I have a DPMS AR 10. I will shoot it suppressed with regular .308 ammo. Do I need an adjustable gas block???

Shoot it and see if it works.

If it does no.

quote:

Originally posted by p dog shooter:
Shoot it and see if it works.

If it does no.

Good advice

As I am sure you already know, shooting with a suppressor (depending on design) will significantly increase both chamber pressure and bolt thrust. An adjustable gas block is designed to lower both. So to say that it will work is missing the point of an adjustable gas block.

It is always a good idea to install a gas block when shooting suppressed. It takes less than a hour to install one. You can also consider something like a Gentech suppressed bolt carrier and increasing the buffer spring.

If you are considering both full loads and subsonic, then a gas block is a must, well, if you want the bolt to cycle properly and not over stress the rifle. Another consideration is the newer suppressors like the OSS Helical. Supposedly it only increases chamber pressure a reported 30 psi. So again, load and equipment matter.

The guys at the Silencer Shop are the folks to speak with about all this - https://www.silencershop.com/

quote:

Originally posted by Opus1:
As I am sure you already know, shooting with a suppressor (depending on design) will significantly increase both chamber pressure and bolt thrust. An adjustable gas block is designed to lower both. So to say that it will work is missing the point of an adjustable gas block.

It is always a good idea to install a gas block when shooting suppressed. It takes less than a hour to install one. You can also consider something like a Gentech suppressed bolt carrier and increasing the buffer spring.

If you are considering both full loads and subsonic, then a gas block is a must, well, if you want the bolt to cycle properly and not over stress the rifle. Another consideration is the newer suppressors like the OSS Helical. Supposedly it only increases chamber pressure a reported 30 psi. So again, load and equipment matter.

The guys at the Silencer Shop are the folks to speak with about all this - https://www.silencershop.com/

All an adjustable gas valve does is regulates the amount of gas going back to the bolt carrier (thus the piston/cylinder) and this is essentially a time delayer and regulated the timing of the bolt opening and also reduces the force the bolt opens with. I really doubt that it increases chamber pressure. The way to regulate your adjustable gas valve is to turn the valve closed some so the bolt doesn't hold open on the last shot. Good idea to only load one cartridge at a time since we're after that hold open. Keep turning the valve open a little until the bolt full locks open. Then go ahead and shoot some to insure you have full functioning, that it fully ejects the case out of the rifle and comes back far enough to pick up another cartridge from the magazine.

An adjustable gas block by definition regulates bolt thrust. Bolt thrust is the amount of back pressure required to operate or cycle the bolt. Too much, and you stress the carrier, too little and you manually operate the bolt. This is the whole idea behind an "adjustable" gas block. Otherwise, it wouldn't be a conversation.

Put a suppressor on the end of the system, and you upset the balance. Thus some genius designed the adjustable gas block. Simple really and the reason why AR military manufactures put one on most every rifle designed for suppressor use.

quote:

Originally posted by Opus1:
An adjustable gas block by definition regulates bolt thrust. Bolt thrust is the amount of back pressure required to operate or cycle the bolt. Too much, and you stress the carrier, too little and you manually operate the bolt. This is the whole idea behind an "adjustable" gas block. Otherwise, it wouldn't be a conversation.

Put a suppressor on the end of the system, and you upset the balance. Thus some genius designed the adjustable gas block. Simple really and the reason why AR military manufactures put one on most every rifle designed for suppressor use.

Well duh! Limit the amount of gas going back limits the velocity the bolt thrusts back. Don't know what you don't understand, I said it in a different manner. Then again that's not entirely correct either because because all bolts have bolt thrust which correctly defined is the pressure put on the bolt. A bolt action rifle has bolt thrust and it doesn't move...if it does you're in trouble.

Let's review... The question was do I need a gas block if I use a suppressor?

The answer is - Yep, a good idea.

quote:

Originally posted by Opus1:
Let's review... The question was do I need a gas block if I use a suppressor?

The answer is - Yep, a good idea.

Got ya!!!

I did answer the op's question. Now here's what bolt thrust is: The bolt thrust exerted on the bolt itself is in direct proportion to the rear surface area of the cartridge in question. Short Fat Mags develop more bolt thrust simply because they have a larger surface area that contacts the bolt face of the rifle. It's the carrier on the AR system that unlocks the bolt via the cam pin and it's inertia from gas siphoned off the bore that forcing it back.

Getting the word terminology here correct seems to be a problem.

quote:

Originally posted by Opus1:

I'm just trying to help people understand on that things that I know. I appreciate learning something from someone that knows about a certain thing or things then I. I'm sorry if I tramp on toes.

quote:

Originally posted by Opus1:
An adjustable gas block by definition regulates bolt thrust. Bolt thrust is the amount of back pressure required to operate or cycle the bolt. An adjustable gas block by definition regulates bolt thrust. Bolt thrust is the amount of back pressure required to operate or cycle the bolt. Too much, and you stress the carrier, too little and you manually operate the bolt. This is the whole idea behind an "adjustable" gas block. Otherwise, it wouldn't be a conversation.

Put a suppressor on the end of the system, and you upset the balance. Thus some genius designed the adjustable gas block. Simple really and the reason why AR military manufactures put one on most every rifle designed for suppressor use.

