AR-15 pistol buffer/spring questions, and other AR gas issue question

[American_Fusilier]

Hey guys,

So I've already built a very reliable AR-15. Well, I built the lower and bought a complete upper (all from PSA). Now I am building an AR-15 pistol lower (it'll be in 5.56 to start), and I'll be buying a complete upper from PSA in a few months time when I can afford it. I am building this AR pistol with the intention of putting a 10 inch barrel and a carbine length gas system on it.

My questions are as follows:

1. Are carbine and pistol buffer tubes the same length?
2. Are carbine and pistol buffers the same weight and length?
3. Can you interchange buffer springs and buffers between more average pistols and rifles without having feeding changes?
4. I know that PSA's uppers are usually over-gassed, should that change the weight of buffer I should use?

I've got a line on a pistol brace, and it uses a pistol tube, but it doesn't come with a buffer or a buffer tube, so I'd have to buy those separately. I am not sure what to buy to make it work. Since I won't have the upper for a couple months yet, I just want to buy whatever should work with my combo of barrel, gas system, and caliber.

On an unrelated note, my cousin has an AR that seems to be a tad under gassed. The gun will cycle just fine, but it won't always lock the bolt the rear. My question with this is: would he need a slightly heavier or lighter buffer? I think he has a "standard" buffer and buffer spring. Do they make "weaker" buffer springs? If we cut of a coil of his buffer spring would that get the bolt to lock back every time? I am not sure how to solve this problem...

Please help!!!!

Any insight would be greatly appreciated! Thanks guys!

 

[Varminterror]

1. Are carbine and pistol buffer tubes the same length?

There are more and more proprietary systems out there, but yes, a standard pistol receiver extension/buffer tube will be the same depth as a carbine extension and use a carbine buffer.

2. Are carbine and pistol buffers the same weight and length?

There’s no such thing as a standard for “pistol buffer,” but rather they’ll typically use carbine buffers. Again, there are some proprietary combos out there, but the standard buffer used in a pistol is a carbine length buffer.

3. Can you interchange buffer springs and buffers between more average pistols and rifles without having feeding changes?

Rifles use different springs than carbines and pistols. It’s 100% about the length of the receiver extension, not the upper attached.

4. I know that PSA's uppers are usually over-gassed, should that change the weight of buffer I should use?

In practice, buffer and carrier weight simply stalls the initial unlocking of the action. An over gassed action with swipe marks might be helped by adding reciprocating weight, but in general, it is better to reduce the gas flow instead. Heavier buffers do slow things down, giving a smoother recoil impulse, so I generally recommend H2 buffers for almost any carbine/pistol build, but with an AGB, even the lightest reciprocating masses will still run fine.

 

[American_Fusilier]

There are more and more proprietary systems out there, but yes, a standard pistol receiver extension/buffer tube will be the same depth as a carbine extension and use a carbine buffer.

There’s no such thing as a standard for “pistol buffer,” but rather they’ll typically use carbine buffers. Again, there are some proprietary combos out there, but the standard buffer used in a pistol is a carbine length buffer.

Rifles use different springs than carbines and pistols. It’s 100% about the length of the receiver extension, not the upper attached.

In practice, buffer and carrier weight simply stalls the initial unlocking of the action. An over gassed action with swipe marks might be helped by adding reciprocating weight, but in general, it is better to reduce the gas flow instead. Heavier buffers do slow things down, giving a smoother recoil impulse, so I generally recommend H2 buffers for almost any carbine/pistol build, but with an AGB, even the lightest reciprocating masses will still run fine.

Thank you for the answers! What about on an under gassed gun? A lighter buffer?

So basically, whatever buffer tube and buffer that works in a standard AR-15 carbine, should also work in an AR-15 pistol, especially if the pistol has a carbine length gas system?

 

[Varminterror]

Yes, if you have a standard pistol buffer tube, it will use carbine length buffers and springs. If you have a proprietary tube, you’ll need to follow the OEM guidance for what works with their length.

