Suppressors cause Increased Chamber Pressure?

[ccmdfd]

I've got a CA Ridgeline Scout rifle in .308, 16 in barrel, about 2/3's through the CA 50 round break in. Put a TBAC ultra 5 can on it, using their CB brake for attachment.

The vast, vast majority of the rounds I've sent through it so far have been unsurpressed. However the past couple of times out I decided to go ahead and screw the suppressor on and see how things went.

I am definitely noticing a much more stiff bolt throw after shooting suppressed as compared to unsuppressed. I've looked at the brass and I can't see any obvious extractor marks or bulging primers, etc, but I'm also rather new at that. Haven't had a chance to see any marks or flattened primers on other guns.

Ammo is factory Barnes 130 TTSX.


I've never experienced anything like this on previous bolt action rifles with other suppressors including TBAC cans. However, this is my shortest barrel rifle as well as smallest, shortest can.

Didn't know if this was supposed to be expected or something else, weird is going on.

Thanks

[Clusterfrack]

I've got a CA Ridgeline Scout rifle in .308, 16 in barrel, about 2/3's through the CA 50 round break in. Put a TBAC ultra 5 can on it, using their CB brake for attachment.

The vast, vast majority of the rounds I've sent through it so far have been unsurpressed. However the past couple of times out I decided to go ahead and screw the suppressor on and see how things went.

I am definitely noticing a much more stiff bolt throw after shooting suppressed as compared to unsuppressed. I've looked at the brass and I can't see any obvious extractor marks or bulging primers, etc, but I'm also rather new at that. Haven't had a chance to see any marks or flattened primers on other guns.

I've never experienced anything like this on previous bolt action rifles with other suppressors including TBAC cans. However, this is my shortest barrel rifle as well as smallest, shortest can.

Didn't know if this was supposed to be expected or something else, weird is going on.

Thanks

Great question, and excellent choice in suppressor. My suggestion is to lube your lugs with a little grease and carry on.

@JCL may have a more technical answer?

[farscott]

One of the ways a suppressor works is to keep the gas volume in the barrel and suppressor long enough for it to decrease in pressure and drop in temperature enough to lower the report. There is some incremental back pressure as the gas enters the restriction of the suppressor as opposed to flowing out the muzzle into the atmosphere. As such, total bolt thrust (pressure times surface area) is higher. The duration of that force is also longer as the suppressor means the pressure in the chamber takes longer to drop. So there is more total force for a longer time working not the bolt face. That explains the stiffer bolt throw.

If the bolt throw is that much stiffer, I would consider a reduced load

[BWT]

I've got a CA Ridgeline Scout rifle in .308, 16 in barrel, about 2/3's through the CA 50 round break in. Put a TBAC ultra 5 can on it, using their CB brake for attachment.

The vast, vast majority of the rounds I've sent through it so far have been unsurpressed. However the past couple of times out I decided to go ahead and screw the suppressor on and see how things went.

I am definitely noticing a much more stiff bolt throw after shooting suppressed as compared to unsuppressed. I've looked at the brass and I can't see any obvious extractor marks or bulging primers, etc, but I'm also rather new at that. Haven't had a chance to see any marks or flattened primers on other guns.

Ammo is factory Barnes 130 TTSX.


I've never experienced anything like this on previous bolt action rifles with other suppressors including TBAC cans. However, this is my shortest barrel rifle as well as smallest, shortest can.

Didn't know if this was supposed to be expected or something else, weird is going on.

Thanks

There is definitely increased fowling (well - the flow through cans are reducing this) and extended duration of pressure in the gun. I’ve heard it’s not unusual to see something like a 20-25% increase in cyclic rate on like a suppressed M4 in full auto.

However, I don’t believe it will increase the pressure peak but it will increase the pressure duration.

