No pressure sign with virgin brass, but significant pressure+slower MV in 2nd firing..reason?

[harry_x1]

Hi All,
Currently developing a load for 33xc in 30 inch bartlein for my AXMC. 299 Grain DTACs, H1000 110 grain, 0.001 neck tension, shoulder bumbed 0.002, 0.015 off lands.
When I fired virgin brass with same load (without body sizing) I did not get any pressure signs (except one odd ejector marks on some pieces) and velocity was ~3150. However in very next firing I am getting punctured primers, cratering, ejecter marks etc with same powder, neck tension and seating depth. I have to say the primers dont look flattened though. The MV has also dropped to 3050. I bumped shoulder by 0.002 before reloading and the round chambered perfectly into my chamber without bolt handle freely falling.
I am trying to understand what might be going on here. If anyone has any hypothesis that they can share, will be great.
thanks

 

[piie]

Did you measure the original cartridges thoroughly ito OAL, headspace - and can you compare that to a pre-fired round in the batch that shows you the pressure signs?

Did you anneal after first firing?

Is there carbon ring in chamber?

Environmental changes ito temp humidity that may have affected powder?

Pull and verify powder load?

 

[harry_x1]

Did you measure the original cartridges thoroughly ito OAL, headspace - and can you compare that to a pre-fired round in the batch that shows you the pressure signs?

Did you anneal after first firing?

Is there carbon ring in chamber?

Environmental changes ito temp humidity that may have affected powder?

Pull and verify powder load?

I still have some virgin brass left and I compared the resized brass with virgin brass and it has same headspace. I also took my barrel off and dropped the case inside chamber and see that the resized case freely drops into the chamber. I also chambered the resized case with my bolt (after removing firing pin) and there was absolutely no force required for closing the bolt. I am quiet sure that I had resized the case enough to have enough headspace.

I fired some bullets after annealing and some without annealing to check if that had an impact.

There is a solid carbon ring after each firing. I am not sure why that is...could it is the very light neck tension I am using?

Dont think there is any environment impact here. 110 grains is on lower end of what other shooters generally settle at which is 111.5+.

also attached image of punctured primer. Primers dont look flattened..primarity punctured or cratering.

 

[piie]

Hmm, perhaps it's only a primer issue / firing pin / bushing issue then?

Do you have another type/brand of primer you could try?

 

[harry_x1]

Hmm, perhaps it's only a primer issue / firing pin / bushing issue then?

Do you have another type/brand of primer you could try?

I am using federal gold match magnum G215M...read in forums that they have a strong cup vs CCI. I can try to get some other brand primers as well. What about the firing pin bushing?

 

[piie]

Disclaimer: have no first hand experience with bushing the firing pin hole in the bolt face, but I recall other threads where that solved pierced primers- if the hole is too big, the primer has space to deform into the gap and cause either excessive raised ridges around the strike area, or pierced primers

 

[piie]

Also, I'm just rambling on to keep your thread purring along - the clever guys are still asleep, they should hopefully start contributing soon and get you to the real solution soon

 

[jimmymac]

No mention of neck diameter in the OP. Did you verify the OD of the loaded round has adequate clearance to fit your chamber? See if a bullet slides into a fired and unsized case with little to no resistance. Just spit balling here.

 

[Ray123]

I'd drop the powder charge 3 whole grains...clean bore especially in the throat...carbon build up ...Iosso if necessary. I like. 002 neck tension.
Seperate 5 new pcs with run through mandrel to get .002 neck tension and same with 5 fired but undamaged cases... install correct primers like Fed LR Mag match...need a good flame to ignite all that powder.
Check COAL of fired and unfired...as they grow..Are they inside max for your chamber?
Try .002 neck tension on 5 each new & fired with same exact 3 gr reduced load shot over the chronograph and there should be no signs of pressure....compare results. Should be similar... Not concerned about the first trial and results, if it doesn't repeat with the 2nd trial with recommendations applied...others velocities are not your velocities, barrels vary, and some order .001" smaller bore dia on purpose.
It doesn't matter what max load others shoot... this is your rifle, your barrel, and may require less powder.
If this continues call Superior Shooting Systems and talk to David Tubb ...it's his round and probably knows more about it than anybody...by the way it appears to be a good round, along with his 375XC. Don't give up without an exhaustive effort..good luck, and don't force it, as it will give you, what it gives you, every barrel is different, and acceptabe accuracy and reasonable velocity are in there...you have to find what it likes..not what you want, with respect to powders, bullets, and velocities for each component.

 

[williepete]

Remove that carbon ring and try a few rounds
I had a similar thing happen when i removed the carbon ring it went went away

 

[moondog]

Make sure your cases have absolutely no residual lube. Either from the media used to clean, or resizing. Not the same thing but my 338Imp brass is tough, I mean tough. It takes a couple of firings to even worry about bumping the shoulders. And yeah, I'd get the bolt bushed if it's not small already. The earlier ones weren't.

 

[Kracken McGraw]

If that’s a ejector mark on the last b of Tubb on that case pictured, your load is too hot.

 

[big5ifty]

Assuming you have one piece of virgin brass of the same headstamp as the fired.

Get a 1/10,000 micrometer. Measure virgin brass just ahead of the extractor groove.

Then measure your fired brass with cratered primers.

What's the difference ?

 

[drumcorpschamp]

Are you single loading these rounds or loading multiple rounds in the magazine? Recoil could be shoving the bullets deep into the case. Especially with only .001" neck tension on a boomer like that!
Jerry

 

[KMart]

There is a solid carbon ring after each firing. I am not sure why that is...could it is the very light neck tension I am using?

What is it that you are calling a carbon ring?
1. Soot around the neck of the brass?
2. A hard carbon build up in the inside of the barrel just at the start of the rifling?

The carbon ring that is concerning would be the build up inside the barrel. I have had carbon rings before, but never after each firing.

 

[jelenko]

Another thing to check is to confirm the bullets are not into the lands.

 

[moondog]

One more thought, if you have a round in the oven too long getting on target. Solved a couple of buddies issues with that.

 

[SKWERLZ]

Fired brass often shows pressure with the same load as new brass, less case expansion typically with fired and resized case.
Drop your charge.

Another thing to consider, H1000 is a bit fast for 33XC especially with solids
Solids create a more aggressive pressure curve than cup/core bullets

I’d really look at R33, 24n41 or similar burn rate powder.