I’ve got a BCM 20" A4 that I got back at the beginning of November and love shooting it, so far I’ve got about 3,100 rounds through it, 0 malfunctions. I’ve gotten interested in adding an M4 style adjustable stock (mine has the A2 style composite stock now) and plan on getting a 16" Mid length upper to add onto it once I’ve taken care of the stock. I’m wondering what the best way to go about this is, reliability is #1. I won’t touch the thing if I can’t keep it 100% reliable. What accessories/tools will I need to make this happen. I apologize if this is a newb question or easier than it seems, never really worked on AR’s besides switching handguards and stocks (M4). I just know there’s a wealth of knowledge on here and want solid advice.
An A2 barrel on a Carbine lower isn’t over gassed with a standard carbine buffer and spring. I’ve been running my 20" Green Mountain barrel (.093 gas port) with a carbine buffer and Tubbs flatwire spring, which is perfect for 5.56 and certainly the upper end for my 223 reloads.
Actually it is. The rifle buffer weighs almost 2x what the standard carbine buffer weighs. You also need to take into account the difference in spring length. The correct way would be an H3 buffer and spring or the A5 system as mentioned.
As a reloader it is easy for me to dial down the gas and see when the bolt stops locking to the rear. When that’s hovering around starting load for 223, it means the system isn’t over gassed.
An M16 BCG + carbine buffer is going to weigh approximately 14.6 oz.
An M16 BCG + H3 buffer (or H6) is going to weigh approximately 17 oz, a 16% weight increase.
Now I have actually used rifle length gas with a carbine spring/buffer and did so without problem for the 5000 rounds that (I’m told) a mil-spec spring is optimal for. No problem with 223 or 5.56 pressure reloads. Now I’ve switched to a Tubbs flatwire CS spring, which according to the maker, applies 20% more pressure on a closed bolt. With around 1000 rounds through that my opinion is if you are going to run a mix of 223 and 5.56, don’t go heavier. I have had some failure to lock backs when the gun has grease is it an it is colder that 50 degrees. I also ran the gun with an H2 and standard spring that showed no discernible difference than the carbine, so I took it out.
Now I’m not seeing anyone else posting much first hand experience in this thread. I will say this though, I’m not to first 3-gunner to combine rifle gas with a carbine lower. The people who are using this combo, like me, aren’t seeing how much weight they can possibly cram into the buffer to slow down the rifles function. It doesn’t mean you can’t, but it isn’t necessary.
I used my PSA A4 upper with a carbine extension and standard carbine buffer for quite a while with no issues. I’d say about 600 rounds at least, before I decided to switch it to a fixed rifle stock. My decision to go fixed was purely for cheek weld issues, not anything related to mechanical problems with the carbine stock setup… though the slightly decreased recoil was a nice side effect.
