosened.

 

[808hondacrguy]

Check the top of the endplate I had a couple with that exact problem that I wrestled with, filing down the detent pin, etc. and it turned out that the charge handle was hitting the top of the end plate .

 

[v0lcom13sn0w]

ive built a dozen or so rifles with Aero precision parts. never had an issue with them.yes,even without the gen 2 setscrew lower, their parts tend to fit tighter. i would be more suspect of a buffer tube not being concentric or a burr somewhere. take the buffer retainer and spring out and the buffer and spring out and see if the problem is still there. might lead ya in the right direction. without physically seeing the rifle its hard to tell.

 

[v0lcom13sn0w]

also, ive heard of guys having parts cerekoted and then their parts all fit tighter too. maybe theres a bit if coating under the rear take down pin hole on the upper that is making it so tight? just thinkin outside the box.

 

[pacnw]

What spring are you using?

Heard of some NOT being compatible with the PWS EBT due to the lip extending into the lower.

 

[kato pup dog]

808hondacrguy is spot on. I had an issue with the spikes lower build and aero upper combo. I had stuck a different upper on the lower and test fired making sure all was well before pursuing building the upper. At some point I changed the reciever extension plate to one with a quick connect. In doing so the charging handle would not cycle. After a few minutes it became apparent the top of the plate needed a little material removed. Easy fix, but a pain in the backside to figure out.

 

[Stomper]

If it were easy... Oregon Cease Fire would be doing it!