Today I learned: 7.62x54r edition

Rim thickness should not impact the OAL, unless its bent/rough/not flat. The rim is above the base. The only accurate way to determine if your getting consistent OAL is to measure off of the ogive. You can remove the seating stem on some dies and use that to measure the ogive to base. You should have 0.001-0.002" max doing it this way. If you have a comparator you can check the variation in bullets. Unless your using high quality match bullets expect to see some spread.

Now if your seating stem is one that has the stem on it, it will not work easily. For those type find a spend 22 LF casing and use it.

If yoiu have deep pockets the RCBS Precision Mic is nice too to have. I have them for when I'm loading for different guns. It will tell me what the difference is between my std setup and what I'm loading. I then just adj shims to give me what i want.

That's with in normal limits of most all bullets with the exception being high quality match bullets.

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HEAVY METAL 1 said:

I don't know if it matters with 762x54, but when I measure brass for my Mausers I have found having the primers out of the brass makes a big difference in the accuracy of the measurements.

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If your primers are affecting case length measurements, you need to seat them deeper. Primers should never stand "proud" of the case head, they should always be recessed a couple of thousandths.

With a tapered rim cartridge such as x54R, rim geometry absolutely makes a difference in how it fits in the shell holder, and can impact COL.

Before I got too hung up on the varying OAL and it's relationship to brands of brass, I'd want to know if all the longest loaded rounds are brand x, shortest are brand y, and intermediate are brand z. For that to happen, the brass itself would have varying lengths...which I'd think would be eliminated if the brass was trimmed to a uniform length.

.003-.005 can be the variance in bullets if you're measuring base to tip.

There are basically 4 manufacturers of Boxer primed 7.62x54R brass; Sellier & Bellot, PPU, Norma, and Lapua. (I suspect those two may be made in the same factory) Winchester is made by S&B, as is Graf's. Remington made it way back, and those rims were much thicker. I've loaded 3 of the 4 (not Norma yet) and the variance in the bases/rims was not a factor in loading and firing in several different Mosins from an 1899 M91 to a 1952 Polish M44. If you were loading for a Finn M28/76, it might be worth sorting by rim thickness, but otherwise as long as they are loading and extracting fine, I wouldn't worry about it too much.