Suppressors First suppressor. Getting hard/sticky bolt lift

[HOLLYW00D]

Got my first suppressor out, and am experiencing hard bolt lift and case head swipe. Same can used for both rifles/scenarios below:

• 6.5 Creedmoor - 140gr Barnes Match Burner over 41.6gr H4350 in a new Lapua case
  • Hard bolt lift starts after 5th shot
  • Hard bolt lift goes away 5 shots after suppressor is removed
  • Round primers
    
• 6BR Norma - 105gr Barnes Match Burner over 29.5gr Varget in a new Lapua case
  • Hard bolt lift starts after 5th shot
  • Hard bolt lift goes away 5 shots after suppressor is removed
  • Round primers

Maybe the chamber is getting coated with a layer of carbon from the backpressure and not allowing the next case to grab the chamber walls, letting the case slide/press into the bolthead?

Is there a way around this? Maybe something as simple as more neck tension?

Thanks for your help.

 

[earthquake]

Back when I was running 6.5 Creed my normal load was too hot for using with my can. I was blowing primers out of the cases. I had to back off considerably. You'll have to do load development again most likely.

I think I was at 42.9-gr H4350 pushing 140's at 2,905-fps. I had to make a note to myself NOT to shoot the rest of that ammo with the can attached.

 

[Huskydriver]

Back when I was running 6.5 Creed my normal load was too hot for using with my can. I was blowing primers out of the cases. I had to back off considerably. You'll have to do load development again most likely.

I think I was at 42.9-gr H4350 pushing 140's at 2,905-fps. I had to make a note to myself NOT to shoot the rest of that ammo with the can attached.

Lol on snipers hide if your not 3 grains over book max you ain't trying.....

 

[Zak Smith]

Throat probably a little tight and it's getting dusted with carbon more with the can on

 

[FuhQ]

Got my first suppressor out, and am experiencing hard bolt lift and case head swipe. Same can used for both rifles/scenarios below:

• 6.5 Creedmoor - 140gr Barnes Match Burner over 41.6gr H4350 in a new Lapua case
  • Hard bolt lift starts after 5th shot
  • Hard bolt lift goes away 5 shots after suppressor is removed
  • Round primers
• 6BR Norma - 105gr Barnes Match Burner over 29.5gr Varget in a new Lapua case
  • Hard bolt lift starts after 5th shot
  • Hard bolt lift goes away 5 shots after suppressor is removed
  • Round primers

Maybe the chamber is getting coated with a layer of carbon from the backpressure and not allowing the next case to grab the chamber walls, letting the case slide/press into the bolthead?

Is there a way around this? Maybe something as simple as more neck tension?

Thanks for your help.

Using a suppressor creates back-pressure due to the nature of what a suppressor does (catches all that gas coming out of the bore)... Therefore increasing your chamber pressures. Back your load down about 2 grains, and then slowly work-up from there looking for pressure signs WHILE using the can. If you plan on shooting suppressed, never do load development unsuppressed.

 

[HOLLYW00D]

Throat probably a little tight and it's getting dusted with carbon more with the can on

Any workarounds besides widening the throat? Any long-term concerns, otherwise (i.e. bolt lug setback)?

 

[kthomas]

^ Just as others are suggesting, a suppressor adds a bit more pressure to the system. If you are running on the ragged edge before the can is added, then you may get pushed over that edge with the addition of a suppressor.

You will have to re-work a load that's safely below pressure with the suppressor. Give yourself some margin for rain, debris, etc.

 

[E. Bryant]

Using a suppressor creates back-pressure due to the nature of what a suppressor does (catches all that gas coming out of the bore)... Therefore increasing your chamber pressures. Back your load down about 2 grains, and then slowly work-up from there looking for pressure signs WHILE using the can. If you plan on shooting suppressed, never do load development unsuppressed.

Peak pressure in the chamber happens barely after the bullet begins to move. The suppressor has exactly jack shit to do with the chamber pressure at that moment, because it's not in communication yet with anything happening behind the bullet.

What happens after the bullet leaves the muzzle isn't so much an increase in chamber pressure but rather a lower rate of decreasing chamber pressure; quite meaningful for many semi-automatics but inconsequential for bolt guns as the chamber pressure peaked a long time ago.

Pretty damn sure that @Zak Smith nailed it (as usual).

 

[FuhQ]

Peak pressure in the chamber happens barely after the bullet begins to move. The suppressor has exactly jack shit to do with the chamber pressure at that moment, because it's not in communication yet with anything happening behind the bullet.

