Just finished my first 100 rounds of .223 on my new Dillon 650. After spending a few years on a turret press, I'm very impressed with the machine as a whole.

It took 20 minutes to get them through the machine, but I took my time and went slow to eradicate some of the learning curve.

However, there was a bit of weirdness with the COL on approx. half the rounds: the first 50 were dead on and within a few thousandths of 2.26.

The final 50 were almost all too long - anywhere from .004 to a full hundredth at 2.27.

I ran them through the seating die again and all came down to the same length as the first 50.

I sort all my brass by headstamp, and I'm aware that there are minute differences in brass - same goes for my bulk Hornady 55gr projectiles.

I'm not expecting match grade ammo on a progressive, but a full .01 deviation in seating depth is a first for me.

Thoughts on what's causing this anomaly?

One thing I did change from my previous turret processes - I added a crimp die in the final station (only because I had one in the Dillon kit and the instructions included it).

I can't imagine how a crimp die would make a difference. in COL.

Any inputs on what's going on?

One final thought - I've measured several batches of factory .223 and some of it was all over the place in COL - even up to 2.28. That being said, I've never had a FTF with factory ammo in any of my ARs.

Should I even give a damn if my .223 rounds are a hundredth too long? I'm an "iron sights only" shooter and I only care about hitting a head-sized target 300m and closer.

Thanks!

I would just attribute that to bulk bullet variances.

When loading, do you go fully to end end of the stroke, and lean into it for a second? That can reduce variances in both powder drop and seating. I've seen others that 'bounce' the press off the bottom of the stroke.

Also I've noticed variances in seating depth when setting up the press and only having one round in, vs when its running and having a round in each station. Do a secondary check/adjust after youve run a few and have all stations full.

Whatever calipers you are using to measure OAL... from the first round to the 100th round... did you rezero the calipers after a while?

Just trying to eliminate one possible source of error.

Yep, dryflash nailed it

Also, as you're new to the 650, you want to make sure that the shellplate center bolt is adjusted correctly and locked with the brass tipped set screw under the shellplate.  The center bolt should be just lose enough to allow the shellplate to turn freely but not so lose that it allows the shellplate to tip.  It's a fine balance between the shellplate being to lose and it binding when turning.

Additionally, for small cases (9mm, specifically in my case) or loads that fill the case nearly full, there are roller bearing conversions that let you get the bolt tighter to make the whole works smoother.

I too have the bearing mod parts but stopped using it as it doesn't work as well as tightening it correctly for me, however, YMMV.