Gas Question

[EnderZen]

Can someone explain this one to me.

AR15 with 9 inch barrel and adj gas block.

Gas block is set to hold bolt open on last shot with no suppressor.

Sandman TI suppressor - Bolt holds open on last shot.

Omega 9k suppressor - Bolt does not hold open on last shot.

Never had an issue shooting it with or without the Sandman. I got the 9k and it will not hold open for suppers or subs. Any thoughts as to how this can be?

[smustian]

Sounds like the Omega has more back pressure and the bcg is out running the follower or less back pressure and is short stroking. No way to tell without seeing it function. Adjust the gas block until you get reliable lock back on the Omega then try the other suppressor and see what happens. You might have to use a different setting when changing suppressors.

[alamo5000]

Can someone explain this one to me.

AR15 with 9 inch barrel and adj gas block.

Gas block is set to hold bolt open on last shot with no suppressor.

Sandman TI suppressor - Bolt holds open on last shot.

Omega 9k suppressor - Bolt does not hold open on last shot.

Never had an issue shooting it with or without the Sandman. I got the 9k and it will not hold open for suppers or subs. Any thoughts as to how this can be?

Depends on how technical you want to get

But yes, it's all about pressure. One can is almost twice as long and has a different design in mind. The Sandman is built for bigger higher pressure rifle rounds. The Omega is not engineered for the same calibers and usage.

In other words it's not surprising to me at all that one will lock back and the other not. You're talking about one can that was engineered for 9mm rounds as the primary use, and the other for up to 300WM. Yeah, those are different.

A more in depth answer would involve a lot of science and physics.

[dellet]

Can someone explain this one to me.

AR15 with 9 inch barrel and adj gas block.

Gas block is set to hold bolt open on last shot with no suppressor.

Sandman TI suppressor - Bolt holds open on last shot.

Omega 9k suppressor - Bolt does not hold open on last shot.

Never had an issue shooting it with or without the Sandman. I got the 9k and it will not hold open for suppers or subs. Any thoughts as to how this can be?

First thought is that you have another problem than the suppressor, or these are not the same loads that worked unsuppressed and suppressed before with the same gas setting.

It's also possible that there is not enough info.

It's unlikely that a sub load that cycled unsuppressed, is loosing so much back pressure that it can not lock back the bolt with a suppressor attached.

Also unlikely that that same sub load would create more pressure than a super and hypercycle.

[EnderZen]

Just to chase this down a little more. I was using the same ammo, Remington 220 for subs and Remington 120 for suppers. No changes to the gun or the magazine. Only thing I did was shoot it without a surppressor both subs and suppers and it locked back. Put on the 9k and it did Not lock back for subs so tried suppers and still didnt lock back. Looked at the magazine and it was fine so scratched my head and put the Sandman on and it locked back for both subs and suppers.

I guess the real question i have is not the sandman vs the 9k but how/why would not having a suppressor on it lock the bolt back on the last round but when you put the 9k on it, it would Not lock the bolt back on the last round. Is it possible the 9k makes less back pressure then no suppressor at all?

Like I said just scratching my head. Doesn't really change anything since I can just change the gas block settings but figured I would ask and learn.

[smustian]

Just to chase this down a little more. I was using the same ammo, Remington 220 for subs and Remington 120 for suppers. No changes to the gun or the magazine. Only thing I did was shoot it without a surppressor both subs and suppers and it locked back. Put on the 9k and it did Not lock back for subs so tried suppers and still didnt lock back. Looked at the magazine and it was fine so scratched my head and put the Sandman on and it locked back for both subs and suppers.

I guess the real question i have is not the sandman vs the 9k but how/why would not having a suppressor on it lock the bolt back on the last round but when you put the 9k on it, it would Not lock the bolt back on the last round. Is it possible the 9k makes less back pressure then no suppressor at all?

Like I said just scratching my head. Doesn't really change anything since I can just change the gas block settings but figured I would ask and learn.

With suppressor on there is too much gas pressure and the bcg is outrunning the mag spring/follower. Adjust the gas down until it locks back with subs. Keep turning down the gas until it does not lock back any more then turn it back up a little. Recheck function. Supers will shoot fine at that adjustment. NOTE: Now it will work when the suppressor is on but will not cycle subs unsuppressed.

[alamo5000]

Just to chase this down a little more. I was using the same ammo, Remington 220 for subs and Remington 120 for suppers. No changes to the gun or the magazine. Only thing I did was shoot it without a surppressor both subs and suppers and it locked back. Put on the 9k and it did Not lock back for subs so tried suppers and still didnt lock back. Looked at the magazine and it was fine so scratched my head and put the Sandman on and it locked back for both subs and suppers.

