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View Full Version : A quick question? Mid length or carbine?


DK9mm
08-26-2009, 7:07 PM
Can anyone tell me the pro's and con's for the mid length or carbine upper? I will be doing mostly target shooting.

Does either one have more options that the other?

Are parts more available for one opposed to the other?

Any info you can provide would be a big help. I am about to purchase my first kit and have all the other options figured out except this one.

Thanks.:cool2:

aplinker
08-26-2009, 7:49 PM
This has been covered a zillion times.

There are no advantages to a carbine now, but it's all you can get if you want a Colt. The only reason to go carbine, from a design perspective, is if the barrel is less than about 14"

The advantages of mid-length are: lower operating pressure and wider operating range for the action, reduced parts wear, longer sight radius, longer length handguard allows more forward (stable) support, and softer recoil.

Years ago mid-length gas tubes were harder to find, but they're widely available now.

If you're getting a 16" barrel, mid-length is a much better option. At 14.5" mid-length is better, but carbine is acceptable.

GunOwner
08-26-2009, 7:55 PM
This has been covered a zillion times.

There are no advantages to a carbine now, but it's all you can get if you want a Colt. The only reason to go carbine, from a design perspective, is if the barrel is less than about 14"

The advantages of mid-length are: lower operating pressure and wider operating range for the action, reduced parts wear, longer sight radius, longer length handguard allows more forward (stable) support, and softer recoil.

Years ago mid-length gas tubes were harder to find, but they're widely available now.

If you're getting a 16" barrel, mid-length is a much better option. At 14.5" mid-length is better, but carbine is acceptable.

How hard is it to convert a 16" carbine upper to a mid-length? Just to be clear I know how to swap an upper - want to know if an upper can be converted

Agro
08-26-2009, 7:55 PM
Good timing. So here is my recent post on ARFCOM. Good discussion

http://www.ar15.com/forums/topic.html?b=3&f=4&t=457350

Axewound
08-26-2009, 8:20 PM
How hard is it to convert a 16" carbine upper to a mid-length? Just to be clear I know how to swap an upper - want to know if an upper can be converted

i dont think its possible, you can prolly only retrofit to a piston. Or change the barell

Agro
08-26-2009, 8:24 PM
i dont think its possible, you can prolly only retrofit to a piston. Or change the barell

ASFAIK the only difference is in the gas tube, barrel (the position of the gas port), buffer and the tube. I've believe I've seen posts on ARFCOM before where a gunsmith would plug the gas hole and drill a new one. Ghetto IMHO.

MonsterMan
08-26-2009, 8:28 PM
Just get both. :-)

aplinker
08-27-2009, 12:11 AM
How hard is it to convert a 16" carbine upper to a mid-length? Just to be clear I know how to swap an upper - want to know if an upper can be converted

Conversion isn't really the right choice.

Either swap the upper, or simply buy a mid-length barrel when you shoot out your current.

ASFAIK the only difference is in the gas tube, barrel (the position of the gas port), buffer and the tube. I've believe I've seen posts on ARFCOM before where a gunsmith would plug the gas hole and drill a new one. Ghetto IMHO.

The gas tube length and position of the gas port, along with a handguard that's longer, are the only differences. Buffer type depends on how the upper is tuned, for carbine or mid-length.

Good timing. So here is my recent post on ARFCOM. Good discussion

http://www.ar15.com/forums/topic.html?b=3&f=4&t=457350

That thread isn't particularly helpful. The people responding are not particularly well informed.

The AR was designed as a 20" rifle. Any changes from this system will affect reliability. When we went to shorter barrels, everything had to change.

I don't feel like explaining the entire operation of an AR (if you want to understand, find a link to Randall's very well written one), but suffice to say a gas system should be chosen to be as far down the barrel as possible (to allow pressure to drop and lengthen time to extraction, for the brass casing to contract) while still maintaining sufficient length past the gas port (to allow enough gas to be put into the action for operation).

The problem is that, instead of re-designing the XM177 into a 14.5" carbine, they simply used a longer 14.5" barrel. This meant that they still had the (bad) shortened time to extraction and high pressures, but also were feeding a ton of gas to the action (lots of barrel length past the port).

What does this mean? Well, for M4 armorers it means they see about a 30% failure rate of bolts, while M16 armorers will see maybe one or two in a lifetime.

It also means carbine "fixes" have become the norm - things like high tension extractors (O-rings, stronger springs), heavier buffers (H, H2, H3) to increase lock time and slow extraction a bit. These only treat the symptoms. Port erosion is also increased with the higher pressures, so armorers also need to add heavier buffers over time to keep up.

M4 feedramps also came about, to keep the faster cyclic rates and strong bolt bounce from keeping the rounds from tilting during feeding.

Also, a typical commercial 16" carbine is even worse than a 14.5".

Anything you can do to make the gas system more like the M16 is a good thing. In an ideal world every barrel length would have a unique port location.

