Hodgdon CFE Black Low Max Pressure?

[WinJim1863]

The Hodgdon loading guide for the 300 Blackout, 150 grn bullet, 16" barrel shows a max recommended load (20.5C grns) that only produces 33,500 PSI max pressure. This is compared with H110 at 52,800 PSI and IMR 4227 at 48,700 PSI. Despite this huge disparity in pressure, muzzle velocity of the three is about the same (1,940, 1,971, and 1,899 FPS). How can this be?
I thought this might be explained by burn rate but CFE is #69 vs. H110 at 51 and IMR 4227 at 58. All three powders are relatively close together (on a list of 150 powders). It seems unlikely that burn rate would explain it, but I don't know much about burn rate and the effect on max chamber pressure.

 

[sht4brnz]

Misprints do occur.
Hornady's 1st print of it's latest manual had disrepancies with the 300blk

 

[MarinePMI]

Barrel time. (At least that would be my guess, if the data is accurate).

With the retardant coatings that Hodgdon has developed, I'd wager it has everything to do with barrel time, and a burn rate that has been optimized for a 16" barrel (the most popular barrel length for the 300BO). I'd suspect what is happening is that the powder is not being fully burned before the bullet leaves the barrel, but that the burn rate is consistent enough (for that barrel length/volume) that it (the load of powder) never has a chance to fully peak (completely burn), and so you end up with low pressures in comparison to velocity (which remains consistent, based on the reliability of the retarded burn rate). While pressure usually is an indicator or analogy to velocity, that only holds true when assuming all the powder is ignited within the barrel. If the burn rate is consistent, it simply doesn't matter if the case is over charged, since it just gets blown out the end of the barrel. (though I'd wager if you fired these at night, you'd see a huge ball of flame at the muzzle).

I'd guess with a longer barrel, that you would see higher pressures/velocities. This is similar behavior that has been noted with the .22 Hornet and Lil'Gun. That is, pressures do not increase linearly, and in fact, plateau (as do velocities) for a period, and then rapidly spike (if barrel length is increased; after all, you can't cheat physics, but you can use their properties in your favor). Again, this behavior has been displayed in .22 Hornets, where velocities above 3000fps have been observed (with fairly low pressures), where as H110 or W296 would show pressure signs on cases long before that velocity could be achieved.

Again, just a guess/suspicion on my part...

 

[WinJim1863]

Thanks for the responses, I'll stay on the lookout for info, maybe Hodgdon will eventually explain or change if wrong.