Pressure increases with hot chamber?

Eric H said:

Just started using a suppressor th7s year and have yet to run into that problem of finding pressure sooner with the can.

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haisardao said:

Hi all, I was shooting a load I developed for a 6.5 PRC, Lapua virgin brass, RL26 (57.0 gr), CCI BR2. Shooting suppressed at 3250 fps. I'm at least 1 gr below pressure according to the ladder test I did before.
Now the problem, firsts 3 shots all great, consistent velocity, 4-5 shot velocity spikes 40 fps more, 6 shot got an ejector mark and bolt lift.
I let the rifle cool off, and tried again, first shots perfect, then pressure spikes.
Have you seen this before? Never had an issue with Hogdons powders, I'm guessing RL26 doesn't like hot chambers.
Thanks

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Jepp577 said:

I have yet to hear this discussed, but it has become evident to me that there is an issue that occurs when shooting suppressed. Especially when the weather is cooler or also when there's more humidity in the air. I have noticed a similar thing take place when I know my loads are under pressure but upon consecutive suppressed firings the same load spikes and I've experienced heavy bolt lift and significant ejector pin marks. What I realized was that as the suppressor gets hotter, and a lot of those hot gases get trapped in the can, that heat and those gases will return back towards the chamber and condensate on the chamber walls creating a wet chamber resulting in increased pressure. You'll notice upon ejecting a fired case the smoke gases coming out from your chamber. The first time I experienced this was with Hornady factory prc ammo. While frustratingly wondering what was going on i chambered a round and immediately extracted it without firing, I case was wet. There was the issue. Not a hot chamber. I'm sure if a case sat in a hot chamber long enough it could cause an increase of pressure but not nearly like a wet casing. I've seen this with multiple rifles all shooting suppressed. Factory ammo and proven under pressure hand loads. I haven't done it yet but I'm fixing to make or buy a chamber fan that will push air into the chamber and through the barrel to keep those hot gases going out through the suppressor and also help to cool the suppressor quicker while at the range. A quick google search will show several different types of fans including diy fans guys have made with rechargeable compact mattress pumps. FWIW this has been my findings.

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Teri Anne said:

This is not a new issue. Going back to my Army high power match shooting days back in the 70s through early 90s when shooting slow fire standing at 200 yards or especially prone at 600 yards, both slow fire events (20 shots in 20 minutes). We did not load ammo into a hot chamber until right before we were going to shoot. When I say right before shooting, I mean close bolt, aim, and fire within 10 seconds or less. Way back then, there was no such thing as temperature stable powders. Putting a cartridge into a hot chamber would immediately start heating the cartridge, and after as little as 15 seconds the temperatures could rise well over 100 degrees or more. This would cause not only a rise in pressure, but an inconsistent one at that. Those were the days before any of the temperature stable powders were developed. Even today, if you load a cartridge into a hot chamber, even with the stable powders, this is an issue. Check the temperatures where the powder is stable, and you will find it is stable only under a certain temperature range, none of which include baking in a hot chamber to temps over 100 degrees.

Over the years I witnessed many rifles blowing up on the range on hot summer days, simply because of someone loaded to max pressure only to have the internal temperature, as well as pressure of the cartridge increased to where it blew up the firearm. Fortunately, nobody was seriously injured, but lessons were learned. ALWAYS WEAR PROTECTIVE EYEWEAR!!!!!! Prescription eye wear is seldom sturdy enough to stand up to a firearm blowing up a few inches away. Even with polycarbonate lenses, frames are not sturdy enough in most cases, to hold together under situations like that. If you need prescription lenses to shoot, buy a pair of prescription safety glasses. Better safe than sorry.

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