Lead splatter

[Sharpeye]

On cases after firing, gun in question is a BFR 500 7.5" barrel. Specs are a .500 bore and .501 throats (slugged) bullets are a Mountain Mold 700 gr PB boolit of my design cast at .502 water dropped WW and ran through a Lyman .501 die with Felix lube over 29.5 gr of SR 4759 with a heavy Factory Taper Crimp (rifle style does not re-size) no signs of any pressure issues cases come out easy and primers are flat but not cratered or pierced. Cases are getting just a small splatter of lead on them and I have never ran into this before. I have ran them over a chrono at 1180-1200 fps at about 10' any input on why this is happening would be great.

Thanks.

[44man]

I have to guess the boolit is way too heavy, hard to move and you get gas cutting before the boolit is all the way in the throats. 4759 is a fast powder and is peaking right away.