What are the major concerns from anyone’s prior experience. I want to make sure I’m not missing anything. Change buffer weight, concern over port size/function, etc.
I’ve got a 14.5 and 16" noveske so I’m looking to go the SBR route with this one before anyones panties get all bunched up about cutting a colt barrel.
Thanks for any help.
Send the barrel to ADCO, they’ll do whatever is needed to the port.
If you’re into cosmetics, that M4 profile barrel looks kinda funny cut to 12.5", there’s barely any flat left after the m203 notch, doesn’t hurt anything though.
That makes sense, so probably go 11.5 or 13 if that would be a concern.
I got some advice from a friend in the industry about a quality smith capable of doing the cutting so I may go that route, if he’s concerned about it or too backed up I’ll likely contact ADCO.
Thanks for the reply.
12.5 is a perfectly acceptable cut on a 203 profile barrel.
You wouldn’t/shouldn’t need any port work.
I believe the port needs to be around .076 or so. So it will need to be opened some.
Maybe a little. .070" worked great… I mean just perfect on my 11.5. The port would probably ba .065" now?
My BCMs are .076 if I recall and they have always run great. You may be able to run it at .072-.074 but I can’t say that 100%.
You should dust them off and bring them out this weekend. I have your TBOC patch in my glove box for 3 weeks now. :mad:
Roger.
Thanks to everyone for the help so far. Anyone have a picture of a m4 profile barrel cut down to 12.5? I’d like to get an idea of which rail I’m going to go with. I was thinking a centurion carbine cutout.
Didn’t Troy used to make one
Sent from my T7575 using Board Express
What would be the concerns/symptoms of an undersized port be? I did exactly what the OP wants to do, except I had the barrel cut down to 10.3" for a MK18 build. I’ve had the gas port opened up to .070 in preparation for this (based on the MK18 technical thread).
I’ve tested it and it fails to lock back on an empty mag (one round mag). It also only throws the brass a meager two feet or so to the 1400 position.
I’ve tested it with Speer Gold Dot, Serbian surplus, M855, and LC. All have the same results. I’m using the same carbine length gas tube, Colt auto BCG, and MK12 low pro gas block. Mags used are PMAGs.
I am still doing my research but this thread isn’t that old so I figured I’d ask. It’s my first true SBR build and I was never issued one in the service or in LE so I’ve never had to familiarize myself with any of this.
Your suffering from a lack of gas. That port needs to be opened. I may be wrong, but I am pretty sure I am not.
Huh. Despite the fact that that gun should be running fine, you actually do seem to be undergassed.
Check to make sure the gas block is properly seated.
Check to make sure your gas rings are functional, and that you’re not getting a carrier leak or anything.
Also make sure you’re not running a buffer heavier than H2 with that setup.
Thanks guys. I’ve done all those checks already. The bolt and BCG is brand new and I don’t see any signs of leakage around the gas block area or the carrier key. I’m only using a H buffer as well.
I thought it was under gassed as well but wanted to come to the best place to find out for sure…
I want to say I did a fair bit of research (on this site) before assembling this clone build and I didn’t expect this. Needless to say I’m a bit disappointed.
If you open it up to around .076 I think it will be fine. If you put a suppressor on at this point it would probably be fine.
I’m with IG. .076’’ should work.
(Which is weird, because LMT uses .071’’ on a 10.5’’ and their guns function fine.)
Is that port size 100% verified? Just curious because it doesn’t seem right.
I’m about 90% sure it was right. I think it was Robb Jensen who stated those numbers. I can’t be sure, and I don’t wanna put words in his mouth.
I know it’s stupid to recite that number without having actually measured it, but I remember getting it from a good source, here on M4C.
I went to a local smith that said the MK12 gas block I had on it was much too large for the barrel. I told him I followed specs I read from this site to a T. Was I wrong in starting out with a M4 barrel and having it cut down?