New 6mm HP mould

[Glen]

PS -- I agree that the Greenhill Formula provides guidance, and not a hard and fast, rigid limit. But also keep in the mind the history of the .243 Winchester and the .244 Remington. The .243 succeeded because it was promoted as a dual-purpose cartridge (75-80 grain varmint bullets and 100 grain deer bullets) because it had a 1 in 10" twist that would stabilize both bullet weights. The .244 was originally released with a slower twist rate (1 in 12") that only stabilized the varmint weight bullets, the slightly longer 100 grain bullets would not group. The .244 failed to sell, and was dropped. It re-emerged as the 6mm Remington, with a 1 in 9" twist (which shoots both weights of bullets very well) and has been trying to catch up with the .243 ever since.

 

[Glen]

Update -- the shorter bullets didn't group any better than the as-cast bullets (5-shot groups at 50 yards), and some of the bullet holes were still oblong (although not as bad as the as-cast). I think I will reserve this bullet for my Ruger #1 6mm Remington (with its 1 in 9" twist) and go get a lighter mould for the 6PPC Contender.

 

[fiver]

something else is going on.
the un-stabilization can't just be a length thing, otherwise speeding it up would cure it.
you have to have some stripping, or some slump going on.
the slump could be accounted for by the launch being a bit hard.
so could the stripping.

 

[Glen]

I agree with you, in principal (and in fact, that's the point I was trying to make earlier). But I doubt it's the launch per se since I was using 4895, which is pretty slow for the 6PPC at 1800 fps, so the initial engraving should be pretty gentle (which, in fact, is exactly why I chose 4895). In this case, I think it's more the velocity closer to the muzzle leading to the stripping/instability as a result of high speed rotational velocity (about 130,000 rpm) on a small diameter cast bullet.

 

[fiver]

getting 1800 in an 11" barrel is actually pretty good.

yeah I'd imagine you do have quite a bit of pressure and acceleration still going on at the muzzle.
the muzzle blast might be disrupting the boolit at the muzzle too.
this is a bit of a unique circumstance ain't it.
can't make use of the gas volume and if you play nice in the barrel you lose your velocity.
about all you can do is search the powder cabinet until you find that balanced combination. [shrug]

 

[Glen]

I tried slowing the 6PPC down to about 1670 fps, and 5-shot groups at 50 yards settled down to about 1 1/4" (a little of which was probably my wobble), but the bullet holes STILL were not quite round. As a control experiment, I loaded up some 6mm Remington ammo with this 102 grain HP at similar velocity (9.8 grains of Red Dot, 1637 fps, 1 in 9" twist), and bullet holes were round, and the 5-shot group was just over 1/2".

 

[Texas Hillbilly]

I just got my 6mm mould back from Erik, and he did an excellent job with his inset bar HP conversion. The starting mould was the RCBS 100 grain GC. We shortened the bullet a bit, and put in the HP cavity, so I'm guessing that the final HP will weigh 92-93 grains. I am aiming for ~2000 fps from my 6mm PPC Contender. This is going to be a fun project!

View attachment 1589

Nice looking after you pour a few,please let us know how they turned out,I've been thinking about doing the same things,but starting with a 95gr.which should give me a 87gr HP. To shoot from a 240 banshee.