Progressive pressure signs

[Poc]

A friend of mine bought a new Christensen Arms 300 Win Mag with a carbon fiber barrel and he shoots it suppressed. He was having trouble finding a factory load that would group to his satisfaction so I had him shoot a few of my 168 HHT loads. The first shot showed no ejector marks and there was no sticky bolt lift. Because you can’t feel the true barrel temp wrapped in carbon, we waited a few minutes between shots. The next two shots showed progressively greater resistance with bolt lift and clearly more defined ejector marks. First, second and third shots left to right.

I have more than one 300 win mag so I color coat the head stamp of the brass to match the rifle so I don’t mix loads. It actually makes seeing the ejector marks easier.

Questions:
Did an increase in barrel/chamber temperature with each shot cause this?
Does the suppressor play a role due to back pressure?
When I do load development I always wait for the barrel to cool before taking another shot, because the cold barrel shot is usually the one that counts. I couldn’t feel the barrel temp being carbon wrapped, so would this pressure also show up on my steel barrel rifles if multiple shots were fired without adequate cooling time?

As always, thanks for the knowledge!

 

[Koda]

My guess is if you found pressure in just 3 shots its from something else than barrel temp. It could be you are right on the edge in your rifle. I would check his rifles distance to the lands to make sure your not touching them with your handloads.

 

[jrebel]

Another thought….your to close to the jam point, meaning your bullet is right against the lands and grooves. I have seen this before with hammers and simply seating them deeper by 0.02 to 0.05 would likely solve the problem.

I will also say….its not the safest thing to be shooting your reloads in another rifle without verifying all aspects of the reload. Powder charge, seating depth, shoulder bumps (brass sizing), etc. This is the exact reason you color coat your brass for the different rifles.

I seriously doubt in three shots, you generated high enough temps to change anything.

 

[BFD]

The answer is simple. You had a system in place to prevent this kind of thing, then you FAFO.

 

[OutdoorEdventure]

Clarification: same load or increase charge per shot?

 

[Muddyboots]

I have read Christensen Arms 300WM have some interesting "pressure" signs with double ejector marks on brass and bolt lift.

Couple questions:
Was a 168HHT ladder run or "just a load"?

What is the 168HHT load data? Crimp? Your brass and not his fireformed brass , correct?

Was the barrel scrubbed clean for baseline load testing?

Round count of barrel?

The more data you can provide the more likely someone can offer up a recommendation.

 

[BFD]

I have read Christensen Arms 300WM have some interesting "pressure" signs with double ejector marks on brass and bolt lift.

Couple questions:
Was a 168HHT ladder run or "just a load"?

What is the 168HHT load data? Crimp? Your brass and not his fireformed brass , correct?

Was the barrel scrubbed clean for baseline load testing?

Round count of barrel?

The more data you can provide the more likely someone can offer up a recommendation.

I get that Bro said, "Bro, your rounds not working good, try one of mine, whoah Bro, that doesn't look right!"

 

[gltaylor]

All above good points!
Wouldn't shoot a load that hadn't been worked up in that specific rifle first

 

[Koda]

All above good points!
Wouldn't shoot a load that hadn't been worked up in that specific rifle first

One of the "golden rules" of handloading..

 

[Poc]

Clarification: same load or increase charge per shot?

Same charge.

 

[Poc]

One of the "golden rules" of handloading..

I agree, I shouldn’t have done that. The only reason I did was because the charge was not over published Nosler load data. Still not a good idea as an afterthought.

 

[Poc]

I have read Christensen Arms 300WM have some interesting "pressure" signs with double ejector marks on brass and bolt lift.

Couple questions:
Was a 168HHT ladder run or "just a load"?
A good load in my rifle
What is the 168HHT load data? Crimp? Your brass and not his fireformed brass , correct?
New Lapua brass with 1/2 crimp
Was the barrel scrubbed clean for baseline load testing?
Barrel was cleaned
Round count of barrel?
20 rounds
The more data you can provide the more likely someone can offer up a recommendation.

 

[Koda]

I agree, I shouldn’t have done that. The only reason I did was because the charge was not over published Nosler load data. Still not a good idea as an afterthought.

This is why I like how Hammers load data doesnt list a max charge since no two rifles are the same.
I do find max velocity useful.

 

[Poc]

Another thought….your to close to the jam point, meaning your bullet is right against the lands and grooves. I have seen this before with hammers and simply seating them deeper by 0.02 to 0.05 would likely solve the problem.

I will also say….its not the safest thing to be shooting your reloads in another rifle without verifying all aspects of the reload. Powder charge, seating depth, shoulder bumps (brass sizing), etc. This is the exact reason you color coat your brass for the different rifles.

I seriously doubt in three shots, you generated high enough temps to change anything.

I have the rifle now and I was 90 thou off the lands. I will try to begin loading for it if it ever stops raining around here. Given all the opinions, I believe I was at the very edge of pressure and a slight bit of extra heat with each shot revealed the ejector marks? Also, while I was near the top of Noslers load data, it was 3 grains over Hodgdons load data.

 

[Koda]

I believe I was at the very edge of pressure and a slight bit of extra heat with each shot revealed the ejector marks?

My guess is 3 shots shouldn't heat up a gun enough to trigger overpressure in a stable handload. My guess is your load was already at the upper limit in your gun (and would have showed up eventually), and your friends guns chamber was just enough to show it, I think the progression you saw was just a coincidence and if you had fired those 3 in any order they would have shown the same marks.
Just my guess.

 

[BFD]

My guess is 3 shots shouldn't heat up a gun enough to trigger overpressure in a stable handload. My guess is your load was already at the upper limit in your gun (and would have showed up eventually), and your friends guns chamber was just enough to show it, I think the progression you saw was just a coincidence and if you had fired those 3 in any order they would have shown the same marks.
Just my guess.

This

 

[Poc]

Update: I was able to start loading for this rifle yesterday. The load I tried a few weeks ago from my rifle had 73 grains that showed the progressive pressure.

I started his load at 70 grains of H4350, new Lapua brass, 1/4 crimp, 3.400”, fed 215 primers and no pressure. Accuracy was fair Chronograph showed 3150 fps

Next I tried 71 grains and ejector marks showed up so I went back to 70 and attempted different crimps with no real change in group size (1.5”). I then went to a Federal 210 primer and the 5 shot group was .7”.

Incidentally, this is the second 300 win mag I’ve loaded the 168 HHT in that performed much better with a non magnum 210 primer and H4350.

Moral of the story is still always start low even if the it’s within Noslers book specs.

 

[BFD]

Next firing you will have longer cases with little more capacity, and you can either leave charge weight alone or load another 1/2-1gr grain of powder.