and more mysterious drama, seating depth changing

[Papa Charlie]

If you haven't measured and sorted your rounds before loading then my guess is that the rounds are causing the variations.

I have found as much as 0.007" variations in my Berger Juggernauts. Usually, they are +-0.003" but have found an occasional one that is excessive. Small variations like this depending on the slope of the Ogive, can cause excessive seating variations depending on where your seating stem contacts the round.

 

[Sweetyzfd]

Try adding a little graphite lube. I used to have the same problem with Forster micrometer seater. Graphite fixed the problem

 

[Lone Hunter]

If you haven't measured and sorted your rounds before loading then my guess is that the rounds are causing the variations.

I have found as much as 0.007" variations in my Berger Juggernauts. Usually, they are +-0.003" but have found an occasional one that is excessive. Small variations like this depending on the slope of the Ogive, can cause excessive seating variations depending on where your seating stem contacts the round.

I'm with PC. There is a lot of variance.. I measure each one. I also bought the VLD Seating Stem too..

 

[rhovee]

Only time I see this is when the inside necks are not prepped the same. Arbor press will show you real fast. Take a case and leave the neck alone for a week. Take another and dry neck line with Nylon brush and seat bullets. You’ll get different lengths for sure.

 

[rockwind1]

I checked my seating stem and it is not vld. Not using vld’s but turns out hybrids are very pointy and are too long. Possibly could be the problem. Plus I got rid of cam over on seating die. Not good. Thanks.

 

[Ned Ludd]

I checked my seating stem and it is not vld. Not using vld’s but turns out hybrids are very pointy and are too long. Possibly could be the problem. Plus I got rid of cam over on seating die. Not good. Thanks.

If the bullets are bottoming out in the seater die stem, you will observe the same variance in seating depth (CBTO) that exists in your Lot# of bullets between the meplats and the point on the bullet ogive where your caliper insert seats. This is because when the bullet bottoms out in the seater stem, the stem is actually pushing the bullet in from the meplat (bullet tip) instead of the normal point farther down the nose. Any nose length variance will translate directly to seating depth variance. It's all about bullet length variance between the point where the seater stem contacts and pushes the bullet in, and the point at which you actually take the measurement.

Likewise, as I suggested earlier, even when the seater stem contacts the appropriate point on the bullet ogive (i.e. if you were using a VLD stem), there is still a finite critical distance (and therefore potential bullet length variance) between where the seater stem and caliper insert contacts the bullets (see image below). Sorting bullets base-to-ogive will not fix seating depth variance caused by this problem, because the critical region is outside the sorting region. Sorting bullets by OAL may help, but not completely alleviate seating depth variance caused by bullet length variance in this region. The best way to minimize this type of seating depth variance is by sorting bullets into length groups based on the distance between the seating die stem and caliper insert contact points. This the region on the bullet for which Bob Green's (or similar) Comparator tool sorts bullets.

 

[D-4297]

Since you are already using a expander mandrel , I might suggest using some Imperial Dry Lube , both to expand , and to insert the bullet . I did have this same issue with one box of "Unnamed"-expensive bullets . Checked the base to Ogive and found a rather nasty .020-.028 variation in length . Then you get to check all the rounds left , sort them , and adjust the press accordingly . And use the bad ones for sighters . And you thought this was easy .

 

[muleystalker]

but i mandrelled all the necks so they would be very consistent, and i thought they were, at least i measured them and they all seemed the same

When was the last time the cases were annealed?

 

[rockwind1]

When was the last time the cases were annealed?

It is once fired Norma brass from used prime Ammo

 

[muleystalker]

It is once fired Norma brass from used prime Ammo

Ok, that eliminates that variable.