OAL length- Seating depth and RMR 124 JHP

Ghost In The Fog · May 18, 2017

Good afternoon everyone- I once again need your expert advise/opinions
Here's my quandary:

Old style 9MM .355 RMR 124 JHP
Bullet length: .579
OAL 1.090

New 9mm .355 RMR In House 124 JHP
Bullet length: .558
OAL ??????

Let me first say I will load both 1.090 and 1.069 to run across the chrono to see the actual difference. But I am looking for more of a definitive answer in principles of reloading.

So- .021 difference in length of the old to new bullets.
I know loading the new in house bullets at 1.090 will decrease pressure and more than likely velocity somewhat along with seating depth decreasing.
I need to be over 1100 FPS according to Jake and his tests in ballistic gel which I am getting with both BE-86 and AutoComp using S&B primers and mixed brass.
I understand it is splitting hairs somewhat but I am wondering what you all do as a general practice.

Do I shorten the OAL .021 and keep same pressure?
I also know and understand OAL is based on what feeds in all of my guns, minimum OAL, plunk test, push test etc-
I have a really difficult time expressing with words what my thoughts really are. I know what I want to say, but it often comes out wrong but makes perfect sense to me until I get feed back- and then it's...
DOH! Why didn't I just say it that way?!?!

I guess what I really want to know is shouldn't there be a seating depth MAX on any given load/bullet weight? Then work with OAL etc? To me, it would make sense to know not to seat deeper than "X" and then adjust to your guns ability to feed and then accuracy. It seems to me that that then would also keep pressure to a predetermined amount not to be exceeded.
Perhaps I am chasing an absolute that just doesn't exist and I just don't get it.

Thanks for reading this and any advise you might have to make me understand.

LiveLife · May 18, 2017

RMR 0.579" length 124 gr JHP (Left) and RMR 0.558" length 124 gr JHP (Right)

With the 0.579" length RMR 124 gr JHP (Left in the picture), my KKM/Lone Wolf/carbine barrels will allow 1.125"+ to fully chamber but since you used 1.090" for your barrel, I brought out my newest Lone Wolf barrel with almost no leade. For this barrel, 1.125" will hit the rifling and 1.090" allowed to fully chamber with a "plonk" and spin without hitting the start of rifling.

With the 0.558" length RMR 124 gr JHP with shorter/rounder nose profile/ogive (Right in the picture), I needed to decrease the OAL to 1.040" to fully chamber with a "plonk" and spin without hitting the start of rifling for the new Lone Wolf barrel with almost no leade (1.125" chambered in older Lone Wolf barrels and 1.120" chambered in KKM barrel).

As to powder charge, when I use shorter OAL than published, I usually drop my start/max charge by .2-.3 gr.

Ghost In The Fog said:
shouldn't there be a seating depth MAX on any given load/bullet weight? Then work with OAL etc?

Even for same bullet weight, different bullets can have varying nose profile/ogive, bullet length (as you found out) and sized diameter so we must determine the "maximum OAL/COL" that will fully chamber without hitting the rifling and then "working OAL" that will reliably feed and chamber from the magazine.

I usually determine the max/working OAL first then conduct full powder work up to determine the most accurate charge. Then to obtain greater accuracy (to determine if increased neck tension will overshadow less gas leakage from longer OAL), I will incrementally decrease the OAL by .005" to where I won't compress the powder charge. That's how I verified 9mm 115 gr FMJ with 4.8 gr of W231/HP-38 produced greater accuracy with shorter 1.130" OAL than 1.160".

If I am loading for multiple pistols/barrels, I will use the OAL and powder charge that will work for all of them.

Ghost In The Fog · May 19, 2017

First, let me thank you for your response. Second, your photography skills are amazing! Your picture really emphasize the difference in the two bullets. I could see it with my eyes, but your pictures, wow. So much more obvious.
I have read this and re-read it since late last night trying to understand.
I have not loaded any of the new bullets yet, but I have made dummy rounds for the push and plunk. 1.090, the same as the old style works in all of my guns.
So, with that being said, and this is where it all comes off the rails for me, if I keep the 1.090 OAL that means using the standard 9MM case length of .744 my seating depth is .212 as compared to .233 of the old style bullets.
I would have to decrease OAL of the new bullets to 1.069 to have the same seating depth/pressure.
I asked Jake a while ago what the recommended OAL length was for the old style and he said to use the same info for the XTP bullets which is 1.060.

