RMR 115 MPR (JHP) Load Development

Discussion in 'Handloading and Reloading' started by KASarich, Feb 20, 2019.

  1. KASarich

    KASarich Member

    Jan 11, 2019
    Akron, Ohio
    For those that don't know, Rocky Mountain Reloading has released new in-house 115 and 124 grain JHP 9mm bullets. The price is very attractive, and since I have always been happy with everything else I've gotten from RMR, I decided to try out these new bullets. I went with the 115 for 9mm Luger. With this being a new bullet, there is not much information out there for loading it, so I thought I would post load development and results here for anyone interested in trying these out.

    So far, the only powder I have tried out with them is CFE Pistol, but I will update this as I play around with more powders if anyone is interested.

    These loads were all developed in CBC (Magtech) once-fired brass, with Hodgdon CFE Pistol and CCI 500 Primers.

    The first thing that I learned about these bullets is that the need to be loaded somewhat short. My first rounds were loaded at 1.125'' with 5.3, 5.5 and 5.7 grains of CFE Pistol. I test fired them through my Glock 17, G4. I had one round where the slide didn't go into battery, but with a light touch on the back of the slide, it did...no other problems with the Glock and these rounds.

    Chrono Data:

    5.3 CFE Pistol 1.125''

    1.) 1096
    2.) 1089
    3.) 1095
    4.) 1091
    5.) 1090

    5.5 CFE Pistol 1.125''

    1.) 1079
    2.) 1139
    3.) 1124
    4.) 1128
    5.) 1160

    5.7 CFE Pistol 1.125''

    1.) 1167
    2.) 1170
    3.) 1150
    4.) 1161
    5.) 1186

    Since I had the slight hiccup with the Glock 17, I decided I should try some of these in the CZ 75B....yes, I should have used this gun's barrel for a plunk test, since these are know for there short leads but I was feeling lazy....and that's is where the saying 'why is there never time to do it right, but always time to do it twice' comes from.

    The first round chambered and fired....the second round required a lot of pulling on the slide to get the cartridge that would not fit into the chamber back out...back to the bench.

    This time, I used the CZs barrel as a cartridge gauge and ended up with a COAL of 1.065''. A big difference, but they chambered perfectly in the CZ. Because of the large reduction in OAL, I backed way off on the powder and started over. Seated to this depth, there is .210'' of bullet seated into the case, which is perfectly fine for a 9mm Luger. I consider anything up to .300'' of bearing surface in the case safe for 9mm, but I work up accordingly, just as I did here.

    Hodgdon lists a starting charge of 5.3 grains of CFE Pistol for a 115JHP, but this is seated much longer, and since I did not have the same bullet for comparison, backed off .5 grs. and started at 4.8 grains for the new shorter rounds, and also loaded a few 5.0 grains. These were fired from the CZ 75B.

    Chrono Data:

    4.8 CFE Pistol 1.065''

    1.) 1086
    2.) 1062
    3.) 1073
    4.) 1049
    5.) 1070

    5.0 CFE Pistol 1.065''

    1.) 1093
    2.) 1128
    3.) 1144
    4.) 1137
    5.) 1138

    Both of these loads cycled the CZ just fine, and made a nice pile of brass close to where I was. The 5.0 grain load was my favorite, and the most accurate of the bunch. Jake at RMR says these need to be loaded to 1100 fps of faster for reliable expansion, and I would say the 5.0 load accomplishes this with good accuracy as far as I'm concerned, so I don't really see the need to try for more velocity, although I may mess with some different powders. I'll add more info as I get more time to mess with this bullet.

