Mid-Length Gas Conversion?

I agree with the above; I like sabre very much, and I love your idea of a pencil bbl... very old school, especially if you go with a 1/12 or even better , a 1/14 twist.

I don't know how you would adequately block the carbine gas port.

Nothing wrong with a 14.5" midlength. Here is a pic of a couple of mine. BUT..... plugging the gas port would be the thing that concerns me.

I really like midlengths; but I would be concerned about the old gas port location. I don't think any benefits from the midlength would outweigh those concerns.

If your main goal is faster follow-up shots, then a good muzzle brake will get you the most benefit. After that would be a lighter carbine buffer (not heavier) and a reduced weight bolt carrier group (less reciprocating mass) - the lighter mass will also narrow the window where the rifle will run reliably though.

The heavier buffers help delay the cycle time (which helps with carbine gas systems with longer dwell times) and some people prefer the way recoil feels with a heavier buffer (kind of a slower push compared to the standard carbine buffer)

Have heard of people dropping a pin or screwing a set screw into the old gas port and welding it into place, but can't find any references right now.

I have no problems at all with my 14.5" midlength, but if I had to do it again, I'd seriously consider a CAR/M4 gas system (as much as I dislike it) with this barrel length due to the added dwell time. On the other hand, I do like the longer sight radius and the lower gas pressure is probably a lot better for my bolt. If you keep the CAR/M4 port location, think about a good quality bolt like LMT or Colt.


CMMG 14.5 Midlength Pencil Barrel with pinned Phantom flash suppressor

Going from carbine to midlength will require reprofiling the barrel to use the next size smaller gas block. I.E., a rifle with a standard .750 gas block will require a .625 gas block. In the grand scheme of things, all this work is probably not worth doing. You might consider just selling the barrel you have, and using the proceeds to fund the midlength barrel you want.

I wouldn't change to mid-length but not because of gas port, I've plugged many without ever a problem, I thread, install grade 8 set screw Tack weld and file flush just don't do any of that into rifling The old gas port fills with carbon and becomes invisable and causes no problems. The reason I wouldn't do it is dwell time and Issues with battering of parts. If not done correctly the bolt tries to move before bullet exits barrel. Now several guy's are going to jump on and say not so but every broken bolt but one I've seen had the gas tube position moved. Colts biggest problem with the origanal XM177 was dwell time.
I'm happy to see people finally considering dwell time, can cause so many problems which don't show till catistrophic failure of upper assembly.
The choice of buffer spring, buffer, carrier weight, bolt and gas port position were all carefully calculated by Colts and just copied by later manufacturers (except some top drawer builders who caliculated pressure time curve).

I wouldnt do it.

That sounds like, a whole lot of issues for a theoretical benefit.

I wouldnt turn a barrel down either so, take that for what its worth.

I would sell the upper <like thats not the easiest thing to do in the world for ARs.> and buy the upper I wanted pre-done.

Yep, I'd sell current upper, and buy the new one.

I wouldn't change to mid-length ...The reason I wouldn't do it is dwell time and Issues with battering of parts. If not done correctly the bolt tries to move before bullet exits barrel. Now several guy's are going to jump on and say not so but every broken bolt but one I've seen had the gas tube position moved. Colts biggest problem with the origanal XM177 was dwell time.

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Navy, you have that backwards. Going to a Midlength from a CAR/M4 gas system fixes that problem. A CAR/M4 gas system has the gas port closer to the chamber and has a longer dwell time than a Midlength gas system on the same barrel length.

Yup. the Carbine will begin to move the carrier before the middy.

I wouldn't bother having your carbine changed to a middy. Leave it alone and add a H2 buffer if needed to slow things down.