6 BR Berger 80 Varmint Hard Seating

[vtmarmot]

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?

 

[Terry]

All brass chauffeured?

80's bigger in diameter?

 

[vtmarmot]

All were identically chamfered inside and out. All bullets miked within about .0003 of each other.

 

[jonbearman]

Was or is it a compressed load?

 

[searcher]

If bullet is not "much" larger and not a compressed load - with all brass being the same, logical to assume the additional friction created from going all the way into the neck would be my bet. I notice this when loading 7mm Mag and .375 H&H hunting bullets using Barnes TTSX bullets. Big time friction over my other bullets because these too are far longer and seat well into the case, whereas my other bullets don't seat to to the shoulder/neck junction. They may also be a little larger - but as you noticed - there can be a big difference in seating resistance.

 

[vtmarmot]

I think they were just deeper and may have hit the junction.

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.

 

[lpreddick]

i'v noticed the same thng and suspect you'r right...the thickness of most, if not all, necks increase as you go toward the neck/shoulder junction. the pressure ring on flat based bullets meets increased resistance as it encounters this thicker brass and using a very sensitive press, i can definitely feel this. you note this increasing neck thickness when lightly turning necks...just a little comes off, then more as you go toward the shoulder. boattail bullets don't seem to have this pressure ring and seat differently. i have an ongoing experiment where i'm reaming necks after bushing sizing. the pressure from resistance seems more uniform. time will tell if this helps accuracy.

 

[vtmarmot]

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.