COAL for 124 gr. 9mm Hornady XTP

I see the conventional wisdom is to seat the 124 gr. XTP to ~1.120" and my manual gives a min. OAL for generic 124 gr. jacketed bullets as 1.090".

However when I go to do the plunk test in my new CZ 75B barrel with bullets seated for a COAL any longer than 1.080" the bullet profile engages the lead before the case rim "plunks" on the edge of the chamber. This is confirmed as I can't freely spin the cartridge in the chamber, as the bullet is engaging the rifling. If I seat to <1.080 I get a nice "plunk" and the bullet can be rotated freely. And I'm confident that my setup can hold 1.075"-1.080" tolerance, so that is my plan.

However, at 4.6-4.7 gr. HP38, my charge is a little on the warm side (at least by the latest "wussified" reloading manual standards). I've easily launched >1,000 124 gr. rounds (both plated and jacketed) down range with this load over the years. But I am normally seating RN bullets at ~1.150"

I've measured the bullet and space above the powder to confirm that this is not a compressed load.

So I'd like to canvas the forum:

Is this a result of the XTP bullet profile? or does the CZ have a short lead?
What is the COAL of a factory load with the 124 gr. .354" XTP?
Does this load pass the "reasonable man" test?

Thanks in advance for any helpful comments.

1.075"-1.080" is what I meant.... corrected my type-o

One additional note... I'm only shooting these in steel framed full size semi-autos (BHP and CZ75B)

Thanks for the replies....

Looks like my COAL of 1.075" to 1.080" passes muster in comparison to factory ammo. So whether or not that spikes the pressure at 4.7 gr HP-38 is the only concern remaining.

I find it a bit frustrating to see load manuals change their max. load data over time, as it's hard to know whether that's based on better science (pressure measurements, etc...) or more conservative lawyers (liability concerns, etc...). One trend I'm noticing is that older load manuals seem to rely upon Copper units to measure pressure and generate higher acceptable charges, while data published with psi. units for pressure appear to have lower max. charges.

Apart from test firing and looking for signs of over-pressure, I don't have any means of proving this out myself.... which of course, points out the need for a decent chronograph.

In general, I strive to practice with "full power" loads that mimic factory loaded self defense loads, as my purpose is training for competent use of my firearms in a self-defense scenario (not gaming IDPA rules or loading low power plinkers, etc...).

But based on my limited experience with +P factory loads, I'm not a fan, so I don't want to go into that territory.

Thanks for all the input guys. Here's some additional data that I have....

1. A fellow THR member sent me a link to the original CZ forum with very detailed info about the short lead on CZ chambers and how it affects reloading. It turns out that the COAL of 1.080" I came up with via. my seat of the pants plunk test engineering is consistent with that info.

2. We had a mini Indian Summer over the weekend with temps in the low 60s, so I was able to get out to the range and had a productive time doing mag. and load testing.

I started with the 4.7 gr. charge of HP38 pushing a 115 gr. Ranier plated RN and had very good accuracy (this CZ 75B Omega is proving to be a real winner). These loads were within published maximums and the primers retained their rounded edges after firing.

Next I tested the 4.5 gr. charge of HP38 pushing the 124 gr. Berrys RN, seated at 1.15" COAL and also had no signs of over pressure on the primers or case heads.

Next I tested 4.7 gr. HP38 pushing the 124 gr. Berrys RN, which were seated at 1.15" COAL. The primers were just starting to flatten out, but still retained most of their rounded edges. The brass still looked good.

Finally, I tested the 4.7 gr. HP38 pushing a 124 gr. Hornady XTP seated at 1.08" COAL. The recoil and report was not noticeably different than the 124 gr. Berrys and again, the primers were just starting to flatten out, but still had rounded edges and the brass looked good.

So I think I'm still foxtrotting on the dance floor here and haven't yet ventured into dangerous territory. I did think of bullet setback, and was sure to apply a firm taper crimp.

I'm more than a bit mystified by the published load data, as it's all over the place.

I have published loads going up to 4.7 gr for HP38 (these typically express the max pressure in CUPs, so I suspect that they are older). And I have published max. loads for W231 at 4.5 gr (these always express the max pressure in psi). So I'm back to the same question (which I expect I will not ever get an answer for) has something changed (powder formulation, accuracy of test equipment, etc...) or have the manufacturers conservatively reduced their max. published loads for other reasons (i.e. liability).

As noted earlier, I have launched many, many plated 124 gr. RNs down range with 4.7 gr. loads of both W231 and HP38, with no mechanical problems, no signs of over pressure, and no indications that the plating is shedding off. The issue for me in this thread is all about COAL.

Next step is to get a decent Chrony set up and get some hard velocity data.

Again, thanks for all the constructive input.