Pressure vs velocity

Ragin_cajun · Monday at 7:27 PM

I’m trying to save ammo material so I figured I would verify what I’m thinking with you guys.
If I’m getting extra pressure from my suppressor and getting pressure signs trying to get to 2700fps on my hunting rifle. I was thinking about trying my muzzle break or my other suppressor to reduce the pressure but pressure is directly related to velocity (for that barrel) correct? My understanding is that the barrel controls the speed so if I removed the suppressor and put the brake on then I would reduce pressure and also loose velocity. Then when I add powder trying to get the velocity back I would once again be over pressure. Is this correct from your experience? A barrel has a max speed and that’s just what it is?

Macht · Monday at 7:37 PM

A suppressor does not increase peak chamber pressure. Back pressure is really only relevant for gas guns.

Ragin_cajun · Monday at 7:41 PM

I’m not exactly sure what you call it but I’ve seen it on that rifle and heard about others having it. The suppressor add velocity but also causes pressure signs. When I remove the can I loose velocity but also all pressure signs are gone.

Old Man with Gun · Monday at 8:43 PM

One has nothing to do with the other. Chamber pressure pushes the bullet out of the barrel.

Suppressor back pressure is gasses from the suppressor after the bullet is gone venting both forward and backwards twords the chamber because the bolt unlocked on a gas gun.

Ragin_cajun · Monday at 8:52 PM

Old Man with Gun said:
One has nothing to do with the other. Chamber pressure pushes the bullet out of the barrel.

Suppressor back pressure is gasses from the suppressor after the bullet is gone venting both forward and backwards twords the chamber because the bolt unlocked on a gas gun.

I’ve heard this and as an engineer I understand what you’re saying. It’s logical but I also understand logic doesn’t always come into play. I’ve heard from reputable sources about this happening before and it’s what I see. If I load 20 identical rounds and shoot 10 randomly suppressed and 10 with the break then the 10 shot with the brake will have no pressure signs or flattening of the primer. The 10 shot suppressed will have the signs and an increased velocity. Call that whatever you want but when the only change is can to brake then something is happening. But that’s leading us off topic

Old Man with Gun · Monday at 9:10 PM

Ragin_cajun said:
I’ve heard this and as an engineer I understand what you’re saying. It’s logical but I also understand logic doesn’t always come into play. I’ve heard from reputable sources about this happening before and it’s what I see. If I load 20 identical rounds and shoot 10 randomly suppressed and 10 with the break then the 10 shot with the brake will have no pressure signs or flattening of the primer. The 10 shot suppressed will have the signs and an increased velocity. Call that whatever you want but when the only change is can to brake then something is happening. But that’s leading us off topic

My experience is that in a bolt gun, muzzle device has no effect on chamber pressure, flat primers, etc.

Suppressors can slightly increase the velocity of the bullet, but very minimal. It is like adding more barrel length, although a very loose inefficient one.

On gas guns that use chamber pressure to work a piston or hits a gas key to cycle the action it can matter to how the rifle functions.
If a bolt opens faster it may be beating itself up or slower it may be unreliable.

At least in theory a violent loading cycle could effect the ammo like pushing bullets into the casing or something that could change pressure.

But after shooting and reloading for about 40 years, I've never seen a load show pressure signs with a suppressor on, that goes away when you remove it.

straightshooter1 · Monday at 9:48 PM

Ragin_cajun said:
I’m trying to save ammo material so I figured I would verify what I’m thinking with you guys.
If I’m getting extra pressure from my suppressor and getting pressure signs trying to get to 2700fps on my hunting rifle. I was thinking about trying my muzzle break or my other suppressor to reduce the pressure but pressure is directly related to velocity (for that barrel) correct? My understanding is that the barrel controls the speed so if I removed the suppressor and put the brake on then I would reduce pressure and also loose velocity. Then when I add powder trying to get the velocity back I would once again be over pressure. Is this correct from your experience? A barrel has a max speed and that’s just what it is?

As Old Man with Gun mentions above, a can and the length of it act like adding additional barrel length (barrel length being a key factor in changing muzzle velocity). A break, with it's venting, won't act in that manner because of the venting. A can is just not going to a any pressure, only the length of time for diminishing pressure as the bullet exits.

CoryT · Monday at 10:47 PM

If that is happening what you have is a powder that is much too slow and is having so much unburned material ejected into the suppressor that it is detonating inside the can. The old Pressure Trace system from RSI had an article showing the high chamber pressure from just such a situation, but it seems to have disappeared from the internet. What is the cartridge and load, and from what manual did you get it?