It’s interesting it’s doing this with a shorter barrel / shorter suppressor. I’m wonder if there’s a tighter suppressor bore that’s more constricted.

https://thunderbeastarms.com/products/ultra-5

APPLICATION NOTES
Minimum barrel lengths2:

6" .300 Blackout (subsonic)
8" .300 Blackout (full power)
10" 6.8 SPC, 7.62x39
11.5" 223 Rem, 5.56, 6.5 Grendel
14.5" .308 Win, .260 REM, 6.5 Creedmoor, .243 WIN, .22 Creedmoor
16" 6.5 SAUM, 6.5 PRC, 7 WSM, 7 SAUM, 7STW, 7RM, 300 WSM
18" 26 Nosler, 28 Nosler, 300 WM, 300 WBY, 6.5-300WBY
22" 7 RUM, 300 Norma, 300 RUM, 300 PRC
Please contact tech support for:
7mm cal loads exceeding 90 powder grains,
30 cal loads exceeding 100 powder grains.
For questions about a particular rifle/load combination please contact us.
* SBR use in these calibers, CB brake mount or Direct Thread recommended.

Is there anyway you’re exceeding 100 powder grains?

ETA: I would guess with the smaller suppressor - high push for performance, etc. you’re on the edge-ish of what they support at 16”. Something may else may be going on.

I’d contact them.

[ccmdfd]

There is definitely increased fowling (well - the flow through cans are reducing this) and extended duration of pressure in the gun. I’ve heard it’s not unusual to see something like a 20-25% increase in cyclic rate on like a suppressed M4 in full auto.

However, I don’t believe it will increase the pressure peak but it will increase the pressure duration.

It’s interesting it’s doing this with a shorter barrel / shorter suppressor. I’m wonder if there’s a tighter suppressor bore that’s more constricted.

https://thunderbeastarms.com/products/ultra-5



Is there anyway you’re exceeding 100 powder grains?

ETA: I would guess with the smaller suppressor - high push for performance, etc. you’re on the edge-ish of what they support at 16”. Something may else may be going on.

I’d contact them.

Don't know for certain as it's factory ammo but I highly doubt that it's over 100 grains. If you look at the Barnes load data online for the 130 grain, the absolute maximum charge weight is about 56 grains and that's compressed. Don't see how they're going to get over twice that amount in.

I thought about switching out to a couple of my low back pressure suppressors. It's a bit of a PITA as I would have to switch out the muzzle device, but not impossible by any means.

Thanks

[SecondsCount]

There is definitely increased fowling (well - the flow through cans are reducing this) and extended duration of pressure in the gun. I’ve heard it’s not unusual to see something like a 20-25% increase in cyclic rate on like a suppressed M4 in full auto.

However, I don’t believe it will increase the pressure peak but it will increase the pressure duration.

It’s interesting it’s doing this with a shorter barrel / shorter suppressor. I’m wonder if there’s a tighter suppressor bore that’s more constricted.

https://thunderbeastarms.com/products/ultra-5



Is there anyway you’re exceeding 100 powder grains?

ETA: I would guess with the smaller suppressor - high push for performance, etc. you’re on the edge-ish of what they support at 16”. Something may else may be going on.

I’d contact them.

You can't fit 100 grains into a 308 case. TB is referencing magnum cartridges in that document.

@ccmdfd
Have you tried the rifle with and without the suppressor on the same day? Powder is affected by temperature


How do the fired primers look? Radius edges or completely flat?

[ccmdfd]

You can't fit 100 grains into a 308 case. TB is referencing magnum cartridges in that document.

@ccmdfd
Have you tried the rifle with and without the suppressor on the same day? Powder is affected by temperature


How do the primers look? Radius edges or completely flat?

Yes, shot it both ways today in fact. A very humid day if that makes any difference.

To me the primers look okay but I'm really not great with picking up on abnormalities. I've looked at several websites and often I will not see what the person is trying to explain. Maybe I'll take it out later today again and just do a couple of rounds, one suppressed, one unsuppressed and post pictures.

Thanks

[ccmdfd]

And here's a few shots just done in the backyard. One suppressed, one unsurpressed.

Suppressed




And not suppressed




Thanks @SecondsCount

[SecondsCount]

The primers are not flattening but you are getting a little bit of primer flow into the firing channel in both suppressed and unsupressed scenarios. That tells me that the load is a little on the warm side, or the chamber is a little tight.

If you have a decent set of dial calipers, measure case diameter .200" above the base- just above the extractor groove, and see if there is a difference between the two.

[JCL]

Great question, and excellent choice in suppressor. My suggestion is to lube your lugs with a little grease and carry on.

@JCL may have a more technical answer?

Nothing to add. I’m guessing that a can will alter the shape of the pressure curve, but it’s not obvious how it could contribute to overpressure.