Mid length Carbine

**Abraxas** · 02-27-08, 16:36

It was always my understanding that the shortest barrel one could get a mid gas system to work reliably on was a 16". Anything shorter than 16" did not offer enough bullet travel past the gas port to reliably cycle the bolt.Or so I have been told. Noveske rifles are top quality, and I noticed that he offers a mid gas on a 14.5" weapon. I am assuming that he knows what he is doing so, have I been mislead or does he do something different to some how make it work?

**Robb Jensen** · 02-27-08, 16:43

My wife owns a 13.6" with perm. mounted SOCOM length M4-2000 mount (make it 16") Noveske midlength which started as a 14.5" but had to be cut down. Randall at AR15barrels.com cut it down, threaded it and opened the port a little and it works great.

**Abraxas** · 02-27-08, 17:02

Originally Posted by gotm4

My wife owns a 13.6" with perm. mounted SOCOM length M4-2000 mount (make it 16") Noveske midlength which started as a 14.5" but had to be cut down. Randall at AR15barrels.com cut it down, threaded it and opened the port a little and it works great.

So then is Noveske opening the port on his 14.5 mid for it to operate reliably?

**Robb Jensen** · 02-27-08, 17:04

Originally Posted by Abraxas

So then is Noveske opening the port on his 14.5 mid for it to operate reliably?

Noveske makes his barrels from blanks, meaning he installs the barrel extension and drills the gas port. He makes it work from the get go.

**Abraxas** · 02-27-08, 17:06

Originally Posted by gotm4

Noveske makes his barrels from blanks, meaning he installs the barrel extension and drills the gas port. He makes it work from the get go.

I see, thank you for the info.

**GaryXD** · 02-27-08, 18:26

My 14.5" midlength CMMG has never malfunctioned.

**cqbdriver** · 02-27-08, 19:12

I also have a 14.5" midlength CMMG. It was been very reliable. 2 malfunctions in 3000rds. The 2 jams occurred with a 1st generation PMAG that also caused jams in 3 other rifles (2 Colt & 1 BM).

**Failure2Stop** · 02-28-08, 16:28

Could someone get into the nitty-gritty with this?

Is it highly dependant on gas port size?

It seems to me that gas systems without sufficient dwell time after the gas port get finicky (10.5 with carbine gas, 17 with rifle gas), and guns with too much dwell time have excessive bolt velocity (16 with carbine gas) from being over-gassed.

It seems to me that about 5"-7" of barrel past the port (I assume no change in gas port size) provides the "right" amount of dwell. I assume that opening the gas port provides more volume of gas to the gas tube and bolt, but the duration of that gas flow will still be regulated by the barrel length, which is why (it seems to me) those systems are more "picky" about ammo.

However, there is still the issue of obturation and lock time. Shorter systems (carbine) do not leave the bolt locked long enough after firing for the fired case to contract, forcing the bolt to unlock and extract the fired case when it is firmly fixed in the chamber. Gas ports that are located further from the chamber naturally allow longer lock time than gas ports located closer to the chamber, regardless of dwell time.

Does the longer lock time of a middie reduce the dwell time necessary to ensure proper function with an array of ammo? How important is gas port size in 14.5 middies (relative to 10.5 and 20)? I see gotM4 above saying that his 13.6 had to be opened up, so I assume that a standard gas port size doesn't work.

Just looking for some input, as I have been thinking about this for a while, and now that Abraxas has brought it up, I would like to know the deal.

Will going to a 14.5" mid give me 20" rifle recoil, but will only be reliable with specific ammo choices, or does it bridge the gap in OAL/performance? Does it take personal (boutique) attention to produce it correctly, like the 10.5(-) family, or is it easy enough to rely on mass-producers to do it right?