What's the difference between 9mm (.355" bullets) and .357 Sig (.355" bullets)?

Mikej · Mar 27, 2025

I'm just finishing off the last of my several thousand Montana Gold 115gr JHP bullets. I want to stay with 115 grain hollow points. I'm figuring on getting RMR bullets. They make a point to list 9mm and .357 Sig bullets HPs of the same weight in "round nose".
These MG HP bullets I've been using all these years had a longer bearing surface than others, so I had to load them shorter OAL than recommended because of that longer bearing surface getting into the lands and not chambering.
I'm wondering if the bullets listed for .357sig would have the same issue?

these are what I'd like to get....

9mm 115 Gr. RMR JHP (MPR NUKE) | RMR Bullets

We have been wanting to make a really good self defense HP for a while now. In the past our biggest issue with the MPR (Multi Purpose Round) was that it required 1150-1200 fps to reliably expand. This was doable through full size firearms, but left the short barrel conceal carry guns without...

www.rmrbullets.com

lucusloc · Mar 27, 2025

To the extent that a bullet manufacturer will differentiate, .357 Sig bullets will be designed for optimum expansion at higher velocities. If you are trying to tune things for maximum effectiveness you may find it worthwhile to differentiate the bullets, but that seems to be pretty rare. Most people just make sure they are not pushing their 9mm HPs so fast they fragment and call it good (which can still be significantly faster than 9mm of the same weight). But I suppose if you are trying to wring every last bit of performance out of the cartridge you may need to find HPs that are tuned to slow their expansion so the higher velocities do not grenade them on impact. Of course this slower expansion may translate to unreliable expansion if you load them at standard 9mm velocities for that weight. If you are loading both and decide to go down this route it would probably be best to label things clearly so you do not wind up trying to troubleshoot odd terminal performance problems.

But you did not say which one you were loading for, 9mm or .357 Sig. Context clues could go either way. I only ever noticed an OAL issue with the heavy ".357 Sig" bullets in a 9mm. They were not listed as .357 Sig, just your normal .355" bullets, but obviously heavy enough that they would only really work effectively with .357 Sig. I tried setting them up for a standard 9mm carbine load, but there was not enough case capacity for what I was trying to do (big heavy bullet, slow burning powder, still fits in the mag and feeds reliably in a 9mm PCC). That was years ago though, before I got out of the PCC space (and then got back into it more recently, which makes me want to try to work up a load like that again).

I do not load much other than plinking ammo anymore, so I stock the same FMJs for both, unless I have a particularly heavy or light bullet I am playing with that is only practical for one or the other. I never felt it worth the time to optimize an HP loading for the .357 Sig since I run mostly factory defensive loads, and I have not had much opportunity or desire to hunt with .357 Sig.

aasbra · Mar 27, 2025

Hard to say for sure without having both side by side for comparison and taking some measurements. I have not loaded the MPR NUKE 115 grain from RMR. You may try contacting them, sharing your experience with the 115 grain Montana Gold JHPs, and see what they say as to how it may compare to their bullet as for the ogive shape and potential impact to the OAL you may need to adjust for?

I have quite a few different 9mms that I load for. I find that some of them have a shorter chamber leade than others. Those on the shorter end do sometimes require me to load the rounds shorter than the "suggested" OAL for a given bullet weight, or even specific bullet. When making ammo to be shared among all of my 9mms, I find the firearm with the shortest leade (in my case, my CZ PCR) and do a push test in a fired case whenever I start with a new (not previously loaded before) projectile. This helps me to establish the "maximum" OAL for that bullet that will work in my range of different 9mms. I record this in my reloading log, and reduce the starting powder charge accordingly if i have to shorten from the recommended OAL.

Koda · Mar 27, 2025

You might get lucky if you call them and ask for the length of the bearing surface. They may or may not want to give up their proprietary information as ogive shapes technically can be anything.

Mikej · Mar 28, 2025

aasbra said:
Hard to say for sure without having both side by side for comparison and taking some measurements. I have not loaded the MPR NUKE 115 grain from RMR. You may try contacting them, sharing your experience with the 115 grain Montana Gold JHPs, and see what they say as to how it may compare to their bullet as for the ogive shape and potential impact to the OAL you may need to adjust for?

I have quite a few different 9mms that I load for. I find that some of them have a shorter chamber leade than others. Those on the shorter end do sometimes require me to load the rounds shorter than the "suggested" OAL for a given bullet weight, or even specific bullet. When making ammo to be shared among all of my 9mms, I find the firearm with the shortest leade (in my case, my CZ PCR) and do a push test in a fired case whenever I start with a new (not previously loaded before) projectile. This helps me to establish the "maximum" OAL for that bullet that will work in my range of different 9mms. I record this in my reloading log, and reduce the starting powder charge accordingly if i have to shorten from the recommended OAL.

Thanks guys for the responses. I am not loading for terminal performance. I suppose I should check that out someday with water filled milk jugs or phone books. I feel that I tend to load on the lower end velocities. I just like HPs, because that's what I started with I guess? (silly) I would like to be loading all 9mm rounds closer to book recommended OAL and have them fit our several 9mm guns. The data I have seen is all around 1.120"ish for 155gr, I needed to load at 1.070"- for a Tanfoglio, 1.085" for a Kimber Pro Aegis and 1.095 for the other 9mm guns, powder weight adjusted, of course. Otherwise the bullets are into the lands, or even stopping chambering of the rounds. I guess it would be a good idea to call RMR and ask if the bearing surface on their 115gr round nose is the same as the 155gr nukes.