Good morning folks, Does anybody happen to know the nominal length for Hornady's 124 Gr. and 147 Gr. FMJ RN bullets? I can't seem to find it online anywhere. I'm just starting to work up loads for some RMR 124 and 147 Gr FMJ bullets (just opened the bags and measured some sample bullets this morning), and would like to use Hornady load data as a starting point. They'll need to plunk in my CZ85, and with RMR's more "blunt" nose profiles this typically means I'll be using significantly shorter COAL than the published Hornady Data. Generally, the blunter nose profile also means a shorter bullet, so a shorter COAL actually produces similar remaining case volume for the powder charge so pressures don't spike. This is what I found when working up loads for their 115 Gr bullets, but I actually had the Hornady bullets on hand to measure for those. I don't have any of the Hornady in 124 or 147 Gr, but I'd like to know the Hornady bullet lengths so I can confirm for certain that I won't be reducing case volume. Thanks very much!
Fantastic - thanks for such a fast response! Next question... I'm averaging the following for the RMR FMJ bullets: 124 RMR FMJ: 0.585" (0.005" shorter than Hornady) 147 RMR FMJ: 0.666" (0.026 shorter than Hornady) Looks like the RMR 147's are quite a bit shorter so I'm probably fine there... But with the 124 Gr, Hornady specifies a COAL of 1.150", but I have to bring the RMR 124 Gr FMJ down to 1.130" to get it to plunk in my CZ. I want some additional cushion, so I'd like to load them at 1.120" COAL, or 0.030" under the listed Hornady data. Can some of you seasoned folks suggest how much to back off powder charges for that much reduction in case volume (basically the bullet will be sitting 0.025" deeper than published - COAL will be 0.030" shorter, but bullet is 0.005" shorter)? For reference, I'll be using FC cases, Winchester SP Primers, and probably BE86 or CFE powder (I'm very happy with the W231 so far with 115 Gr 9mm loads, but data is scarce for heavier bullets, and my online "research" suggests there's a good reason for that). Hornady (10th Ed) suggests the following ranges for these 2 powders at their listed COAL: BE86: 3.9 (900fps) 5.2 (1100fps) CFE: 4.2 (900 fps) 5.3 (1150fps) Is there any sort of "rule of thumb" for backing off powder charges for a given case volume reduction? Thanks very much!
I had some Xtreme 124 RNs laying about that didn't shoot as accurately for me as the my RMR bullets so I ran a little OAL test with them. 5" 9mm 1911, very mixed range brass, S+B SP, charges as thrown after setting measure 5.0gr is not close to MAX so as pressures get higher things will behave differently, but for what it's worth String: 4 Date: 4/23/2017 Time: 12:54:31 PM Grains: 124 Hi Vel: 1089 Low Vel: 1052 Ave Vel: 1076 Ext Spread: 37 Std Dev: 14 Xtreme 124 rN 5.0 BE86 OAl 1.11 Velocity Power Factor Ft/Lbs 1089 135.036 326.497 1076 133.424 318.748 1084 134.416 323.506 1052 130.448 304.688 this one skewed the #s a bit 1080 133.92 321.123 String: 3 Date: 4/23/2017 Time: 12:53:05 PM Grains: 124 Hi Vel: 1092 Low Vel: 1056 Ave Vel: 1072 Ext Spread: 36 Std Dev: 15 Xtreme 124RN 5.0 BE86 OAl 1.13 Velocity Power Factor Ft/Lbs 1058 131.192 308.173 1084 134.416 323.506 1056 130.944 307.009 1070 132.68 315.203 1092 135.408 328.298 String: 1 Date: 4/23/2017 Time: 12:50:35 PM Grains: 124 Hi Vel: 1065 Low Vel: 1038 Ave Vel: 1056 Ext Spread: 27 Std Dev: 11 Xtreme 124RN 5.0 BE86 OAl 1.155 Velocity Power Factor Ft/Lbs 1038 128.712 296.632 1064 131.936 311.678 1065 132.06 312.264 1062 131.688 310.508 1055 130.82 306.428 I would expect the MAX charge to be 1.-.2 less given the shorter OAL but I am just guessing. (this is 1/10th to 2/10ths decimal is hard to see, getting blind in my old age) Working up with a chrono would give you a good idea, but of course the chrono is not giving you pressure numbers just vels so you don't know. Flip side is if the vels are higher than the Hornady MAX then it is fairly safe to assume pressure is higher as well TNSTAAFL.
Thanks a ton Dudedog - that's perfect. Your drop from 1.155" to 1.130" is almost exactly what I'm proposing. I'm starting and ending 0.005" shorter than you were, but it's still about a 2.2% reduction in COAL/case volume. I know none of this is linear, but everyone seems to think powder/case volume to pressure/velocity is more of an exponential... which means treating it as linear in this situation should be more conservative. Meaning I could use the 2.2% drop in case volume and just drop my charges 2.2% as well. Based on your results that is indeed conservative, as you only saw an increase in velocity of about 1.5% for your case length reduction of 2.2%. Of course as you pointed out that's velocity, not pressure... On that note... the Hornady manual doesn't list pressures, but my Lyman does. Just for grins, I took the powder charge, velocity, and pressure figures from a 124 Gr JHP they have listed and calculated the percent change in velocity and pressure for a percent change in powder charge. Obviously this is relating everything to powder charge instead of COAL, but I thought it might help show the relationship between velocity and pressure. Turns out it's a bit of a mixed bag. For most of the powders listed in that particular table, pressure increases faster than velocity does (by a factor of 2, more or less). But there are one or two that increase at the same rate, and even one (Clays) for which pressure increased half as quickly as velocity. I should note that since this is based on powder charges, we're talking about changes in 20% here, not the 2% COAL changes this thread has dealt with up. Since none of this is linear, we can't directly apply the "2x rate of increase" we see with a 20% change to the 2% changes we're talking about. Having said that, I think I'll keep my conservative 2% charge reduction just to keep things safe. I think that's plenty of confirmation for me to proceed. I don't have a chrono yet, but I'm starting to think that might be a sound investment if I'm going to continue using un-listed bullets (and I'm a fan of RMR so far). Thanks again for all your help! -Bill H