Pressure in measurements but not with traditional signs?

[SDHNTR]

So I’m getting significant growth in base diameter of Alpha brass in my 6 GT. No ejector mark, no flattened primers, zero stiff bolt lift, but the base (just above extractor groove) diameter is growing a lot. .0015 to .002”. That’s a lot more than I’m used to with other cartridges. I ran this same load up another 1.8 gr of powder before I saw even the faintest ejector mark. I’ve never seen this kind of brass growth without other pressure signs showing up before. Ideas?

 

[seand]

First thing I’d want to know is if it’s way over saami pressures. Checked against book max velocities with same powder and adjusting for barrel Length. Ignoring charge weight, are you getting more velocity than the book max loads?

 

[SDHNTR]

First thing I’d want to know is if it’s way over saami pressures. Checked against book max velocities with same powder and adjusting for barrel Length. Ignoring charge weight, are you getting more velocity than the book max loads?

It’s a 6GT so there isn’t much book data. But no, I’m not way over max for what is out there.

I’m at 35 gr Varget with a 90 gr hammer HHT, right at 2980-3000 with a 20” bbl. I ran it up to 36.8 before I saw a faint ejector mark. Primers still round and bolt lift was easy. I’m just surprised Alpha brass isn’t handling reasonable pressure better.

 

[parshal]

I'd email or call Alpha. They've always been responsive to me. I also have a hard time seeing that much growth in that area without other signs. That's pretty significant growth.

 

[TaperPin]

I’ve seen a big jump like that early, but subsequent firings produced much less expansion as the case head work hardened. Those big jumps early on are why I eventually started combining case head measurements with reloading 5 cases enough times to fail. The case head measurements gave a rough idea, and the number of times to failure are more definitive, but a lot harder to do if the range is time consuming to get to.

 

[Lawnboi]

What’s your velocity? Some of this brass handles pressure so well I don’t think common pressure signs are a good sign of pressure. Speed is pressure.

Also who cut the chamber?

Excessive brass growth in that area is going to cause problems down the road reloading.

 

[SDHNTR]

What’s your velocity? Some of this brass handles pressure so well I don’t think common pressure signs are a good sign of pressure. Speed is pressure.

Also who cut the chamber?

Excessive brass growth in that area is going to cause problems down the road reloading.

See above, 2980-3000 fps. Seems right in line where things should be.

Kampfeld did the barrel work.

 

[Lawnboi]

See above, 2980-3000 fps. Seems right in line where things should be.

Kampfeld did the barrel work.

Might be worth a try shooting something other than copper, I know it can cause different pressure but that dosnt sound out of this world at all.

I’d call the smith first and explain your findings.

 

[seand]

Hornady has data now for 24” barrel. You should be pretty much right on max pressure at 3k fps. Definitely not way over. I’d be calling alpha

 

[SDHNTR]

Well I sent Alpha an email. They quickly responded asking what my measurements were. I told him .4670 on unfired and .4685-9 on once fired.

He replied back with: “those numbers are perfect.” Stating saami of .4710” so these numbers are what they’d expect to see.

Interesting, but I guess I’m gonna just carry on and monitor things closely. I know I’m still under Saami specs but I’m not expecting the brass to survive long.