What happens after the bullet leaves the muzzle isn't so much an increase in chamber pressure but rather a lower rate of decreasing chamber pressure; quite meaningful for many semi-automatics but inconsequential for bolt guns as the chamber pressure peaked a long time ago.

Pretty damn sure that @Zak Smith nailed it (as usual).

Then how can you explain why everyone who runs a can with handloads that were already right under the limit UNSUPPRESSED, creating excess pressure suppressed, and then it goes back to showing no pressures signs when you remove the can? Does the carbon magically disappear when you take the suppressor off?

I've tested this theory myself with my own rifles and suppressors. I can't explain exactly what is causing it, but obviously it has something to so with the suppressor being on the gun...

Unsuppressed - Slight pressure signs (flat primers)
Suppressed - Severe Pressure signs (ejector swipes)
Unsuppressed - Slight pressure signs (flat primers)

How does carbon have anything to with that, when you shoot all 3 rounds back-to-back with suppressed in the middle, and get the same results?

And, if you look at a gunshot in slow motion, there is pressurized gasses being ignited and pushed out in front of the bullet, and exit the muzzle before the bullet does...So there is pressure in that bore BEFORE the bullet, and after. My guess is that as the bullet is being propelled down the bore, that the pressure change taking place inside of the bore, is increasing with the suppressor, because the bullet is trying to push all that dear air out of the bore first, so the bullet can exit, and when that air hits the baffles in the suppressor before the bullet exits (compared to unsuppressed where it just exits straight out of the muzzle into the open atmosphere), it must be creating a slight bit of excess chamber pressure on the back-end, because it's exerting more pressure on the front of the bullet that's trying to exit... This excess pressure could also be what causes the phenomena of "suppressor boost" where you get a slight increase in FPS (usually 10-15 FPS) when running suppressed, becuase of the excess pressure that's being built inside of the bore as the bullet is being pushed.

 

[E. Bryant]

I haven't personally seen what you're reporting, so I'm not going to speculate on the cause - especially when I've yet to hear a rational hypothesis on the mechanism at work.

 

[FuhQ]

I haven't personally seen what you're reporting, so I'm not going to speculate on the cause - especially when I've yet to hear a rational hypothesis on the mechanism at work.

Re-read my post... It's self-explanatory if you have an IQ higher than a potato.

 

[HOLLYW00D]

Pretty damn sure that @Zak Smith nailed it (as usual).

Let's say this is the problem. Any suggestions on a solution aside from getting the throats reamed out to a "suppressor spec" on the various chamberings/barrels?

 

[E. Bryant]

Re-read my post... It's self-explanatory if you have an IQ higher than a potato.

1) Asking me too "re-read" your post when you edited it five minutes after I posted my reply?

2) Your expanded explanation still makes no sense. If the primer didn't flatten and the case didn't stick at the moment of peak pressure - once again, that happens pretty much as the bullet begins to engage with the bore - then any increased pressure much later won't have any effect because it's still lower than the peak pressure.

Show me some instrumented chamber pressure data and I'm willing to change my mind.

 

[FuhQ]

1) Asking me too "re-read" your post when you edited it five minutes after I posted my reply?

2) Your expanded explanation still makes no sense. If the primer didn't flatten and the case didn't stick at the moment of peak pressure - once again, that happens pretty much as the bullet begins to engage with the bore - then any increased pressure much later won't have any effect because it's still lower than the peak pressure.

Show me some instrumented chamber pressure data and I'm willing to change my mind.

Go for it haus... Nobody is stopping you from spending all that money on equipment. Until then, my theory still stands, and you still refuse to admit that I might be right. Unlike you, if someone unequivocally proves me wrong, I'll admit I'm wrong.

Simple physics... If the bullet is still in limbo somewhere in the bore, and the dead air in front of it creates more pressure for the bullet to exit, it will automatically create more pressure buildup behind the bullet, as well, due to the fact the propellant and gasses are still expanding and on fire, while the bullet is still in the bore. It's very similar to the theory of drive pressure in turbocharged engines.

 

[st1650]

Lol on snipers hide if your not 3 grains over book max you ain't trying.....

View attachment 7817669

come on, isn't the generic accuracy node for H4350 and 140s in between 41.5 and 42.0 ?