I guess the real question i have is not the sandman vs the 9k but how/why would not having a suppressor on it lock the bolt back on the last round but when you put the 9k on it, it would Not lock the bolt back on the last round. Is it possible the 9k makes less back pressure then no suppressor at all?

Like I said just scratching my head. Doesn't really change anything since I can just change the gas block settings but figured I would ask and learn.

Adding a can to a gun in essence lengthens the barrel. By doing this it increases dwell time and many other factors.

When a round goes boom there is a chamber pressure which before was measured using units called "CUP". They basically put a small piston attached to a test chamber and inserted a highly calibrated piece of copper and after test firing they would see how much it got smashed. Now, a more modern approach is PSI.

If you look at Hogdon's reloading data online it uses both units.

Anyway those PSI gradually but drastically fall off as your bullet goes down the barrel. In 5.56 for example a 10.5" gun will still be at around 11,500 PSI. Add 4 inches of barrel and that PSI is down to just over 8,000 PSI.

Now in 300BLK your baseline PSI is pretty low to start with, but adding a suppressor (IE what people refer to as back pressure) is generally actually more pressure down the bore of the barrel going back towards the shooter. This is why on an AR platform the at the ear numbers for sound suppression matter a lot. Port pop matters.

Also the shorter the barrel the louder the bang all other things being equal. If you uncork a bottle that is under pressure it goes 'pop'. If you increase that pressure exponentially the pop is louder. Hence shorter barrel louder gun.

In an unsuppressed gun the PSI spike at the time of ignition, the bullet travels down the bore, and the part past the port is considered 'dwell time'. The system is still under total pressure and allows the gun to function when everything is put together right. The minute the bullet exits an unsuppressed gun the those pressures fall off to nothing almost instantly.

The dwell time is the dwell time for a particular ammo, but then you have to consider adding a can in the mix.

With your bigger longer rifle designed can, it's designed to function as an extension of the barrel. It's pressure driven. Too little pressure and it won't be as efficient as possible. It basically keeps your whole system under pressure for slightly longer and thus increased the dwell time.

Suppressors are not designed to just 'catch and trap gas'. They are designed to regulate the flow and harness that pressure and release it systematically per a given caliber and host weapon. Most suppressors get optimized for given barrel lengths, ammunition, hosts weapons, etc.

Your pistol can that is rated to handle 300BLK definitely will work on 300 BLK, but if you compare the PSI of a 220gr sub plus it's barrel length to that of a 9mm pistol can typically used on a 4 or 5 inch long barrel you're talking about apples and oranges about how those suppressors are designed to handle those gas pressures.

For example a 147gr sub 9mm round is between 27K and 34K PSI (with a 4 or 5 inch barrel consideration). A 220 grain sub 300 BLK is between 18k and 28k PSI typically with a 9 ish plus inch barrel with about a 4.5 inch long gas tube. In an AR platform the gas not only has to go 4+ inches before it gets to the port (with a pistol length gas system) it also has to travel BACK another 4+ inches as well to the BCG key.

Most pistols are blowback designs with tilting barrels and hence the suppressors have nielsen devices. The rearward "equal and opposite" force is what cycles the gun, not a gas system.

At the muzzle a 147gr sub 9mm round out of a handgun will actually have way more PSI than a 9" barrel 220 grain 300 BLK sub would. Basically put your pistol can is, well, tuned for pistol rounds being shot out of a pistol. Higher pressures from a shorter barrel means the design of the can needs to be more efficient in how it dissipates and releases those gasses.

Keep in mind both cans will suppress quite well in most instances, but in the AR platform the change in the gas pressure dynamics is altered in between cans. There is nothing wrong with this at all. That is one small part of the reason why using an adjustable gas block can be a positive. Open your gas block to allow more flow for the one can and you will be good to go.

Did I nerd you out there or no? LOL!

[golfindia]

Hole in the 9mm can is bigger than hole in 30 cal can. Pistol can baffles are sometimes designed differently than rifle. Clipped, no clip... No idea what either models look like inside. They are both sealed as far as I can tell, so there is not really not much advantage to using the Omega 9 can on 300blk. Edit: use a fixed barrel adapter for a 9K.

[EnderZen]

Thanks guys for your time and responses. I didn't think about over pressure but it is actually shooting softer with the 9K and it has less gas in my face then with the Sandman. I am just going to chalk it up to too much going on to really understand it all and I cannot explain everything here. Basically as you guys already pointed out, this is the reason why an adjustable gas block is a good idea.