Ar10 bolt wont close 100% sometimes

[Mike14_07]

My buddy has been collecting parts for his ar10 for a while and we put it together saturday and took it out. Sometimes it wouldnt close the bolt all the way. Reach up and push it closed with thumb and it would seat the rest of the way. It would even do it when racking the charging handle. Tried hornady american gunner and some cheaper winchester. Build specs for diagnosis
Aero upper, lower and lpk
Ballistic advantage 20" stainless barrel(ill ask what profile)
Jp enterprises adjustable gas block
Gun tech buffer setup(has the stubby buffer and carbine tube)
Slr handgaurd (shouldnt matter)
Not sure what brand gas tube
Any ideas on a possible problem?

[Iraqgunz]

Make sure that the gas block/tube is straight. You can test it by stripping the BCG down to the carrier only and then insert it into the upper. If it stops or binds, the gas block is crooked.

The other potential cause could be an issue with either the bolt lugs, or the barrel extension.

My buddy has been collecting parts for his ar10 for a while and we put it together saturday and took it out. Sometimes it wouldnt close the bolt all the way. Reach up and push it closed with thumb and it would seat the rest of the way. It would even do it when racking the charging handle. Tried hornady american gunner and some cheaper winchester. Build specs for diagnosis
Aero upper, lower and lpk
Ballistic advantage 20" stainless barrel(ill ask what profile)
Jp enterprises adjustable gas block
Gun tech buffer setup(has the stubby buffer and carbine tube)
Slr handgaurd (shouldnt matter)
Not sure what brand gas tube
Any ideas on a possible problem?

[Mike14_07]

Ill check that. But it seems to only do it witha round. But i guess the round could make it go in straighter causing the gas tube to bind?

[Iraqgunz]

Since you didn't specifically mention it only when chambering rounds, I provided the standard checks. So, I would at least check those items first. If there is no issue, then I would start looking closer at the bolt/barrel extension interface and a potential chamber issue.

Ill check that. But it seems to only do it witha round. But i guess the round could make it go in straighter causing the gas tube to bind?

[09stanggt]

The bolt will close if you cycle it when empty? If yes, how did you adjust the gas block? That guntec buffer and extension IS for a .308?

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[Mike14_07]

Yes on the buffer. The bolt will close when racking the charging handle without any rounds. Throw a round in there and most of the time it wont close. Id have to look at the directions again to tell you how we adjusted the gas block.

[veeref]

Have you checked headspace with go/no-go gauges?

I had a bolt that wouldn't close on a Mega 308 DPMS-pattern build. I isolated it to the Ni coated bolt causing headspace issues like you described.

[09stanggt]

Pure guessing at this point. Chamber, feed ramp, or crappy mag.

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[oddballmkg]

I would check to see if they installed two of the rubber o rings under the extractor on the bolt head. If they are using two o rings, I would try removing one of the o rings and see if that fixes your problem. Some times using two o rings under the extractor will not allow the extractor to slide over the end of the brass case as the bolt cycles closing the chamber. If this is happening, it will not allow the bolt to fully close. When you get the gun broken in all the way you may have to start using two o rings to get it to extract 100 percent of the time. This is kind of a common problem with .308 AR's. Their is no set standard with the Ar10 rifle. Some manufacturers use two to four springs on the extractor to help with extraction of the spent round. The extra heavy spring tensions can cause issues with the extractors having too much tension to let them slide of the top of the brass case as the rifle cycles closing the chamber.

[Mike14_07]

Well i checked all the suggestion last night. Bolt had no orings on it. Head space was fine. Was getting frustrated with it and he dropped the mag with the bolt not closed all the way and it snapped shut. Looked at the mag and could kind of see something dragging on the front of the mag, but maybe just barely. Sanded it a bit and now it works fine in the shop. Well test it this weekend. Idk if he got a bad pmag or what.