 

[Zak Smith]

Hearing the symptoms of the OP, I am surprised it "went away" when he fired more rounds unsuppressed. In the cases of this I've seen before, it did not get better, but swabbing out the chamber/throat immediately returned to initial conditions.

 

[E. Bryant]

Go for it haus... Nobody is stopping you from spending all that money on equipment. Until then, my theory still stands, and you still refuse to admit that I might be right. Unlike you, if someone unequivocally proves me wrong, I'll admit I'm wrong.

Simple physics... If the bullet is still in limbo somewhere in the bore, and the dead air in front of it creates more pressure for the bullet to exit, it will automatically create more pressure buildup behind the bullet, as well, due to the fact the propellant and gasses are still expanding and on fire, while the bullet is still in the bore. It's very similar to the theory of drive pressure in turbocharged engines.

An RFQ has been submitted to Kistler for the appropriate sensor, and sources have been identified for other equipment. We'll need to see how this fits the budget compared to other things that have a better ROI.

Anything involving interior ballistics and suppressor behavior is not "simple physics". The so-called "dead air" in front of the bullet has negligible mass (maybe 0.5 grain for a typical 6.5mm bore plus another 4 grains inside a large suppressor) and is highly compliant and minimally constrained, and once the bullet exceeds the speed of sound there is no longer direct communication between it and this air column. It is not at all similar to the interaction between exhaust gases and the turbine of a turbocharger, at least not in the engines that I operate because the exhaust gases have a velocity under the speed of sound and the up pipe is not tightly sealed with a piece of lead and copper and the exhaust turbine is not a tube with static baffles.

 

[FuhQ]

An RFQ has been submitted to Kistler for the appropriate sensor, and sources have been identified for other equipment. We'll need to see how this fits the budget compared to other things that have a better ROI.

Anything involving interior ballistics and suppressor behavior is not "simple physics". The so-called "dead air" in front of the bullet has negligible mass (maybe 0.5 grain for a typical 6.5mm bore plus another 4 grains inside a large suppressor) and is highly compliant and minimally constrained, and once the bullet exceeds the speed of sound there is no longer direct communication between it and this air column. It is not at all similar to the interaction between exhaust gases and the turbine of a turbocharger, at least not in the engines that I operate because the exhaust gases have a velocity under the speed of sound and the up pipe is not tightly sealed with a piece of lead and copper and the exhaust turbine is not a tube with static baffles.

Keep trying..

 

[Freediver111]

Older thread but I just experienced the same symptoms. Shooting a 300 wsm, 212 eld x, Norma 2x fired brass, and 65.5 gr of H4831sc. Tikka action with a 22” benchmark barrel.

I just got my TBAC U7 about a month ago and prior to the can it was moving 2780 fps. Now I’m getting 2820 and in my case it’s not reliably having a sticky bolt lift, but it seems like out of 30 rounds fired I had tighter bolt lift on about 5 cases. No other signs of pressure. Just the tighter bolt lift.

I really hesitate to mess with it much as it’s shooting absolutely lights out. Max load with 4831 and 212 gr bullets is 66 gr, so obviously I’m close to max.

 

[kthomas]

Older thread but I just experienced the same symptoms. Shooting a 300 wsm, 212 eld x, Norma 2x fired brass, and 65.5 gr of H4831sc. Tikka action with a 22” benchmark barrel.

I just got my TBAC U7 about a month ago and prior to the can it was moving 2780 fps. Now I’m getting 2820 and in my case it’s not reliably having a sticky bolt lift, but it seems like out of 30 rounds fired I had tighter bolt lift on about 5 cases. No other signs of pressure. Just the tighter bolt lift.

I really hesitate to mess with it much as it’s shooting absolutely lights out. Max load with 4831 and 212 gr bullets is 66 gr, so obviously I’m close to max.

Just bump it down ~0.5 to 1 grains and see how it shoots.

I have to do the same thing with some hunting loads I just developed. Haven't settled on a seating depth yet, but the rounds I tested with projectiles closer to the lands had the odd sticky bolt lift. My plan is to just back it down 0.5 grains and go from there.

 

[M4orturnate]

come on, isn't the generic accuracy node for H4350 and 140s in between 41.5 and 42.0 ?

Ime about 41.2-41.9 then another around 42.4 if youre chamber allows you to run that hot

 

[M4orturnate]

Id really like to test this. Im goi g to see if we can thread one of our test barrels and actually measure suppressed vs unsuppressed. Im inclined to believe it wont affect peak chamber pressure but its speculation at this point. Probably will take a few weeks to make it happen

 

[Freediver111]

Just bump it down ~0.5 to 1 grains and see how it shoots.