What does "Bolt thrust" have to do with a gas pressure operated system & how is an "adjustable gas block" going to change bolt thrust?

quote:

Originally posted by vzerone:
Getting the word terminology here correct seems to be a problem.

quote:

Originally posted by tsturm:

quote:

Originally posted by Opus1:
An adjustable gas block by definition regulates bolt thrust. Bolt thrust is the amount of back pressure required to operate or cycle the bolt. An adjustable gas block by definition regulates bolt thrust. Bolt thrust is the amount of back pressure required to operate or cycle the bolt. Too much, and you stress the carrier, too little and you manually operate the bolt. This is the whole idea behind an "adjustable" gas block. Otherwise, it wouldn't be a conversation.

Put a suppressor on the end of the system, and you upset the balance. Thus some genius designed the adjustable gas block. Simple really and the reason why AR military manufactures put one on most every rifle designed for suppressor use.

What does "Bolt thrust" have to do with a gas pressure operated system & how is an "adjustable gas block" going to change bolt thrust?

Exactly!! Bolt thrust only occurs while the bolt is close, locked, stationary, which ever you choose. Controlling the gas going back to the carrier/bolt on AR's only changes the time it takes the gas to get there and the pressure of it. It can change the opening of the carrier/bolt group from violent to softer and can change the time it first opens the bolt. If you notice for example on an AR15 shooting normal ammo that is not hot by any means, that upon firing the primer looks very flat like high pressure. David Tubbs, the competition shooter noticed this, and he came out with a carrier weight to slow down the bolt opening time. Trouble with it is that bolt/carrier mass is increased and beats the barrel extension and bolt/carrier group more then what is necessary. The adjustable gas valve eliminated that.

Most suppressors increase the back pressure on the rifles operating system causing an increase in the peak chamber pressure dwell time. This results in excessive extraction on the fired case, and increased rearward bolt carrier group thrust and additional forces on the BCG and buffer parts. An adjustable gas block system helps to regulate BCG movement and stress on the system.

What part of that is incorrect?

quote:

Originally posted by Opus1:
Most suppressors increase the back pressure on the rifles operating system causing an increase in the peak chamber pressure dwell time. This results in excessive extraction on the fired case, and increased rearward bolt carrier group thrust and additional forces on the BCG and buffer parts. An adjustable gas block system helps to regulate BCG movement and stress on the system.

What part of that is incorrect?

The group thrust! I don't think you comprehend what bolt thrust is. It's the pressure put on the bolt upon firing the cartridge. When the bullet is gone the thrust is gone too. The bolt is definitely not suppose to open when there is pressure in the chamber/bore. Obviously this can never happen on a manually operated action, but it can on semi-auto and full auto. Okay after the firing is done over with bolt thrust doesn't exist anymore. All you have then in the AR system is whatever stress the inertia of the of the bolt/carrier group carries with it. The recoil spring and buffer absorbs this. When the gas first enters the chamber in the carrier it tried to push the carrier back and the bolt forward. You really need to study exactly how all this works. Yes I know the bolt isn't going to go forward when that gas hits it. Just explaining what the gas tries to do. In normal AR's the amount of gas is more then needed to operate the system and it's a harsh action on the system. So you can see an adjustable gas valve cuts down the amount of gas getting to the bolt/carrier group. You can adjust them to where the bolt won't even cycle all the way. Elementary that suppressors change things on an AR.

I was speaking about the BCG and not the face pressure on the bolt.

quote:

Originally posted by Opus1:
I was speaking about the BCG and not the face pressure on the bolt.

That face pressure is called bolt thrust!!!

You do know that the bolt doesn't come back on it's own right? The carrier pulls it out of batter after unlocking it.

It's called battery and yes I understand that. And I also know the physics of thrust in all forms.

So back to the original question - Should I install an adjustable gas block when shooting suppressed?

Pretty much yep.

Do you need an adjustable gas block? Probably not. Try it first. I have fired tens of 1000’s of rounds through suppressed fireams and most did not have (adjustable) gas blocks. They functioned fine.

Safe shooting

quote:

Originally posted by Opus1:
It's called battery and yes I understand that. And I also know the physics of thrust in all forms.

So back to the original question - Should I install a gas block when shooting suppressed?

Pretty much yep.

With no gas block you will have a single shot. maybe with all the thrust confusion you mean Adjustable gas block?

tsturm you are correct on all counts. I am pretty sure we are all refering to the need/don’t need for adjustable gas blocks. I modified my post to reflect that.

As long as you don't mind more gas entering the action and more stress on the BCG, you can run all day long without an adjustable gas block while shooting suppressed. However, if you care about such things, then an adjustable gas block is useful.

Pretty much like shooting a 500gr bullet at 2,400 fps - a decelerator pad isn't necessary, but they're nice to have.

I am not an engineering expert; I have just had a lot of experience with M4 platforms under very demanding conditions. I never experienced or witnessed any of the problems or issues some are claiming may or could occur. However, it does seem to be the fad to put as much crap as possible on an M4 platform and change out all the parts so maybe it does make it “better”. Everyone should do what makes them happy and confident in their kit.

You probably do need an adjustable gas block, to not be over-gassing the system and causing premature wear to rifle and brass...
But personally I wouldn’t touch the gas until I’ve got the buffer loaded with tungsten and a weight pinned into the back end of the bolt carrier.

Then adjust gas as described in earlier posts, ideally with a well cut chamber brass should be coming out clean on the outside.