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vtmarmot
06-25-2013, 09:22 PM
I recently prepped 100 new Lapua 6 BR cases, all identical from the same batch. I seated 6 different types of bullets, ranging from 60 grain Sierras to 88 grain Berger varmint. All were flat base, all measured .243 and a skooch and all took about equal seating pressure except the 80 grain Berger varmint. That took quite a bit more. I am not sure why. Perhaps because it had the longest bearing surface and was seated the deepest? The 88's do have quite a long pointy snout. Any other ideas why?

abintx
06-26-2013, 08:51 AM
I recently prepped 100 new Lapua 6 BR cases, all identical from the same batch. I seated 6 different types of bullets, ranging from 60 grain Sierras to 88 grain Berger varmint. All were flat base, all measured .243 and a skooch and all took about equal seating pressure except the 80 grain Berger varmint. That took quite a bit more. I am not sure why. Perhaps because it had the longest bearing surface and was seated the deepest? The 88's do have quite a long pointy snout. Any other ideas why?

Was time a factor?

RELOADING TIP--Neck Tension vs. Time

Lesson learned: for match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing.

We've learned that *time* (between neck-sizing and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you'll see dramatic improvements in ES and SD, and your groups will shrink. Typically you'll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how hard the neck grips your bullets.

However, James Phillips recently discovered that another critical factor is at work. He loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases--not even close. Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the "older" cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet).

Conclusion: In the two weeks that had elapsed since neck-sizing, the necks continued to get tighter and stiffen.


Source: http://bulletin.accurateshooter.com/2008/08/tech-tip-neck-tension-vs-time/

vtmarmot
06-26-2013, 09:24 PM
These were new Lapua cases right out of the box. I have a Cooper with a no-turn neck. It only has about 20 rounds through it and I'm trying to find out roughly what it likes. I chamfered the cases and primed them, then charged them and seated them all in a couple of hours. I seated 40 Hornady 70 grain varmint, then 12 60 grain Sierras, 12 64.2 Berger Columns, 12 68 Berger flat base, 12 80 Berger Varmint and lastly 12 88 grain Berger Varmint. With the Hornady's, I'll be doing more of a break-in routine with frequent cleaning, although I seated them in groups of five at 8 different depths. Each group of 12 was seated in groups of three at 4 different depths. I plan to shoot them all in one long afternoon with plenty of time for cleaning and cooling. I will chrono them all and precisely record shot placement within the groups. The more I think about it, the more I think that the 80's had the most bearing surface in the case.

Don
06-28-2013, 10:57 PM
These were new Lapua cases right out of the box. I have a Cooper with a no-turn neck. It only has about 20 rounds through it and I'm trying to find out roughly what it likes. I chamfered the cases and primed them, then charged them and seated them all in a couple of hours. I seated 40 Hornady 70 grain varmint, then 12 60 grain Sierras, 12 64.2 Berger Columns, 12 68 Berger flat base, 12 80 Berger Varmint and lastly 12 88 grain Berger Varmint. With the Hornady's, I'll be doing more of a break-in routine with frequent cleaning, although I seated them in groups of five at 8 different depths. Each group of 12 was seated in groups of three at 4 different depths. I plan to shoot them all in one long afternoon with plenty of time for cleaning and cooling. I will chrono them all and precisely record shot placement within the groups. The more I think about it, the more I think that the 80's had the most bearing surface in the case.

Compressed powder charge.

DeltaBravo
06-29-2013, 12:15 PM
I didn't see any mention of what you're using to size your brass/necks. I shoot the 80's in my 6BR and use either a .266 or .267 neck bushing in my Redding Type S die. I end up with a .268 loaded round and that's just perfect for my no-turn .270 neck. Regardless of which bushing I use, neither one causes hard seating. I use the Redding Competition Seater die and a Lee handheld press.

Dennis

vtmarmot
06-29-2013, 09:34 PM
These were brand new brass, blue box Lapua, just chamfered and loaded up. I did have to straighten one neck a tad as it was slightly out of round. The charge for the 80 Bergers was 28.0 of H322, not even close to compressed at the depths I was seating. I seated three each at .004, .022, .032 and .044 off the lands. I shot them today and got about 2940 average velocity. The first 100 yard group at .004 was about 1/4 inch, the second was one hole that was hardly even elongated, the third and fourth were around .2 each. Conditions were fairly calm. I haven't done the "official" measurement yet.

88 Bergers shot almost as good, but the wind was picking up a tad by then. The 88's have a longer, skinnier nose that doesn't intersect the lands as quickly as the more rounded ogive on the 80's, therefore, the 80s are seated closer to the shoulder junction, which I think was the issue. When I size these cases, I'll set up an "S" die with a .267 bushing so neck tension will be less.