OK, here is an update. Believe the problem is now solved.
Did load development with once fired Alpha brass with 140 gn Berger Hybrids, with H4350 loaded from 39.0 gn to 42.0 gn in 0.3 increments. Powder came from a fresh bottle and did not sit in the powder thrower for weeks sucking up moisture. To recap: Trying to avoid “cold welded bullets” increasing effective neck tension and significantly increasing SD.
My working theory was stimulated by a section from Glenn Zediker’s book: Powder absorbs moisture and swells, increasing in volume, and burn rate goes down. My theory was that the powder inside the case releases moisture and cause the inside of the neck and the bullet to corrode and stick to each other. [No way to confirm that without access to a materials science lab...]. If true, this could be mitigated by keeping the powder in the bottle and not exposing it for long periods if time to the atmosphere. Once powder is in the case, seat the bullet fairly quickly after weighing and don’t let it sit open for long. Drop a bullet in the neck wrong way round to act as a plug.
The brass was tumbled for only 2 hours, using fresh corn cob with a small amount of Nu Shine polymer based car wax added to the tumbling media. Still some carbon visible in the necks. Used an ear bud to coat the inside of the necks with Imperial dry lube (graphite, a good lubricant, less scrathing of bullet and case neck during seating operation, less direct contact between the two metal surfaces). Dipped bullets in dry lube as well to double up the amount of dry lube in the beck, tapped on table to remove excess amount, then seated via Wilson hand die to book length, via a K&M arbor press with force messurement. Seating force was between 12 and 22 lbs, which is nice and light and adequate consistent in my prior experience.
Intentionally let the ammo sit for a week. This previously caused accuracy problem and SD exceeding 25 fps. Reseated today at the bench 0.015” deeper, and seating force was light and consistent, same as before. That is a good result!
Alpha brass was AMP annealed, neck sized only, used a Federal Magnum Match primer, inside neck was deburred, primer pockets cleaned with a brush. No trimming required as the brass got 0.002” shorter after fire forming. Alpha brass was sorted into a batch of 50 that was about 0.6 gn weight range. Superb weight consistency, hopefully indicating very consistent case volume.
Best SD was 3.3 fps, second best was 4.4 fps, most were below 10, loads above 41.2 gn exceeded 10 fps (11-15 fps). Best group was 0.35”, and two at 0.45”. Most were below 0.8”. Lowest SD corresponded with smallest group size at 2750 fps. Typical accuracy node for this rifle.
Problem seems to have been cured by combo of Nu Shine car polish added to the corn cob, avoiding powder sitting in the thrower for weeks sucking up moisture, and double application of dry lube. [I doubt the reseating made any difference as neck tension was essentially unchanged, jump was very long and an extra 10 or 15 thou would not have a material effect. Will skip this step next time.]
Thank you for the ideas, it really helped. Case closed.
Did load development with once fired Alpha brass with 140 gn Berger Hybrids, with H4350 loaded from 39.0 gn to 42.0 gn in 0.3 increments. Powder came from a fresh bottle and did not sit in the powder thrower for weeks sucking up moisture. To recap: Trying to avoid “cold welded bullets” increasing effective neck tension and significantly increasing SD.
My working theory was stimulated by a section from Glenn Zediker’s book: Powder absorbs moisture and swells, increasing in volume, and burn rate goes down. My theory was that the powder inside the case releases moisture and cause the inside of the neck and the bullet to corrode and stick to each other. [No way to confirm that without access to a materials science lab...]. If true, this could be mitigated by keeping the powder in the bottle and not exposing it for long periods if time to the atmosphere. Once powder is in the case, seat the bullet fairly quickly after weighing and don’t let it sit open for long. Drop a bullet in the neck wrong way round to act as a plug.
The brass was tumbled for only 2 hours, using fresh corn cob with a small amount of Nu Shine polymer based car wax added to the tumbling media. Still some carbon visible in the necks. Used an ear bud to coat the inside of the necks with Imperial dry lube (graphite, a good lubricant, less scrathing of bullet and case neck during seating operation, less direct contact between the two metal surfaces). Dipped bullets in dry lube as well to double up the amount of dry lube in the beck, tapped on table to remove excess amount, then seated via Wilson hand die to book length, via a K&M arbor press with force messurement. Seating force was between 12 and 22 lbs, which is nice and light and adequate consistent in my prior experience.
Intentionally let the ammo sit for a week. This previously caused accuracy problem and SD exceeding 25 fps. Reseated today at the bench 0.015” deeper, and seating force was light and consistent, same as before. That is a good result!
Alpha brass was AMP annealed, neck sized only, used a Federal Magnum Match primer, inside neck was deburred, primer pockets cleaned with a brush. No trimming required as the brass got 0.002” shorter after fire forming. Alpha brass was sorted into a batch of 50 that was about 0.6 gn weight range. Superb weight consistency, hopefully indicating very consistent case volume.
Best SD was 3.3 fps, second best was 4.4 fps, most were below 10, loads above 41.2 gn exceeded 10 fps (11-15 fps). Best group was 0.35”, and two at 0.45”. Most were below 0.8”. Lowest SD corresponded with smallest group size at 2750 fps. Typical accuracy node for this rifle.
Problem seems to have been cured by combo of Nu Shine car polish added to the corn cob, avoiding powder sitting in the thrower for weeks sucking up moisture, and double application of dry lube. [I doubt the reseating made any difference as neck tension was essentially unchanged, jump was very long and an extra 10 or 15 thou would not have a material effect. Will skip this step next time.]
Thank you for the ideas, it really helped. Case closed.
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