9mm Questions

lpsharp88 said:

First one, are Hornady HAP not the same as XTP?

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HAP is essentially XTP without the expansion cuts and made for reliable feeding than expansion.

lpsharp88 said:

I’ve read that the HAP are pretty accurate projectiles

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Yes they are.

lpsharp88 said:

Does .001” make that much of a difference?

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It can depending on your barrel's groove-to-groove diameter, size of the bullet diameter, OAL/bullet seating depth, powder and charge used. If you are using mid-to-high range load data without bullet setback, probably not. If you are using max load data with bullet setback, it could.

lpsharp88 said:

I planned on finding a working OAL and starting low and working up

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Sounds like a good plan.

lpsharp88 said:

Second, it also seems the RMR MPR 124gr looks promising, but I have no data for it. So, would using published 124/125gr JHP data be advisable assuming my working OAL is the same

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This list of bullet lengths show 124 gr XTP to be .603" in length - http://jbmballistics.com/ballistics/lengths/lengths.shtml#Hornady

As shown below, RMR MPR has shorter rounded nose with .558" length which will result in shallower bullet seating depth when using the same OAL as longer XTP bullet. But as you can see from the comparison picture below, due to different nose profile/ogive, RMR MPR needs to be loaded to shorter OAL, which will seat the bullet base deeper in the case. To not complicate things, it's simpler to first determine the working OAL (read below) then conduct your powder work up from published start charge and reduce start/max charges if using significantly deeper OAL/bullet seating depth.

For my load development with RMR MPR, I referenced published load data for JHP/Gold Dot HP.

BTW, here's Speer load data for TMJ/GDHP bullets and various powders with start/max charges (Unlike Alliant's load data which only shows max charges) - https://www.speer-ammo.com/download...m_caliber_355-366_dia/9mm_Luger__124_rev1.pdf

lpsharp88 said:

Lastly, when you’re establishing your working OAL for your guns, how much deeper do you seat the bullet when you figure out the max OAL? For example you figure the max OAL is 1.14” for that projectile, do you set your dies to 1.13” to allow for variance in projectile size or other variances?

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When I am determining the max OAL using the barrel, I decrease the OAL until the round drops in the barrel freely with a "plonk" and spin without hitting the rifling. Next working OAL is determined by feeding the dummy round (no powder/no primer) from the magazine starting with max OAL, and incrementally decreasing the length (say by .005") until the round reliably feeds and chambers when the slide is released without riding it.

BTW, here's a reference thread on max/working OAL for various bullets and barrels for your review - https://www.thehighroad.org/index.p...let-max-working-oal-col-for-reference.848462/

If you are pushing the limits at max OAL and concerned about bullet nose contact with rifling, consider this also. Resized brass will vary in OAL by as much as .005"+. To prevent bullet nose to rifling contact, measure a sample of your resized brass and use shortest length case for your max OAL determination. Then rounds with longer resized length cases will headspace off case mouth and rounds with shorter resized length cases will headspace off extractor without contacting the rifling.

It's always great to read a question, say to yourself "wonder what bds is going to say?" And then scroll to a superb answer.

I'm much less informed but 9mm is my primary cartridge and I order mpr and match winners. With those in my cz shadow 2 the only things holding me back are eyesight and dexterity. I can't offer a flaw with those pills

lpsharp88 said:

Thanks for the excellent information BDS!

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You are very welcome.

lpsharp88 said:

Erief0g said:

It's always great to read a question, say to yourself "wonder what bds is going to say?" And then scroll to a superb answer.

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I won’t lie, that’s exactly who I hoped would respond

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Only the best for fellow THR members.

But I gotta give credit where credit is due. While I came to THR with a lot of "knowledge" learned from seasoned USPSA/bullseye match shooters, much of what I post on THR now are "wisdom" shared by seasoned THR members (current and past like Walkalong, rcmodel, etc.) who pushed me to narrow my reloading focus with objectivity and to "myth bust" with measurable and repeatable data - Facts not claims.

