7.5x55 with w860 ?

[legend]

anyone had any luck with cast in 7.5x55 with w860 ?
any starting point ?

thanks

[Ricochet]

All I can say is, DON"T start with a neck sized case packed full with 4.0cc (right at 60 grains), seat a .311" 200 grain boolit of heat treated wheelweights on it with a very tight Lee Factory Crimp AND starting right against the chamber throat. Gave badly flattened primers and sticky cases, and a recovered boolit showed that acceleration forces had badly obturated the ogive of the boolit. Compressed loads of this powder up to 100 grains in my .300 Weatherby with 200 grain jacketed bullets can't even quite reach full power load velocities and apparently give very moderate pressures, so I thought in the smaller case it couldn't possibly run hot. But several factors running up the "shot start pressure" did the trick. The Weatherby's long throat keeps pressures mild.

[Maven]

legend, I've used another slow powder, IMR 5010 (almost the same burning rate as WC 860) in my K-31's with more than satisfactory results. Were I to try WC 860, I'd start with 44grs. and maybe work up to 48grs., but do not compress it or use fillers of any kind. Also, use LR magnum primers to improve burning. Btw, the CB's I use range from ~166grs. - ~200grs. and are generally seated so that their bases are below the neck/shoulder junction. Keep an eye on the OAL as you don't want to heavily compress 860. However, the OAL issue can be resolved if you bump the noses and 1st driving band of CB's such as Ly. 311291 & -041 or Saeco #301/RG-4 & 315, down with a die made to fit the throat of your rifle. (The die fits your Lyman or RCBS lube sizer, but doesn't lubricate.) PM Smokemjoe if you're interested: His workmanship is first rate and the price is extremely reasonable. E.g., before using the bump die, I couldn't seat Ly. -291 any longer than ~ 2.73" or the rifle wouldn't go into battery. With the bump die I can seat them at least as long as 2.83" and often as long as 2.90"

[legend]

RICOCHET,and MAVEN;

thank you both for sound advice.

I have 5010 also,and i will try it also.

legend

[madsenshooter]

After all I've read about a case full of 860, where did "don't compress" come from? Curious, because I have some 30/40 Krag loaded, a NOE 311284 over 53gr of 860 fired with a Rem 9 1/2M, that appears to be a mite hot for a Krag. It is slightly compressed and the nose is engraving. Maybe it's the lot, it says it's faster burning than H870. I hate pulling loads down, maybe I should buy a Ruger #3 in 30/40, sounds like a good excuse to me, I'll put it on Santa's list.

[Ricochet]

It's not the powder compression per se, it's the combination of a bullet that's tightly jammed in place and hard to start, with the limited gas space left in the case with the dense compressed charge also causing the early pressure rise to be more rapid than usual. Very tight fitting hard bullets jammed hard against the rifling origin and tight crimps can combine to make the force necessary to start the bullet moving a lot higher than usual. Consider how high the pressure has to be to obtain that much force (which can amount to a few thousand pounds of thrust) from the limited cross sectional area of the bullet, that the powder's burning rate climbs steeply as the pressure rate rises, and how the pressure rises as that increasingly rapid gas production has to fit in the space between the powder kernels in the case, so it all "snowballs" to rapidly increase pressures. Cast bullets are softer than jacketed bullets, we usually use relatively light loads, and we tend to neglect issues affecting the "shot start pressure" that gets the bullet moving from rest. But as I learned from the above experience, that can lead to unexpectedly high pressures.

[Maven]

legend, If you're going to try IMR 5010 in the 7.5 x 55mm, use LR mag. primers and seriously consider using spherical shot (aka poly-) buffer and ~175gr. CB's or heavier. My notes show 47grs. IMR 5010 + 0.7cc (Lee dipper) poly- buffer was a good performer with Ly. #'s 311291 & 311466, Lee #309-180-1R, and Saeco #315. Velocity was ~1,800fps with those CB's (sized to .309").

[madsenshooter]

I see Richochet, that partially explains why the same amount of powder, compressed by a 308329. didn't show any pressure signs. Besides being a 25gr lighter boolit, it had a jump before hitting the rifling, unlike the 311284 which was seated to engrave. The base of both boolits however were at about the same level in the case. I'm on my way to the range today, I've seated a few of the 311284s deeper to give them a little jump (little is right, seated to the crimp groove, the slightly out of round nose still touches the rifling at two points). I'll try a couple see if that lets some of the initial pressure past the boolit before the bore closes.

Made it to the range, not a good day for experimenting, too many people, hard to get a cease fire for a target change, maybe I'll get up earlier tomorrow. Some people bring 4 or 5 rifles to play with at time and a van load of gear to clutter up the place with, it's enough to make a fellow want build his own private range.