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Dang. I never thought of this problem because I only have one press, a single stage Orange Crusher. I suppose if I shot more semi auto I'd get a progressive press. It stands to reason that different dies and different presses might have different specs.

CDFingers

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This is indeed interesting. Almost all of my presses are Lee presses, and even the Dillon XL650 uses Lee dies. I think it's as much the dies as anything else, because my OAL's seem pretty regular across all of my presses, once I set 'em.

If I'm understanding you properly, it does make sense that there would be some variability when you adjust the die snug, if you're using a seating/crimping combination die. Can I assume that you're using RCBS dies here? What I believe may be happening is that the crimping is starting a little bit sooner on some rounds, due to the variability of bullet/case combinations. Some case walls are a little thicker than others. My thinking is that when--or if--the crimp starts a little early, the bullet won't get pushed in quite as far before crimping is done. That might explain the OAL variation, especially if you're using mixed headstamps, like I do and a lot of others do with handgun rounds.

Thoughts on this?

I have two Dillons and an RCBS.

Years ago, when I was actively studying reloading technique, I ended up calling Dillon over the variation I was getting for OAl on a Dillon 650. The RCBS was better, but there was still variation.

I don't remember the numbers we discussed, but I remember his reaction-- he said something along the lines of "they're (the presses) not built to that standard. There is always going to be variation unless you move up to a ten thousand dollar machine."

At that time, an industrial reloader from someone like Ammoload with about 12 stations was around ten grand. I'm sure they're way more, now. (Yes, I looked. I drooled over the average speed of three to five thousand round an hour.)

He told me I could probably hold OAL within 15 thousandths, 7 or 8 each way, on a Dillon 650.

I've used ± .007 ever since, with great success.

I've tested it hard, and haven't found that variation within that tolerance affects accuracy. (I suspect that I am a lot less accurate than anything caused by variation in the OAL.)

And that's going to be the case with progressive presses, which is why, generally, match rifle shooters (PRS and such) use a single-stage to load their ammo. Heck, the Lee Loader (yep, the "whack-a-loader") will be more consistent than any progressive press, which is designed for high-volume at the trade-off of a bit of precision. For handgun rounds, that trade-off makes complete sense. For events like 3-gun with an AR-15 in, say, 5.56 NATO, same thing; all you need is 1 to 2 MOA for such events. A progressive press is great for that sort of competition.