Quickload / GRT - powder choice/data question...

[Qwertyzmate]

Looking to develop a load for my .308 using Sierra Game kings 165gn SBT

I have 2 powder options CFE 223 and Vhit N140.

By inputting my rifle/fire-formed case dimensions into the relevant areas of GRT I can see that there are predicted velocities, pressures, case fill etc. with the different powders and I can produce a stepped load prediction up to GRT 'MAX' Load - I understand about the user data implications of this software and have compared to powder manafacturers data, Lee manual etc.

Sierra state "Previously considered “too hard” for expansion, they perform well at the 2500 fps muzzle velocities achievable in the 308 Winchester and larger cartridges" on the website (referring to these bullets), I can get 2500FPS from either powder, it's the other variables that I need to understand.

CFE clearly creates the better velocities across the suggest load ranges from all three data sources (Powder manafacturer, Lee manual and GRT), they start at 2500 (Ish) FPS and go up from there
N140 is markedly slower and the centre of the load ladder is about the 2500 FPS mark...

Essentially, what is likely to be better; CFE223 with a 95%+ case fill, well over the 2500FPS MV and a 90-95% (ish) burnt propellent rate; or, N140 with a 85-90% case fill, all MV around the 2500 FPS mark, 100% powder burn rate and a higher effective efficiency rate?

Interestingly, published load date for one powder option matches across all 3 data sources, the other option has significant differences in start loads and max loads!

Yes, I could load up a load of each and see what is best but which shows more promise from the data?

Pics for a sample of max or near max loads for reference

 

[trickie]

Your photos show with. Max loads. When you drop to just below those options what do you see then. I’d not expect anyone would recommend start at max pre for your chamber.

Having said that, the photos do show a higher percentage of powder burn and corresponding increase in efficiency using N140.

 

[Qwertyzmate]

Sure, I wouldn't ever advocate starting so high with load development, GRT accepts a 'powder charge' and you set the ladder step to what you want and it calculates down rather than up....

Interestingly, for the CFE223, Hodgeson, my Lee manual and GRT suggests a charge weight of 45.4-48.3 gn

For the N140 Vhit say 39.4-43.4; Lee say 40.1-46.3! And GRT tops out at 45.6 due to pressure...

Running the software to aim for 2500 fos for both, the burn and efficiency I better on the N140, slightly better case fill on the CFE...

Guess N140 might be a better choice overall?

 

[ashray]

have you tried using p-max internal ballistics ?. my richard lee manual states n140 @ start 40.6 and a MAX charge of 44.9. <43.1 gr for 2500fps from a 22" barrel>

 

[Qwertyzmate]

have you tried using p-max internal ballistics ?. my richard lee manual states n140 @ start 40.6 and a MAX charge of 44.9. <43.1 gr for 2500fps from a 22" barrel>

Just had a look, not heard of it before.

Same data in has a different data out... this is the same data 'In' as GRT (43.5 gn N140) including the rife and case variables

P-max:

Load density:​

82 %​

Pressure P-Max:​

41353 psi​

Bullet travel to P-Max:​

1.8 in.​

Muzzle velocity:​

2420 ft/sec.​

Muzzle pressure:​

8638 psi​

Muzzle energy:​

2146 ft-lbs.​

Barrel time:​

1.18 msec.​

Powder all burnt at:​

19.8 in.​

P-Max has a 100fps lower MV, 8% lower Load density (case fill) and 1100 PSI less in Pmax?

I think I will work up a load using N140, starting at 40 gn and go from there. I have a mate with a Lab radar so will check the actual MV of the lead/rifle combo and see which software/programme/manual is the closest!

 

[borbal]

The best powder choice is one which:

• fills the case. Otherwise the cartridge is too large and you are not using it efficiently. Too, you usually get better accuracy with a full case
• is all burnt just as the bullet exits the barrel. This gives you maximum velocity for minimum chamber pressure. If the powder is too fast it is all burnt too soon and you get high chamber pressures with disappointing muzzle velocities. If the powder is too slow then it is not all burnt when the bullet exits the barrel and you waste powder. (Powder is expensive!)

So, see which powder most nearly fulfills these criteria and that is the powder most suited to your cartridge/bullet/barrel combination.

 

[Qwertyzmate]

The best powder choice is one which:

• fills the case. Otherwise the cartridge is too large and you are not using it efficiently. Too, you usually get better accuracy with a full case
• is all burnt just as the bullet exits the barrel. This gives you maximum velocity for minimum chamber pressure. If the powder is too fast it is all burnt too soon and you get high chamber pressures with disappointing muzzle velocities. If the powder is too slow then it is not all burnt when the bullet exits the barrel and you waste powder. (Powder is expensive!)

So, see which powder most nearly fulfills these criteria and that is the powder most suited to your cartridge/bullet/barrel combination.

Excellent

Thank you!