Little help with pressure

[allaroundhunter]

I was looking through Hodgdon's reloading data center today at different .308 rounds and found something that made me curious.

I was looking at .308 155 gr loads and found that some of the max loads had pressures in excess of 60,000 psi, while other max loads were under 50,000 psi.

An example:

Bullet: 155 GR. SIE HPBT
Powder: Hodgdon CFE 223
Bullet Diameter: .308"
Powder charge: 51.0 grains
MV: 2966
Pressure: 60,500 PSI

Bullet: 155 GR. SIE HPBT
Poweder: IMR 4007 SSC
Bullet Diameter: .308"
Powder Charge: 49.5C
MV: 2751
Pressure: 49,900 PSI

Can anyone explain the differences in MV and pressure to me? And also what the 'C' stands for in the powder charge of the second round?

Is it due to the CFE 223 being a faster burning powder? What is a "safe" max pressure for a .308?


Sorry for all of the questions, just trying to get some stuff figured out.

 

[rcmodel]

C means a compressed charge, which means they couldn't get any more powder in the case.
Which means the pressure and velocity were lower.

Which means IMR 4007 SSC is to slow burning for that caliber / bullet combination.

SAAMI Max pressure for the .308 is 62,000 PSI.

rc

 

[allaroundhunter]

That being the case, would you then say that that is not an ideal powder to use with a .308, rc? It seems as if it is only able to get a 155 gr projectile to 2750 fps that it is not a good powder for shooting at any distance.

But could it be useful as a reduced recoil load?

 

[rcmodel]

No, I would say it isn't an ideal powder for that light of bullet.

It goes quite well with heavier, 175 grain & up bullets in .308.

It would be a terrible "reduced load" powder.
Muzzle blast would be horrendous with lighter bullets and a compressed charge.

rc

 

[allaroundhunter]

Interesting, thanks for that, rc.

What would be good recipes for a reduced recoil load?

 

[hueyville]

Powder choice for reduced.recoil load is on that fills the case 55% to 75% and group well with your bullet. Enough powder for consistent ignition without flashover, light enough charge to be somewhat economical but not a case filler to send sunburn this wasted powder out the muzzle behind the bullet. Your barrel length and bullet selection will cause your powder selection to vary. If it doesn't shoot well though, not much point.

 

[rcmodel]

What would be good recipes for a reduced recoil load?

http://www.hodgdon.com/PDF/H4895 Reduced Rifle Loads.pdf

rc