Starline brass anomalies

I've just finished loading group of ammo using U-die and RCBS sized Starline 1X-fired as the variable.  While seating, some brass needed more pressure to seat than others.  The brass needing more pressure had around .004" higher COL than the easier-seating brass.   I know the difference will not appreciably affect poi but this is my first experience with the condition.  Anyone else have the same experience?   I'm using 125 HAP, .356 dia. and 1.120 COL.

Assuming all else is consistent (brass from same batch, expanded all in same session, etc.) you might want to use your calipers to see if the HAPs have variations in their diameter.  Another idea to test is whether your seating die is pushing the bullet in straight every time.  Taking out the seating stem and sitting a bullet in the stem (upside down) should tell you if the bullet is being consistently seated.

All bullets the same diameter ?

Since your seating by hand and can feel the difference then load them by feel. I have felt the same thing your experiencing with jacketed bullets and just stop when I feel I have crimped enough. I seat and crimp in a separate motion so this has no effect on COL. I can't do this with my Loadmaster but works great on the turret press. I crimp lead all the way down. Or up depending on your perspective.

Len

Sorry I forgot to mention my seating die is the Redding Competition with the micrometer adjuster so I'm certain centrality is good.   I only crimp enough to close the bell with an Lee Factory Crimp die.  Yes my 125 HAP's are all the same diameter on my digital calipers.  The issue seemed to be more prevalent on the RCBS-sized brass.  The pressure difference does not occur when loading range brass.  I've not heated the brass more than 150 F during ultrasonic cleaning so I'm ruling out a hardness change but the COL difference seems to infer some kind of neck tension change.  I'll be certain to keep an eye on seating parameters when I do another batch.

From a video I watched, 9mm brass is made as a straight case until the final forming when it is “coned” to give its taper. Also, 9mm is in such high demand, I’d bet that what you have here is brass made on two sets of draw dies/punches and there’s a very slight difference. Hence the “two” seating feelings in this one batch. Other than segregate, I don’t know what to do about it though. Does it make any difference on the target?

Wobblley, I haven't shot yet as the winter cannot let go.  I'll put an ID on the longer COL's before I do.  Good advice.  Thanks.

The range yesterday was cold but shootable (light snow flurries) if I warmed my hands every 20 minutes.  The distance was 25 yds.  There was no difference in the "tight" seated cartridges of Starline.   Curiously, the CCI range brass of mixed unknown number of firings with 115 HAP and 125 HAP grouped tighter than Starline with the same loads.  I only had 10 of each variable so I will repeat the exercise at 50 yds.  The 2x scope I mounted on the 986 has brought in the extreme flyers I was getting with the HD Micro and MDII, also tightening the center of the group.  Very pleased with the scope. If the 50 yd. results are the same and my 10-shot e.s. is 2" or less the MDII will be for sale.