    All in all, this is a great bullet, and I hope this gives some people enough info to give it a try...Maybe I'll pick up some of the 124s for 9mm and .357 Sig biggrin.gif

    Also posed on thefiringline
    Lee Q. Loader, Dudedog and Stew0576 like this.
  2. Dudedog
    • Contributing Member

    Dudedog Contributing Member

    Oct 19, 2013
    Southern CA
    Haven't tried the 115s but I really like the 124 MPRS, RMR bullets are good stuff.
    RMH, Lee Q. Loader and Walkalong like this.
  3. Harriw

    Harriw Member

    Nov 8, 2018
    I realize it's generally poor form to necro-post in old threads like this, but here I am 5 months later working up a load for this exact same bullet (RMR 115Gr. MPR or Multi-Purpose Round, which is really a JHP). As luck would have it, my most restrictive barrel is from a CZ 85B, similar to the OP as well. Consequently, I thought it would be more useful for those searching in the future if I kept this in the same thread. Please let me know and I'll start a new thread if that's preferred. But I'm quite new to this whole reloading thing, and was hoping to get some "second opinions" from those more experienced than I.

    Anyway as I said, I'd like to work up a load for this same bullet. My own plunk testing indicates that 1.065" just BARELY does NOT plunk in my barrel (it's so close that the grooves will only catch the bullet head if dropped in at certain orientations). 1.060" plunks safely for me. But to give myself a bit of breathing room in the chamber I'd like to go with a target COAL of 1.055" (this is largely because I load on a Hornady LNL AP, where the COAL tends to be higher when loading in progressive mode after doing the initial setup in single-stage mode).

    The only similar bullet I have on hand to measure for comparison is a Hornady 115 Gr XTP (also a JHP). It has a drastically different o-give profile, but it's the closest I have. I carefully measured 8 of each bullet and averaged the results:

    Hornady avg. length = 0.5453"
    RMR avg. length = 0.5116"​

    Turns out the RMR bullet is significantly shorter than the Hornady bullet. In hindsight, this should have been expected... A thicker nose profile means more weight up front. So if the overall bullet weight is going to be the same, there has to be less material in back, making the bullet shorter overall.

    Previously, I worked up a load using the Hornady XTP bullet with a COAL of 1.09" based on my plunk testing. This matches the specified COAL from my Lyman manual (#50), while Hornady (#10) calls for a COAL of 1.075". While the COAL I'm looking at for this bullet now is significantly shorter than any of these, the shorter bullet length more than makes up for this:

    XTP Load: COAL of 1.09" - Bullet Length of .5453" = remaining case depth of 0.5447"
    XTP Load: COAL of 1.075" - Bullet Length of .5453" = remaining case depth of 0.5297"

    RMR Load: COAL of 1.055" - Bullet Length of .5116" = remaining case depth of 0.5434"
    RMR Load: COAL of 1.060" - Bullet Length of.5116" = remaining case depth of 0.5484"​

    So with the minor exception of the 1.09" XTP to 1.055" RMR comparison (where remaining case depth does decrease by a whole 0.0013"... which incidentally is smaller than the standard deviation for the 8 case lengths I measured for this study), The remaining case volume for powder will generally be the same or greater than it was with my previous XTP loads, or the XTP loads specified in both manuals. So I shouldn't see any increase in pressure due to my short COAL with this bullet.

    All that to say... Please feel free to correct me, but I *think* I'm perfectly safe using the Lyman and Hornady load data for the Hornady 115 Gr XTP directly for the RMR bullet, even at a COAL as short as 1.055" (in fact, the numbers indicate you *could* go even shorter if necessary). I will of course start with the suggested starting loads and work my way up slowly and carefully. I'm planning to use W231 and Winchester primers in FC brass. Given that I've already worked up this combination with the XTP bullet, I think I may start this work-up at the 4.1Gr suggested starting load from the Hornady manual instead the 3.5 Gr. suggested by Lyman. I'm thinking I'll try 4.1gr, 4.4gr, and 4.7gr and see how it goes.

    Has anyone tried W231 with this bullet yet? If so I'd be curious what your experience was. And I'd greatly appreciate any feedback on my thought process and/or conclusions as I'm still quite new to this, and would like to keep all my digits intact if possible :) Thanks very much!

    -Bill H
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