How to read a pressure curve [Archive] - Glock Talk

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Snapper2
05-01-2011, 13:23
when starting from scratch. Caliber 400 corbon. new starline 400cb brass. cci 500 spp. Oal-1.189. Bullet 155grxtp. No data for 800x in 400cb so I started close to high end 10mm data . ProChrono results..... 10grs-1254fps.....10.5grs-1324fps.....10.8grs-1373fps.....11grs-1427fps. Fired brass measurements and primers not all that bad. I will not push past 11grs anyway because theres no data from Cor bon pushing 155grs past 1300-1350fps with any powder. The last bump in powder 10.8 to 11grs gave the same 50fps rise in velocity as the 10.5gr to 10.8 did. How do you read this in terms of pressure? Cor bons data for the same with #7 is 13gr-14gr, 1250- 1300fps. Which I've also tested. Seems like a sharper curve at high end with #7?

Gokyo
05-01-2011, 13:27
I do not see any pressure data here. I am not sure I would count on velocity to = pressure.

Snapper2
05-01-2011, 13:31
I do not see any pressure data here. I am not sure I would count on velocity to = pressure.

Thats what I'm trying to learn.

WiskyT
05-01-2011, 14:05
There simply is no way to know if you are within pressure limits without a pressure measuring device. There is no concrete correlation between pressure and velocity. That doesn't mean your 800X loads aren't safe, it just means you really have no way of knowing without a testing lab.

Snapper2
05-01-2011, 14:25
There simply is no way to know if you are within pressure limits without a pressure measuring device. There is no concrete correlation between pressure and velocity. That doesn't mean your 800X loads aren't safe, it just means you really have no way of knowing without a testing lab.

Can you tell anything from velocities....ie. which powder burns slower in particular cartridge? #7?
800x 10gr-1250fps.....11gr.-1427fps
#7 13gr-1250fps.....14gr.-1300fps

fredj338
05-01-2011, 15:01
when starting from scratch. Caliber 400 corbon. new starline 400cb brass. cci 500 spp. Oal-1.189. Bullet 155grxtp. No data for 800x in 400cb so I started close to high end 10mm data . ProChrono results..... 10grs-1254fps.....10.5grs-1324fps.....10.8grs-1373fps.....11grs-1427fps. Fired brass measurements and primers not all that bad. I will not push past 11grs anyway because theres no data from Cor bon pushing 155grs past 1300-1350fps with any powder. The last bump in powder 10.8 to 11grs gave the same 50fps rise in velocity as the 10.5gr to 10.8 did. How do you read this in terms of pressure? Cor bons data for the same with #7 is 13gr-14gr, 1250- 1300fps. Which I've also tested. Seems like a sharper curve at high end with #7?
You can't read pressures from vel data. Pressures are rarely if ever linear, so even if you could establish a base line & plot a curve, going 0.1gr over max can push pressures vertical. There is just not a lot of room in smaller cases using relatively fast burning powders.
Can you tell anything from velocities....ie. which powder burns slower in particular cartridge? #7?
800x 10gr-1250fps.....11gr.-1427fps
#7 13gr-1250fps.....14gr.-1300fps
Sure, you can determine that equal charges of diff powders & one gives a higher vel, it is producing higher pressures. All things being equal, pressure often equal vel. So same bullet, same powder charge wts, higher vel will almost always mean higher pressure. So in your example, AA#7 is acting slower than 800X in the 400Corbon. In most burn rate charts, that is what I would expect.