Suppressors Newbie suppressor owner - Condensation causing pressure?

[Shootnwrench]

Tried searching and didn't find much. Total suppressor newb here but was out today with my new Ultra 7, 2nd time to the range with it.

Chilly day
25f
5mph gusting 6-8 for wind
32% RH

Shooting same load I’ve been shooting.

175 SMK, 44.8 Varget, Lapua case, WLR primer, 2.805 COL, Runs around 2640fps from my 20” FN SPR. Ran 40 rounds through it today, over the course of 3 hours.

All of a sudden I’m seeing pressure signs and what I noticed is there is moisture showing up on the cases, towards the end of shooting I could eject the case after firing, grab another round, chamber it and immediately extract the live cartridge with moisture on it that I could watch evaporate off.

Wind was at 12:30 so blowing down the muzzle more or less. Wondering if the temperature swing with the can getting warm and cooling off is causing condensation that’s is being blown back down the bore to the chamber when the bolts is left open.

I’ve fired thousands of rounds at this range in very similar conditions and have never noticed this before.

Thoughts?

Loving the suppressor otherwise.

 

[308pirate]

You're making connections that don't exist.

 

[sawgunner2001]

FWIW, that's sort of a warm load to begin with. In my 308 AR, I'm shooting 43.5gr Varget in LC brass with 175SMK at 2.805" and was piercing WLR primers. I switched to CCI BR primers to deal with that issue. Back when I was using Winchester brass and CCI BR primers, the primer pockets started loosening at 43.5 of Varget, also. In my rifle, with 2 different barrels, 43.5gr of Varget has been my pressure limit.

 

[ballisticdaddy]

Definitely on the warm side, Berger manual shows max load of 43.0 grains of Varget and that is at 101% fill ratio.

 

[Lunchbox27]

I ran an SPR in 308 shooting the 175 and 178’s suppressed. Using Lapua, my charges were 41.8 with IMR4064 and 42.8 grains of Varget. There was a higher node for both in the 44 grain range, but I had pressure signs.

IMO you should reduce your load.

 

[Shootnwrench]

Roger, will back it down. Zero signs of problems until yesterday but I am aware it’s warm, Hodgdon shows 45.0

Maybe it’s just a warm chamber and chilly ammo combination causing the moisture.

 

[5pins]

I had a similar issue a few weeks ago using Federal 168gr Gold Medal match ammo. Without the suppressor on I was getting normal looing cases and normal bolt lift. With the suppressor, I would get a hard bolt lift and higher pressure signs on the brass. The Winchester 168gr match seemed normal with or without the suppressor on.

 

[Shootnwrench]

I had a similar issue a few weeks ago using Federal 168gr Gold Medal match ammo. Without the suppressor on I was getting normal looing cases and normal bolt lift. With the suppressor, I would get a hard bolt lift and higher pressure signs on the brass. The Winchester 168gr match seemed normal with or without the suppressor on.

Initially I didn’t see anything goofy with the suppressor on but the last 15 rounds were pretty much 1-2 shots a minute and I could easily see the water on the cases. Wondering if the can, chamber and bore where warm enough that when I chambered a frozen cartridge it’s actually hit the dew point and condensed on the case.

12.5 yrs of hand loading and shooting at this range and it’s the first I’ve ever noticed this happening.

 

[LRhunter13]

Same experience encountered at my home range yesterday.

6creed
New Alpha OCD SRP brass
Cci 400s
39.7 of h4350 (very mild)
109 eldms going 2878fps
26” SS proof prefit comp contour
Impact 737
Thunderbeast ultra 7

Wind from 12:00 (which is part of the culprit)

43f
38% rh

Chamber is clean, confirmed with borescope.

Heavy bolt lift after 3-4 rounds fired with visible residue/water marks on the cases with heavy bolt lift, slight primer flow around the pin.

Let the chamber dry out for 20-30mins, wind died, ran 20rds with no more pressure signs.

Waited 20-30mins, heavy bolt lift after 3-4rds. Wind was again 12:00 at 5mph.

It’s a thing, it happens, conditions have to be conducive. Wind at 12:00 seems to be an important part of making this happen. It’s seldom in my experience, but I know others that have it happen often. Larger sized cans, larger bore diam, shorter barrel length and CF wrapped barrels seems to exhibit this far more often than my setup listed above.

