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In the military throated m38 that I have, the lands are too far away to be a consideration. I seat for connectivity. Haven't had any issues though a guess some projectiles may be more jump sensitive than others.
Using win760 and going to imr4831 when I've finished that . Hope to squeeze a little more speed within my m38 pressure limits.
Would go Slower Burn with 7828 if not satisfied
Concentricity
Many rifles have a 1-2 degree taper in the throat area so to talk about touching lands can be quite a vague notion. i my S&L bbl the bolt fact to lands (touching the start of the taper) is 2.422" while moderate jam is 2.480". For my bullet seating calculation I use 2.472". (bolt face to ogive)
Most of my rifles ,when shooting a secant ogive bullet seem to like a jump of 40-200 thou" rather than any sort of jam. In the instance of trialling this bullet and loads I will use a jump in the order of 45-80- thou' to start. COAL approx 3.15-3.18" and see how we go.
haven't tried eld's but other projectiles I've loaded in mine and especially lighter ones or bergers are only just being held by the case neck at jam OAL..
I had a load I liked using 120 sierra's, unsure now of OAL but several years ago and the rifle has been with a mate since then.
I just got it back and have been thinking about developing a load with some 140s and experimenting with jump distance.
Other rifles I have often seem to like quite a big jump
120 thou in my 7rm. for example
Would shorter barrel length have any influence on the type of powder best suited?
maybe faster burn required for shorter barrel?