Gunsmithing Cutting a CHF chrome-lined barrel

[samb300]

I'm considering buying a CHF chrome lined AR-15 barrel and chopping it down to 12.5" in order to have a mid length gas system.

Both Marvin Pitts at Nefarious arms and Parker Mountain Machine aren't taking any work right now. Does anyone know of any other gunsmith with experience cutting/crowning/threading chrome lined AR barrels?

Thanks,

Sam

 

[Yondering]

Midlength on a 12.5" barrel - why? It's a great way to make sure your rifle is really picky about what ammo it'll function with, assuming you're talking about 5.56.
I've noticed a trend lately for some people to assume the longest possible gas system length is best, but that's false. There has to be a balance, and to have reliability across a wider range of loads you really need more barrel in front of the gas port than the ~2-3/4" that you'll end up with. That's my experience anyway, from playing with different gas system lengths.

If you're just after a soft shooting rifle, I recommend carbine gas for that barrel length and tuned gas metering, either by careful gas port sizing or gas block tuning. If you're not equipped to drill a gas port yourself, and don't like adjustable gas blocks, then you can use a gas block with a bushing in it to meter the gas. The bushing can be drilled out in small steps up in diameter until you get the right function, or there's at least one company that'll sell you different bushing sizes.

Whichever way you go about it, gas metering tuned for your particular rifle will give you a softer shooter than going too long on the gas system with a port size that most likely isn't perfect for your rifle.

 

[samb300]

Midlength on a 12.5" barrel - why? It's a great way to make sure your rifle is really picky about what ammo it'll function with, assuming you're talking about 5.56.
I've noticed a trend lately for some people to assume the longest possible gas system length is best, but that's false. There has to be a balance, and to have reliability across a wider range of loads you really need more barrel in front of the gas port than the ~2-3/4" that you'll end up with. That's my experience anyway, from playing with different gas system lengths.

If you're just after a soft shooting rifle, I recommend carbine gas for that barrel length and tuned gas metering, either by careful gas port sizing or gas block tuning. If you're not equipped to drill a gas port yourself, and don't like adjustable gas blocks, then you can use a gas block with a bushing in it to meter the gas. The bushing can be drilled out in small steps up in diameter until you get the right function, or there's at least one company that'll sell you different bushing sizes.

Whichever way you go about it, gas metering tuned for your particular rifle will give you a softer shooter than going too long on the gas system with a port size that most likely isn't perfect for your rifle.

Thanks for the info!

My plan is to have a 12.5" SBR that is 100% suppressed and tuned for factory/mil spec brass cased ammo with a non-adjustable gas block. I didn't think it would be too hard to tune being suppressed, I've heard that going down to an 11.5" middy makes things more complicated.

I shoot left handed so I'm really trying to minimize gas blowback and thought going to a 12.5" carbine gas would increase the gas quite a bit.

 

[alamo5000]

I vote for that you are making this way more complicated than it needs to be. I have a 10.5 that runs like a champ.

I don't know why some people don't want to use an adjustable block, but at best that's only part of the equation.

As for gas in the face that's going to depend on what suppressor you use and what ammo you use. Gas blocks and all that have almost no bearing on how much gas comes back to the shooter.

 

[TonyTheTiger]

Midlength on a 12.5" barrel - why? It's a great way to make sure your rifle is really picky about what ammo it'll function with, assuming you're talking about 5.56.

I don't know, I bought a 12.5" mid as an experiment, assuming I'd have trouble. I can't make the darn thing malfunction, with a wide variety of ammo. I don't even know what buffer I threw behind it.
Recoil is night and day compared to my 10.5" carbine gas. Some buddies were so blown away by the difference they tossed their carbine gas 10.5-12.5" barrels in favor of 12.5" mid, even after I warned them about potentially smaller operational windows. No problems at all, completely unsuppressed also.

 

[alamo5000]

I don't know, I bought a 12.5" mid as an experiment, assuming I'd have trouble. I can't make the darn thing malfunction, with a wide variety of ammo. I don't even know what buffer I threw behind it.
Recoil is night and day compared to my 10.5" carbine gas. Some buddies were so blown away by the difference they tossed their carbine gas 10.5-12.5" barrels in favor of 12.5" mid, even after I warned them about potentially smaller operational windows. No problems at all, completely unsuppressed also.

