18" barrel with carbine gas?

[Goose910]

Hi first off id like to say in new to the AR15 world and this doesn't apply to an m&p 15 but a Colt competition.(I own a few m&p pistols hence the reason I have an account) I asked this question on ar15forum but as I expected I didn't get nice replies...snobs. Anyway I'm asking you AR gurus out there if this Colt Competition 1518 with an 18" barrel and "carbine-length port" would function reliably? I have a small knowledge of the gas systems and how ar-15s work and that most 18s use rifle or mid length but I couldn't find a lot of info on an 18" with carbine length. I found this rifle for about 1000$ and am debating on "pulling the trigger"....(had to say it).

Any suggestions would help. Thanks!

 

[427mach1]

I'm sure it would function properly, assuming the rest of the action is in good working condition. I put an 18" barrel on my AR but went with the mid-length port. Putting the port further down the barrel results in lower port pressure, gentler cycling of the bolt, less perceived recoil, and maybe a little less wear and tear on the gun. I believe the AR-15 first came out with the 20" barrel and rifle-length port. Shortening it to a carbine put the gas port closer to the chamber, resulting in higher port pressures and a harder cycling action.

 

[MichiganScott]

It should work fine.

Remember that you can always tune it with different weight buffers, springs, and/or bolt carriers.

 

[Neptune VooDoo6]

I did something similar with a carbine conversion. I had a DB15B carbine. I converted to an MK12 Style SPR with an 18 heavy barrel, I changed the gas system from carbine length to rifle length. (Frankly, just needed a longer gas tube using the same low profile gas block) Additionally, I replaced the adjustable stock (a Magpul CTR) with the old school AR15 A2 fixed stock and went with a heavy duty buffer spring and buffer.
No issues and cycles beautifully

 

[WR Moore]

A little late to the party, but I have to agree with several others. If you have an 18" barrel, the carbine length gas system makes no sense. Of course, that kind of depends upon your intended use.

The carbine length gas system is less tolerant of ammunition variations and operates at higher internal pressures than the mid or rifle length gas systems. You probably can play with heavier buffers, but you're new to the system and playing with such stuff is of questionable actual effect.

I don't know what a Colt 1518 is or its intended purpose. I'd suggest you figure out what you want an AR for and shop around. Rock River makes some 18 inch guns with mid or rifle length gas systems for around what the Colt is going for. They have a better warranty too.