.378 revisited

[444shooter]

icehunter121
I would wait until post 505 to ask for my token rifle!

Hmm, so now I know who was crazy enough to buy that rifle

 

[Gibbs505]

Hmm, so now I know who was crazy enough to buy that rifle

LOL, hard to get scope eye from a rifle with no scope!

 

[Boomer]

Boomer,

I always shoot over the chrono when working up loads but never found consistency with this method. I most often see minute ejector marks before encountering any significant velocity plateau. Is it possible that this is case size/pressure curve/burn rate related? I have seen evidence of plateaus in my 223, 308, and 416 Rem.

What do you think?

In a .223 sized cartridge I think I would be inclined to increase by half grain increments, where as with the larger cartridges 1 gr increments are what I use. I have used the velocity plateau method of determining the safe maximum loads successfully in cartridges up to the .416 Rigby, and it also works reliably in my .375 Ultra, so I do not think that the volume of the cartridge prevents velocity plateau during load development.

While I do not doubt that you have not observed a velocity plateau when loading the .378 Weatherby, perhaps the cause is due to the geometry of the neck, or perhaps the plateau occurs at a velocity below what would be the normal starting load for this cartridge with the current batch of slow burning propellants we would typically use when loading this cartridge. The .416 Rigby has a similar powder volume to the .378 Weatherby, and although my records were lost, I seem to remember that my maximum safe load was a 350 gr X at 2800 fps using H-4350. A 285 gr .375 bullet has exactly the same sectional density as the 350/.416, and if both cartridges have the same volume, it might mean that one might observe the 285 gr bullet's velocity plateau between 2800 and 2900 fps.

 

[MTM]

Just for the record, I used to shoot 350 Xs out of my Rigby at 2850. Never saw any pressure signs and it shot very well, just didn't see the need to go faster.