AR - M4 vs Mid length

[Pilot]

I'd eventually like to get an AR-15 in 5.56 to replace my CAR-15. I've always wanted a Colt 6920, but looking around I've noticed that mid length AR's have become popular and there seems to be a better experience with reliability with the mid length gas system.

Does Colt make a mid length version of the 6920? If not, what are some good choices in manufacturers of these? Am I worrying over nothing as the M4 length system must be reliable or it wouldn't be so popular.

 

[MrCleanOK]

Assuming 16" barrels, mid-length is better than carbine gas in every way. BCM has lots of great offerings. If the only changes you're looking to make are in the upper receiver, have you thought about just swapping that instead of replacing the rifle?

 

[Pilot]

Yes, I have thought about just getting an M4 Upper. I hear good things about Spikes, CMMG, etc. I would like a 16 inch barrel with bird cage flash suppressor. I am a pretty no nonsense guy, so just want a flattop that I can mount an optic on with regular hand guards. I want to keep it light and simple.

 

[HGUNHNTR]

I like my Spikes, but to be fair I only have a few hundred rounds through it. It does feature some fine components, and appears to be assemblesd with great attention to detail.

 

[RavenTai]

Am I worrying over nothing as the M4 length system must be reliable or it wouldn't be so popular.

The M4 and its gas system is designed for a 14.5" barrel, unless you want to pay a $200 short barrel rifle tax civilian rifles have 16" barrels, this extra barrel length after the gas port makes a difference and cases the gun to cycle harder than necessary, there are work arrounds, heavier buffers, heavier bolt carriers etc, but for a 16" barrel the mid length gas system is just a better fit.

 

[KW]

Is the mid-length gas system a little better than a carbine on a 16" barrel? Probably. Does that make a carbine bad? Hardly. You'll still get very very good service from a 16" carbine, and if you wanted there are some companies (like BCM) that sell a 14.5" M4gery with an extended flash hider to make legal length. Just keep in mind that a lot of the hype around mid-lengths is the usual AR-15 flavor of the month action.

 

[Zerodefect]

I prefere carbine gas systems on my carbines because I shoot left handed often.

Otherwise there is little difference in performance.

The biggest thing is you get longer grips on the middy, and that gives you a better stance. My 6920 requires an obsolete stance, I'll be cutting it's front sight off soon and useing a DD 12" foreend so I can reach out better.

But other than the need for a 12" rail, the Colt 6920 is one of the best carbines you can buy. Mine has never failed.

 

[RatDrall]

Carbine gas systems and M4 style barrels are for the military, where they have grenade launchers and whatnot, and the gas system and goofy barrel cuts and weights have a purpose. Aside from that, there is no reason to use one.

A lightweight barrel profile with a midlength gas system would be ideal, for both weight savings and less recoil.

 

[possum]

i don't know if colt makes a mid length, but i would go the BCM route, that is what i did. A good mid length upper, with the right buffer, and comp and you will have a very easy shooting rifle, with minimal perceived recoil, and almost no muzzle climb.

 

[Quentin]

I love my 16" midlength and its soft gas stroke but it is slower to maneuver than an M4 profile. You might want to compare both before choosing.

 

[Bartholomew Roberts]

The gas port on the M4 is actually an artifact based on the gas port location developed for the XM177 (a 10.5" barrel). It isn't really ideal for either the 14.5" or the 16" barrel. However, from a practical use standpoint, it is an extremely minor difference.

The LE6920 is going to have all of the upgrades to deal with the issues raised by the shorter gas system - H buffer, upgraded extractor insert and spring, M4 feed ramps, etc.

My preference is for the midlength but it has less to do with reliability/durability and more to do with different recoil impulse, more handguard real estate and better sight radius. The difference in reliability appears to be mostly thereotical/speculative in any case. While the M4 system has been extensively tested in a variety of conditions, there is a lot less data on the midlength systems. The only one I am aware of looking at long term use of a midlength gas system with a heavy shooting schedule would be the midlengths Pat Rogers uses in his EAG Tactical classes. However, with at least one at 39,000 rounds now, it looks like they hold up OK.

 

[Z-Michigan]

Everything Bart said above. If you stick with carbine length gas, I would suggest trying even an H2 buffer over the H model.

 

[wnycollector]

Not to hijack this thread, but I have been waffling recently between two uppers to go with my Cav Arms lower. The two uppers are a carbine with 14.5" barrel and pinned PWS FSC556 or a lightweight 16" (.625" under the FSB) mid length. One day I'm ready to pull the trigger on the carbine, then I read some more and the 16" mid length is back on top!

 

[Bartholomew Roberts]

Just as a reminder, the difference in unlock time between an M4 and an M16 is 175 microseconds - that is 175 millionths of a second. The difference between a midlength is even less. This should give you a clearer idea of what type of difference we are discussing in cycle times.

 

[taliv]

and what is it? just under 3 milliseconds from hammer strike to bullet exiting the barrel?

 

[Pilot]

Great info guys. Bart, I hear you on the sight radius and handguard positioning. I'm leaning towards a 16 inch M4 profile barrel with mid-length gas system/handguards. I may just get one to throw on my DPMS lower and sell the CAR-15 upper seperately. I just don't like the H-BAR 16 inch barrel of my CAR-15. It kind of defeats the purpose of a short, handy carbine.

I've been shooting a lot of 5.45 from my AK-74's and Tantal, and just miss the old AR. I think its the best all around platform and for mounting optics there isn't much better.