I've been wanting to build a 12.5 actually. It's been on my radar for a long time already.

That said I think with just about any relatively good components you can make one run like a sewing machine. That kind of goes back to my first point of not getting too complicated.

 

[roosterpig]

@unclemoak likes chopping and threading. He’s a wizard.

 

[TonyTheTiger]

I'm considering buying a CHF chrome lined AR-15 barrel and chopping it down to 12.5" in order to have a mid length gas system.

Just re-read this, why not just buy a 12.5" mid if that's what you want? Adding the extra step of sending off a longer barrel to be cut down seems silly to me. Unless the chromed bore is an absolute requirement and can't be had off the shelf.

 

[Yondering]

Thanks for the info!

My plan is to have a 12.5" SBR that is 100% suppressed and tuned for factory/mil spec brass cased ammo with a non-adjustable gas block. I didn't think it would be too hard to tune being suppressed, I've heard that going down to an 11.5" middy makes things more complicated.

I shoot left handed so I'm really trying to minimize gas blowback and thought going to a 12.5" carbine gas would increase the gas quite a bit.

OK, 100% suppressed is a different story, and I don't see any issues making that work.

Minimizing gas face is still going to require tuning the gas system though, and it has to be tuned for your gun and your suppressor. Buffer weights are only part of the solution and can only do so much; the rest is all about the gas port size or whatever the smallest restriction is in the gas system (could be the gas port, or an adjustable gas block, bushing in the gas block, or even an adjustable gas key, all accomplish the same thing in different ways). There are companies like Roscoe that sell suppressor barrels, set up to run 100% suppressed, but unless you get very lucky you'd still benefit from tuning the gas system to suit your setup.

I don't really understand why some people are so against adjustable gas blocks, but you can use the simpler set-screw type to set it and forget it; most of the complaints are all about not being able to adjust them once they seize up, but that's pretty much what you want if I understand correctly. The cheaper Seekins gas block is a good example (the set screw version for about $60, not the one with the lever). Once it's set correctly, you don't need to dick with it again, ever. Functionally it's the same as a perfectly sized gas port, or a perfectly sized bushing in the gas block. It makes no difference how you get there, but getting a perfectly sized gas port requires machining equipment that it doesn't sound like you have access to or experience using.

 

[Yondering]

Gas blocks and all that have almost no bearing on how much gas comes back to the shooter.

That part is not true. Adjusting the gas correctly has a huge impact on the amount of gas the shooter experiences; correct gas metering delays the bolt from unlocking too soon, so pressure has dropped off more in the barrel and can, and a lot less gas comes back down the barrel when the case is extracted. That's not theory; it's easy to prove for yourself by tuning the gas on a rifle that needs it, and you can see the difference in slow motion video too.

Keep it simple is good, but not when taken to the extreme of having your stuff not work as well as it should. Occasionally you'll see people in the car world saying the same thing - "I keep it simple, don't need to adjust the carburetor, I just drive it" - while their car has trouble starting, sputters when they give it full throttle, etc.

Adjusting the AR gas system isn't complicated, and it can be a huge help when using suppressors.

 

[st1650]

AGB and a JP SCS with the springs and weight kit and you’re in business.

 

[longshot2000]

Thanks for the info!

My plan is to have a 12.5" SBR that is 100% suppressed and tuned for factory/mil spec brass cased ammo with a non-adjustable gas block. I didn't think it would be too hard to tune being suppressed, I've heard that going down to an 11.5" middy makes things more complicated.

I shoot left handed so I'm really trying to minimize gas blowback and thought going to a 12.5" carbine gas would increase the gas quite a bit.

It is true, that a very short dwell time with a suppressor works well. I have seen how hard it was for Crane to get the 10.3" barrel tuned correctly, and have long advocated to have longer dwell times, but the guys who make some of the best suppressors showed me one day what a difference a mid-length barrel cut down close does with a suppressor. I would get some serious advice about the gas port. I know gas ports pretty well, but not for short dwell and suppressed.

Cutting a chrome lined buttoned cut barrel is not a problem. Keep in mind, that there is a certain percentage that are scrap. We do a lot of barrel work, and cutting down barrels is probably 5% waste (I mean, throw away), so yours could be that 1 in 20, mostly due to lack of concentricity. As long as you know that going in, your good.

