Hidden Pressure Reading: A Method

[DoneNOut]

Maybe. Or maybe I am late to the party...

I have a chamber right now that isn't showing pressure signs, primers look the same whether I have a stout or light load. Sometimes I am getting fairly high velocity in a load and I know there is no free lunch.

The thought dawned on me, like an epiphany, "Hey, I trash my brass after the primer pockets wear out. Why don't I measure a virgin piece of brass and then compare virgin brass primer pocket size to primer pocket growth after firings?"

Present virgin brass primer pocket internal diameter ID .2085.

One 10ct string of fired brass still measures .2085" ID.
Another 10ct string of fired brass measures .2095" ID.

Well, maybe I should keep on with the recipe that isn't enlarging the primer pocket even after the first firing?!
I also started punching primers before tumbling because I think primer pocket cleaning sucks and I might as well let the tumbler & walnut media do it. It's way easier to knock out the walnut media stuck in the holes. In doing this I also get to inspect the spent primer. I noticed one load was producing primers with soot on the sides of the primer. Hmm, looks like pressure wanting to eek out the primer pocket, I consider this a clue!

 

[cape cove]

What cartridge are we talking about.

 

[NorthernWhitetails]

Most experienced loaders have a go/ no go guage , to check the pocket for excessive enlargement. If the no go end fits throw the case away. If your finding that after a few loadings your loads are toooo much pressure! Back off your asking toooo much from your firearm.

 

[Wedgy]

Small and Large Primer Pocket Swage Gage ® Set

Swage Gage Small Primer Pocket Gauge

ballistictools.com

 

[Muddyboots]

Knowing @Gingerman's flavor, I'd be SHOCKED if it wasn't 7-08 or .308. Leaning toward 7-08!

But oh great, another measurement to take! But if the primer pocket measurement can be tied to specific load it might be worth it. If on rare brass, really might be worth it. On common brass? Not sure if brass isn't just a throw away.

 

[cape cove]

Reason I asked is some of the AI cartridges don't show pressure very well.

 

[DoneNOut]

I am fireforming 708 brass in a 708AI chamber...

 

[Phil Rizzo]

I usually back my load down significantly when blowing out shoulders.
Sorta use the minimum required to do the job and "condition" the brass.
it's recommended by the manufacturer also. How close are your velocities to the speed you expect the blown out cases to achieve ?

 

[Bob Wright]

Nosler brass has been soft for me. Slowly weeding out that brass in favor of Peterson or ADG.
I use a go, no go pin as well. It's very fast to check.

 

[Phil Rizzo]

Amen Bob Wright.
This very afternoon I'm forming Peterson for my 25 Sherman LA.
my high dollar nosler was good for 3x. Except the ones that leaked on round 2!

 

[john k]

Nosler brass has been soft for me. Slowly weeding out that brass in favor of Peterson or ADG.
I use a go, no go pin as well. It's very fast to check.

Concur. Nosler primer pickets do not hold up nearly as well as brass mentioned. Petersen for my .280AI's, Lapua for my 7-08, and ADG for my 7saum.

 

[cape cove]

Used both Weatherby and Nosler brass in my 257 Weatherby mag. The Nosler brass primer pockets just didn't hold up. Three reloads with the Nosler brass and they were done. I would get up to 8-9 firings with the Weatherby. JME

 

[nksmfamjp]

I find bolt lift to be a pretty consistent pressure indicator….better than primers. The only real issue is it is more of a ~70000 psi indicator, it seems so I find I need to back off about 1gr on a 60gr load.

I do also find pre-bolt lift are ejector marks under 10-20x magnification.

I would warn you straight walls like 458 Lott don't really exhibit bolt lift IME.

Are any of you not seeing bolt lift?

I have only once had a primer pocket issue. That was clearly a brass issue.

 

[VinceMule]

Some years ago, I had a couple of brands of brass tested for Rockwell hardness. Brass varied 6% in Rc hardness over a brand and as much as 12% over several brands. So, you can have some soft cases in a lot#, cull soft ones out.