Bolt not locking

[Mdt]

Need some help to figure this problem out. I built this Gun myself with quality parts and did not take any short cuts.
WHAT I HAVE : Aero Precision Billet upper and lower. Aero. Precision bolt carrier group, carbine length buffer tube, H2 buffer & heavy red spring(got from LaRue), Superlative Adjustable gas block, Proof Research barrel 6.5 Creedmoor
WHAT is PROBLEM: The bolt will not lock back on the last round even with gas block wide open.
I also noticed that the bolt when manually charged is only locking back on the mag follower(empty mag) and not the bolt catch. Therefore when you press the mag release the bolt goes into the battery.Now I can manually lock the BCG back on the bolt catch, but this isn’t proper function.
Thank you for your help

Mike

 

[Old Man with Gun]

Was it well lubricated?

How much has it been shot?

Have you double checked the alignment of the gas block to barrel?

Have you tried a lighter buffer? And or spring? With an adjustable gas block you probably don't need extra resistance.

 

[Huskydriver]

What trigger?

 

[Precision Underground]

Look inside and see if the follower is pressing the bolt catch up like it’s supposed to. I don’t think the bolt can catch the follower. The carrier itself is probably hanging on the bolt catch. When you release the Mag the catch will fall if that’s the case.

 

[Mdt]

Need some help to figure this problem out. I built this Gun myself with quality parts and did not take any short cuts.
WHAT I HAVE : Aero Precision Billet upper and lower. Aero. Precision bolt carrier group, carbine length buffer tube, H2 buffer & heavy red spring(got from LaRue), Superlative Adjustable gas block, Proof Research barrel 6.5 Creedmoor
WHAT is PROBLEM: The bolt will not lock back on the last round even with gas block wide open.
I also noticed that the bolt when manually charged is only locking back on the mag follower(empty mag) and not the bolt catch. Therefore when you press the mag release the bolt goes into the battery.Now I can manually lock the BCG back on the bolt catch, but this isn’t proper function.
Thank you for your help

Mike

Well lubricated ,shot 12 times, gas block is align(barrel has dimple)
That is the lights spring and buffer.
Wanted to get some advise before I started buying parts.
Do you think the Carbine buffer tube has any negative effects?

Have built several AR15. No problems. My first AR10 platform

 

[Mdt]

What trigger?

Gesler

 

[6.5SH]

If you bought both the buffer and spring from LaRue they are the wrong length for an Aero receiver set and bolt carrier. Aero M5 use the short 2.5" buffers.

 

[6.5SH]

AR-10 308 AR Compatibility Reference Guide | AR 308 vs AR 10

Compatibility Reference Guide - Understand and research the parts interchangeability and differences between the AR-10, AR-15, 308 AR and AR 308 rifles

308ar.com

 

[Hellbender]

Sounds like your buffer is a little long for the rest of your build.
Here's a post that explains proper bolt to mag catch clearance.....

Gunsmithing - 10. HOW-TO: Ultimate AR: Bolt Catch Overrun

Part 10: Checking and adjusting Bolt Catch overrun. The amount of Bolt Catch overrun is important, as too little may not allow the Bolt Catch time to fully engage, and too much (most common) beats excessively on the Catch and causes a "slamming" feel when the bolt locks back on the last shot...

www.snipershide.com

 

[Huskydriver]

Gesler

Do you have another to try?

 

[PDXGS]

Focus on the Spring and Buffer.
Where is your brass landing after ejection/extraction?
I assume you meant a Geissele trigger?

 

[Huskydriver]

I have seen at least 3 instances of exactly what the op is describing and the trigger ended up being either slightly out of spec and was dragging on the bcg preventing it from having enough energy to lock back all the way or the lower trigger pin holes were slightly off causing the same issue.


Could also very well be the buffer

 

[LawnMM]

Hard to diagnose without being there to see it. Sounds like too much bigger weight / too heavy a spring.

Where does the brass land on ejection?

 

[Yondering]

I have seen at least 3 instances of exactly what the op is describing and the trigger ended up being either slightly out of spec and was dragging on the bcg preventing it from having enough energy to lock back all the way or the lower trigger pin holes were slightly off causing the same issue.


Could also very well be the buffer

+1 to both of these. It sounds like the buffer, from the op description, but may be the trigger too.

Way too many people are getting into large frame ARs without doing their research and assembling a pile of parts that don’t work together.

 

[Precision Underground]

If you bought both the buffer and spring from LaRue they are the wrong length for an Aero receiver set and bolt carrier. Aero M5 use the short 2.5" buffers.

Ahh. AR10. Here’s your answer

 

[Mdt]

Focus on the Spring and Buffer.
Where is your brass landing after ejection/extraction?
I assume you meant a Geissele trigger?

Yes sir spelling is not one of my strong points. Brass landing at 3:00

 

[Mdt]

Hard to diagnose without being there to see it. Sounds like too much bigger weight / too heavy a spring.

Where does the brass land on ejection?

Brass lands at 3:00

 

[Yondering]

Brass lands at 3:00

Unfortunately brass ejection pattern doesn’t mean nearly as much as some people think, and doesn’t do anything to diagnose the potential wrong combinations of buffer system parts that are possible in large frame ARs.

Your first step should be to verify whether the carrier can move back too far (bottoming out with the gas key against the receiver) or not far enough (won’t lock back on the bolt, only on the carrier).
No reason to try diagnosing anything else until you figure that out. Read the info posted by 6.5SH above.

 

[Mdt]

Yes have order buffer and spring. Should arrive this week. Will post results

Thanks to all who have helped with this issue