A5 buffer setup using A2 extension with spacer?

[Casswick]

Im in process of planning out a 6.5 Grendel AR that will have a fixed stock, either the Magpul PRS or Fab RAPS. I would like to use a rifle length system as I already have the spare parts, and would like to try a low weight carrier and buffer setup. My intention is to try to make a A5 buffer system with a rifle length tube. Based on what I have found online:

Carbine extension: 7 - 7.25"

A5/SR25 extension: 7.75 - 8"

Rifle extension: 9.5 - 10"


Sources:

https://www.ar15.com/forums/ar-15/Rifle-Buffer-Tube-Question/4-770078/

https://www.reddit.com/r/AR10/comments/p5mutt/775_buffer_tube/

So does it a fair assumption that putting a ~2" delrin spacer within a rifle tube would give it effectively the same internal depth as an A5 extension?

Brownells has some premade options that could work, however they may add an extra 1/2" or more to convert into a carbine length rather than A5.

https://www.brownells.com/gun-parts/rifle-parts/rifle-stocks-parts/ar-15m16-buffer-spacer/

https://www.brownells.com/gun-parts/rifle-parts/rifle-stocks-parts/ar-15-a2-stock-spacer/

[Bob R]

I put together a couple Buffer Tube Spacers a while back. I set mine up for Carbine Spring & Buffer into a Rifle Buffer Tube.
Do the math from your numbers above, and make it on the long end to start with. Easier to shorten the Spacer, than to make it longer. I used some Exotic Medical Grade Plastic Rod Stock from On Line Metals for mine. You could probably get by using a Wood Dowel and a Washer or Quarter between the Wood Dowel end and the Buffer Spring.

To test the length push the Bolt Carrier into the Buffer Tube with Buffer, Spring, and Spacer in place, until it bottoms out. What you are looking for is approximately the thickness of Two Nickels between the back of the Carrier Key, and the receiver when bottomed out. For the more precise that is approximately 0.150. You do not want the Carrier Key to hit the receiver and damage it. Adjust the Spacer length until the Carrier Key spacing is correct.

You can also get a good measurement for your spacer by adding Quarters to the Buffer Tube until you arrive at the correct Spacer Length, and then cut the spacer to the length of your stack of Quarters.

Bob R

[LRRPF52]

That A2 stock space is meant to go on the back of the Rifle RET, which came from the original M16/M16A1 and their shorter stocks.

It goes outside of the RET (buffer tube), not inside of it. There is also a longer screw that holds the buttplate to the RET, and pinches the A2 spacer between it and the RET.

Why not just use a rifle buffer with rifle spring inside of a rifle RET?

There is no benefit to using a shorter buffer in that set-up.

The basic mechanical engineering for this is already well-established since 1957.

[Old Bob]

I have A1 stocks on 4 of my 6 ARs. Of the other two, one has a Magpul fixed length Carbine stock & one has a Vltor A5 stock. Despite only being about an inch longer than the A1, the A2 stock feels too long for me me. It's not comfortable ...

[Bob R]

The Original Question. He is wanting to use an A5 Buffer and Spring in a Rifle Length Buffer Tube. The A5 Buffer Tube (Adjustable Carbine) is in between the M4 Carbine and Rifle Length Buffer Tube Lengths. The A5 is a little longer than the Carbine Length. What this means is the Buffer is also in between the Standard Carbine and Rifle Buffers in overall length also.

Why use an A5 Butt Stock Assembly? For one thing it makes the Multi Position Carbine Stock Longer than an M4 when fully extended. Valtor, a big Duck In The Puddle on the A5 Assembly makes the A5 Buffer in Five different weights. The original poster is wanting to use a Light Weight A5 Buffer as well as a Light Weight Carrier. He is also wanting to use a Rifle Stock, requiring a Rifle Length Buffer Tube.

If you run the A5 Buffer in a Rifle Length Buffer Tube with out a Buffer Tube Spacer, the Carrier Key "Can/Will" hit the back of the receiver under recoil. The Buffer Tube Spacer is required to limit the rearward travel of the Buffer as well as the Carrier. The Buffer and Carrier need to bottom out in the Buffer Tube before the Carrier Key hits the Receiver. The Buffer Tube Spacer is what will limit the rearward travel of the Carrier keeping the Carrier Key from impacting the receiver.

His pictures show both an internal Buffer Tube Spacer (What he is needing only too long, M4 Buffer in a Rifle Buffer Tube) as well as the A1 to A2 Butt Stock Spacer. Two completely different things.

Bob R