BCM 14.5 Mid Length gas, cut down FSB, and MLOK rail questions

[DacoRoman]

Howdy,

I have a BCM 14.5" Mid Length stripped upper and I'm finally going to build it out. I'm getting a local crew to cut down my FSB. I'd like to put a BCM MCMR MLOK rail on it, but I'm not sure if the cut down FSB gas block will fit under there..any thoughts? I do have a BCM low pro gas block if needed, but I figure the pinned FSB remnant is more solid, and might as well use it since I have it.

Also, I'm having a few second thoughts about going with a 14.5" Mid Length set up. I do have a 14.5" carbine gas barrel somewhere in my pile, and it is a DD LW profile CHF too, if I remember right. The BCM is a standard, govt profile. So I can convert at this point to 14.5" carbine gas for more across the board reliability, as I do have some Geco .223 for training/classes. On the other hand I'm tempted to put the 14.5 Mid Length to use and save the DD for later.

I'll be running a standard carbine recoil system. Any issues running good quality .223 (Geco) with a BCM 14.5 Mid Length? What spring and buffer combo can I consider for the gun to run well, also going up into the 5.56 ammo realms?

Just to clarify I'll be getting a local shop to do the FSB cutdown, and the rest of the assembly.

[Chain&Boom]

As for the reliability, I currently own a BCM 14.5 CHF ELW mid length upper with apx 2k through it. The lower I have it on uses a bcm carbine buffer. Last November, I ran it through a Green Ops two day class in Texas and didn’t have any issues(round count in the class was slightly under 1k). I’ve shot 223 55gr PMC bronze, wolf, PPU, Speer Gold dots, 5.56 55&62gr federal, PMC, PPU, and some 77gr match from Fiocchi and IWI. I don’t think you’ll have any reliability issues with the mid length. I don’t have any experience with cut down FSBs. Mine’s running the BCM low pro gas block assembled by them.

[17K]

Cut down FSB will definitely fit and is better than a low pro gas block.

I’d use a standard carbine spring and H buffer for 5.56 ammo. Cold weather and weak ammo might require a 3 ounce carbine buffer.

[Steve-0-]

It should work depending on how they profile around the tube and the bottom. Keep in mind though, the area where taper pins are dilled can vary in the placement of the hole. Some FSB's get drilled higher for pins then others allowing more material to be removed.

[DacoRoman]

As for the reliability, I currently own a BCM 14.5 CHF ELW mid length upper with apx 2k through it. The lower I have it on uses a bcm carbine buffer. Last November, I ran it through a Green Ops two day class in Texas and didn’t have any issues(round count in the class was slightly under 1k). I’ve shot 223 55gr PMC bronze, wolf, PPU, Speer Gold dots, 5.56 55&62gr federal, PMC, PPU, and some 77gr match from Fiocchi and IWI. I don’t think you’ll have any reliability issues with the mid length. I don’t have any experience with cut down FSBs. Mine’s running the BCM low pro gas block assembled by them.

Good data poinst. Thanks! I do have a carbine buffer in my parts box so I'll try running it with an H and carbine buffer to see how they compare.

[DacoRoman]

Cut down FSB will definitely fit and is better than a low pro gas block.

I’d use a standard carbine spring and H buffer for 5.56 ammo. Cold weather and weak ammo might require a 3 ounce carbine buffer.

Roger that, thanks for the input. Sounds like it will pay to have a carbine buffer around for the .223 stuff.

[DacoRoman]

well, the gas system is settled then, I'll just keep the 14.5 MidL on it and play with the buffer weights if it gives me issues with .223 ammo..the rail is coming in a few days so I'll find out about the fit with a cutdown block

thanks y'all

[GTF425]

I had ADCO shave the FSB of a 14.5" SOCOM barrel and it fits under a 13" MCMR without a hitch.

[DacoRoman]

I had ADCO shave the FSB of a 14.5" SOCOM barrel and it fits under a 13" MCMR without a hitch.

Sweet! Thanks for the info!

[Deadman William]

i mean theres chopped fsbs and then theres chopped fsbs... i dont think i have any pics readily available of some of the ones ive done, but i shape the chopped fsb to be as minimal as possible... some chopped fsbs ive seen would not actually fit under some handguards. just make sure whoever you have do it is gonna truly shape it lowpro n you wont have a problem.

ive been out of the marketing loop for a while, but last i knew, a chopped and shaped fsb was still the single lowest-profile gas block option there was

[DacoRoman]

i mean theres chopped fsbs and then theres chopped fsbs... i dont think i have any pics readily available of some of the ones ive done, but i shape the chopped fsb to be as minimal as possible... some chopped fsbs ive seen would not actually fit under some handguards. just make sure whoever you have do it is gonna truly shape it lowpro n you wont have a problem.

ive been out of the marketing loop for a while, but last i knew, a chopped and shaped fsb was still the single lowest-profile gas block option there was


Verrrry interesting point! good to know...well the rail is being delivered soon, and I will review with the shop what you brought up...I dare say that it's looking good then, so long as they do their part. I'm hoping that the chopped FSB route works out as it is probably the most, or one of the most, robust options out there I'm thinking.