Does A Can or Suppresor Increase Back Pressure and Decrease Velocity??? Well????

[John215]

Just my experience, but with my Sig Cross in 6.5 Creedmoor 16" barrel the can increased my velocity with an average of 27 feet a second. These were all match reloads.

 

[Veteran]

My experience is with a can, velocity decreases.

Any data you can share and type rifle, ammo, temp conditions, etc?

 

[FlyGuy11]

I searched LRH and found this thread which is very interesting and it has a lot of comments by folks who make and sell
muzzle brakes and understand fluid flow dynamics through both suppressors and muzzle brakes. Very interesting.
Especially comments by IdahoCTD and JE Custom in this thread.

Can switching muzzle brakes change muzzle velocity??

So I recently had a new muzzle brake installed on my 338 RUM, and my muzzle velocity dropped about 47 FPS. With the last brake I had this rifle/load dialed in. I'm using a Magnetospeed and have fully characterized this load several times across temperatures and it has always been very...

www.longrangehunting.com

Looks to me like the conclusion is suppressors increase velocity very slightly in the range of 10-30 fps on most rifles and that
muzzle brakes have no statistical difference if they are designed correctly, though this thread details a member who lost
47 fps when he changed muzzle brakes......pretty unusual.

Seems like you are looking at side affects of a suppressor instead of intended purpose. Intended purpose is sound reduction and the side affects are slight velocity increase, possible point of impact shift, reduction in recoil, and can be used with a muzzle brake for all of the benefits. I personally do not use hearing protection while hunting but do use a suppressor which a hunting guide really liked because it reduces / eliminates the concussion of a brake. I do not really understand what back pressure has to do with shooting other than recoil reduction or are you concerned with a possible increase in chamber pressure? A high quality suppressor with muzzle brake makes for a really nice hunting experience for all. The major downside is extra paperwork with the ATF and wait times.

 

[mxjoe35]

Yes in every rifle I have ever shot it will increase back pressure. It is easy to seen in a gas gun with an adjustable gas block. You will need to close down the gas block or your rifle will be over pressured. As for velocity, i have seen an avg of 20fps increase. This will depend on the suppressor, but you should see a slight increase on average.

 

[RockyRandy]

To be completely honest I don't think the 10x2 shots I took amounts to anything other than the "match grade" factory ammo I was using was trash. SD 32 on 10 shots is embarrassing. ES pegged on the fourth shot of twenty to 96 FPS; the entire suppressed string shot fell inside the ES of the unsuppressed string. My data might really be a case of statistics finding trends in random noise.

That's all I've got though because I've never run a string of that many rounds suppressed/unsuppressed back to back again.

Crappy load or not. If you shoot 5or10 shots. and average them and do the same without can your still see the difference.

 

[cb4128]

In all of my rifles that I handload for - some customs, some factory guns, muzzle velocity and pressure increases when I install a suppressor. In the same range that others have reported - 10-30 fps usually.

However, on 2 rifles I have worked up loads with the muzzle brake only and when I switched to shooting suppressed it wasn't shooting as tight - both with thunderbeast ultra 7 cans. On 1 gun, it increased pressure enough that I wasn't comfortable with my load anymore and had to back of a full grain because there were shiny ejector marks and a plunger mark. This was with Retumbo in the same atmospheric conditions as before.

I always work up loads with the can on now, and haven't had any trouble with this since.

I've never heard or read of anyone losing velocity when installing a can, but I guess it's possible depending on the can design.

 

[Veteran]

Seems like you are looking at side affects of a suppressor instead of intended purpose. Intended purpose is sound reduction and the side affects are slight velocity increase, possible point of impact shift, reduction in recoil, and can be used with a muzzle brake for all of the benefits. I personally do not use hearing protection while hunting but do use a suppressor which a hunting guide really liked because it reduces / eliminates the concussion of a brake. I do not really understand what back pressure has to do with shooting other than recoil reduction or are you concerned with a possible increase in chamber pressure? A high quality suppressor with muzzle brake makes for a really nice hunting experience for all. The major downside is extra paperwork with the ATF and wait times.

