breech seating bore diameter pp

[bruce moulds]

well, 800 metres has happened.
please bear in mind that 800 mts is about 880 yds, so closer to 900 than 800.
2 strings of 10 to count and 2 sighters for each.
the vert for each group was about 3.5 moa except for 1 shot that hit high on the target.
wind was 12 to 20 mph, fishtailing from 10.30 to 1.30.
there was a trend for many shots to hold vert close to the v bull (x ring) height, but other shots blew out to vert described.
disappointment has caused much food for thought.
breech seating has still shot better at all ranges than fixed ammo, so that is a positive.
at 100 it shoots like an fclass rifle. at 300mt, vert seems to go to about 2 moa, or bullseye height. at 800 mt it is bigger again.
so what can the causes be?
bad bullets? bullets from the mould in question are not perfectly round, particularly on the nose. plans are in place to address this.
bullet length? these bullets are 1.55" long, and instability could be creeping in as distance increases. imperfect bullets will not help here, if they are off balance, the fast 1:13 twist will have them dizzy.
powder column height? my droptubed charges show slightly differing heights in the cases. some careful use of a compression die might help here.
barrel condition? a bore pig pushed with a dry cloth possibly allows variation in bore condition. any variation here causes variations in muzzle velocity which translates into vert.
time to break out the chronograph.
powder? used was swiss 1.5 looking for velocity. 1.0 might be better for grouping.
shooter? the always present question!
atmospheric conditions? much to learn here.
crimp on cases to hold wad? initial testing did not include this. could it cause variable ignition or differing pressure curves.
patch damage? when breech seating a pp bullet, could patches be getting rearranged somehow in an inconsistent way?
velocity s.d.? could droptubed charges cause higher than optimum s.d.
for long range shooting s.d. should be as low as possible. more work for the c.e.d.
patching technique? my bullets have some overlap, underlap, and most are quite good that way. how off balance is a bullet improperly patched.
these are some of the questions that need answering, and can only be done one at a time to have meaningful answers.
in retrospect I dropped 13 points per range, mostly to wind. the vert was not ideal, and in the end I started to make some good wind calls based on experience gained.
sometimes you feel that it is quite hard and it is, but there is always something positive to add to the learning curve.
experience with breech seating has shown it to be superior in accuracy to fixed ammo so far, if you go to the trouble to get it right.
experiments with both techniques will continue.
for pure long range target shooting, it does appear that ammunition needs to diverge from that suited to bison hunting in the day.
both types have their place, but the right one used in the right place is superior.
hinman's writings suggest that creedmoor shooting ended up as a breech seating game, and this would have been because it was what you had to do to win.
keep safe,
bruce.