OAL Wackiness with Mixed Brass

[Little Bill]

I have been shooting / loading 9mm major since January this year. I am using a Dillon 650 set up with a Lee “U” sizing die, a Redding Seating Die, and a Dillon Crimp Die.

In the past, I have been using headstamp-sorted brass with great results on OAL consistency with the Redding die. For example, last month I loaded about 2k rounds of ammo for match use using 1x fired R-P brass, 125 JHP Zero, WSR, and 9.3gr 3n38 @ 1.150 (It IS a compressed load with 3n38). I case-gauged AND checked OAL on every round. Not a single rejection. ( 1.153-1.148 was my acceptable range)

Sooooo, I recently acquired a bunch of mixed headstamp 1x fired brass (Fed, R-P, Speer, Win, Pmc) and decided to run the mixed brass for practice. While reloading the mixed brass, I stopped to check a few rounds for OAL, and low and behold, my OALs were wild, 1.142-1.155, with the low OALs (1.142ish) seemingly only on the Fed brass. The other brass brands seemed more normal, 1.147-1.155.

What gives? I can’t think of a logical reason why it is so wild with Fed brass. It is consistently low with Fed brass, so it is consistently about the same low OAL with Fed.

[eric nielsen]

The brands don't all seat themselves in the press's shell plate the same way.

Also, tilt of the shell plate is a factor - even on a new, tight press:

1. Load only one round at a time in the press & your OAL will be different than with 4 or 5 rounds in the shell plate, because of tilt.

2. Load with full shell plate but have some fired cases much harder to size than others. OAL is different, because of tilt.

BTW, depending on your particular breechface & extractor, the different brands may not even chamber & headspace the same way, even at the same OAL.

If you want accuracy, you MIGHT get it with mixed brass.

If you want consistent chrono velocities, you WON'T get it with mixed brass.

I shoot mixed only for practice.

[Guest Larry Cazes]

This is not unusual in my experience. This is why I sort headstamps when Im loading .40sw for my limited gun and only load those together that give me a consistent finished OAL. Right now I favor PMC and Federal brass because they work together well with the same die setup in my press. If I throw others into the mix the spread increases. Not such a big deal in .45acp and .40 loaded long but keep in mind that with 9major, your chamber pressures are probably all over the place as well.

[Little Bill]

Thanks for the responses fellas. I never thought about tilt being involved. If it (the problem) was tilt related, wouldn't it show up on other brands?

The mixed brass stuff is just for practice, but I have a healthy respect for the pressures I am flirting with in 9mm major, and I don't particularly want any rounds .010 too short.

[Flexmoney]

If you use all the same brass...the tilt will be the same. Use various brass...the tilt will vary.

[Little Bill]

Ah-Ha! The logic stares me in the face! I guess I will either sort my practice brass, or set the press to load longer to avoid any undesired consequences.

[slughammer]

I loaded 230 rounds of 9 x 19 in mixed brass this morning. Just so I would have something to add to this thread I measured the first 20. My lengths ran from 1.157 - 1.161. Only one was 1.157 and it was a Federal . Most were right there at 1.160.

Two things about the way I have my press set that may make a difference.

For the shell plate I tighten it with the ram up and no die plate in place. I tighten it until it bottoms out. I then snug the set screw. With the set screw snug, I take the 1/4" hex key and losen the shell plate bolt with my right hand while indexing the shell plate with my left thumb. When the shell plate indexes freely I stop. (Kind of like over tightening your wheel bearings and then backing them off till the wheel turns freely.)

I think what I have done to the die plate makes the biggest difference. The flange on the die plate is about 3/8" and the slot in the press is .020-.030 larger. So with the differing force of mixed brass, the die plate is pressed up differently each time. I take a center punch and go around the lower edge of the outer surface of the flange and raise up some metal. This bulges the lower surface and pushes the die plate into the up position which is where we want it to be.

Might not be orthodox, but the reuslts are what matters...