So most of what I post is "Paying It Forward" the knowledge and wisdom others have generously shared with me over the decades.

Just about the only thing I can claim as my own is testing of neck tension/bullet setback with resulting claim that "It's not the finished OAL/COL that matters rather chambered OAL" after bullet nose bumps the feed ramp and experiences any bullet setback as result of insufficient neck tension from sizing of case neck, bullet diameter, case wall thickness, reloading practice with dies, etc. along with well known fact of "Holes on target speak volumes" regardless of what reloading notions we hold to produce accuracy (Thanks jmorris, bart b, Nature Boy, jwrowland77, etc. who actually shot long-range matches and know what they are talking about instead of this rifle reloading newbie) - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

bds said:

Facts not claims.

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Oddly enough, the reloading of 9mm has given me, over the years, about as many fits as reloading 7.62mm for my M1a... albiet for different reasons. In the Early Years of my reloading, I reloaded almost everything to max charge... including 9mm... and it got me into trouble. I'm certain it was a combination of bullet OAL, loaded cartridge OAL, and starting at or near the maximum charge... but, hey, I was young and indestructible back then.

It's nice today... that we have sites like this and people who can provide substantive data. At this point, I'm almost not afraid to load 9mm again...

You are welcome.

Having shot 9mm for USPSA, I didn't give much thought for squeezing out utmost accuracy like my reloading mentor who was a bullseye match shooter. For "action pistol" shooting, my match loads just had to be "good enough" as I didn't need "bullseye match" level of accuracy; and instead, I focused on powder/charge that produced the "right amount" of felt recoil/muzzle flip to get my sights back on the target faster for quicker double taps as USPSA scoring benefits from faster stage times over slightly less accuracy.

But since joining THR and particularly when I started loading for blow back action Pistol Caliber Carbines, I kinda had to start over for 9mm as now I had to factor in the additional variable of "dwell/case mouth on chamber time" of case mouth pushed against the chamber before bolt/buffer moved the case back. Whereas locked breech pistols produced efficient enough powder burn for even slower burn rate powders, now I looked at faster and faster burn rate powders to maximize my powder burn efficiency as I had already increased the buffer weight of my carbines for longer "dwell time".

And when bulky Promo produced smaller groups than other more popular powders known for accuracy, I wondered if case fill to 100% had any contribution as semi-auto pistols/carbine essentially fire with "powder forward" when the round is chambered. With dense powders that require small powder charges, we are essentially forcing primer flash to jump across air gap before igniting powder granules, at times, top down. So I found incrementally reducing the OAL, especially with lighter target loads with lower powder charges, had the effect of increasing powder case fill so the powder granules covered the primer and now I recommend people use the working OAL to identify the most accurate powder charge but to consider incrementally decreasing the OAL to see if group size gets smaller.

This revelation prompted me to reduce my OAL even shorter from 1.135" for 124 gr FMJ/RN and 1.130" for 115 gr FMJ/RN down to 1.110" (After case powder fill calculations to not compress powder charge) depending on the powder I used. And deeper seated 9mm FMJ/RN bullets, especially for 115 gr FMJ/RN with shorter bullet base/bearing surface, produces greater neck tension which probably helps with chamber pressure build and more efficient powder burn.

Yes, as many people experienced, 9mm can be more difficult to load accurate than 45ACP but not much more difficult to produce accurate loads.

I find it interesting that hardly anybody shoots the same load in his PCC as his PCP.

Jim Watson said:

I find it interesting that hardly anybody shoots the same load in his PCC as his PCP.

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Maybe that's due to breech lock vs blow back action necessitating different burn rate powders?

That seems the thrust of your work, but a lot of gamers are just pulling 16" power factor down to standard load pistol values.

Jim Watson said:

I find it interesting that hardly anybody shoots the same load in his PCC as his PCP.

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I do. Our club matches don't have any power factor requirements.