Shouldn't seating depth also be in relation to case fill?
You mentioned compressed powder charge. How do I know when I get there or close to that? This is not something I have given much thought to or known about.
Alliants website lists BE-86 max at 5.9 and I am loading at 5.6 and getting 1154 FPS so I am safely under max charge but BE-86 fills the case slightly more than 5.3 grains of AutoComp for comparable speeds. (Hodgdon says 5.4 max) Which means 5.3 of AutoComp gives more room in the case at the same OAL and less likely to compress the powder.

I also understand that if longer OAL works, why shorten it? This is the whole thing, I don't necessarily want to shorten it, I just want to understand. Grrr! I see things in my head of how they should be and when I can't make them match it drives me absolutely bonkers!

Perhaps it isn't maximum seating depth for a given cartridge I should be chasing, it should be not to compress the powder in the case?????

Anyway, I want to thank you for taking the time to give me such a detailed reply. I appreciate it very much.

dgod · May 19, 2017

Very Well Done, excellent presentation.

LiveLife · May 19, 2017

Thank you.

Ghost In The Fog said:
Shouldn't seating depth also be in relation to case fill?

As Walkalong illustrated in his thread, I always first determine the max OAL/COL then working OAL before conducting powder work up - https://www.thehighroad.org/index.p...rel-find-a-max-o-a-l-with-your-bullet.506678/

By starting with the longest working OAL, once I determine the accuracy node, I can incrementally decrease the OAL by .005" (thus increase neck tension) to see if shot group size decreases until point of compressing powder charge.

Since different barrels have varying leade/freebore lengths, if you start your load development with an OAL shorter than SAAMI max, you may miss out on accurate loads that use longer than SAAMI max length. Example of this is SAAMI max of 1.135" for 40S&W 180 gr bullets. With most 180 gr TCFP bullets, my barrels produce greater accuracy with longer 1.142"-1.143" working OAL. With RMR Hardcore Match RNFP bullet, even longer 1.155" working OAL produced greater accuracy than 1.135" - https://www.thehighroad.org/index.p...ick-plated-bullets.761471/page-4#post-9645513

Ghost In The Fog said:
You mentioned compressed powder charge. How do I know when I get there or close to that?

I determine max case fill by subtracting bullet length from working OAL.

So for bullet length of 0.558":

1.090" - 0.558" = 0.532"

Then measure some resized case lengths and subtract 0.532" from average case length (let's use SAAMI max of 0.754" for the calculation)

0.754" - 0.532" = 0.222"

Then measure 0.222" down from case mouth using the end of calipers and mark the inside of case (I know, the picture shows me measuring primer pocket depth)

Then fill the case with powder to mark and weigh.

- If the powder charge weight is less than max powder charge you are going to use, you will compress the powder charge.

- If the powder charge weight is more than max powder charge, you won't compress the powder charge.

Ghost In The Fog · May 19, 2017

I have had the rare luxury of having several free hours to read at work today. I have to say I have learned more in depth details from you and @Walkalong than I have from reading all of my reloading manuals combined. Although I have read much of your content before, I have never read it with the purpose of looking for the exact answers I have been searching for, if that makes sense.

Have you considered writing a reloading manual of your own? Seriously. Or have you and the joke is on me? I would definitely buy it.

I am pretty dense and it took a while but the light is on- dim but on

I'm sure I can figure it out, but how do you mark the inside of a case accurately?

I have one more question if you don't mind.... What is the result if I find that I am compressing the powder charge? Even if slightly?
According to my math a case length of .754 would only have to be 70.6% full to have the bullet seated at .222 to touch the powder. Now I am freaked out- I have 950 of the old style loaded. They work perfect but I also have 1300 target loads using various powders and formulas, none of them checked for compressed powder charges.

I can't express to you my gratitude for your help. I am beginning to really understand what it is I am doing and why I am doing it instead of following instructions.
Sincerely, thank you.

