I built an AR Pistol recently and have had no problems with it. This past week I installed a new pistol brace, the SBA3, which comes with a mil-spec carbine receiver extension. I went to the range today, and my BCG would just not function properly. It wouldn’t travel far enough back to insert a round from any of my mags and it also wouldn’t go far enough back for my bolt catch to be able to lock the bolt back. The only way it would shoot is if I pulled the charging handle back far enough to slide one round in.
This is my first AR, so I’m still relatively new to all the parts. I read another thread that said it might be because my buffer spring isn’t meant for the tube that came with the pistol brace.
I have a complete BCM upper. VLTOR Charging Handle. VLTOR A5 Pistol Buffer Kit. All of this on an Aero lower and Geissele LPK.
I wasn’t for sure if I should post this in the General Discussion or Technical Discussion, but I figured it would be seen first here.
I have a rifle class next weekend, so I would really like to have this figured out soon.
Do you think that will definitely fix the problem? This pistol brace came attached to the carbine receiver extension, so I don’t believe it can be changed out.
Would that mean I just need to buy a new spring? Also, what are some recommended carbine springs? The SpringCo blue spring is the only one I have come across in my short time searching.
The best long term solution is to install an A5 RE, especially with the A5H2 buffer and the Sprinco green spring when you get a chance to buy one. Changing REs isn’t difficult.
If you decide to stick with the carbine RE that came with the SBA3 (currently my favorite arm brace) use an H2 buffer and a carbine spring, preferably the Sprinco blue spring.
lajs1, if you are using an A5 buffer in the carbine receiver extension, it won’t let the carrier travel far enough to operate correctly. Did you see if the action would lock back on an empty mag when manually manipulated? When expereincing problems with an AR, the first thing you should do is perform a lock back check, manually first, then with a single round in the mag.
Did you assemble the bolt in the BCG correctly? There isn’t much you can do wrong but make sure it is all working smoothly. Take the bolt out and see if it locks up in battery without the bolt carrier. If it does it probably isn’t the barrel or the barrel extension. Do you have a flat top or low profile gas block? Make sure the gas block isn’t on backwards, if it is your gas tube will be too out of position (back towards the stock as the roll pin is back instead of forward towards the muzzle) and it will bottom out the bolt carrier. In fact I am gonna guess this is highly possible in the case if nothing else seems off.
Make sure you get at least an H1 carbine buffer. H2 as mist indicated above would be the better choice but done use a straight up carbine weight buffer. Sprinco blue works well. I would recommend that also.
All ammo used was Federal XM193 5.56. Did try some Hornady Training .223. The .223 didn’t even try and cycle back the spent case. I pulled the bolt out of carrier a couple of times during trouble shooting before the Bushmaster try. The gas key bolts are tight, I pulled the bolt apart and just for shit’s and giggles I put the o-ring over the spring just to make it stronger but that shouldn’t do anything if the bolt is not coming back far enough to eject spent case. Front sight block and gas tube has been pulled and inspected. Made sure port was not clogged or covered with gas block. All looked good. Yea I know it doesn’t make since,
As stated in the other topic in the SBR forum. This rifle ran with no problems until I pulled the bolt carrier and put in the Colt and It did not run in the Colt. Put back in my rifle and has not ran since. Something broke just don’t know what happened.
The reason I pulled my bcg was to help a friend trouble shoot his Colt. He was having some issues with his, I said well lets try my bcg and see if it clears up. It didn’t, shot once and failed to eject just like the problem I started having. So I took my bcg back out and put it back in my rifle, later that day went to shoot mine and it has not ran since. Seems like the Colt done something to it but damn that sounds crazy too.
I know when we put the Bushmaster bcg in my rifle with same ammo Federal XM 193 5.56 with same magpul mags it ran 2 full 30 round mags with no problem. The Bushmaster had my bcg and it shot once and failed to eject the bolt carrier only came back far enough to see half the spent case.
I should have went further and narrowed it down to the bolt. Used his bolt in my carrier and then his carrier and my bolt.
