Which powder for more velocity?

[BCBRAD]

Start pressure goes like this, the default in the QL program is 3625 psi for jacketed bullets. If the bullet is jammed into the lands add 7200 psi for a total for a jammed bullet being 10,825 psi. Now, for every 0.005" from jammed subtract 146 psi.

Todbartell's example is correct.

The further back from the rifling the less start pressure you will have to a point of diminishing returns as you will start to encroach on the powder space of the cartridge.

 

[cbh560]

Start pressure goes like this, the default in the QL program is 3625 psi for jacketed bullets. If the bullet is jammed into the lands add 7200 psi for a total for a jammed bullet being 10,825 psi. Now, for every 0.005" from jammed subtract 146 psi.

Todbartell's example is correct.

The further back from the rifling the less start pressure you will have to a point of diminishing returns as you will start to encroach on the powder space of the cartridge.

Thanks, that's good info. My loaded rounds are 2.820" OAL and this rifle has a generous throat for heavier, longer bullets. So jump is about 0.060" if I recall correctly. So if I'm doing the math correctly, I could knock another 846 psi off the total for the extra jump and maybe a bit more for the bullet being seated 0.020" longer than Todbartells's example. Call it 1000 psi. That's not a lot but it's at least something.

I guess I'm going to have to get my hands on a copy of Quickload. This is very interesting stuff and I love crunching the numbers and looking at the data.

Given your guy's experiences, how much of a difference does a "fast barrel" make in velocity vs. pressure? Is a "fast barrel" a real thing? What makes it fast? I ask because when I look back at my loading data I am not seeing any signs of pressure until I hit 45.5 gr of Varget and over 3000 fps. At this point I was just starting to see a very wee bit of shine from the extractor, so I know I was at the limit here. But down at the 44.6-44.8 gr node that I'm pursuing I don't see any signs of pressure other than very slightly flattened primers (I don't put much stock in primers as an indicator) and I have velocity of 2950 fps. I guess my primer pockets might be my ultimate indicator, but it'll take a while to find out. These brass are on they're 3rd loading (pockets are still tight) but it's in a hunting rifle that isn't going to see a large volume of shooting.

 

[RonR]

On a side note, in my testing I have found some temperature "sensitive" powders aren't too bad in typical hunting conditions (-15c to +15c), it's the really hot weather than can/will spike results.

Similar cartridge, the 6.5 Creedmoor

-15c
H4350 (stable) ~ 2635 fps
IMR 4451 (stable) ~ 2710 fps
IMR 4831 (sensitive) ~ 2449 fps
Win 760 (sensitive) ~ 2534 fps
RL16 (stable) ~ 2694 fps

+13c
H4350 (stable) ~ 2622 fps
IMR 4451 (stable) ~ 2657 fps
IMR 4831 (sensitive) ~ 2453 fps
Win 760 (sensitive) ~ 2555 fps
RL16 (stable) ~ 2675 fps

+29c
H4350 (stable) ~ 2646 fps
IMR 4451 (stable) ~ 2679 fps
IMR 4831 (sensitive) ~ 2526 fps
Win 760 (sensitive) ~ 2606 fps
RL16 (stable) ~ 2675 fps

And 308 Winchester :

-15c
H4895 (stable) ~ 2502 fps
IMR 4166 (stable) ~ 2570 fps
IMR 4064 (sensitive) ~ 2435 fps
Alliant AR Comp (stable) ~ 2358 fps
Win 748 (sensitive) ~ 2419 fps

+13c
H4895 (stable) ~ 2440 fps
IMR 4166 (stable) ~ 2511 fps
IMR 4064 (sensitive) ~ 2438 fps
Alliant AR Comp (stable) ~ 2360 fps
Win 748 (sensitive) ~ 2432 fps

+29c
H4895 (stable) ~ 2477 fps
IMR 4166 (stable) ~ 2526 fps
IMR 4064 (sensitive) ~ 2497 fps
Alliant AR Comp (stable) ~ 2347 fps
Win 748 (sensitive) ~ 2482 fps

Tod, thanks for your work on this and posting.

It is interesting and changes my thinking on ball powders, specifically how W760 relates with my findings and cold weather hunting conditions.

Always on my mind to do this type of analysis and you saved a lot of effort on my part...albeit in Sask cold white tail rifle conditions.

FWIW, thank you.

Regards
Ronr

 

[209jones]

Interesting, Tod's figures with the 140/760 are close to my 700, I use cci250's in it though. Haven't had an issue with it at -25 or 75-80F with the load at 48gr. Think the lowest chrono figure I have with that load is 2820 in cold weather, believe it was @ -10f, over my Oehler, normal is 2850. Old Nosler manual is 49.0 max. Been using it that way for 30+ yrs. Not sure if the load I tried with the new #1 was 47 or 47.5, F210, didn't crack 2725 though. Maybe the CCI 250 will up it a bit, maybe it won't.

 

[todbartell]

Tod, thanks for your work on this and posting.

It is interesting and changes my thinking on ball powders, specifically how W760 relates with my findings and cold weather hunting conditions.

Always on my mind to do this type of analysis and you saved a lot of effort on my part...albeit in Sask cold white tail rifle conditions.

FWIW, thank you.

Regards
Ronr

you're welcome