Zendude · May 19, 2017

Ghost In The Fog said:
I have had the rare luxury of having several free hours to read at work today. I have to say I have learned more in depth details from you and @Walkalong than I have from reading all of my reloading manuals combined. Although I have read much of your content before, I have never read it with the purpose of looking for the exact answers I have been searching for, if that makes sense.

Have you considered writing a reloading manual of your own? Seriously. Or have you and the joke is on me? I would definitely buy it.

I am pretty dense and it took a while but the light is on- dim but on
I'm sure I can figure it out, but how do you mark the inside of a case accurately?

I have one more question if you don't mind.... What is the result if I find that I am compressing the powder charge? Even if slightly?
According to my math a case length of .754 would only have to be 70.6% full to have the bullet seated at .222 to touch the powder. Now I am freaked out- I have 950 of the old style loaded. They work perfect but I also have 1300 target loads using various powders and formulas, none of them checked for compressed powder charges.

I can't express to you my gratitude for your help. I am beginning to really understand what it is I am doing and why I am doing it instead of following instructions.
Sincerely, thank you.

You can use published load data to check for a compressed charge if you know the length of the bullet in the published load data. Since compressed charges are usually designated as such in published load data, you can assume that the max powder charge in load data is not compressed if not designated as such. So then, knowing the length of the bullet in the load data, you can compare the seating depth with the seating depth in your handloads. If your seating depth is not deeper than the one in the load data and you are under the max charge in the load data, then you can assume you do not have a compressed load.

To all:
Does this sound correct?

LiveLife · May 20, 2017

Ghost In The Fog said:
Have you considered writing a reloading manual of your own? Seriously. Or have you and the joke is on me? I would definitely buy it.

Thank you for the compliment.

I am flattered by your comment as there are so many more on THR who are vastly more knowledgeable than me. If I do anything, it will be on THR. I have been capturing some of my posts into different categories in Q&A format in the Advanced Reloading Concepts and Discussions thread but I haven't had a chance to sort them with index page links as I intended on the OP. Perhaps after my retirement in 2-3 years, I will sort them by topic and do the index page with links - https://www.thehighroad.org/index.p...ed-reloading-concepts-and-discussions.778197/

BTW, here's one for rifle - https://www.thehighroad.org/index.p...ed-reloading-concepts-and-discussions.778221/

Ghost In The Fog said:
I'm sure I can figure it out, but how do you mark the inside of a case accurately?

I usually mark with the tip of the calipers (Caliper metal should be harder than brass) but you can use pencil, marker, etc.

Ghost In The Fog said:
What is the result if I find that I am compressing the powder charge? Even if slightly?

Depends on the powder and charge. Larger flake powders like Unique can be compressed slightly without significantly increasing chamber pressure but more dense powders, especially faster burning, could significantly raise chamber pressure. One example is WST for 9mm. While I post 9mm loads that do not compress the powder charge, match power factor meeting loads are compressed loads and pressures spike at the top. I think for this reason, Hodgdon does not publish 9mm load data for WST even though it is a popular powder with match shooters.

Ghost In The Fog said:
I can't express to you my gratitude for your help. I am beginning to really understand what it is I am doing and why I am doing it instead of following instructions.
Sincerely, thank you.

You are very welcome. I am glad to have helped.

Ghost In The Fog · May 22, 2017

Update time-
I'll keep this short.
After marking the case and measuring distance to powder I made an excel spreadsheet to keep track of the math and results.

Loading BE-86 and RMR 124 JHP what I found to be is:

Loading at 1.090 OAL
Case .747 (Lee resizing is .747 85% of the time w/ .745-.749 variations)
Bullet length .558
Seated depth .215

Space between bullet and powder
5.6 grains .047
5.9 grains .019

Take that down to Jakes recommendations of loading (old style) same as XTP's of 1.060 (Not used)
5.6 grains .017
5.9 grains minus -.002

From my testing I have found that I do not have compressed powder at these load rates and I will be increasing my OAL to 1.100 for added safety.
All of my guns shoot and feed at 1.100 and I have had very accurate loads at these lengths but will rework to find the sweet spot.

LiveLife · May 22, 2017

Great!

Thanks for the update.

OAL length- Seating depth and RMR 124 JHP

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