Acme 9mm 135gr RN COL Caculation

[santacruzdave]

Got some new bullets. Acme 9mm 135 gr. RN. Without specific load info I thought I'd do some interpolations to calculate a starting COL (plunk test for my shortest leade barrel to follow) and a starting load. My concern is seating depth and the possible resulting over pressure from having the bullet seated too deeply int the case.

The published COL for ACME 145 gr RN bullets (1.10) works in all my 9mm barrels. I measured 10 145 gr bullets and have an average bullet length of .660. I also measured 10 of the new 135 gr RN bullets and have an average of .6136.

So I'm figuring that with a COL of 1.10 for the 145 gr bullet with a length of .660, and a bullet length of .6136 for the 135 gr bullets, calculating the 135 COL should be simple math. Subtracting the length of the shorter from the longer: .660 - .6136 = .046. And subtracting .046 from 1.10 should give me a starting place (1.10 -. 046 = 1.054).

Does this make sense? I don't know why. but 1.05 seems like too low a COL for a bullet length of .6136. Next to make up a dummy round or two and eyeballing resulting space left in the case. Once I'm comfortable with the COL, I can start to figure out some starting loads of Sport Pistol.

Thoughts?

 

[KASarich]

I have never loaded the Acme 135 gn. bullet, but I have loaded alot of Blue Bullets 135 Truncated Cone. 3.5 Grains of Sport Pistol, under a BB 135 TC, seated to 1.13 with a CCI500 was good for ~990 ft/sec out of a Glock 17 and a CZ75. Although I did have the occasional hiccup with the CZ, so I may play around with shortening these rounds a little, but recoil was mild and it was quite accurate...especially for any sort of action shooting.

As far as COAL goes, I follow a general rule of thumb when reloading the 9mm, and it is this: Never seat any bullet deeper than .300'' into the case. I don't remember where I read this so long ago, but it has never steered me wrong.

Following that logic, you say that your bullets are .6136, and I used the trim-to length of a 9mm case (.749) for the case measurement. If you subtract .300 from .6136, you end up with .3136. Add .749 for the case length, and you end up with a cartridge of 1.062'' OAL with .300 of the bullet seated into the case. Were I loading this ammo, and the 1.10'' OAL worked, and fed fine I would stick with it. A bullet that is closer to the rifling will experience less jump/wobble/etc... and should lead to better accuracy.

Always follow published load data...I believe Alliant has load data for the Acme bullets on their site.

 

[docv]

What source of published data are you using? I am loading Acme 145g with Winchester's Autocomp published COL of 1.150. Winchester lists 1.150 as the COL for Acme 135 on all powders.

 

[rfwobbly]

The barrel will tell you all you need to know about Max OAL, with 1.000" being the Min OAL.

Then you can split the difference between the loads for 124gn and 147gn to obtain the loads for 135gn. It's a very rough estimation, but by doing your incremental loads and reading the spent cases you can see where you are. Always begin at the Starting Load and work up in small increments.

 

[santacruzdave]

What source of published data are you using? I am loading Acme 145g with Winchester's Autocomp published COL of 1.150. Winchester lists 1.150 as the COL for Acme 135 on all powders.

I'm using Alliant Sport Pistol data from the Alliant website. Thanks for pointing out the Hodgdon data. I did not see that in my searching for published COL for Acme 135 gr RN. Makes things much more simple. With the short leade in my SP-01 and XD9 Tactical pistols, and the 135 bullet both, barrels plunk at 1.12. So it looks like I'll load at a COL of 1.1 and start with a fairly low powder charge. Say 3.1 or 3.2 gr of Sport Pistol, which is right around the starting powder charge for the ACME 145 gr bullet. Thanks to all for the input!

 

[Tilos]

Find a fired case that the bullet just slips into with some resistance.
With the bullet barely into the case push them into the barrel with the shortest throat. You'll feel the bullet hitting the rifling, continue to push until you feel the case hit the chamber shoulder.
Carefully remove the case/bullet assembly, pinch the case/bullet juncture between you thumb/index finger, and measure the OAL with a caliper.
That measurement is the max OAL for that bullet in that barrel.
No research of conflicting data/opinions or interpolation, just a direct measurement.
Do it a couple of times, if you like, to check for consistency.
just the way I do it,