So heavier neck tension and/or bullet jam would lead to higher pressure and better burn? I was using .003 neck tension and .006 in from "touch". IIRC the distance from touch to jam in this case was .040.
In general...yes. Given proper
neck clearance on a 30BR, you can see the powder residue in the neck go from blackish to grey as neck tension increases and the 'jam' increases with a given powder charge weight.
On a 30BR (assuming a case neck that isn't work-hardened), mine have all liked a bunch of neck tension (a button .004 under what a loaded round measures across the pressure ring).
I confess to paying less than zero attention to the -jam-touch-jump jargon
. Being kind of simple, I chamber a dummy round and keep seating the bullet back a few thou. at a time until the rifling marks just disappear and then measure the seating stem length and adjust it .020 shorter. This gives a solid 'jam/seat'.
To summarize, my recipe to start has always been:
-An absolute minimum of .002 neck clearance (.0025-.003 is better)
-Well prepped case necks that aren't hardened from the expansion process
-Case length at least .020 shorter than chamber length
-.020 jam/seat
-.003 neck tension
-Fed 205M primer
-H4198 @ 32.5
Start here and go up by .3's with the powder until it groups well. Then, give it another .001 of neck tension and reshoot the powder charge that gives you the best groups. Finally, back the seating depth off .005 at a time if you feel it needs tweaking.
Done this way, a 30BR will 'tune up' quickly and predictably, provided everything else in the rig is up to the task.
For what it's worth.... -Al
