I had the Brenneke slug project on the back burner for quite some time now, but finally most of the kinks has been straightened out.
Here is the three different stages of design with the original Brenneke to the right. The final design ended up quite similar to #2, but with a little different nose shape - and since the wads and slugs are now glued together I did away with the screw hole in the base, which allowed for a larger sprue hole.
A picture of the latest design. The helical fins was something of a headache to program for in the EDM sinker, but they came out quite well:
I ran out of epoxy for the wad mold so, being a cheapskate, I switched to polyester resin instead. Unfortunately the difference in shrinkage meant a new wad mold had to be made:
This is what the finished combination looks like. The combined weight is close to 1-1/4 ounce (540 grains) with the wad weighing 60 grains.
(notice how a few hours in the sun has bleached the yellow/green color to a grey hue)
And finally the end result... Loaded shells! I came across a batch of old 2-1/2" paper hulls with gevelot primers. Loaded with 30 grains Herco and a 3/8 felt wad under the slug they are just the right length for a nice roll crimp. The speed is 1250 fps.
I have only done a little testing with the slugs so far and while the results are as good or better than the previous design, there are still room for improvement. At fifty yards the groups are 4-5" on average and a five shot group at 100 yards gave a decent 12" group, but still a far cry from the 3-4" groups George Vitt claimed from his Vitt slugs. So far I have only used a gun with modified choke (0.02 constriction) a cylinder- or improved cylinder bore will probably produce better results. Next project will be adding a holosight to my skeet gun for testing. I'm also on the lookout for a cheap single barrel gun which would be perfect for scope mounting.
At this time in the project I must admit it has mostly become a fun hobby. The original goal was a slug for my Czech friends to kill running hogs at distances from zero to forty yards - and the slug will easily accomplish that. Now it is more a question on how much accuracy you can wringe from a smoothbore shotgun barrel. Only time will tell.