| 400NitroExpress |
| (.400 member) |
| 20/07/07 09:14 AM |
Re: New DR project
|
Quote:
Originally posted by Bramble:
Do the same with the cartridge you plan to use. ie 450 3 1/4 NE av. 34,000psi = .233 x 34,000 = 7927 lbs
16 g at proof pressure is .430 x 32,000 = 13,760lbs
No. The original pressure standards for these cartridges (17 tons for the .450 NE; 13 tons for the .450 No. 2) were BaseCUP measurements of bolt thrust, not chamber pressure in PSI. For your calculation above, CIP standardized pressures in true PSI (radial chamber pressure) should be used, as that is the current standard that factory ammo for the normal load can be loaded to. Further, that standard is used to determine the legally required proof pressure.
The .450 Nitro Express has a CIP Max Average Pressure of 3050 BAR or 44,236 PSI, not 34,000 PSI. In other words, CIP permits factory ammunition in the normal load to produce this AVERAGE pressure. Using your calculation for base area: .233 X 44,236 PSI = 10,307 lbs thrust, not 7,927.
Quote:
This does not mean that it wont work but it should be bourne in mind. This was why i used the .450#2 as the ave pressure is 26,000 psi. For the same balistics.
Again, not the correct pressure data. For comparison, CIP max average chamber pressure for the .450 No. 2 is 2800 BAR / 40,610 PSI. Base diameter is larger than the .450 NE though. Using your method for calculating base area then: .251 X 40,610 = 10,193 lbs thrust.
Hmm. Not a lot of difference.
Quote:
My rifle was re-proved at 52,500 psi.
Actually, it wasn't. Since the London Proof House didn't have any proof loads for .450 No. 2, and simply oiled a handloaded cartridge instead, you have no idea what pressure it was proved to. I still can't believe the criminal did that.
Britain is a member of CIP, so CIP proof standards are law there. CIP requires proof cartridges for rifles to produce 125% of the standard MAP for the cartridge. MAP for the .450 No. 2 = 2800 BAR / 40,610 PSI. Proof is therefore 125% of that - 3500 BAR / 50,763 PSI (not 52,500). Thus the current standard pressure mark for the .450 No. 2 is "3500 BAR" - as yours is now stamped, even though the actual chamber pressure that it sustained during proof was unknown.
Quote:
you are using up a lot of the safety margin.
You can put that up in lights. Actions are not proved, complete guns are. There is no "safety margin" until the "conversion" is re-proved - properly.