9mm, RMR 124gr truncated-cone MatchWinners, 1.10" OAL . . . and Accurate #7

[MEHavey]

Fairly specific, since online (and even paper manual) data is all over the place.

`Chose the 124 RMR-Matchwinners due to reputation (so far proven out)
`Chose relatively slow Acc#7 on multiple recommendations
`Shooting out of both Walther 99-AS (4") and Full Size S&W M&P 2.0 (4.75") @ 1.10" OAL
(barrels are measured traditionally cartridge-base-to-muzzle)

No "official" reloading data on the RMR bullets themselves that I can find

"Recommended" 7.5gr of ACC#7 giving "surprising" LABRADAR velocities (1,190 / 1,210 fps respectively)
QuickLoad (adjusted burn rate/velocity-matching) indicates 30,000 psi

QUESTION: Is anyone else shooting this bullet/powder combination (at whatever powder weight) ?



(and no... I haven't loaded a zillion of them yet)...

 

[GeoDudeFlorida]

Fairly specific, since online (and even paper manual) data is all over the place.

`Chose the 124 RMR-Matchwinners due to reputation (so far proven out)
`Chose relatively slow Acc#7 on multiple recommendations
`Shooting out of both Walther 99-AS (4") and Full Size S&W M&P 2.0 (4.75") @ 1.10" OAL
(barrels are measured traditionally cartridge-base-to-muzzle)

No "official" reloading data on the RMR bullets themselves that I can find

"Recommended" 7.5gr of ACC#7 giving "surprising" LABRADAR velocities (1,190 / 1,210 fps respectively)
QuickLoad (adjusted burn rate/velocity-matching) indicates 30,000 psi

QUESTION: Is anyone else shooting this bullet/powder combination (at whatever powder weight) ?



(and no... I haven't loaded a zillion of them yet)...

Powder - Yes.
Different bullets - REM 124gr GS and WIN 124gr JHP. Both are happier at 7.0gr. 7.5gr is knocking on maximum with both of those bullets and tends to sling them a little wild.
My old Star M30 loved the combo of No.7 and the 125gr ACME “Green”. I don’t have the data for that one on my phone though.

 

[Howa 9700]

Not the RMR TCFP match winners, but have loaded #7 and 124 gr RMR nukes (JHP). Current version. No load data for that either, so here is the logic of what I did.

When evaluating load data, the iron clad rule is never seat deeper / go lower than published COL. The load was developed by placing X amount of powder inside the volume defined by the case itself and the bullet's base. Seat deeper and you decrease the volume the expanding gas has to work with. Pressures go up. Seating further out increases the volume, pressures drop. Compared to where the base starts out, where the nose ends up is largely irrelevant, yet that is what gets measured. Which in my mind has it backward. So I have adopted the practice of measuring off the base of the seated bullet.

To determine depth of seated base, I start with measuring the bullet itself. In case of the RMR 124 nuke, if memory serves, that is 0.560". Standard 9mm case is 0.740", so as an example......if case length with seated bullet is 1.060...........and I subtract the case length (base to mouth), then exposed nose of bullet is 0.320". Then 0.560 - 0.320 = 0.24". So the base of the bullet is buried inside the case 0.24". I have also done that with every bullet I have.......which by now is about 6 of them. The point?

There is no published load data for the RMR nuke, but I have 3 highly similar......not identical.....but high similar 124 gr JHP bullets. Ones from Sierra, Nosler and Speer. There is an abundance of load data for those, as well as others like the Hornady XTP......which has a different nose profile, but one can still measure seating depth. As long as the base of my nuke is not seated deeper than the base of these known bullets, the load data ought to be usable for the nuke. Again, where the nose ends up being largely irrelevant.

So.....following that logic.......here is where I wound up. I found 7.2 grains of #7 under the nuke.....which is seated to COL of 1.060 gives me an nice, easy shooting load that on my chrony is running around 1075 to 1100 fps. If I bump that to 7.4 or 7.6 grains, velocity revs up to around 1150 to 1200 fps, but things start to get a little angry up there, so I settled on 7.2. You wouldn't want to be standing in front of it when it goes off.

 

[Hooda Thunkit]

My old Star M30 loved the combo of No.7 and the 125gr ACME “Green”. I don’t have the data for that one on my phone though.

I have a Star 30M myself. Bought it new, back in the 80s. It's a big, robust, accurate pistol that eats full power loads easily.

 

[lordpaxman]

I haven’t developed loads for that combination but I’ve found the accurate load data for #2 and #5 to be ”non-conservative”. Meaning I usually velocities close to what they publish.

When evaluating load data, the iron clad rule is never seat deeper / go lower than published COL.

I have a similar methodology, pick a comparable technology bullet and try to get seating depth the same. But there are times when you might have to load shorter than the published COL so you need to make an adjustment to the powder charge to account for that. There’s no formula for “how much”, and it’s somewhat powder dependent. I use my historical load data to make adjustments if I need to.