Pressure increasing with continuous shots?

[CBB1]

I ran into pressure signs on some 308 I was shooting today at the end of a 5 shot group. The first 3 shots seemed fine and I was visually inspecting each brass for pressure signs. The fourth shot had a heavy bolt lift and slight ejector mark. The 5 was more noticeable with bolt lift and ejector mark. I’m shooting a Remington 700 with 18” barrel and suppressor. Load was Hornady brass 44gr Varget, federal primer and 168eldm loaded to 2.800”. Each shot was single loaded and fired.

I am new to reloading so there is still a lot I don’t know, any guidance would be appreciated.


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[bmart2622]

The only time I had something similar happen was when a carbon ring developed, but I was shooting a 300 Ultra burning 95grs of powder. Sure seems like it would take a lot of shots from a 308 to do that but maybe?

 

[strikerfired]

How are you measuring your charge weight? Depending on your system there could be a bit of a variance in throw.

Varget should be fairly temp stable, and I wouldn’t expect a major pressure change in 5 rounds.

How many loads on the brass? Re-sized & trimmed? Crimp?

Silly question, but how many rounds down the pipe since your last cleaning? Insane buildup could cause increased pressure. But it would be fairly impressive for it to be that dirty outside of some really really bad copper fouling.

 

[Gunsandfitness]

My first thought also goes to carbon ring… as others have said it shouldn’t cause build up after a few rounds, but we are all unsure of your cleanliness routine. Also cans are fairly dirty (trapping gases in the system) so that could have helped with expediting build up.

Only other thought is maybe primer variance? If you’re using standard federal and not match grade primers and your loads are on the high end (don’t know what’s high for .308 off the top of my head) the difference in QC of non match primers might lead to enough of a burn variation to make one stick.

 

[CBB1]

I’m using a standard RCBS charge thrower and weighing each charge on a digital scale and trickling to the desired weight. All the brass is once fired Hornady. The gun have less than 300 rounds through it.

It’s my first experience with a suppressor, didn’t know if that was a factor.


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[zrodwyo]

I had two barrels over the years that would pressure up after just 10-20 rounds only when shooting suppressed. Factory ammo or light loads it didn’t matter.

The explanation I got from someone at Thunderbeast was that suppressors make a gun run a lot dirtier. The chamber necks on these two barrels were likely cut very tight and the additional carbon fouling from the suppressor was causing the pressure spikes.

 

[Duh]

I had a similar experience the other week in my Seekins Havak 300 win mag. Was running a Banish suppressor and working a relatively little load up.

Cleaned the barrel and action before shooting it. It shot the first 10ish rounds fine but started getting the pressure and heavy bolt lift. I know the barrel was heated up a bit but it wasn’t that hot.

What I think happened was excess bore cleaning fluid got into my action and on the bolt face. I visually inspected and noticed the excess moisture on the bolt. Cleaned that off and ran a dry patch into the throat and action. Pressure signs went away.

Not sure if that’s what happening I’m your case but it helped me.

 

[Brusso89]

I take it you’re not shooting through a chrono? Is your recipe towards max charge?

 

[Harvey_NW]

Did you start with cold bore? Possible that you're right on the verge of pressure and a warm chamber on the 4th and 5th were just enough to show some pressure, especially if you let them cook at all getting on target. Hornady brass is pretty soft and doesn't hold pressure well either. I'd drop the charge weight and try it again.

 

[Weldor]

I know my match chambers are finicky about oil or and wax on the cases. I wipe every round with achohol or acetone. I work up very carfully when shooting suppressed. Flat primers are common. Only had hard bolt lift with improperly sized brass or oil in the chamber.

 

[Lawnboi]

I fought this with one barrel. Tried a whole bunch of things. Ended up just pulling the barrel. L

 

[CBB1]

Thanks guys, good to know I’m not crazy. I’ll do a good cleaning and drop the charge and see what happens.


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[Formidilosus]

Thanks guys, good to know I’m not crazy. I’ll do a good cleaning and drop the charge and see what happens.


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If cleaning is the issue, you need to address your chamber/throat. Thousands and thousands of rounds with suppressors and 308’s should not be causing issues.

 

[Castle Rock]

Only other thought is maybe primer variance? If you’re using standard federal and not match grade primers and your loads are on the high end (don’t know what’s high for .308 off the top of my head) the difference in QC of non match primers might lead to enough of a burn variation to make one stick.

Stop making up nonsense
The only real difference between std and match primers from federal is the match primers are visually inspected before packaging

 

[Vern400]

I shoot 44 grains of varget and a 165 Sierra bullet in my 308. If I want to convince myself I'm going to die very soon, I simply wipe some RCBS Case lube on a cartridge. It'll extrude into the ejector hole, maybe flatten the primer and look like the world is ending. Tech support at Sierra told me, " yeah, that happens. You probably got Case lube in your chamber". And they were right.

The guys here talking about a carbon ring and suppressors might have a point. I have no experience with suppressors. But a 308 is one of the most forgiving cartridges you'll ever work with. You can send hundreds of shots without cleaning.

If you were shooting RL15 you could have been cooking the round in a hot chamber while you pick your nose and get comfy for the shot. I've done that. Not happening with Varget.

One grain off of Max with Varget tends to be magic. Don't back off til you get the oil out of your chamber and the lube off the brass.

 

[Vern400]

Stop making up nonsense
The only real difference between std and match primers from federal is the match primers are visually inspected before packaging

Yep. David tubb might be able to tell a difference. But no ordinary human!

 

[strikerfired]

Vern makes a great point. What is your brass prep process? What kind of case lube and after processing do you do?

For my bolt guns, I use walnut, size, then run them through a sonic cleaner before loading anything.

 

[CBB1]

I use hornady one shot lube and wipe it off with an alcohol rag after sizing.


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[Jimbee]

I ran into pressure signs on some 308 I was shooting today at the end of a 5 shot group. The first 3 shots seemed fine and I was visually inspecting each brass for pressure signs. The fourth shot had a heavy bolt lift and slight ejector mark. The 5 was more noticeable with bolt lift and ejector mark. I’m shooting a Remington 700 with 18” barrel and suppressor. Load was Hornady brass 44gr Varget, federal primer and 168eldm loaded to 2.800”. Each shot was single loaded and fired.

I am new to reloading so there is still a lot I don’t know, any guidance would be appreciated.


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I had the same issue with Varget in my 6GT. I backed off close to a grain and fixed it. I actually had to pull a bunch of loaded ammo and re-reload it.

 

[Packmansion]

I ran into pressure signs on some 308 I was shooting today at the end of a 5 shot group. The first 3 shots seemed fine and I was visually inspecting each brass for pressure signs. The fourth shot had a heavy bolt lift and slight ejector mark. The 5 was more noticeable with bolt lift and ejector mark. I’m shooting a Remington 700 with 18” barrel and suppressor. Load was Hornady brass 44gr Varget, federal primer and 168eldm loaded to 2.800”. Each shot was single loaded and fired.

I am new to reloading so there is still a lot I don’t know, any guidance would be appreciated.


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If your barrel is getting really hot and you are cooking the rounds in the chamber you can increase pressure. Do not chamber a round until you are pretty close to shooting. Let the barrel cool down between groups. Varget is not supposed to be temperature sensitive but all powder is sensitive to an extent.