It’s been well over a decade since I was active on here so I apologize if this is the wrong section or the topic has been covered. But I’m sick of searching the internet only to find mixed responses. And then I remembered- sigforum!!!

So… carbine length gas system with a 10.5” barrel. What weight buffer works well with the SBPDW pistol brace? I have a Spike’s T2 that is unused. I’m hoping that will suffice or would I need lighter?

I’ve been out of the game for oh… a long time, but would like to start building and shooting again now that my daughters are older and show an interest.

Side note- good to see many of the same old people still on here.

I just put together a 10.5" for my wife. I went with a Springco "Hot White" buffer spring & H2 buffer.

I've had a Larue Super Duty buffer spring and a H2 buffer (whose vendor name escapes me) in my DD 10.3" for around 4 years now and have been completely satisfied. No cycling or bolt issues of any kind.

Along with the OP's question... how is one too know?

I need an AR book for dummies.

A regular carbine buffer will work just fine for you AR pistol (or SBR).

Excam_Man, not sure if this is what you're asking, but you can tell what is what by looking at the buffer's flat end. Regular has no marking, H-buffer has the "H", then you have "H2". Spike's has their own marking "ST2". And then, you have the "A5" buffer from VLTOR, which is intermediate between carbine and rifle...

quote:

Originally posted by Excam_Man:
Along with the OP's question... how is one too know?

I need an AR book for dummies.

Sometimes you can tell that you need a heavier buffer (or less gas!), if the rim of the extracted cartridges have a very faint bend from the extractor pulling the case out of the chamber before the pressure has completely subsided.

More commonly, recoil will be noticeably harsh.

It depends on ammo. It also depends on your barrel.

If the gas port in your barrel is sized to work with any ammo (even weak loaded steel case), you may be overgassed with hot M193 military surplus 5.56 ammo.


You can fix an overgassed rifle with an adjustable gas block or a heavier buffer and heavier spring. Or sometimes a combination thereof.

The simplest and probably best solution would be a +10% Wolff buffer spring with an H2 buffer.

Adjustable gas blocks allow more precise tuning but they are more expensive and more difficult to install.

If you are feeding your 10.5 carbine a steady diet of cheaper steel cased ammo, a standard buffer might be just fine.

I use Geissele Super 42 springs with their H2 buffer. Geissele recommends H3 if suppressed. Of course, it also depends on the gas port size. Mil spec you should be OK with the H2.

quote:

Originally posted by 12131:
Excam_Man, not sure if this is what you're asking, but you can tell what is what by looking at the buffer's flat end. Regular has no marking, H-buffer has the "H", then you have "H2". Spike's has their own marking "ST2". And then, you have the "A5" buffer from VLTOR, which is intermediate between carbine and rifle...

You've listed the different ones, but now, how do you know which one to use?
Carbine length (short) gas systems vs mid-length vs rifle length (long)?

What about the springs?

Then what happens when you start changing uppers to other calibers?
(when to change the buffer and/or spring)

I've been told 223/5.56/300/7.62x39 all take the same buffer and spring?

quote:

Originally posted by Excam_Man:

quote:

Originally posted by 12131:
Excam_Man, not sure if this is what you're asking, but you can tell what is what by looking at the buffer's flat end. Regular has no marking, H-buffer has the "H", then you have "H2". Spike's has their own marking "ST2". And then, you have the "A5" buffer from VLTOR, which is intermediate between carbine and rifle...

You've listed the different ones, but now, how do you know which one to use?
Carbine length (short) gas systems vs mid-length vs rifle length (long)?

What about the springs?

Then what happens when you start changing uppers to other calibers?
(when to change the buffer and/or spring)

I've been told 223/5.56/300/7.62x39 all take the same buffer and spring?

For mid-length and carbine length gas systems, it seems like folks prefer the H-buffer for softer shooting, but the standard buffer will function fine. Same spring for both, but the buffer weights are of course different.

Rifle length uses rifle buffer (longer) and rifle spring (longer). These can only be used in the rifle stock with rifle extension tube and cannot be fitted to work in the carbine stock system above.

