Suppressors What causes condensation in a barrel, particularly the last 6-8”?

[Roadrace33]

I had to take a flight to Texas, so I didn’t have very much time to test other things. I live in Illinois. It’s cooled off to about 60* ambient temp, 35% humidity. I have a new 6.5cm barrel in an AXSR, running Berger 153s in lapua cases with BR4 primers and h4350 @2650 FPS. On the end I’m running a TBAC 338 ultra gen 2. (Super stupid quiet BTW)

I missed a coyote the other evening at 350 yards, and I scratched my head for a long time about it. Yesterday, after work I went out and re, checked zero. It was slightly off, no big issue. Re-zero and starting hitting steel from 300-800yards. Then, after roughly 10 rounds I have moderately heavy bolt lift, groups opened up big time again. We’re talking can’t hardly hit a full ipsc at 700. Take it back to 100 yds, groups are 2 moa, and hitting low. I’m like dude wtf, took it inside, ran a borescope. All looks normal, except the last 6-8” of barrel is soaked. Wet. This barrel has exactly 200 rounds down it, never been touched nor cleaned, absolutely no reason anything should be wet. So I ran the borescope down the suppressor, it’s pretty damp looking too.

So I ran a dry patch through it. Came out wet looking, ran a few more, got it all out.

I thought I was going f-ing nuts so I took it back out and shot it. Same thing. About 10-15 rounds later, somewhat of a heavy bolt lift, I run the borescope through it and there it is, more moisture near the end of the barrel.

I was going to go shoot it without the can and see what happens but I didn’t have the time last night.

It is very dew’ey in the evening and morning here, so by 6pm the grass is soaking wet. So just because the humidity isn’t terrible -30-45%, there is a lot of Dew.

Here is a pic of the SR brake that is wet, and a pic of the first patch I ran through the barrel, wet aswell.

 

[jabonra]

I will preface this by saying I have no idea if it's right but -

- Pre firing, barrel and can are filled with ambient cool air.

- fire, air in both are expelled by bullet and gases. Barrel and can warm.

- air rushes back to fill the void of the barrel/can lower pressure zone.

- air in barrel and can heat, raising moisture capacity.

- air in barrel and can suck up more moisture.

If you keep shooting, nothing happens but if you let it start cooling the air drops below dew point and condenses. you might just have the perfect storm of high local RH (dewy at the ground) on top of the huge extra air volume of a monster can. I think you're on to it with removing the can, as the air volume will be nil without it.

 

[carbonbased]

As far as water in the air, I go by dew point and not relative humidity. Dew point is an absolute thing, and for me, it better corresponds to how the weather actually feels.

But that is neither here nor there.

Can’t see how heavy bolt lift factors in here unless you have a carbon ring. Carbon, I think, can hold moisture, and if it’s really wet out then maybe it could exacerbate the carbon ring/bolt lift issue.

Carbon and moisture are why I stopped storing my rifles with cans attached. Over time, the theory goes, the slight dampness of the carbon in the can might corrode the crown.

I do know that storing with a can attached may lead to big chunks of carbon falling into the action. Depending on how on top one is about can cleaning, of course. Had that happen at least twice, which led to the bolt seizing up.

Let us know how you resolve the issue. I’m just taking a wild-ass guess.