 

[carbonbased]

I shoot left handed so I'm really trying to minimize gas blowback and thought going to a 12.5" carbine gas would increase the gas quite a bit.

If reducing gas in the face is very important (lefty), then is there a reason you don’t want, say, a PWS piston gun?

It sort of sounds like you are looking for a SHTF gun with lots of normal AR15 parts for future compatibility. That’s cool, but just wondering.

 

[Hippy_Steve]

I'm considering buying a CHF chrome lined AR-15 barrel and chopping it down to 12.5" in order to have a mid length gas system.

Both Marvin Pitts at Nefarious arms and Parker Mountain Machine aren't taking any work right now. Does anyone know of any other gunsmith with experience cutting/crowning/threading chrome lined AR barrels?

Thanks,

Sam

Morgan, who runs class 3 machining, recently did a great job cutting my scar 17 barrel. Very professional and a fast turn around time relative to other smiths that work on chrome lined barrels.

Alternatively, Do your research and just buy another barrel. There are so many options these days that you’re likely going to find exactly what you want at a price similar to the cost of getting a barrel chop, without the hassle or unknowns of a barrel chop.

And to repeat what other posters have already said well, tune your rifle with different gas jets, springs, and buffer weights. I’m cursed to shoot left handed too, so i’ve had to do my homework to minimize getting gassed. FYI, piston gas systems with sub-16” suppressed barrels will also require tuning.

 

[Bantam1]

Class 3 Machining in the Dallas area. It's $75 to cut, thread and crown. He usually turns then in less than a week for the two times I used him for work. You have to provide a return shipping label too. Flawless work and concentric threads.

 

[samb300]

@Hippy_Steve @Bantam1 - thanks for the info on Class 3 Machining, I'm going to reach out to Morgan and see if he can do it and what the cost would be. Parker Mountain Machine got back to me and said they'd do it, but their site says 12 week lead time and their price is pretty damn high. I think they charge more due to being one of the only places that advertises doing SCAR barrels, but I'm not sure what would really warrant charging 2-3x more than a standard cut and thread.

I appreciate all the info. With all AR stuff, there are so many options and I tend to get overwhelmed with everyone and their mom having an opinion on what the best build is. Ultimately I wanted to build my first SBR, and am trying to balance having better ballistics than a 10.3", and decent handling with full-time suppressor use.

I've been waiting and waiting to find a Faxon 12.5 middy in stock, so I said F-it and bought a Noveske CHF barrel, then of course today I get an in-stock notification for the Faxon . Noveske does offer a SS 12.5" middy, but I wanted to do chrome-lined for more of an SBR blaster build.

I was also thinking about getting a BRT Eztune gas tube and talking to them about my setup to help dial it in that way.

I shoot my SCAR 17 suppressed with an Omega 300 and it's pretty horrible to shoot Left Handed. So I ordered a SiCo Velos LBP to see if that will help on the 556 AR in terms of gas backpressure. I know they're totally different animals but it makes the SCAR so not fun to shoot as a lefty compared to suppressed bolt gun or 22LR. If SiCo comes out with a 762 Velos or the Huxwrx 762 turns out to be good on a SCAR, I might pick one of those up.

 

[Hippy_Steve]

.

I shoot my SCAR 17 suppressed with an Omega 300 and it's pretty horrible to shoot Left Handed.

Two words: gas jets. Enjoy the rabbit hole.

 

[st1650]

Nothing wrong with 12.5 mid. Nothing wrong with 12.5 carbine. Anything can be done if you understand the relationship between the pressure from the ammo, gas port size, mass/style of BCG, mass of buffer and spring tension. Adding a dedicated can will obviously increase the back pressure. Then you can play with those variables accordingly. Even some charging handles can reduce the felt gas although I think these are mostly gimmicks.

 

[samb300]

Two words: gas jets. Enjoy the rabbit hole.

I've gone down in jet size as small as I can go, I might look into the DiSCARder

 

[tucaz]

you’ll be fine chopping a 16” mid down to 12.5. i’ve done that to 2 barrels, an FN and noveske and left the gas ports alone. both cycle perfectly with all ammo and suppressed/unsuppressed with H buffers

i liked the longer sight radius on the FN with the full FSB and have it set up with iron sights only as a truck gun.