[Guinness66]

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?

 

[Xman]

6.8 Headstamps

I intend for this to be a bit of a catalog of the ages, if you will, with no real greater goal than showing what we've had and perhaps where we're headed. We know that companies like Hornady and SSA have made multiple changes over the years, and sometimes it gets confusing as to whether a...

www.68forums.com

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.

 

[Nativeman30]

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.

 

[Guinness66]

6.8 Headstamps

I intend for this to be a bit of a catalog of the ages, if you will, with no real greater goal than showing what we've had and perhaps where we're headed. We know that companies like Hornady and SSA have made multiple changes over the years, and sometimes it gets confusing as to whether a...

www.68forums.com

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.

 

[Guinness66]

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.

 

[flyingdog]

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.

 

[Nativeman30]

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.