I have a 16" Colt 6940. It is for home defense and sometimes for patrol. I want to shorten it up, but also use it with or without a suppressor.
I have read a lot about the issues with suppressed SBRs, especially 10.5" DI guns. For this reason, I would want to send it off to ADCO, SAW, Grant (does he do that?) or another reputable shop to be cut to 11.5" and the gas port re-sized appropriately.
The can would be a SilencerCo Specwar 5.56 with Trifecta flashider. My buffer is currently an ST-T2, which I would like to keep as all my rifles use the same one. I use Rainier Arms Raptor charging handles, which unfortunately do not have the gas bleedoff channels like the Gas Buster. Sure wish they did.
Would it be plausible to think that it can be done and be reliable both with and without the suppressor? Any recommendations on gas port sizing, or should I leave that to the shop it is sent to?
I usually suggest trading or selling your factory barrel for a Daniel Defense 11.5 inch barrel or if you can find one, a Colt 11.5 incher to go with your existing parts. You will have to make sure you have a proper headspace on your bolt/barrel, but it may be less expensive than cut and milling a new gas port. Either way make sure you have the current extractor bumper or o ring and lube it properly until it is broken in.
My old agency tested the Colt 14.5 inch carbine (727) and Colt 11.5 shorty back in the later 1980’s. The 14.5 incher beat the shorty hands down for reliability, but I think it has more to do with the fact that the 14.5 incher was well broken in and the 55 grain ammo did not make a big different in timing on the 1/7 twist barrel. The 11.5 inch shorty was brand new and did not go through a single mag without a feeding issue or hammer down on empty chamber. The colt rep swapped out the 11.5 inch upper for a 14.5 upper and the gun ran fine. I bought the 11.5 inch upper from the Rep for a small sum and he suggested lubing it properly and firing some Milspec SS109 ammo, which was hard to get at the time. Jim Frigiola was an Olin rep at the time and offered my shooting buddy a small supply of Olin’s heavy 5.56 ball round known as the “Penetrator”. That 11.5 inch upper fired trouble free from then on mounted on my civie legal M16 carbine lower. It was extremely accurate out to 300 yards (range limit) and except for the loud blast, was easy to shoot (although it did recoil slighlty more).
I am currently building a buddy in the Navy Special Ops community a special Mk18 pistol for his VA CCW permit, and when test firing the 10.3 inch barrel I had the same sort of stoppages. A Navy armorer loaned me a Knight Triple tap comp and although the flash is great, it functioned 100% so opening the gas port or adding a bore constriction/muzzle comp does help.
ADCO can cut down your barrel and open the port as they do it all the time. They can also dimple the barrel for cooling or coolness.
Ken Elmore is a pro, but he is usually back logged and he may not be able to get to your project quickly.
This is exactly what I am considering doing. I have a 6940 that I would like cut to 6945 configuration.
SAW is where I would prefer to send it.
If you go this route, update as you go.
Cutting an M4 barrel to 11.5 inches puts the muzzle right in the middle of the notch
It isn’t that difficult to get a 10.5 inch upper to function reliably. Mine uses a .082 inch gas port which may be a little on the large size, but it 100% reliable with a carbine RE and an H3 buffer or rifle RE and rifle buffer. I’ll be experimenting with an adjustable gas block next
Unfortunately, the 6940 series uses a unique barrel extension and nut, so simply swapping in another barrel won’t work.
I would love to, but the uppers cost more than a complete 6945/3, which is outrageous. If they were sub $1000 then yeah, but at $2k not going to happen. Sucks.
yeah I don’t mind it being in the notch… Maybe I would have them turn the exposed barrel down, maybe I’d leave it M4 profile, maybe I’d make it slightly longer to have the whole notch available for M203 mounting. The latter is unlikely though.
Cutting down to 10.5 wouldn’t be bad if it is gassed correctly. You could also try running it with a LMT enhanced carrier. I had a 14.5 colt barrel cut to 10.5 and no gas port work done running adjustable gas block, enhanced carrier, and a h3 buffer suppressed all the time with no issues so far.
If you are going to do this, do not let anyone but Ken at Specialized do it. He had purposely built tools for the front sight, barrel, etc… It’s a pain in the ass.
Given Colts current “SBRs need a PD letterhead” policy, DSG might not get anymore. Overnight every one of my LE suppliers dropped Colt SBRs from their catalog. Some full retail establishments still have them.
There are a few on GB at reasonable prices. Still definitely the cheapest way to do this.
I just had SAW convert a 6940 upper to 6945 specs. The work is phenomenal, as far as how it was cut and put together. Cost was $240. This was an upper I had.I will get this out to the range within a week and give a rundown on how it performs. Ken was adamant about using an H3 buffer. I have an H6 I will be running instead.
Ok thanks for the info. Please let me know how it goes.
I really like my Spikes ST-T2… I will try that in it and see the results, whenever I get around to getting my upper converted like yours.
From my experience, neither the H6 or the Spikes powdered buffers have lived up to their expectations in function. There’s many things on the market now with claims that myself and at least a few others cannot duplicate. The only one that has made a noticeable improvement in function is a properly sprung and weighted A5 system.
I may not agree on other items, I have my own idea on porting, but accept researched products as their end goal may be different than mine or others when they show results.