Your ammo will have something to do with it, some stuff is really underpowered. I run an H3 on my 10.5 and it runs flawlessly but it is very overgassed. I would warn you to measure that action spring during cleaning and make sure it stays within the proper parameters as the 10.5 is a jerk to your internal components. I could give you lengths but it depends on who is making your spring so I'd ask the manufacturer. Take a good peek at the rest of your components as well.

My 10.5 runs a Sprinco white spring and a H2 buffer. The white spring is standard power but seems to last longer than OEM. SBRs can be rough on springs. My upper is pretty over gassed and was tossing cases so hard I'm pretty sure they broke the time space continuum. H2 buffer calmed it down nicely. When I shoot this barrel out I'll get one with a smaller gas port and go back to a standard buffer.

It's trial and error to find what works best for your gun. How far is it throwing cases and where is it throwing them? How is the gun running? Many SBRs run just fine with the standard set up.

For the record, a Carbine-weight buffer, one with steel weights only and no tungsten, belongs in exactly ZERO rifles. It is underweight in every application outside of a specifically tuned gun that requires it. It comes in so many guns and kits because it's cheap and it's a short-term bandaid to make an AR run with any ammo at the expense of excessive cyclic rate, increased bolt stress, and some other issues it brings to the party. Those issues get worse with shorter gas systems.

For a 10.3" I would go with an H2.

"Duty" applications are generally H2 on carbine, H/H1 on midlength. The guns might tolerate a heavier buffer, especially when clean, but the idea is to err on the side of underbuffering vs. overbuffering. [Edit: this is assuming Crane-spec ("mil spec") gas ports, or something close to it]

A Sprinco 'blue' spring is another common recommendation. A heavier spring helps get everything moving and back into battery against fouling, taking advantage of the ample gas to add reliability to the overall cycle.

Unfortunately the fact that AR15s are made by so many brands, so many different parts and kits and accessories, is the very thing that makes it difficult to figure out how to tune the gun. Anything that changes the gas pressure, velocity, and volume entering the bolt carrier. Anything that changes the mass or springrate of the system reacting to that gas impulse. Anything changing the efficiency of that system like lubrication (or lack thereof), fouling, parts in the gas system not quite fitting right, or too tight, or leaking. It all changes how the gun behaves. A lot of Chefs out there with a recipe, but no idea how to cook it.

Knowing the gas port size to start with makes things a bit easier in selecting a buffer.

A lot of barrel makers use a dry phosphate BCG and open the port till it cycles weak ammo, then open it a bit more just to be on the safe side.

This is a decent list of different barrel gas port sizes.
https://docs.google.com/spread...EQoLq2JXXrk/htmlview
Using known good barrels like Colt, FN, SOLGW, ect you can get an idea what they are using for buffers in factory rifles and use that as a baseline.

Your Spike T2 should work just fine.
Standard is 3.0 oz
H or sometimes called H1 is 3.8 oz
H2 is 4.6-4.7 oz
Spike T2 is 4.05 oz.
I would install the T2 to start with as it is very close to H weight and it's on hand.
Standard would probably be to light.
( weights are approximant, but the spread is about right)

I have that same SbCQB set up. Apparently, I didn’t realize when I put it together I used an old carbine buffer spring that was off spec and to short, not enough coils. Went with the Spikes tactical T2 buffer which is about 4+ ounces and a flat wire spring. Ejection was perfect and no recoil. Put same combo in my other builds, same results. You should be fine.

My 10.5" has an H in it. I remember when I assembled it I tried all of them & it was smoothest & 100% reliable. The H2 was even softer shooting, but occasionally failed to pick up the next round. FWIW, I keep one of each weight in my stash to try out on any build. Because I lean most toward 16" mid-length gas, the unmarked are used most often.

I use a standard Colt carbine spring and H3 buffer in my SBR. Either a 10.3” or 11.5” barrel. Never an issue.

Instead of buying heavier buffers (I use H or H2 buffers in my ARs) I bought a half dozen of Tungsten weights to change out the steel weights in carbine buffers…this is the website that I bought from…(when I ordered two packs of three weights each they were under $20 for each pack…that was in 2019 or 2020)…OOPS, now showing “out of stock

https://pur-tungsten.com/produ...coil-buffer-weights/

Or here…in stock

https://www.tungstenman.com/Tungsten-Buffer-Weight