Home Forums Reloading Handgun Reloading 10MM load discrepancy

I’m getting ready to work on a load for my CZ 10MM that I started working on back in June, 180 grain HAP bullet, A#9, Starline cases. From Ramshot website, max load with 180 grain XTP is 13.5 grains A#9 at 1.25 OAL at 1242 fps. In Hornadys 10th edition manual, max load with the same bullet/powder combination, is 14.9 grains at 1250 fps, 1.26 OAL.
My results:
13.5 grains 1255 fps
13.9 grains 1278 fps
14.4 grains 1295 fps
14.9 grains 1324 fps (this was the tightest group but obviously very high pressure).
14.9 grains from STI 10MM 1377 fps (barrel 3/4” longer than the CZ plus flat bottom firing pin stop)

BTW I didn’t just jump to these charge weights I worked my way up with both guns. I would have stopped if I saw anything troubling. I’m just highlighting the questionable results.

I believe these velocities are accurate but don’t understand why Hornady data seems to be inaccurate even though their test barrel is different than mine. I’m going to call Hornady to get their opinion.

Have any of you had similar results?

I had similar results a few years ago With Hornady data and #9. Glock 30 with a conversion Barrel Incredible velocity but brass only lasted two or three loads ....

I believe it. I should have measured case head expansion.

What primers do both list and what did you use?

Mark in GA

I wouldn’t and haven’t trusted Hornady data for anything since 92. Too damn many discrepancies.

Not too long ago I read about discrepancies in the Hornady manual and Accurate # 7.

FYI: Here is the link: http://10mm-firearms.com/reloading-10mm-ammo/warning-for-10mm-older-hornady-manuals/

HAP bullets are larger in diameter, and according to Hornady's data in a few calibers/cartridges, they develop a lot more pressure than XTP. That data isn't transferable. Don't make the mistake that it is.

Interesting, seems quite a few people got confused as there are many threads on the net over the issue. One thread on The Firing Line posted an email from Hornady that using XTP data with the HAP was perfectly acceptable.

I’ve got 3k “45” caliber HAP bullets on the shelf that measure .451 and I use xtp data . Haven’t seen that issue .

But I’m in agreeance that Hornady 10mm load data is sketchy , specifically with AA#7 . I won’t use it

Hornady lists a correction for their 10mm data on their website:
https://press.hornady.com/assets/pc...on-Handbook-Updates-Errata1522702377.pdf

Page 910, 10mm Auto – 180gr data section, do not exceed 14.2 grains of Accurate No. 9 powder.

I was using Federal primers. I called Hornady some time back about being able to use the HAP bullet for back woods loads, is it constructed the same as the XTP. They said it’s the same bullet sans serrations.
14.2 grains max. Thanks for the info. That’s quite a difference at the top end of a high pressure load.

Hornady's data always seems all over the place. Usually used other sources to compare to, and it was always different, but most of the time seemed more conservative. 13.5 seems a little low and the pressure of 34k seems a little on the light side for a Max load. Wonder if that is because of concern for KB in not fully supported cases.

I had similar results with their load data for 200 grain XTPs. 13.2 grains A#9 1.26 OAL, is the book max load. 1150 fps. I was at 1220 fps.

I treat velocity data from reload manuals only as a go-by. There are many, many factors that affect velocity. I rely on my own chrony data obtained from my own loads fired in my own firearms.