View Full Version : Chopping a barrel
LowSpeed_HighDrag
11-13-17, 22:10
Trying to make a solid, suppressed only upper. Sending a 6920 OEM2 to ADCO to have it chopped at 11.5". I think that the smaller gas port will be beneficial in suppressed shooting. My worry is that a government profile barrel couldnt be chopped and threaded at 11.5 due to the 203 notch.... Anyone know about this?
Trying to make a solid, suppressed only upper. Sending a 6920 OEM2 to ADCO to have it chopped at 11.5". I think that the smaller gas port will be beneficial in suppressed shooting. My worry is that a government profile barrel couldnt be chopped and threaded at 11.5 due to the 203 notch.... Anyone know about this?
I had one done, the threads are in the notch, which is larger than 1/2” diameter. It works.
tango-papa
11-14-17, 10:45
I had one done, the threads are in the notch, which is larger than 1/2” diameter. It works.
Curious - leaving gas port as is?
tp
I want to say somewhere almost 11" will put the threads in the notch with a full shoulder behind it.
The dwell time 11.5" fans like over 10.5" does not apply to dedicated suppressed. The can adds more than enough dwell time for either, so it comes down to handguard length and looks.
The dwell time 11.5" fans like over 10.5" does not apply to dedicated suppressed. The can adds more than enough dwell time for either, so it comes down to handguard length and looks.
Do you consider the 10.5" to be a better choice than 11.5" for dedicated suppressed use?
Trying to make a solid, suppressed only upper. Sending a 6920 OEM2 to ADCO to have it chopped at 11.5". I think that the smaller gas port will be beneficial in suppressed shooting. My worry is that a government profile barrel couldnt be chopped and threaded at 11.5 due to the 203 notch.... Anyone know about this?
You can only get about 11.25" barrel length before the shoulder gets into the taper down for the notch.
A good option may be to chop to 10.5" which removes the whole notch and thread 5/8-24 if the suppressor mount has that option.
5/8-24 has advantages if, as Clint stated, your mount allows. You can tell Adco to put the shoulder where the barrel begins to taper rather than specifying a specific length. I have a DD barrel that was done this way and it's about 11.2" and runs great suppressed. .067 port.
Curious - leaving gas port as is?
tp
Yes.
It was a stag upper I no longer had a use for, so I chopped it to 11.5” for a pistol build for an iron sighted range gun.
Gp measures .075” with calipers (I know it’s not proper, hence the call-out on method).
Clint’s post reminded me- I think there was a slight convex taper to the shoulder which would make up about .25”. I wasn’t worried as I’m running an a2 with a crush washer.
The gun has an h buffer and shoots very smooth. No suppressor, so it seems .075 would be a little over gassed for a dedicated silenced upper, but I’ll let others provide more detail on that.
This might sound like some hall of shame stuff, but it’s a junk range gun I’m just playing around with just to see how it works and how I like the length.
SeriousStudent
11-14-17, 20:15
Out of pure idle curiosity, why wouldn't you just buy one of these?
http://sionicsweaponsystems.com/store2015/5/21-5-chrome-lined-w-low-profile-gas-block.html
http://sionicsweaponsystems.com/store2015/5/61-5-chrome-lined-stripped.html
titsonritz
11-14-17, 21:10
Out of pure idle curiosity, why wouldn't you just buy one of these?
http://sionicsweaponsystems.com/store2015/5/21-5-chrome-lined-w-low-profile-gas-block.html
http://sionicsweaponsystems.com/store2015/5/61-5-chrome-lined-stripped.html
I was actually wondering the same thing.
Do you consider the 10.5" to be a better choice than 11.5" for dedicated suppressed use?
...thread 5/8-24 if the suppressor mount has that option.
I prefer the shorter length myself.
Great tip on threading 5/8-24 if possible. I have made a few custom barrels for myself with 5/8-24 threads.
For anyone wondering, a 14.5-16 carbine barrel with a spec gas port is just right for a suppressed only barrel when cut down.
LowSpeed_HighDrag
11-14-17, 23:09
Guys,
as always, solid advice on M4C!
So, I am chopping the 6920 barrel because the gas port is smaller, thus giving me the perfect suppressed barrel.
I did not go with an aftermarket barrel because most gas ports on short barrels are opened up too much.
I will get ahold of Adco and let them know I want the shoulde where the barrel begins to taper.
I cant do 10.5, because the BCM MCMR 10 is actually a 10.4" rail....
LowSpeed_HighDrag
11-14-17, 23:11
Can somebody explain to me the benefits of 5/8x24 vs 1/2x28?
The barrel is thicker at one of the most critical points - the muzzle.
titsonritz
11-15-17, 10:19
So, I am chopping the 6920 barrel because the gas port is smaller, thus giving me the perfect suppressed barrel.
I did not go with an aftermarket barrel because most gas ports on short barrels are opened up too much.
