OK guys I just had my first range session with my new sandman S. I just installed a new adjustable gas block from superlative. I have 4 types of ammo for my AR68. 2 hunting rounds and 2 target rounds. Today I only brought my target rounds so that was a mistake. So I start out with the cheapest ammo I have so I can see where my casings are flying. They are coming out at the 1 o'clock area so I shut off some of the gas and get it coming out at about 4 to 5 oclock and it shoots perfectly on this cheap 115gr FMJ. Not one single hick up. So I shoot another 30 or 40 rounds of this fmj playing around and loving the new pitch/sound from the gun and I think I am done. I decide to try my other ammo (Wilson combat BHTP 110Gr). It will shoot 1 round and boom it is jammed up. I do it a few more times and exactly the same. Cartridge seems to be coming out at 3 oclock on the WC ammo. So I was hoping not to have to adjust the gas block for different types of ammo but evidently I am wrong. Next range session I will bring my hunting ammo and see what happens. Just curious if this is normal for suppressors?

I clicked on this thread because it said "basics". Ooh! I can answer basics! ...I don't know the answer.

^^ That is correct. The cycling of the AR with an adjustable gas block is based off the pressure of the ammo you are shooting. When you change ammo, each one can have different pressures, which will effect your cycling. But, if you are locking up the bolt, then that's a whole other problem. The ammo is most likely too hot to begin with, and you can't close the gas block to reduce the actual pressure of the round itself. That won't help. Also, your cheap ammo, like a FMJ round, is generally not loaded as hot as your hunting or more expensive ammo is.

Also, when you add a suppressor to a rifle, it will raise the pressure of a round about 3K-5K psi, depending on a few factors. If the ammo is loaded at the high end of pressure, adding a suppressor will increase the pressure even more and can cause the ammo to be too hot in that rifle. I've seen this with the 28 Nosler. There are many hunters who shoot the 28 Nosler suppressed. It's a stout over bore cartridge to begin with, and adding a can cold push it over pressure.

The next "basic" item would be spelling "suppressor" correctly!

Thank you Chad for the lesson on pressures and hot rounds. My hunting ammo is Wilson combat also so I guess I need to get back out to the range and get to working the problem out.

If you are locking up your bolt due to over pressure of the WC ammo, you won't be able to work that out. That's a different problem all together. I've had some 6.5 Grendel ammo be too hot for some guns. I've shot the same load (same bullet, powder, and powder charge) in my brother's AR and several load work ups on the 6.5 Grendel with zero issues. But some AR's show pressure signs in different customers' rifles, it happens. You have to back to load down some (reduce the pressure) on the ammo for the AR to handle the pressure and not lock the bolt up. That's the only solution for ammo that is too hot. I wouldn't recommend shooting the WC ammo, if that's what it's doing.

Looks like Chad covered everything.

I am not sure of the exact definition for "locking up". I think it is stovepiping. Not ejecting enough and another round 1/2 way out of the mag. Either way I am headed back to the range in the next day or 2. Its just part of getting familiar with your new equipment I guess. Hunting season is coming up so have to get it worked out now and be ready. Hopefully this ammo isnt too hot. I have at least 600 rounds of WC hunting ammo in barnes 95 gr and 110 gr. I will try to tune my adjustable block to them and see what happens. Thanks for the heads up. I think I should be ok. Ive shot a dozen rounds or so of this ammo out of my gun with suppressors my guide loaned me for his property. They shot fine on a normal brake so I am hoping it is just under gassed with that BTHP WC ammo.

I've seen the claim multiple times that adding a suppressor will affect chamber pressure but I cannot understand how or why. By the time the bullet gets to the suppressor the gas pressure has gotten quite low and Peak chamber pressure would be when the bullet is an inch or two down the bore. I can see how a suppressor would add pressure to the gas system of a semi-auto but I can't understand why it would have any effect whatsoever on a bolt gun.

