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WheelGunRealGun
July 11, 2012, 07:31 PM
I have a KAC SR-15 16" carbine, and a RRA 20" A4 upper. I'd like to put the 20" upper on my carbine lower, but I heard you have to replace the buffer tube, spring and stock with the A2/A4 version because the rifle length system needs the longer buffer tube.

How would I go about changing my 16" carbine to a 20" rifle with my upper? I've heard you can't convert some carbine cause the buffer tube is staked?

cannonfire
July 11, 2012, 07:39 PM
I have never heard of such a claim about changing the buffer tube. As far as I know there are two sizes; commercial and mil spec. But that has to do with the diameter of the tube to fit what size stock you want.

Assuming it is all the same caliber you should be fine to just switch uppers

Quentin2
July 11, 2012, 07:47 PM
As long as there are no issues mating a KAC receiver with a standard AR receiver the buffers should work.

Justice06RR
July 11, 2012, 08:33 PM
Im no expert either, but think the standard buffer tube/buffer/spring should work. I do recommend an upgrade to a heavy buffer like Spikes T2 or T3 for better cycling.

Mobuck
July 11, 2012, 08:51 PM
I'm amazed at some of the "stuff" people think up.
I have "pistol" AR lower that uses a standard carbine buffer/spring and have used uppers in barrel lengths from 11.5"- 22". Push the pins and shoot.
The only problem I see with a 20" upper on a carbine (telescoping stock) lower is the longer, heavier barrel upsets the balance or the rifle.

madcratebuilder
July 12, 2012, 06:14 AM
The RRA 20" well run fine on the KAC carbine lower. You well notice a difference in the recoil impulse, what little recoil there is.

Willie Lowman
July 12, 2012, 08:49 PM
No you don't need a rifle length buffer for a rifle length barrel. That's just silly.

If you have both of these guns, why haven't you just tried it?

They are AR 15s, push the pins out switch the uppers and tell us what happened.

WheelGunRealGun
July 12, 2012, 09:41 PM
No you don't need a rifle length buffer for a rifle length barrel. That's just silly.


It's not the barrel, it's the gas system, which is longer. I've heard from others that you need an A2 buffer assembly.

madcratebuilder
July 13, 2012, 09:42 AM
Quote:
No you don't need a rifle length buffer for a rifle length barrel. That's just silly.

It's not the barrel, it's the gas system, which is longer. I've heard from others that you need an A2 buffer assembly.

You're correct about it being the gas system length. Both rifle gas and mid-length gas well run fine with the carbine RE/buffer. I have seen rifle gas installed on a carbine RE with a H3 buffer that ran under gassed and needed to H3 replaced with a standard buffer.

raimius
July 13, 2012, 02:32 PM
Just don't mix and match A1 and A2 length parts in the stock and buffer tube. :o I have a friend who got one with mix and matched parts that didn't lock back!

bamaranger
July 14, 2012, 05:58 PM
If the stocks, buffers and springs are interchangeable, why are carbine buffers and A2 buffers different?

When we tweaked a number of A2's to 14.5" M4 config carbines, the buffer and spring, as well as a new extractor spring and damper, were items that had to be switched to get reliability. Now our mod was the opposite the OP, but there seems to me there's some correlation.

DnPRK
July 14, 2012, 08:12 PM
The carbine buffer tube is shorter than the rifle buffer tube and requires a shorter buffer. The buffer length is matched to the tube length to allow the buffer/bolt carrier group to bottom out during recoil and strip a fresh cartridge as it returns to battery.

Using a rifle buffer in a carbine lower will not allow allow the bolt to get behind the cartridge and strip it out of the magazine as it returns to battery.

Using a carbine buffer in a rifle lower causes the bolt carrier key to impact the lower receiver's rear ring, eventually cracking the ring and ruining the receiver.

madcratebuilder
July 15, 2012, 08:25 AM
^^^^^^^^^^^^^^^

What DnPRK said.

The RE length and buffer length needs to match, just as the RE springs need to match.

The carbine RE has three different buffer weights. There are aftermarket buffer weights for both carbine and rifle length RE's, plus the custom buffers from Slash at heavybuffers.com.

The carbine and rifle springs are different length/rates, number of coils, wire diameter, and there are aftermarket springs available.

Add in some of the odd pistol RE parts and it can be confusing.