WC860 high pressure signs.

[mto7464]

I have been getting high pressure signs with this in 3006 under 200 lee from 56-58 (my max this morning) grains. I still have unburned powder in the barrel and velocities between 2000-2200 fps. Why am I getting these higher pressure signs? (Primers flattened, ejector marks). Fired in a 03a3 with a light crimp. Groups were awful.

[Ricochet]

I've had a few experiences with encountering pressure signs with cast boolits with a load that I expected would be mild with jacketed bullets of the same weight. One was with the 7.5x55 K-31 with the 200 grain HBC boolit over what I thought a medium load of 7383. Got sticky extraction, and a recovered boolit had slugged the long tapered oven treated wheelweight ogive till half of it was fully engraved in the rifling! When I blithely loaded a compressed full case of WC860 in the Swiss under the Lee 200 grainer, I thought it couldn't possibly be even a full working presssure load, as loading manual tested data for .300 Weatherby with compressed loads of H870 and AA8700 under 200 grain jacketed bullets show moderate pressures with that far bigger case. But I found later when depriming those cases that all of the primers were rather more flattened than usual, with extrusion around the firing pin. I still don't believe those would've been especially stout loads with a jacketed 200 grain bullet.

Perhaps the "slugging" effect of the boolit obturating under pressure increases the friction against the bore wall sufficiently to run pressures up? (I know it can be really hard to drive a boolit through a bore with a rod and hammer.)

At any rate, my former belief that if a load is OK with a jacketed bullet it'll certainly be OK with cast has been seriously shaken. And over on Mountain Molds' forum in the "Pressure" section he's got some .30-06 data showing excessive pressures with cast boolits and quite ordinary jacketed bullet powder charges.

[mto7464]

That was my next plan, to try it with JB's.

[maxF]

I've been experimenting with 860 in my 7rmag and have horrible groups also (like 2 holes 3/4" and then one verticly 7" higher???). I found that 58 grains with no booster and no polyfill gives me an accurate (1&1/2") load with 140gr jacketed chrono'd @ 2276-2305. I get more consistant chrono readings with a 4grain booster (AA230c) and 1.grain of polyfill. For instance 61.5 gr.860, 4 gr. booster and 1.gr poly chronos 2814-2827, a very low standard deviation but didn't group well (4") while the exact same load without the poly chrono'd at 2632-2678 but grouped 5 into 2" (best so far @ a reasonable speed). Other loads showed similiar (200 fps) increase with poly but grouped worse. I would try a lighter load but put a medium speed booster under it and use a magnum primer to try and get good ignition.

[Ricochet]

I've had very good results with it in maximum loads in 7mm Rem Mag with 175 grain JBs, and .300 Weatherby Mag with 180, 200 and 210 gr. JBs.

[mto7464]

tried some nosler 168 grain match in the 03a3 with the WC860. Got nice groups with it at 50 yards, was very windy that morning, and no pressure signs but the powder still didn't burn completely, which was no surprise. The bore seemed really dirty compared to the cast though. I think I will try some COW on top of a slightly reduced load and see what happens in a cast load agian.