Sounds like you have already moved forward with the 6920 barrel, but FYI that second link SS posted is a reduced gas port barrel specifically made for dedicated suppressed weapons.
Spin Drift
11-15-17, 11:07
I was actually wondering the same thing.
$219, plug and play, no muss, no fuss.
OP, Good Luck.
The RGP Sionics GP diameter is still too big for dedicated suppressed use with 5.56 IMO.
Official Kremlin Transmission
Can somebody explain to me the benefits of 5/8x24 vs 1/2x28?
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/628419704.jpg
SeriousStudent
11-15-17, 19:07
The RGP Sionics GP diameter is still too big for dedicated suppressed use with 5.56 IMO.
Official Kremlin Transmission
Again, I am curious. What was your experience with those barrels? How did you have them set up?
Mine run just fine.
He can only run a suppressed SBR for a duty gun. I told him a cut down 6920 barrel would run better than any other option.
LowSpeed_HighDrag
11-15-17, 22:31
He can only run a suppressed SBR for a duty gun. I told him a cut down 6920 barrel would run better than any other option.
Exactly right, and I'm dutifully following your advice.
LowSpeed_HighDrag
11-16-17, 09:57
Again, I am curious. What was your experience with those barrels? How did you have them set up?
Mine run just fine.
Bill,
Another reason for me doing this is it's only costing me $130 to have a barrel that's already headspace with my bolt cut down and have my new rail installed as well. A lot cheaper than the new barrel route and I know the gas port will be sized right for my application.
What MD/suppressor will you run? I'm curious as it pertains to the muzzle thread options.
jethroUSMC
11-16-17, 13:22
Curious - leaving gas port as is?
tp
No. New gas port .067
GeneralPurpose
11-16-17, 13:34
No. New gas port .067
That's a big port for dedicated suppressed use. My 10.5" is 0.047" and I've put a ton of trouble-free rounds through it. Kinda wish I had gone with 0.042" sometimes.
That's a big port for dedicated suppressed use. My 10.5" is 0.047" and I've put a ton of trouble-free rounds through it. Kinda wish I had gone with 0.042" sometimes.
Pistol gas?
For most cans and 5.56 pressure ammunition, you would not want a .067" carbine length gas port for dedicated suppressed only use for a 10.x"-11.x" AR.
For suppressed only use similar to the above with a regular M16 chamber, throat, and bore, most would not prefer the .042" gas port.
Spin Drift
11-20-17, 20:25
https://dqzrr9k4bjpzk.cloudfront.net/images/812059/628419704.jpg
Excellent pic, thanks.
It's going in the "I told you" folder.
Sometimes a picture is worth a thousand words...
Now, to get manufacturers to make 5.56-sized muzzle devices threaded in 5/8-24...
It's not just 5/8" threads, but how the devise registers to the barrel. There's a few paths that we can go down for this.
Jwknutson17
11-24-17, 08:39
The Sionics is .071 and from the ones I had owned I agree it is too large for a dedicated suppressed gun. Especially on a 11.5 car barrel. It wasn't made to be a suppressed only barrel.
I prefer the .0625 and less on the 10.5ish barrels for suppressed use and still MAY be able to function without a can pending your ammo, buffer and spring choice. .058 if you can get there for suppressed use is a good spot. A5H2 and Colt spring.
Rayrevolver
11-24-17, 13:14
I did a clean sheet build on a lightweight 11.5 mid-length for suppressed only. Barrel was 17 oz, which is ~4-5oz lighter than a government 11.5".
I think my only "issue" is that I used an adjustable gas block whereas something like a fixed BRT port would mean less moving parts. No issues or failures with the gas block and it doesn't keep me up at night. Just not quite bomb-proof as a "dumb" gas block. I pinned it though, so I am gonna leave well enough alone.
GeneralPurpose
11-24-17, 16:34
Pistol gas?
Sorry for the late reply, just saw this. Carbine gas, thread-on suppressor that hasn't left the muzzle since day one.
What base barrel, ammunition, and silencer?
This drawing will give you a good idea of what cuts to a 16.1 barrel will look like when finished. There will be about 0.120 of the M203 cut at 11.5 inches.
48852
GeneralPurpose
11-25-17, 09:34
What base barrel, ammunition, and silencer?
Me? Faxon Firearms 10.5" pencil barrel with a MicroMOA Baby Govnah gas block drilled to 0.047", XM193, and Griffin Armament Spartan 3. I've also used several different buffers and they've all worked fine.
I'm not familiar with that can and do not use that type of orifice to control gas. Assuming a base barrel with a standard M16 chamber, throat, bore, US issue M193 as a base to compare to. That porting size, if done in the base barrel, falls below an acceptable level for a porting size on that for most when colder and normalized, with fouling. It is possible that the mentioned silencer has that much higher pressure reversion, but that direction is not one that most would prefer.
What buffers/ springs did you use down to what temperatures in a fouled example?
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