So the question is, when buying an upper, which is better? The system that yields a more reliable running system (FTF/FTF), better longevity for parts, wider operating range for ammunition (higher/lower pressure), doesn't require "fixes" (extractor/buffer) which have their own issues, and costs nothing, or the one that's always been used?

This really is a free lunch.

supermario
08-27-2009, 3:23 PM
Conversion isn't really the right choice.

Either swap the upper, or simply buy a mid-length barrel when you shoot out your current.



The gas tube length and position of the gas port, along with a handguard that's longer, are the only differences. Buffer type depends on how the upper is tuned, for carbine or mid-length.



That thread isn't particularly helpful. The people responding are not particularly well informed.

The AR was designed as a 20" rifle. Any changes from this system will affect reliability. When we went to shorter barrels, everything had to change.

I don't feel like explaining the entire operation of an AR (if you want to understand, find a link to Randall's very well written one), but suffice to say a gas system should be chosen to be as far down the barrel as possible (to allow pressure to drop and lengthen time to extraction, for the brass casing to contract) while still maintaining sufficient length past the gas port (to allow enough gas to be put into the action for operation).

The problem is that, instead of re-designing the XM177 into a 14.5" carbine, they simply used a longer 14.5" barrel. This meant that they still had the (bad) shortened time to extraction and high pressures, but also were feeding a ton of gas to the action (lots of barrel length past the port).

What does this mean? Well, for M4 armorers it means they see about a 30% failure rate of bolts, while M16 armorers will see maybe one or two in a lifetime.

It also means carbine "fixes" have become the norm - things like high tension extractors (O-rings, stronger springs), heavier buffers (H, H2, H3) to increase lock time and slow extraction a bit. These only treat the symptoms. Port erosion is also increased with the higher pressures, so armorers also need to add heavier buffers over time to keep up.

M4 feedramps also came about, to keep the faster cyclic rates and strong bolt bounce from keeping the rounds from tilting during feeding.

Also, a typical commercial 16" carbine is even worse than a 14.5".

Anything you can do to make the gas system more like the M16 is a good thing. In an ideal world every barrel length would have a unique port location.

So the question is, when buying an upper, which is better? The system that yields a more reliable running system (FTF/FTF), better longevity for parts, wider operating range for ammunition (higher/lower pressure), doesn't require "fixes" (extractor/buffer) which have their own issues, and costs nothing, or the one that's always been used?

This really is a free lunch.



The more of these threads i read, the more i understand and appreciate AR's and why they encounter certain problems and a bad reputation sometimes.
I have learned alot from the posts from UCLA PLINKER AND AR15BARRELS and others. This is not my thread but thanks for all the helpful info you guys dish out everyday over and over! Props to you guys:cheers2:
Now i want a 20" Rifle length AR:D

tiger222
08-27-2009, 3:40 PM
Get a bullpup and you won't care about how short the barrel is. A 20" in a bullpup will still be shorter then a 14.5" pinned (16" OAL) AR with a collapsing stock....

high_revs
08-27-2009, 3:45 PM
ummm.. so to not confuse, he still has to have a 16" barrel (if barrel is shorter, must be a permanently fixed flash hider or muzzle break to make it 16". OP still has to meet the 30" overall length with stock in fully closed position for a centerfire rifle.


OP, search button is your best friend here. YOu can probably read a whole night's worth just on this carbine vs. midlength alone. do a search, start on page last page if thread list.

Federalist
08-27-2009, 3:51 PM
The more of these threads i read, the more i understand and appreciate AR's and why they encounter certain problems and a bad reputation sometimes.
I have learned alot from the posts from UCLA PLINKER AND AR15BARRELS and others. This is not my thread but thanks for all the helpful info you guys dish out everyday over and over! Props to you guys:cheers2:


+1

My first AR was a 16" carbine. After getting better educated (mostly from this site and from references found through this site), my second AR (currently being built) is a 16" middy. :gunsmilie:

Thank you guys for taking the time to share your knowledge and experience.

DK9mm
08-27-2009, 7:33 PM
Thanks to all of you who provide information and opinions. It has really helped me find a path to go down when making decissions on what to get and such.

You guys are great!:)

ar15barrels
08-27-2009, 11:41 PM
How hard is it to convert a 16" carbine upper to a mid-length? Just to be clear I know how to swap an upper - want to know if an upper can be converted

Just change the barrel, gas tube and handguard.

ar15barrels
08-27-2009, 11:45 PM
Here is the link to my gas system operation article:

www.ar15barrels.com/prod/operation.shtml

Steve O
08-28-2009, 1:18 AM
Get a bullpup and you won't care about how short the barrel is. A 20" in a bullpup will still be shorter then a 14.5" pinned (16" OAL) AR with a collapsing stock....

Problem is the bullpup looks like a plastic toy P.O.S.

m98
08-28-2009, 1:36 AM
Problem is the bullpup looks like a plastic toy P.O.S.

agreed....IMO...it is a P.O.S. type of weapon that only the brits' uses because they came up with it.