My original question was do you get an increase or decrease in muzzle velocity and why? It really has nothing to do with the sound reduction purpose of the suppressor. I said upfront, I thought depending on design of the supressor, the barrel length, powder burn rate, and other factors, it could go either way, increase or decrease. Some sources say the effect on velocity is so negligible it is not statistically significant. I think it all depends........At least here from those reporting on this thread it looks like slight velocity gains were experienced by most, in the range of 10-30 fps. But, as I said, it could be depending on the set up you could experience no change or slight loss in velocity too.

 

[RockyRandy]

Great thread. I've always heard that a can will help but haven't done a comparison my self. Time to do some work myself. I have noticed though that at 100 yards that my bullet impact is 3" higher without the can versus with the can. Has anyone else seen this?

 

[Veteran]

POI shift that is due to barrel harmonics changing w extra weight at end of barrel. Quite commonly documented.

 

[vortech347]

Yes it does increase backpressure but the slight gain in effective barrel length, IME, has added some velocity. It's not a lot. I've seen 11fps on average out of a 26" 6.5 PRC where my SD is under 10. Obviously, there are a lot of variables. But I've seen the velocity increase the few times I have measured it in more than one rifle.

Your muffler analogy has a little merit but there is a pretty big difference between cooling exhaust gases several feet down the system in a car vs. a rifle bullet still heating up and being propelled by powder in a 1-2.5 foot long barrel.

Any restriction on cooling and slowing down exhaust gases in a car will have a greater affect IMO.

Everyone I have talked to that has actually measured it said the same thing. The can added some velocity.

But as another posted stated, you can clearly tell it adds back pressure in a gas gun because the action cycles much harder if you don't have an adjustable gas block to turn it down. I have one of my AR's set to where it just barely cycles without the can so it doesn't beat the gun up with the can. I almost always shoot it with the can.

 

[GoosePilot]

Great thread. I've always heard that a can will help but haven't done a comparison my self. Time to do some work myself. I have noticed though that at 100 yards that my bullet impact is 3" higher without the can versus with the can. Has anyone else seen this?

One of my guns impacted higher and one lower. Both increased in fps

 

[Veteran]

Yes it does increase backpressure but the slight gain in effective barrel length, IME, has added some velocity. It's not a lot. I've seen 11fps on average out of a 26" 6.5 PRC where my SD is under 10. Obviously, there are a lot of variables. But I've seen the velocity increase the few times I have measured it in more than one rifle.

Your muffler analogy has a little merit but there is a pretty big difference between cooling exhaust gases several feet down the system in a car vs. a rifle bullet still heating up and being propelled by powder in a 1-2.5 foot long barrel.

Any restriction on cooling and slowing down exhaust gases in a car will have a greater affect IMO.

Everyone I have talked to that has actually measured it said the same thing. The can added some velocity.

But as another posted stated, you can clearly tell it adds back pressure in a gas gun because the action cycles much harder if you don't have an adjustable gas block to turn it down. I have one of my AR's set to where it just barely cycles without the can so it doesn't beat the gun up with the can. I almost always shoot it with the can.

Yes, I think this has helped me understand the conflict between my mental model of backpressure which does seem to happen in the rifle system, and the conflict of increased velocity. One would think in a simple world of physics, back pressure would equal decreased velocity, but what is happening is precisely as you say, the increased effective confinement of some length of tube where gas is still behind the bullet exerting force overcomes the back pressure effect so the net effect is increase velocity.

So, its another example of counter intuitive results in the real world vs. a simplistic view of physics where a +b should = c.
But it don't.

Higher charge weights should always mean more velocity right? But the Satterlee curve says it don't. Different thread.
Same counterintuitive kinds of things going on.

 

[GoosePilot]

But as another posted stated, you can clearly tell it adds back pressure in a gas gun because the action cycles much harder if you don't have an adjustable gas block to turn it down. I have one of my AR's set to where it just barely cycles without the can so it doesn't beat the gun up with the can. I almost always shoot it with the can.

Can we really compare a gas gun ejection system changes because of adding a suppressor to a bolt gun chamber pressure? Seems like two totally different subjects to me.

 

[azarcher10x]

I run a can on my .223 AR built for light bullets; 1-12 twist, shooting Varmit Grenades @ 3710...with or without the can! It makes no difference in the velocity! It does shift POI. Definitely dirtier with the can, and I'm still playing with the tune a bit. Still .5 groups @ 200 on a good day.