6.5SH · Monday at 10:58 PM

CoryT said:
If that is happening what you have is a powder that is much too slow and is having so much unburned material ejected into the suppressor that it is detonating inside the can. The old Pressure Trace system from RSI had an article showing the high chamber pressure from just such a situation, but it seems to have disappeared from the internet. What is the cartridge and load, and from what manual did you get it?

I believe the gentleman from RSI passed away.
You might find the article on the Wayback Machine:

http://web.archive.org/web/20230608192024/https://www.shootingsoftware.com/pressure.htm

straightshooter1 · Monday at 11:20 PM

6.5SH said:
I believe the gentleman from RSI passed away.
You might find the article on the Wayback Machine:

http://web.archive.org/web/20230608192024/https://www.shootingsoftware.com/pressure.htm

This thing about Secondary Pressures is really new to me. . . surely something I never thought about. I love learning new things like this! THANKS for the link.

This is were I thought a link in that link was most interesting to me

:

https://web.archive.org/web/20230621145322/https://www.shootingsoftware.com/barrel.htm

Doom · Tuesday at 8:52 AM

There is also some information about what can happen in Hatcher's Notebook. I believe the later editions discussed secondary pressure.

Old Man with Gun · Tuesday at 9:34 AM

I always do my load development with the suppressor on, so I never ran across this.

Still trying to wrap my head around how peak pressure can happen after the bullet leaves the barrel and the bottle is uncorked so to speak.

Unless the back pressure is in front of the bullet while still on the barrel. It does have to push that air out in front of it.

Ragin_cajun · Tuesday at 2:50 PM

straightshooter1 said:
This thing about Secondary Pressures is really new to me. . . surely something I never thought about. I love learning new things like this! THANKS for the link.

This is were I thought a link in that link was most interesting to me :

https://web.archive.org/web/20230621145322/https://www.shootingsoftware.com/barrel.htm

Thank you for the link I needed something to read on 2 flights this weekend and this is interesting enough for me to forget that I hate flying.

45-90 · Tuesday at 3:30 PM

For years there is a known phenomenon that slow burning powders will detonate, rather than burn, when loaded in low volume at low pressures.
That's why the minimum load from the loading manuals should be adhered to.

Could the suppressor be interfearing with the unburned powder as the bullet exits the bore not allowing the unburned powder to exit with the bullet, in a ball of fire, but causing some turbulence to cause detonation to happen inside the barrel....Possibly.
Try a different powder in your hand loads.

Bluewave · Tuesday at 5:21 PM

Ragin_cajun said:
I’m trying to save ammo material so I figured I would verify what I’m thinking with you guys.
If I’m getting extra pressure from my suppressor and getting pressure signs trying to get to 2700fps on my hunting rifle. I was thinking about trying my muzzle break or my other suppressor to reduce the pressure but pressure is directly related to velocity (for that barrel) correct? My understanding is that the barrel controls the speed so if I removed the suppressor and put the brake on then I would reduce pressure and also loose velocity. Then when I add powder trying to get the velocity back I would once again be over pressure. Is this correct from your experience? A barrel has a max speed and that’s just what it is?

Got it! Barrel's the speed limiter, suppressor's the pressure amplifier. You're thinking' it right, buddy.

Ragin_cajun · Wednesday at 7:56 PM

Bluewave said:
Got it! Barrel's the speed limiter, suppressor's the pressure amplifier. You're thinking' it right, buddy.

Maybe but honestly I’m an idiot trying to figure stuff out! But then it could also just be me screwing up something along the line

. Maybe Sunday I will go do some load work and verify some things or just say screw it and go fishing

RegionRat · Thursday at 12:09 PM

Consider that you would get more focused help if you gave the specifics of your rifle and recipe.

I am just guessing since there are no details, that if you are on the edge where the difference between a muzzle brake (not break BTW) and suppressor is enough to tip your brass into showing signs of pressure, you are going to have to make a decision to back off.

By sharing the details, you will get better insight and possibly better advice on what to adjust, or to punt and run something better.

Taylorbok · Thursday at 12:27 PM

If you need more speed go to a larger case.

Taking a case from a safe load to over pressure is rarely more than a couple clicks on the elevation turret and basically meaningless in the wind.

Pressure vs velocity

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