Hybrid AR Question

[Jon_Snow]

Here's a hypothetical question for you guys. When selecting AR components, do you match the buffer to the buffer tube or to the gas length? For example, if you were building an AR with a rifle length gas system but an M4 stock, would you use the carbine or rifle buffer? I assume it would use the carbine buffer, but I'd like to get opinions from people more knowledgeable than I.

 

[68wj]

The buffer has to be matched to the buffer tube. Damage to your rifle may occur otherwise.

eta: A rifle buffer in a carbine tube will be too long and the bolt will not come back far enough. A carbine buffer in rifle tube is too short and the bolt carrier will drive into the lower receiver.

 

[taliv]

the LENGTH of the buffer is matched to the buffer tube (receiver extension)
the WEIGHT of the buffer is matched to the gas system

 

[TonyAngel]

I'd qualify what taliv said by saying that the weight of the buffer needs to be matched to the gas system of the particular rifle. Not all gas ports are created/drilled equally.

 

[esheato]

This is something I didn't know...glad I opened this thread.

 

[Onmilo]

I use a heavy carbine buffer that approximates the weight of an A2 buffer in my collapser stocked 20" rifle.
You also use a carbine length action spring, not a rifle length action spring.
Standard mil-spec spring is fine, don't need to tailor it.
I use this buffer in my rifle with excellent results.
http://www.brownells.com/.aspx/pid=5574/Product/Counterweight_Buffer

A Colt H2 buffer weighs five ounces and will work as well.

 

[Jon_Snow]

the LENGTH of the buffer is matched to the buffer tube (receiver extension)
the WEIGHT of the buffer is matched to the gas system

So I'd want a carbine length buffer that's a little heavier than normal for a mid-length gas sytem going on a M4 equipped lower?

Also, what happens if your buffer weight is out of sync with your gas system? Failure to feed/eject, premature wear, etc?

 

[taliv]

this isn't something you should overthink

if you have a carbine stock, then get a carbine buffer. you can also get a H (heavy) buffer and an H2 (heavier) and H3 (heaviest). The regular and H and H2 (and maybe all of them) should all function reliably with a standard carbine-length or mid-length gas gun with quality ammo.

The tuning comes in when you want to shoot cheap, weak ammo, or use a suppressor, or when you change your barrel length or gas-tube length or if you get an adjustable gas block, etc etc etc

You can use heavier buffers to make the bolt unlock slower, which gives the pressure in the chamber a little more time to dissipate, which in turn makes extraction of the brass more reliable (since it won't be still stuck to the chamber when the bolt starts to open)

They can also change the felt recoil. This is something you'll just have to play with.

Again, stick with the standard unless you've got a good reason to change.

 

[TonyAngel]

taliv gives good advise. Don't go swapping things around just because you're looking for something to buy that will supposedly make things better.

Yes, you can change the weight of the buffer that you are using to tailor the way the rifle shoots and to alleviate small problems. In a lot of cases, these problems are either due to weak ammo that will cause the rifle to short stroke, so you can go to a lighter buffer; or in the other extreme you may have a rifle that is overgassed, which could cause extraction issues (like with steel cased ammo). In this latter case, you'd go with a heavier buffer.

Generally speaking (assuming that everything is in spec), the higher the gas pressure the heavier the buffer for smoother performance. So...for a 16" barrel with a carbine length gas system, an H buffer wouldn't be out of the ordinary or even heavier. The same barrel with a mid length gas system will operate at a lower pressure so you might be able to get away with a lighter buffer. A 20" barrel with a rifle length gas system is going to have even lower pressure, so a standard buffer is likely all you'll need.

Just as an example, my last build was an 18" barrel with a rifle length gas system. This system operates at low pressure and has a pretty short dwell time (determined by the length of the barrel between the gas port and the muzzle) so it shot mild with just a standard buffer. It also did well with an H buffer, but wouldn't cycle cheap ammo at all with a H2 buffer.

Personally, I've settled on the Spike's ST-T2 buffer for all of my rifles. It seems to be just the right weight. I don't know how much they weigh or why they work in all of my rifles. They just do.

A pretty good indicator of whether you are using the right buffer for you is to watch your ejection pattern. If you're brass is ejecting forward at the 1:00 to 2:00 position, you have a lot of gas pressure and a pretty high bolt velocity going on. Try going up on your buffer weight. If your brass is ejecting at the 4:00 position or further behind you, you have too little bolt velocity, try going to a lighter buffer. If your ejection pattern is something around 3:00, you're just right. Don't mess with it. All of this assumes that all else is well with the rifle.

Changing a buffer will likely not cure problems like a way over sized gas port, a bad gas leak or rings on their way out.

 

[gotigers]

Taliv says it all. Just to add a graphic to that.

To much buffer can act as low gas, to little can act like over gassed.

 

[Jon_Snow]

Ok, thanks all for the advice. My mid-length upper came with an ST-T2 carbine buffer, and now I know why they did that. This all came about becuase a friend asked me about matching a carbine stock with a rifle length gas system and I realized I didn't know as much as I'd like.