M*CARBO Brotherhood

AR-15 FTE After Handguard Install

Instead of buying the tools needed to do the job, I decided to pay a gunsmith to install a Matrix Arms FF hand guard and a cheap lo-profile gas block. The GS also runs a pawn shop so I spent the repair time browsing his store. After awhile I walked back to his bench and he was hammering the handguard on with a rubber mallet. He said the gas block was very tight against the handguard. He finished up. I paid and left.

A few days later I was in the yard shooting a few of my guns. Grabbed the AR, chambered a round and it didn’t fire. As I inspected the rifle I noticed the BCG not going all the way forward. Cycling the bolt by hand, I can bump it forward and make it cycle. But it won’t cycle or extract any other way.

I took everything apart and scrubbed the hell out of it, lubed and replaced. Same problem. Thinking maybe the GS bent the gas tube, I ordered another tube and a better gas block. I’ll have to wait on those parts to arrive before going any farther. Do you guys think this will be the solution or could it be something else?

Thanks for reading and I appreciate any help.


Definitely gas related like you said probably slightly bent tube. @ValorSolo any change in ammunition? It was cycling fine before the GS got ahold of it right?

1 Like

@ValorSolo okay the first thing I would do is return to that gunsmith and demand he address the problem. That said, from what you described I wouldn’t have a high level of confidence in his skills.

However, you did say BCG is not fully engaging without the use of the forward assist? I cannot imaging how the gas block or handguard can cause such an issue? Cycling…yes, first round? That sounds more like a mechanical issue such as mags, ammo, BCG, etc.


@ValorSolo there are some missing pieces to this puzzle. Did it fire properly before the GS? When you assisted the bolt forward into battery would it fire? Have you checked head space with a GO/NO GO gauge? What mags are you using? What ammo are you using? If you’ve taken it apart, is it reassembled properly?

1 Like

@Flogrown gas related would be a cycling issue, subsequent rounds not firing, bolt not properly cycling, etc. An AR with no gas can still be manually cycled and fire like a bolt action . :+1:t2:

1 Like

Same ammo and mags as before. It always run flawless.

I did run a CMMG 22lr in it for a couple weeks. This BCG was in it when I took it to the GS.
I swapped back to 223 after the GS. I suppose I should try and run the 22lr kit, see if it still works.

1 Like

@Kona unless the gas tube is protruding to far back and engaging the BCG before it fully comes to battery? And in that case pushing the FA is in fact pushing/flexing the gas tube?


That was my initial thought.

1 Like

I don’t think I want him working on anything else.


@ValorSolo pull the lower and move the BCG forward by hand. See if it engages the gas tube before lock-up.

If it is then the installation of your gas block changed the OAL of your tube and it will need to be shortened on the gas block side.


Working the BCG by hand with lower removed, there is still a catch roughly 1/4" from seating. The BCG can be bumped in all the way, but the catch is still there.

1 Like

Is it short stroking? Can you tell if it goes to full battery?

It seems to after bumping it forward.

@ValorSolo okay you have one of two possible issues here:

First the new gas block changed the OAL dimensions of the gas tube and it is engaging the BCG in the receiver to soon.

Second, the gas tube is not properly/fully inserted into the gas block and by tapping the forward assist you are “pushing it forward”

I would carefully inspect your gas tube to insure you have not damaged it where it engages the BCG, especially where it “bells” to create that seal.

I would also pull the hanguard and inspect the gas block itself and fit of the gas line.


Thats a pretty serious issue…you may be “flexing” the gas line when you tap FA, it is only aluminum after all.

Excellent. That is the plan. I’ll pull the gas block and tube and see what is going on there. I do have a tube and block ordered. Probably just throw the handguard back on and keep it converted to 22lr until the parts arrive. I believe you can run the conversion kit without a gas system. Could be wrong.

@ValorSolo as a single shot…yes.:grin:

Pulled the gas tube and block. Still short stroking. The tube and block look okay. Now I’m starting to worry.

Wait. Isn’t short stroking where it’s not going all the way back.

@ValorSolo you pulled the gas tube and block and your BCG still won’t go fully forward?

What is stopping it?

What is it coming in contact with?

You do have the lower pulled and are doing this WITHOUT AMMO right?

That is a result of not enough gas pressure to fully cycle the BCG. From what you described yours is not going fully forward and engaging the locking lugs without use of the forward assist.

Or I miss read something somewhere?