Author Topic: calculating bullet obturation using psi (Read 729 times)

carpediem · « **on:** November 24, 2003, 04:14:25 PM »

Is there a reloading manual that lists pressure for lead cast bullets in psi? I have a formula to calculate bullet base obturation using psi, (as discovered in Rifle Magazine's Handloader, December 2003, No.226, Page 6; in the article written by Dave Scovill, entitled "BHN and BULLET METAL").

In a nutshell, you multiply the Brinell hardness of your lead alloy by 1,422 to give you "the pressure,in psi, required to cause that particular alloy to upset under pressure in a gun."

Thanks for the help.

Kindest regards,
:wink:

Aladin · « **Reply #1 on:** November 24, 2003, 04:36:45 PM »

Quote from: carpediem

Is there a reloading manual that lists pressure for lead cast bullets in psi? I have a formula to calculate bullet base obturation using psi, (as discovered in Rifle Magazine's Handloader, December 2003, No.226, Page 6; in the article written by Dave Scovill, entitled "BHN and BULLET METAL").

In a nutshell, you multiply the Brinell hardness of your lead alloy by 1,422 to give you "the pressure,in psi, required to cause that particular alloy to upset under pressure in a gun."

Thanks for the help.

Kindest regards,
:wink:

To play devil's advocate for a minute-- how would you prove obturation occurred at this level?

Wouldn't a pressure level equal in force created by say Bullseye vs RL#22 differ in their abilities to obturate a cast bullet? One peaks with bullet movement in the tenth's of inches-- the other over an inch or more into the bore.

How could a bullet 'obturate' if it already was the size of the throat or groove dia to start with?

carpediem · « **Reply #2 on:** November 24, 2003, 07:14:04 PM »

Hello Aladin:
The info from the article stated that obturation would occur while the bullet is still in the cylinder of a revolver. How this would affect a bullet in a semi-auto is, to me, unknown.

Is bullet obturation required when the bullet is already sized to grove diameter? I don't know.

I thought this formula would be of use when calculating alloy to velocity.

Kindest regards,

Aladin · « **Reply #3 on:** November 26, 2003, 11:51:01 AM »

Carpediem I shot the perfect example of about ideal obturation today vs enough pressure to just start opening the groups. This accomplished with air cooled and aged ww alloy and the spread of powder only .7 grs [Blue Dot]. What woulda been interesting is to have pressure measureing devices hooked to the barrel and then hardness testing the alloy. Down the rd I might do such.... :-)

carpediem · « **Reply #4 on:** December 02, 2003, 04:16:45 PM »

Well Aladin, don't keep us in suspense. Do tell what happened.

Aladin · « **Reply #5 on:** December 03, 2003, 02:10:36 AM »

Quote from: carpediem

Well Aladin, don't keep us in suspense. Do tell what happened.

Sorry carpediem, sorta forgot to finish that post. The lower charge wt prodcued 4 of 5 in 1.2" at 100 with one opening it to 2" [which mighta been me]. The higher load strung them horizontally into over 2" with one high impact making the whole group >3".

Sky C. · « **Reply #6 on:** December 03, 2003, 09:34:44 AM »

Hello Carpedium-

Lyman's new #48 is now listing starting load and max load pressure data for their lead bullet info on many of the calibers.

Best regards-

Sky C.

Aladin · « **Reply #7 on:** December 03, 2003, 12:29:51 PM »

Quote from: Sky C.

Hello Carpedium-

Lyman's new #48 is now listing starting load and max load pressure data for their lead bullet info on many of the calibers.

Best regards-

Sky C.

Hey Sky how's it goin'?

Lyman data is likely for a #2 alloy bullet at groove dia. as the Cast Manual. The other factor is Lyman seating depth's tended to be somewhat deep. But a relative reading on CUP they are.

Sky C. · « **Reply #8 on:** December 04, 2003, 06:36:12 AM »

Aladin-

Been following a number of your posts - here and on Accurate. Nice work you're doing at 600 with the old military guns!

Pressure data - Sure. Many variables; but that they are now providing pressure info for the starting loads in addition to max is good material putting us a quantum step up compared to before.

By the way - having followed your discourse on engraving resistance (term correct?), I understand the discussion point and all is good with that for single shot & bolt guns where you can seat into the lands. Any thoughts on how to approach this effect for repeaters (read lever gunz!) where we can't do that due to cycling issues? I'm thinking neck tension (?), crimp, and bullet hardness. Other thoughts?

Best regards-

Sky