For the under gassed rifle, you need to troubleshoot why it is under-gassed. It may have an undersized gas port, the carrier dragging/binding, leaking gas somewhere, under-powered ammo, loose carrier key (technically a gas leak)...

If it is undergassed, the best option is to give it more gas. Reducing the reciprocating mass may or may not work - depends how undergassed it really is.

 

[Elkins45]

Thank you for the answers! What about on an under gassed gun? A lighter buffer?

So basically, whatever buffer tube and buffer that works in a standard AR-15 carbine, should also work in an AR-15 pistol, especially if the pistol has a carbine length gas system?

If a buffer and spring combo works with an upper it should work the same when transplanted into a different lower, unless the tube length is actually different. I’ve never seen an undergassed 223 gun and most of the market for non-standard buffers is for heavier ones, not lighter. I think I would check that the front sight base gas hole is correctly aligned with the barrel port before I did anything else.

Now if we’re talking about blowback guns in pistol calibers then you are almost certainly looking at heavy buffers. My 9mm gun came with a 5 oz buffer and needed an even heavier replacement to work correctly.

 

[ponchh]

Hey guys,

So I've already built a very reliable AR-15. Well, I built the lower and bought a complete upper (all from PSA). Now I am building an AR-15 pistol lower (it'll be in 5.56 to start), and I'll be buying a complete upper from PSA in a few months time when I can afford it. I am building this AR pistol with the intention of putting a 10 inch barrel and a carbine length gas system on it.

My questions are as follows:

1. Are carbine and pistol buffer tubes the same length?
2. Are carbine and pistol buffers the same weight and length?
3. Can you interchange buffer springs and buffers between more average pistols and rifles without having feeding changes?
4. I know that PSA's uppers are usually over-gassed, should that change the weight of buffer I should use?

I've got a line on a pistol brace, and it uses a pistol tube, but it doesn't come with a buffer or a buffer tube, so I'd have to buy those separately. I am not sure what to buy to make it work. Since I won't have the upper for a couple months yet, I just want to buy whatever should work with my combo of barrel, gas system, and caliber.

On an unrelated note, my cousin has an AR that seems to be a tad under gassed. The gun will cycle just fine, but it won't always lock the bolt the rear. My question with this is: would he need a slightly heavier or lighter buffer? I think he has a "standard" buffer and buffer spring. Do they make "weaker" buffer springs? If we cut of a coil of his buffer spring would that get the bolt to lock back every time? I am not sure how to solve this problem...

Please help!!!!

Any insight would be greatly appreciated! Thanks guys!

Unless it's a custom barrel ARs are generally over gassed so manufacturers don't get thousands of calls from people using the cheapest ammo money can buy. If it's short on gas the gas block is probably out of line, but I would check to make sure the bolt catch is working properly. Does it work it's full travel freely with good spring pressure, and not bent or chipped.

 

[greyling22]

I'd recommend a cheap adjustable gas block on any pistol, and any overgassed gun rather than fooling with buffers and springs. I have a really nice agb as well, and it's no better than a cheap one.

For an undergassd gun, after you have made sure everything is assembled properly, the gas block is on straight, and nothing is dragging, I know of 3 options:
1) drill out the gas port. Not hard to do, but rather permanent on a more expensive part.
2) a lighter buffer. Cheapest way to do this is to disassemble your buffer and replace one of the steel weights with a bit of pvc or dowel rod. Easier said than done, but it is possible. I recommend you have a bench vice available before you start.
3) take a coil or 3 off the buffer spring. It's easy, it works, and if you screw up, spring is are like $5. Or you can buy lighter lighter springs and buffers for too much money.

I have done all 3 of those diy mods, and they all work. I'd start with #3 and work up to #1 as needed.

 

[Varminterror]

If you’re cutting coils from a spring, you’re taking Advil for brain cancer.

ETA: gas ports should be reamed for diameter, not drilled.

 

[C-grunt]

On a 10.x inch barrel I'd run either an H or an H2 buffer. It will slow the action down a little and will generally make the gun run better.

For the "under gassed" gun, I'd bet money you have a leak or something else going on. Check the gas key on the BCG to sr if it's looser or lacking gas out the bottom.