when we are looking to shoot heavy's with a small case like a 308, we need to take every bit of case capacity we can get. Throat have a huge impact of course and you are looking to get as minimal contact between bearing wall and neck. If you have a OAL of 3.175 with a 230 (its the same dimension as a 215 but the filling is heavier), its getting close of max internal volume. Some shooter go even higher than that but there must be a point were we don't want do go too long on throat in relation of contact between case and bullets. This throat should provide 0.100contact between bullet and case +/-
So now we got the throat, and max internal volume, we need to be aware of reloading technique to optimise powder column inside a case by using a drop tube. By doing that, H4350 become a proper propellant with its slow burn rate.
I think numbers that Kombayoch been showing are realistic if the pipe is long enough. I've tried even slower than 4350 without any success....just way too slow
A relaoder should recognize the CRITICAL relation between a burnrate and bullets in any given specification (bore size, neck tension,etc...).
this is my humble opinion