Conclusion after reading about carbine vs. mid length gas system...

AR/M4 AR Technical Discussion
1

So after reading a bunch of stuff about the carbine vs. mid length gas system on an AR15 with a 14.5 or 16 inch barrel, I have come to the conclusion that the mid length is the way to go for both reliability and minimizing parts wear. It seems the carbine length gas system really only comes into play with an SBR, where there is not enough room for a mid length gas system.

In fact, if this conclusion is correct, then wouldn’t it be best for AR15 manufacturers to only offer the 14.5 or 16 in. bbls with a mid length gas system, even though we see lots of them out there with mid length gas systems??

Please correct me if I have misunderstood or missed an important piece of the puzzle. Thanks!

2

[QUOTE=500grains;669277]So after reading a bunch of stuff about the carbine vs. mid length gas system on an AR15 with a 14.5 or 16 inch barrel, I have come to the conclusion that the mid length is the way to go for both reliability and minimizing parts wear. It seems the carbine length gas system really only comes into play with an SBR, where there is not enough room for a mid length gas system.

In fact, if this conclusion is correct, then wouldn’t it be best for AR15 manufacturers to only offer the 14.5 or 16 in. bbls with a mid length gas system, even though we see lots of them out there with mid length gas systems??

Please correct me if I have misunderstood or missed an important piece of the puzzle. Thanks![/QUOTE

i agree the middy gas is the only way to fly , with a 16’’ barrel.
i have a carbine gas , 16 incher, then went and built a 20’’ service rife.
sheesh, soooo much better !
so now i’ve sent a 16’’ to adco to go with the mid-length gas.
for my dissy project.
hands down, i like the rifle gas the best.

peabody

3

A lot of the reason that midlengths don’t yet dominate the 16" market is probably corporate inertia. Remember that the original civilian M4-style carbines were very close copies of the M4 in terms of barrel profile and gas port position, and it was a while before manufacturers broke away from the M4gery style and offered other configurations. And while AR’s are quite modular, you still have to retool a little for midlengths if your company is set up to produce nothing but carbine length and full length systems.

Since midlengths are a relative newcomer to the market, it takes a while for new configurations to diffuse into the mainstream, even though they are arguably a better match to 16" barrels.

4

I can just imagine what will happen the day Col. Colt announces a 16" Middie for the LE line.
They will have to drop all their military contracts to keep up with the demand! Sign me up
for a pair, if you please! :slight_smile:

5

Also consider how a company produces barrels in length from ~10.5-16". They may pump out 16" all day long and cut them for any length shorter, as the port location will work.

Does anyone know?

6

I love the way the middy length guards feel - not fond of that crapped elbow with carbine.

7

Not quite sure that I follow. You meant “cramped” elbow, right?

AC

8

If you’re getting crap on your elbow you’re doing it wrong.

9

Let me rephrase - the mid length guard is more comfortable to me than the carbine length - I prefer the longer reach with the supporting hand.

10

My BCM Mid- length just feels “right”. I probably won’t buy or build another carbine length gas system.

11

That makes much more sense; doubly so when we start talking about hanging lights and VFGs and such. The extra rail or handguard space afforded by the mid-gas configuration is very nice to have.

AC

12

Well my carbines are still going strong and haven’t fallen apart… personally, I’m not too concerned.

At the same time I haven’t heard of any obvious downsides to the mid-lengths. I’d also agree that the extra rail space would allow for better control.

13

definitely like the middy better. More comfortable, and looks better with a 16" barrel - the carbine hg/gas system was designed for a 14.5" barrelled M4.

FWIW - there are less feed/extraction issues reported on 6.8s with a mid-length vs. carbine-length gas system.

14

I came to the same conclusion myself and bought a BCM 16" Midlength. I don’t think I would ever buy a Carbine length gas system gun, as I don’t want to go through the hassle of going the SBR route.

15

I got rid of all my carbine length ARs for my middys and I did notice a slight difference in performance. I used to own a DDM4, S&W M&P15 and Bushy ARs and now I have an SR15 and Centurion DMR (rifle length). I do notice a lower recoil and much smoother function of the bolt. I also have less powder residue slamming back at my face. Again what I am about to say is subjective but I did notice the BCG on the Middy runs slightly cleaner. I have less residue being picked up for the same amount of rounds on the middy. Now the mess is mainly the bolt, gas key and sides of the receiver. On my carbines it used to be on the entire carrier. I love my middys and now that is the only thing I will buy.

16

Interesting points.

17

I prefer the middies. So much so that I replaced the barrel on my DD rifle with an Adco barrel. At the same time I still own and will continue to own carbine length systems. My 10.5 SBR and 14.5 LW build are both carbine systems as is my issued M4 that I carry every day on duty.

18

The CARbine gas length was carried on from the 10" barrelled XM177s. IMHO It shouldn’t be used on anything but 10.3"-12.5" short barrelled uppers. 14.5"-16" barrels should be midlengths, 18" should be intermediate gas and 20-24" should be rifle length gas.

19

Yeah, what he said!

20

That is probably the best summary right there.
Many decisions are made based on compatibility with current inventory and other admin reasons. - Not because all other options were tested and were lesser in comparison.

We have been T&Eing a 14.5" Middy for about 1 year (with help from a lot of great shooters and great folks). We built almost 2 dozen different configs before we decided on what our current production would be. About half way through T&E process we were fine tuning the final set up.

Regarding standard production uppers/rifles, we check cycle rates on all samples from all batches to confirm they are within the mil-spec. (Most commercial guns are way way too fast). Checking the cycle rate involves a number a mags filled with 28 rounds, and full auto lower, and a timer set up for the AR carbines. We run a couple mags full auto into a snail drum. I do the cycle tests personally. (benefits of ownership :D)lol

I had a number of M4 Carbine 14.5" and 16" uppers to test (and the one T&E 14.5" Middy on the end). They were lined up on the bench without regard to any specific order. I run some mags on the M4 Carbine 14.5", grabbed more mags and then ran the next set of M4 Carbine 16", then robotically grabbed the 14.5" Mid, ran a full auto mag through it (little over 2 seconds). At about round number 10 my eyes perked up, I was careful not to move in from of the snail drum and kept the trigger pinned until bolt lock. I turned to our production manager and said; “Holy Sxxx, that was awesome. Are you sure those were our normal function ammo”. (yes it was Black Hills 55 blue box). I grabbed a couple more full mags and repeated the mag dump. I finished, and said to the production manager; “Wait until people shoot this gun!” The difference between a milspec carbine is dramatic, especially when you desire to run a NSR (volume of rounds) into small pie plate. Time on target gets much quicker and you get much faster - with the same level of accuracy.

I have since retired all my hot rod, super cool, supercalifragilistic, SBRs that I love so much. My personal set up it a 14.5" middy with a PWS or SF MB.

(As a note; we applied what we learned to our 16 mid as well)