The screw-in rifle tube are better that nothing..
for using SABOT shell. The soft polymer sabot forms faster to the rifleing than the lead slugs.
The foster and brenneke use the same pricipal of a badmidton shuttlecock, having a heavy weight-forward nose and light rear.
The brenneke has the heavy nose but increase the length with the attached wad, they alwayed gave better accuracy from my slug barrels, but are a 100yd MAX range.