buffers

[DaveL]

Hi guys,
I'm in need of an education about buffers. I'm trying to come up with the right combination of parts to make a 300 blackout cycle with sub-sonic rounds. The upper has a 16" 1 in 7" stainless medium contour barrel with a carbine gas system. The bolt carrier is a light weight ar15 carrier. Right now it has an A2 rifle stock which means it has the rifle sized buffer tube, spring and buffer.
So, a few questions.
1) The carbine buffer is shorter than the rifle buffer. Is this because the buffer tube is shorter? Or is there a weight difference because of the shorter gas tube on the carbine?
2) Can I put a lighter carbine buffer in a rifle buffer tube with a rifle length spring to speed up the bolt for sub-Sonic's? Or would that allow the bolt to go to far into the rifle buffer tube?
3)Are the springs the same tension? Or is the carbine spring stronger because it's shorter. In other words, does the carbine buffer assembly have the same spring pressure as the rifle?
I guess what I'm really asking is what's the best buffer setup for sub-sonic 300 blackout rounds?
I'm confused! :eusa_wall:
Thanks in advance to anyone that can help me alleviate my confusion.
Dave

[gwp]

First, the length of the buffer tube (receiver extension) is important. Only use a carbine buffer in a carbine tube and a rifle buffer in a rifle tube. A carbine buffer in a rifle tube will allow the bolt carrier to enter too far into the tube and cause damage. If you use a carbine buffer in a rifle tube you will need a spacer in the tube to prevent the bolt carrier from entering too far.

http://www.brownells.com/rifle-parts/receiver-parts/buffer-tube-parts/buffer-tube-hardware/billet-rifle-stock-spacer-sku100008582-44889-100407.aspx

You could lighten the rifle buffer by replacing some of the steel inserts with a lighter materiel like nylon rod. Also Wolff makes a reduced power action (buffer) spring that may help.

http://thearguys.com/ar-facts/difference-ar-15-buffers/

http://www.gunsprings.com/index.cfm?page=items&cID=2&mID=1#490

I have two 300 BLK AR15 carbines (PSA/DSA) and they shoot sub-sonic and normal rounds with standard carbine buffers, springs, stocks and F/A bolt carriers.

I would try a standard carbine buffer and spring with a rifle stock spacer.

[DaveL]

Thanks GWP.
Your info and links really helped me to understand. So Far I've only shot my Blackout super-sonic. I have a good load worked up for 150gr and 125gr bullets for predator and deer hunting. I have some 200gr Nosler partitions I thought I'd try sub-sonic. I'm going to shoot them at some wet newspaper next spring. I'm real curious if those partition bullets will open up at sub-sonic speeds. I've read that the partitions open quickly and retain their weight. We'll see.
After reading through the info and links you posted, I think I will first try the rifle as is, with the rifle buffer assembly. If it doesn't cycle or lock back, I'll try a Wolfe reduced power spring ($15). If it doesn't operate correctly then, well, I'll start looking at carbine buffer assemblies and stocks.
Thanks again for your efforts
Dave

[gwp]

There are a lot of variables with the AR gas system. The things you can change are increasing the size of the gas port on the barrel to increase the flow or add an adjustable gas block to reduce the flow; increase or reduce the weight of the moving parts; change the spring weights.

If you have an extra spring you could cut a coil or two off the buffer spring until it functions well.

I did not have much trouble with my 300 BLKs. I started out with a H2 buffer and had to change to the standard carbine buffer for them to function correctly.

The reduced power Wolff spring may be just what you need for your carbine to function correctly.

[DaveL]

Update:
I thought I would share the results of the function testing I've done with subsonics in my blackout while the forum was down. I picked up some Nosler Custom Competition 220 Grain Hollow Point Boat Tails that were on sale at Midway. I loaded them with 10.5 grs. of AA1680 with Remington SR primers which should be around 1050 fps. All I did was function test. The snow's too deep and the temp's too low to do any crony or accuracy testing here in the mountains of Vermont right now. I'll get to that when the weather breaks and report back then. I left the rifle buffer assembly on my rifle thinking it wouldn't work, but it turns out that it cycled AND locked the bolt back on the final round! Much to my surprise! Many thanks to gwp for the very informative links. They helped much in understanding the buffer assembly and how it functions to this AR newbie.
Dave