Brent,

the single most important element is: forget about compression - you will never be able to compress the powder column uniformly in a BN case.  Also, forget about the faster granulations.  BN cases do tend to promote faster burning because of configuration, so, the slower end granulations will do just fine.  Enough bullet resistance is important too, but that is also the case with straight cases.  If need be, see that you have some neck tension - but seating the (hard enough) bullet well into the rifling will also work.
A good 'gas barrier' between bullet and powder is also rather more important than with straight cases.
Bottom line, if you start working up loads by compressing powder, you will be disappointed...
Not sure if the 38-72 qualifies as a real BN round though - a bit like a crossbreed between tapered and BN...
I learned the lesson the hard way, trying to work up loads for 577-450 and #2 Musket - especially 577-450 was tough, as I kept on trying to use a slip-fit bullet.  Once I started using neck tension, group size decreased dramatically...  But then, it is very hard to seat out a bullet into the rifling on a 577-450.  They just aren't long enough...   Next one up is 8x60R Kropatschek, this one is a rather delicate one, but it is showing promise...

OK,

thanks Martini

has anyone reloaded the 40/70 BN or any classified bottleneck case "smokeless"with the new super slow powders keep the pressure down and mic. the cases on the way up to keep the pressures in check.

Arjunkie and I had a break through years back with a .33 winchester in a old 86 I believe it was 54grains of reloader 22 and a magnum primer and 200 grain hornaday fp the gun shot just under an inch at 80 yards with iron sights and we could not believe what we saw so three more and came out of the reloader and put down range it too was under an inch and in a perfect trinangle
The bore in the 86 was not bad but it was not good either

any thoughts on this???

rafter-7