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Discussion Starter · #1 ·
I'm seeing some strange velocities reloading 120 MKZ with A2200 powder. for example, a three shot string @27.4 grains COAL 2.295" once fired Hornady brass and Federal Match AR primers gives me:

1. 2631 FPS
2. 2563 FPS
3. 2506 FPS

The group was the best so far at 1.16". The first shot showed a swipe as well. My group size wasn't as good at 27.8, but the standard deviation was much better. Also, the velocities didn't change almost at all:

1. 2530 FPS
2. 2499 FPS
3. 2553 FPS

16" ARP barrel, cases sized to 1.680 All Hornady, some different headstamps (some say Rem SPC others say SPC). measured on a Lyman digital scale. Slight inner bevel, outer deburr, I put a slight crimp on them. I re-read and it's been said not to crimp. Maybe thats it?

Are people getting this swing in velocities? Also, are they getting a velocity node between 27.4-27.8? My group at 27.6 grains was garbage.

Thoughts?
 

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You are going to have to start over. Check the link above. You are using two different brass manufactures. Rem SPC is Hornady. The other is made for Hornady by S&B and has significantly more case volume which is why you have significant velocity deviations and poor groups. Separate your brass to match head stamps. Do not use a load developed in the SPC (S&B) brass in the Hornady brass - you will be way over-pressure.

If you are using a dedicated Lee Collet crimp die, then you are good. If the crimp feature integral to the bullet seating die then do not crimp - it will eventually cause you problems that are hard to diagnosis.
 

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I'm seeing some strange velocities reloading 120 MKZ with A2200 powder. for example, a three shot string @27.4 grains COAL 2.295" once fired Hornady brass and Federal Match AR primers gives me:

1. 2631 FPS
2. 2563 FPS
3. 2506 FPS

The group was the best so far at 1.16". The first shot showed a swipe as well. My group size wasn't as good at 27.8, but the standard deviation was much better. Also, the velocities didn't change almost at all:

1. 2530 FPS
2. 2499 FPS
3. 2553 FPS

16" ARP barrel, cases sized to 1.680 All Hornady, some different headstamps (some say Rem SPC others say SPC). measured on a Lyman digital scale. Slight inner bevel, outer deburr, I put a slight crimp on them. I re-read and it's been said not to crimp. Maybe thats it?

Are people getting this swing in velocities? Also, are they getting a velocity node between 27.4-27.8? My group at 27.6 grains was garbage.

Thoughts?
Ive got to look what I was getting with the 120 Cavity back and AA2200. I think it was around 2500 fps from my bison barrel at 27.5 grains with a COAL of 2.285. Didn't do much load development with it as I was just checking to see what I got.
 

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Discussion Starter · #4 · (Edited)

You are going to have to start over. Check the link above. You are using two different brass manufactures. Rem SPC is Hornady. The other is made for Hornady by S&B and has significantly more case volume which is why you have significant velocity deviations and poor groups. Separate your brass to match head stamps. Do not use a load developed in the SPC (S&B) brass in the Hornady brass - you will be way over-pressure.

If you are using a dedicated Lee Collet crimp die, then you are good. If the crimp feature integral to the bullet seating die then do not crimp - it will eventually cause you problems that are hard to diagnosis.
Thank you. I just separated the cases. These were all from saved from factory ammo. All the Rem cases had swipes from the factory loadings. the S&B don't. I'm thinking I need once fired S&B for the future. I can save the Hornady stuff for another bullet or powder. Maybe 110 AB's. Also, I'm using Lyman MSR small base die sizer. It has a separate taper crimp, but I think I'll just skip it for now if its not doing anything good.
 

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Discussion Starter · #5 ·
Ive got to look what I was getting with the 120 Cavity back and AA2200. I think it was around 2500 fps from my bison barrel at 27.5 grains with a COAL of 2.285. Didn't do much load development with it as I was just checking to see what I got.
The 2500s make sense. I was concerned with the 2600's. Pressure signs evident. At first I thought it was bad/old primers, then I didn't know what to think.
 

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Ive got to look what I was getting with the 120 Cavity back and AA2200. I think it was around 2500 fps from my bison barrel at 27.5 grains with a COAL of 2.285. Didn't do much load development with it as I was just checking to see what I got.
Hello Nativeman
What are your group sizes for this load?And what's length barrel?
I just ordered a couple boxes of the 120 MKZ. Hoping I can work up a 1" group or better.
 

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Hello Nativeman
What are your group sizes for this load?And what's length barrel?
I just ordered a couple boxes of the 120 MKZ. Hoping I can work up a 1" group or better.
16" Bison barrel. Groups are under an inch, but this barrel is super accurate.
 
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