Inconsistent seating depth

[girish]

Update. I have received the custom seating plug for 85.5 gr Berger bullets from Lee. Only had a few pieces of empty brass to try at the moment, but so far none of them have seated to an extreme depth compared to the rest.

 

[MikeRu]

Had a similar problem with a Lee seater recently and fixed it by rounding off the top outside rim of the seating plug. It was too square and was catching sometimes on a lip in the threaded cap, failing to center up, which seated the bullet too deep in the case, by about 0.030”. I put it in a drill and spun it inside some fine sandpaper to round off the edges. Otherwise Lee seaters are Bang for the $ and super accurate IMO.

 

[barefooter56]

I'm having a problem with seating depth in 223. I have been using 77 Sierra Matchkings without issue. I decided to try Berger 85.5 Hybrids, but about 15 to 20 percent of the loaded rounds are seated .030 to .035 deeper (actually 30 thousandths or more too deep) as measured cartridge base to ogive with a Hornady comparator.

I'm using Lapua brass, RCBS Rebel press, and Lee bullet seating die that came with the collet neck sizing die. I routinely seat bullets a second time after turning the case in the shell holder. I have checked carefully and the Bergers do not come anywhere close to bottoming out in the seating stem/plug. The die is clean and the shell holder is clean. Overall length of the Berger bullets themselves base to tip have up to .015 spread but most are less than that. Bullet base to ogive with the Hornady comparator has about .004 spread. I also checked bullet length using the seating plug as a comparator, which contacts the bullet in between the tip and where the Hornady comparator does. That varied about .003.

What can cause some of these Bergers to seat so much deeper?

It's a bit overwhelming the generosity of people here sharing their expertise. It is greatly appreciated. I'll try to address the suggestions here.

Loads are not compressed.
Neck tension is about 1 1/2 to 2 thousandths, as measured by the outside neck diameter before and after seating.
Case mouths are chamfered.
All brass is from the same Lapua box.
I did not get as much freebore with the barrel as I expected, so both the 77 Sierras and 85.5 Bergers are seated way below the case neck/shoulder junction. I'm using lower powder charges because of that.
After firing 60 rounds I get a few, usually less than six, donuts. I check for donuts before loading and remove them. The cases that had donuts do not correlate with the rounds that get seated too deep.
Cases are trimmed to 1.750.
The 80% that are consistently seated with Bergers are about COAL 2.430, with some variation from the bullet OAL. The 20% that are seated way too deep are obviously much shorter than that.
I don't anneal. Induction annealing seems the way to go but it is not in the budget right now.

I'll keep bullet sorting as an option if I don't figure out the problem before that. 80 percent or more of the rounds seat rather consistently, and then those 15-20 percent are way deeper than the rest. The deep rounds are seated deeper by 2 or 3 times the OAL variation of the bullets, and around 10 times more than the bullet BTO variation.

The problem does not happen with the 77 gr Sierras which have a less pointy profile. The Bergers are much more pointy but they still only extend into the seating stem about halfway to the end of the cavity, so the tip of the Bergers do not come anywhere close to touching the stem.

I wondered if perhaps the seating stem/plug was becoming cocked inside the die cap, but after checking I can't even purposely make that happen.

I contacted Lee. They said since the Bergers have more taper that they recommended buying a custom seating plug. I don't understand how the seating plug cavity profile can cause such dramatic depth differences when the bullet tip doesn't touch, but I'm considering buying one.

The LEE DIES do not have a VLD BULLET SEATING STEM I believe. If you are VERY SURE that the tips of the bullets are NOT touching the bottom of the seating stem ( I would check a BIG sample here) then I would suggest you contact JOHN WHIDDEN at WHIDDEN GUNWORKS and order a seating die with a VLD bullet seating stem. Also it sounds like you are seating these bullets to deep. Please contact us for load data
at Support@capstonepg.com
Thank you.

 

[girish]

Had a similar problem with a Lee seater recently and fixed it by rounding off the top outside rim of the seating plug. It was too square and was catching sometimes on a lip in the threaded cap, failing to center up, which seated the bullet too deep in the case, by about 0.030”. I put it in a drill and spun it inside some fine sandpaper to round off the edges. Otherwise Lee seaters are Bang for the $ and super accurate IMO.

This makes sense. I had wondered if somehow the seating plug was getting cocked inside the die but I couldn't make it happen on purpose just pushing on the end of the plug. Maybe it works a little differently with an actual cartridge and bullet in the die. This is worth trying. Thanks.