Comparing two powders: BL-C2 and H-335. These powders rank side-by-side on burn rate charts-- #54 for BL-C2 and slower #55 for H-335 on the Varmint Hunters Magazine burn rate list.
Comparing ballistic data from Hodgdon Data Manual #26 (1994)-- looking at .222 Rem. Magnum:
In 40 gr. bullets, BL-C2 produces comparable velocity at LOWER pressure than H-335 on loads with the same 27.5 gr. charge weight in both powders. -- low end loads.
Then, same bullet, BL-C2 produces comparable velocities and significantly HIGHER pressures at the same 30.0 gr. charge weight as H-335. -- maximum loads.
Moving up the bullet weight to 55 gr.
BL-C2 at 24.5 gr. produces comparable velocity and LESS pressure than 24.0 gr. H-335. -- low end loads.
BL C2 at 26.5 gr. produces comparable velocity and LESS pressure than 26.0 gr. of H-335. -- maximum loads.
Seemingly, as the bullet weights get heavier, the working pressure in the BL-C2 becomes comparably less than H-335 for similar velocities. The BL-C2 takes about a half grain (0.5 gr.) to meet the velocity of the H-335 while producing less pressure.
I understand that nitro cellulose powder (smokeless) reacts under pressure to affect ignition and pressure development. I realize that heavier bullets create more internal ballistic pressure. But I'm stumped as to why BL-C2 should produce less pressures at heavier loads with a heavier bullet, less pressure at similar low end loads with lighter bullets, BUT more pressure with lighter bullets when the load/velocity is increased.
Feel free to get as technical as you wish. What I don't understand, I'll research!
Thanks!
Now . . .
What sort of propellant do I want to look for to get a 40 gr. bullet going 4000 fps in a Rem. .223 Ack. Imp.??? A superficial understandign of "burn rate" suggests that I'd want a "bulkier" powder.
How would hihger velocity in a lighter bullet relate to load pressure as compared to a heavier bullet at a lower velocity?
Short of signin' on for a ballistics course at MIT, is there anyplace (online/library) I should look???