Bigfoot, my guess is that our ammo is loaded with a slower burn rate powder than the other ammo your shooting and will require more gas to function properly. The way to set an adj gas block is to use the lightest ammo and fire one shot at a time gripping the gun loosely to ck for full cycle and bolt stop operation. If the bolt goes to full bolt stop lock you have enough gas. The way I adj mine is to start with too little gas to function, keep opening the gas until I get full bolt stop operation, then open it a "little" more to compensate for variables like cold weather and a dirty gun. In a perfect world I like to see 3-4pm ejection, but I've got guns that eject from 1pm-5pm that run 100%.

Adding a suppressor doesn't increase chamber pressure, but it does increase bolt thrust. The BIG negative with suppressors on a gas gun is how they dirty up the action!!! The ONLY negative to using one on a bolt gun is cost, weight and length.

^^^^ Still not following what you're saying. The only way for bolt for thrust to go up is for the bore diameter to get larger or the pressure behind the bullet to get higher. I understand that the added bore length because of the suppressor will increase dwell time a tiny bit but for my line of thinking by the time the bullet makes it to the suppressor it's going really fast and it doesn't spend much time in the can although the gas is behind it are still flowing even once the bullet has left the bore.

Has anyone done back-to-back testing using a factory style test gun barrel and pressure sensor combo? If so is there published data that I can review?

I'm not sure there is way to test bolt thrust, my engineers tell me this is a fact and I know signs such as ejector swipe and flattened primers are often present when I add a suppressor. Same ammo doesn't show swipes or flattened primers when fired in the same bbl without a suppressor.

The head ballistics engineer at both Sig and Western Powder told me there is no increase in chamber pressure when you add a suppressor. Also no difference in pressure by changing bbl twist rate as long as the chamber, bore dia and lands/grooves are the same.

On another forum a similar discussion on the seemingly higher pressure with a suppressor attached was deduced to a slightly longer pressure dwell time with the suppressor attached.

Longer pressure dwell they said could get the bolt unlocking while still under pressure giving the indications of higher pressure. 16 inch barrel with an 8 inch suppressor is the same length as a 24 inch barrel but the gas port is further out on the 24 inch rifle length tube. Just something I found interesting on a mostly AR forum.

Bill that might be an interesting scenario if a carbine length gas system on a ported barrel gave the same type of "pressure" indications.

Yeah, it's not that the suppressor raises your pressures since the highest pressure spike is well before the bullet is even halfway down the barrel. The suppressor increases your dwell time and the pressure level at the gas port, meaning your bolt will unlock quicker than it would without the can. The ejector swipe you see isn't a "pressure sign" in the traditional sense, but it is still an indication that your gun is being really rough on brass by trying to cycle before the pressure in the case has dropped sufficiently.

I've got my doubts about it causing overpressure in bolt actions. The can doesn't affect anything in the chamber. You might see some additional flattening of primers due to the duration of pressure being applied, but it won't cause a safe load to otherwise be overpressure.

I do not think it causes any over pressure in bolt actions or gas guns just the length of the pressure pulse by thousandths of a second. The added dwell time though would cause a that minute amount of time as the bolt is unlocking and start to move unlocking and moving backwards while there is more pressure and gasses in the barrel. Moved back enough you would get the potential of more hot burning gas/particles back into the action past the brass and show "pressure signs" on the brass like the rotating bolt of the gas gun to move more while under pressure with the small time of the longer pressure curve. I do not know how many times I have heard screw on a suppressor you will get dirty cartridges in the mag and more crud in the action than you would without the supressor on the same rifle. Hope that is clearer.

Thank you Bill and others for the responses. I did go back to the range yesterday and just re adjusted my AR for the barnes ammo and I had no problems at all. I did notice that it did not require much blockage to get them both at the 3 to 4 o'clock position which corresponds exactly to what you were saying about slower burning powders. Runs like a top now!

On another note I have to say that I have not experienced blow back in to my face like others have mentioned nor do I notice any thing different other than my AR is very dirty after less than 100 rounds through it. My POI seems to be the same also for both guns I swapped this suppressor on.. I haven't had to adjust my bolt gun even 1 click. Seems to be dead on still with the new can and muzzle break. I'm very happy so far with the new sound.

Thanks again
Big

thank you!