I have to do the same thing with some hunting loads I just developed. Haven't settled on a seating depth yet, but the rounds I tested with projectiles closer to the lands had the odd sticky bolt lift. My plan is to just back it down 0.5 grains and go from there.

When I did the seating depth tests for the 65.5 gr load unsuppressed, I found it was best at 0.09 off. So that’s not anywhere near the lands to give me cause for concern it’s higher pressure from that.
I can’t recall if this batch of reloads used a fresh can of powder from a different lot. But I seem to recall it was. That would be one variables I didn’t think of.
I loaded up some 65 gr loads tonight to test through. I’ll also clean the chamber as it’s been a little while. Probably don’t have enough time to test before I leave for MT on a hunt.

 

[FuhQ]

Older thread but I just experienced the same symptoms. Shooting a 300 wsm, 212 eld x, Norma 2x fired brass, and 65.5 gr of H4831sc. Tikka action with a 22” benchmark barrel.

I just got my TBAC U7 about a month ago and prior to the can it was moving 2780 fps. Now I’m getting 2820 and in my case it’s not reliably having a sticky bolt lift, but it seems like out of 30 rounds fired I had tighter bolt lift on about 5 cases. No other signs of pressure. Just the tighter bolt lift.

I really hesitate to mess with it much as it’s shooting absolutely lights out. Max load with 4831 and 212 gr bullets is 66 gr, so obviously I’m close to max.

This is precisely what I was talking about in my other posts before stupidity ensued...

It's always best to bump your go-to load down a grain or so, and redo your load development with the EXACT same setup you plan on using in the woods...Including the can. That way you can really dial-in your load for your rifle to avoid issues like excess bore and chamber pressures from the added restriction on the gasses exiting the barrel. And chances are, if that load shoots pretty good suppressed, it will probably shoot pretty good unsuppressed as well...Just your POI might be slightly different.

 

[FuhQ]

Id really like to test this. Im goi g to see if we can thread one of our test barrels and actually measure suppressed vs unsuppressed. Im inclined to believe it wont affect peak chamber pressure but its speculation at this point. Probably will take a few weeks to make it happen

I look forward to the results... Do you also have a way to measure bore pressures, and not just chamber swell. I'm assuming you're using a PTII setup?

 

[Zak Smith]

One thing we have seen is that necks that are just barely large enough can get coated with carbon and then become tight necks. This can be diagnosed by cleaning the chamber/throat really well and then seeing if the first round has a problem, or just the subsequent rounds. We've only seen like 3-5 guns that have this specific problem so far.

 

[M4orturnate]

I look forward to the results... Do you also have a way to measure bore pressures, and not just chamber swell. I'm assuming you're using a PTII setup?

I honestly dont know too much about it yet. Its pretty new to me. It has the sensor on the case. Dont think there's away to measure bore pressure.

 

[Freediver111]

One thing we have seen is that necks that are just barely large enough can get coated with carbon and then become tight necks. This can be diagnosed by cleaning the chamber/throat really well and then seeing if the first round has a problem, or just the subsequent rounds. We've only seen like 3-5 guns that have this specific problem so far.

So the vast majority of these issues you’ve seen are caused from carbon build up in the chamber/throat area? In theory I shouldn’t have sticky bolt lift using the same loads that shoot fine with no can vs with?
I haven’t cleaned this rifle in a while, so I’ll give that a shot!
I will say that I used a 42 gr h4350 load in my 6.5 cm and with can vs without has no change in bolt lift. All smooth. Interesting.
I’ll have a report in the coming week I think.

 

[Freediver111]

Well, had some time to test some 65 gr loads, so .5 gr below what I was shooting. Still shooting amazing, but continued to have slight sticky bolt lift. Also shot some 65.5 gr loads and many cases had no sticky lift. Weird. It happens maybe 30% of the time.
I also cleaned the chamber/throat area prior to shooting and first shot was tight lift. I don’t know. Maybe just a touch of polish with a reamer would help. Or drop the load down to 64.5 and see. Just never saw this before I started using a can. The 65 gr load didn’t have a big drop in velocity, so maybe it’s still essentially doing the same pressure wise.
My other rifle in 6.5 is fine though. No difference with that gun.

 

[Freediver111]

Pics of swipe marks on the tight cases. Can’t feel it with a fingernail, but it’s a slight polish on the brass.