Ar-15 last round bolt hold open

[Cicirich]

I am having some an issue with an ar I put together. I put the lower together myself without any problems. The issue I'm having is sometimes the bolt doesn't hold open after the last round. I'd say about 15-20% of the time. I tried different magazines (pmags, lancer, usgi) and different ammo. I did put a phase 5 bolt catch and am wondering if that might be the problem. Other than this the rifle's been great. Any suggestions??

 

[Cicirich]

O I forgot to mention it's an Engage billet lower and I bought a complete Engage upper(billet) with an Engage branded BCG. Thanks in advance

 

[iH8DemLibz]

A call to Engage may help to sort things out.

 

[lx1x]

Put in empty mag.. Pull bcg manually and see if it locks.. If it doesn't.. Cycling issue.

 

[Cicirich]

A call to Engage may help to sort things out.

Yea I will go that route if need be just don't have a lot of time lately. I was hoping if it was something I could check or do that was relatively easy it would save me a trip.

 

[Cicirich]

Put in empty mag.. Pull bcg manually and see if it locks.. If it doesn't.. Cycling issue.

The bolt does lock back if I pull it manually on an empty mag. It cycles fine and always goes boom. The bolt just doesn't hold open "sometimes " after the last round.

 

[lx1x]

The bolt does lock back if I pull it manually on an empty mag. It cycles fine and always goes boom. The bolt just doesn't hold open "sometimes " after the last round.

If you can manually lock it... Cycling issue..ie bcg not going fully back to trigger the bolt lock up. (Short stroking)

 

[NateIU10]

What gas block and barrel (length, gas length, manufacturer, etc)? Of the different types of ammo, what kinds and did it occur more or less frequently with any type? What weight buffer are you running? Standard buffer spring?

 

[lx1x]

What gas block and barrel (length, gas length, manufacturer, etc)? Of the different types of ammo, what kinds and did it occur more or less frequently with any type? What weight buffer are you running? Standard buffer spring?

He said he bought the complete upper from you guys..

So I doubt its the upper issue.

Sounded more buffer and spring issue .

 

[clandestine]

The bolt catch extensions can be problematic. Take it off and see if you have the problems.

I can't tell you how many ghosts I have chased with those bolt catch extensions. Some guns run fine with them, some dont.

 

[Cicirich]

What gas block and barrel (length, gas length, manufacturer, etc)? Of the different types of ammo, what kinds and did it occur more or less frequently with any type? What weight buffer are you running? Standard buffer spring?

Yea I think I'll just bring it in when I get a chance. I bought the upper complete from you guys but all I can remember is its a 16 inch WOA Hbar barrel, don't know the gas block/length manufacturer, billet upper.
I put a Bravo Company stock mounting kit which came with a standard buffer spring and H2 buffer. I used independence 556 55 grain FMJ and most of the time I use American Eagle 223 AR tactical 55 grain FMJ. Also new PMC bronze. Can't quite remember the specs on that. Can't really seem to narrow it down by ammo. It's just random with all the types of ammo I use.

 

[clandestine]

I have seen tons of issues with PMC ammo. I would not troubleshoot with it.

 

[NateIU10]

Yea I think I'll just bring it in when I get a chance. I bought the upper complete from you guys but all I can remember is its a 16 inch WOA Hbar barrel, don't know the gas block/length manufacturer, billet upper.
I put a Bravo Company stock mounting kit which came with a standard buffer spring and H2 buffer. I used independence 556 55 grain FMJ and most of the time I use American Eagle 223 AR tactical 55 grain FMJ. Also new PMC bronze. Can't quite remember the specs on that. Can't really seem to narrow it down by ammo. It's just random with all the types of ammo I use.

Interesting. Bring it by, but I would guess an H or Carbine Buffer may help if you're running mostly 223 ammo. Sorry I missed the fact it was a complete upper, was reading it all on my phone.

 

[Captnstabn]

I have a friend that is having the same problem with an engage lower. Comparing it to my 3 engage lowers (which are fine), his magazine well is clearly cut further forward in the lower preventing the bolt catch from reaching the follower. We got them together before the 2013 ban, difference being his came from the second batch (SN around 1500's IIRC) vs mine that came from the first batch (SN under 1000).

He hasn't contacted engage yet, but I suspect the only remedy is to use a 9mm bolt catch and file it down to reach the follower of the magazine.

We measured it with digital calipers, compared to an in-spec lower. You should check yours as well.

 

[Sharpeneddark]

Did you get your problem sorted?

I had a similar problem with a build I made. I think the LPK I put into it was a Rock River set and I had issues with the bolt catching on the last round some of the time. I found that the bolt catch wasn't always being engaged on the follower of the magazine because the bolt catch was able to move just a little too much in the bolt catch well. I put some shim material in the bolt catch well and haven't had an issue with it since.

 

[precisionfire]

I would definitely change the h2 buffer to either a H or Standard. Heavier is not always better. By the symptoms, I would say the problem is most likely in too heavy of buffer for the ammo being used.

Doubt it is the lower or Bolt catch since he states it locks back manually every time.