 

[Conrad]

I know this is an old thread, but I just wanted to add confirmation to this. If there's decent humidity and cool air coupled with a 12:00ish wind I've found moisture on my cases which caused heavy bolt lift. I would do the same as LRHunter by drying out chamber and resuming until it would occur again. I've witnessed this on multiple occasions and the last 1-2 times realized the 12:00 wind component. It's a pain in the ass for load development.

 

[Mordamer]

I've had the same experience multiple times with different suppressors and different cartridges and rifles. If I shoot fast like on a timed PRS stage everything is normal. If I shoot a shot or two and wait a minute super heavy bolt lift all of a sudden. If I shoot and wait 10 minutes no heavy bolt lift. This phenomenon was very repeatable for me. I also found that the fired rounds that had heavy bolt lift came out of the chamber with what felt like condensation on them.

 

[B y r o n]

Roger, will back it down. Zero signs of problems until yesterday but I am aware it’s warm, Hodgdon shows 45.0

Maybe it’s just a warm chamber and chilly ammo combination causing the moisture.

But it also shows it being loaded in a Winchester case.

 

[JR1200W3]

It's an El Nino year guys. Gotta back them charges down if you're in the southern US. For all you northern and Ohio valley guys it's finally your winter to hotrod 'em!

 

[Yondering]

Very interesting stuff. I've never encountered it, but can see how it'd happen when conditions are just right (or just wrong?).

The simple fact is, our air can contain a lot of water, especially this time of year if you're not in one of the really dry parts of the country. I've been noticing 95%-99% humidity readings in the evenings several times recently, when we were in the 20%-30% range back during the summer; that stuff can make a difference.

It's also worth understanding the power of steam, which is why you'll see higher pressure signs with wet chambers. IIRC, steam can expand to over 4,000 times its original water volume at 1,000° F (and your powder burns hotter than that). Of course, that 4,000:1 expansion ratio is at atmospheric pressure, but the point is that water turned to steam by firing the rifle can generate significant pressure increase. If you're already using a pretty warm load, be careful with firing the brass or chamber wet.

 

[E. Bryant]

The simple fact is, our air can contain a lot of water, especially this time of year if you're not in one of the really dry parts of the country. I've been noticing 95%-99% humidity readings in the evenings several times recently, when we were in the 20%-30% range back during the summer; that stuff can make a difference.

I did some work in pneumatic suspension systems in the past. This time of the year in many parts of the country is the absolute worst for condensing humidity because of the crazy temperature swings.

I remain skeptical that steam is the culprit, but moisture on the cases and in the chamber could act as a lubricant of sorts and cause problems - especially for loads that are a bit spicy.

 

[Yondering]

I did some work in pneumatic suspension systems in the past. This time of the year in many parts of the country is the absolute worst for condensing humidity because of the crazy temperature swings.

I remain skeptical that steam is the culprit, but moisture on the cases and in the chamber could act as a lubricant of sorts and cause problems - especially for loads that are a bit spicy.

Lubricant on cases does not cause high pressure - even if water did act as a lubricant in that condition.
It doesn't take a Phd in steam engines to recognize that water subjected to extremely high heat and pressure creates steam, which can and does raise pressure of a closed system.

 

[Rio Precision Gunworks]

Ya. Those are two separate issues. Moisture/Water in chamber is going to end up with higher pressure than a dry chamber. Lube in the chamber only increase thrust against the bolt face but the chamber pressure is the same. It's debatable if the extra amount of thrust is enough to matter.

Pressure problems stem from relatively incompressible fluids.

 

[Yondering]

Lube in the chamber only increase thrust against the bolt face but the chamber pressure is the same. It's debatable if the extra amount of thrust is enough to matter.

Agreed. And even then, the difference in bolt thrust comparing maximum extremes of "lubed" vs "friction" is very small relative to normal bolt thrust.
- At the "lubed case" extreme, if we assume the case is perfectly lubed then the bolt thrust is equal to pressure times area inside the case head - pretty common knowledge.
- At the "high friction" end, assuming the case sticks to the chamber wall, the amount of bolt thrust the case can support is limited by the strength and area of the brass cross section - easy enough to calculate with some basic measurements, but it's not a large percentage of the bolt thrust. When this happens (usually with a rough rusty chamber) and an unsupported bolt head (excess headspace) you generally get case head separations on the first firing, like the old 303 Brit my buddy had, because the brass cross section isn't strong enough to support any significant amount of bolt thrust in a moderate to high pressure cartridge.