It wan't so much a discussion, just you claiming we couldn't possibly know how the diameter of a bullet and then lowering your sights when it proved we did. I do find diameter of jacketed bullets to matter. I have loaded thousands of RMR-produced jacketed bullets of various types and regardless of OAL I reach max velocities with them with a few tenths less powder than with the actual 0.3550" bullets the load data uses. This factor is easily ignored when you are using really long OALs that depend on a healthy leade to chamber, as the loads tested in generating the published data are going to chamber without leade.
Comparing OAL isn't really telling you much. You have to take it to the seating depth before you are comparing anything functional. I agree seating depth matters, but so does diameter.
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And no, you can't compare these OALs - one is a hollowpoint and one a RN. A thousandth in diameter makes a BIG difference, and I do not believe a half-thousandth can't be noticed in carefully controlled pressure testing. The tighter the fit, the less pressure it's going to leak, physics being somewhat inflexible. Have a different view? You are welcome to it.
What was proven? bds stated he has super accurate calipers and probably thousands of bullets measured. I think a high quality micrometer would be better .You did not indicate how your measurements were taken.
What does posting the Hodgdon reloading data have to do with anything? No, you can't compare the bullets so why post it?. Sierra is listed at .355 and Hornady at .356. Not down to 5/10,000. Sure, diameter will make a difference in pressure, but that all depends on the EXACT bore diameter and even if there is any fouling in the bore to make such a minuscule difference. Plus you have no way to measure the actual pressure.
I also said "seating depth" not just OAL Bullet companies give diameters to thousands of an inch not ten one thousandths
What velocities??
" I have loaded thousands of RMR-produced jacketed bullets of various types and regardless of OAL I reach max velocities with them with a few tenths less powder than with the actual 0.3550" bullets the load data uses"
Of course it will be different as you can not duplicate the test or any test done by someplace else.. Plus factor into the equation the powder(s) and primer(s) used and all the other different test parameters. Your velocity even though related to pressure means little as you can not compare it to Hodgdons test data.
So yes, I have a different view on dealing with insignificant factors.
So for the OP. yes, he is probably approaching +P pressure/velocity and should be careful with his powder charges and seating depth but there is +P data for 9mm but why bother with it? Better to keep the powder charge lower . But there again that is only the data from Alliant, if there are other verified test data in manuals it may be different as is most load data. But his velocity is going to be greater in a carbine than a 4" barrel.