Pressure Signs under max load
- Thread starter BeagleBoy360
- Start date
I think of you mentioned the minimum load you would probably get a fair response
Oh crap, and Magnum primers?!? You're effing crazy!
I hope you sense the joking around. On all seriousness though, I'd like to know the best ways to be able to tell high pressure too...But also I'd like to know if these techniques even work for calibers that generally are lower pressure. If a large rifle primer will flatten out with a max load on a 308, then won't it ALWAYS flatten out on a 338LM? What about a smaller/lower pressure large rifle primer'd cartridge....if I loaded that up above max load, I'd still be well below the 308 pressure zone, so could I expect to see flat primers there? I'd assume not....
This matters to me because I'm trying to figure out the max I can push 455 Webley to and it is very low pressure....so this thread is of interest to me.
Back on topic....how about those Magnum primers? This guy is nuts....
Well, first off, the .338 Lapua is far from being the hottest load of the gang. Actually, under CIP, the .308 Win MAP is 60 000 PSI while the .338 Lapua round is rated at 61 000 PSI. As a comparison, the .308 and .358 Norma Mag and the various Ultra Mags are rated at 64 000 PSI MAP.
And this doesn't mean that the .338 can't be loaded to higher pressures, but it's how it was spec'd when introduced to CIP.
All the commercial loads are made to fit in those specidfied MAP (Maximum Average Pressure) using very tight barrel and chamber specs.
As a general rule, the firearms are proofed at 1.25 times the MAP.
Actually, unless using pressure transducers no one can say what pressure he gets with his loads. Tool like Quickload only gives an estimate.
And, for what it worth, the pressure rises at the square of the velocity increase with a given case / primer / powder / bullet / firearm combination. This means a 1.2 times velocity increase will result in a 1.44 times pressure increase for a given combination.
High pressure signs which badly flattens the primer will also most of the time open up the primer pocket - hence loose primers -, but the most common cause of flatened primers is too much resizing - then, when the striker hits the primer, it pushes the case forward and the pressure pushes the primer rearward, then, the pressure rises and push the case head back, extruding the ballooned shape primer, making it look flattened. Some primers are "softer" than others, some cases are, too. But they are also tested to fit the pressure range they are intended to cover.
If there is really too much resizing, the case will show signs of cased head separation, it first shows as a shiny ring about 0.200" above the base.
See it that way; Norma, in the '60s, made very tough brass available to the reloaders, so tough it was handling close to proof loads without any damages.
Then, what they found the hard way that because they could, reloaders were pushing way too hard. They went back to a milder brass which will show pressure signs within the MAP the case is designed for - this topic have been covered by PO Ackley and by Norma in their "Gunbugs Guides".
Now, the Webley is another story and again the problem is the action strenght. A lot of these were reamed to accept 45 ACP, but a lot of them are also known to have excessive play... you can shoot 300 rounds of perfectly looking spent cases and then, one day, the gun will suddenly burst or develop excessive play all over.
The .455 Webley had different MAP over it's history, but currently, CIP's MAP for the Mk II round is 13 000 PSI MAP.
For that reason, you may want to get some tested loads published by a reliable source.
