6UM alternative

[Axlrod]

I've followed a few of your posts. Access to the right reamer certainly makes the process more complex than just click and buy. It's beginning to feel like I'm going to have to buy a reamer. You must be running a shorter barrel as well. I'd think your velocity would be higher on N570, though perhaps you're not stepping on it either. I'd be interested to your your charge weight vs where you hit pressure signs.

It's a 20" Bartlein with a Scythe-Ti. I corrected my earlier post, it's ave velo is 3292 w/ 69.5 gr. N570. Before I turned necks this load was prob. max. I can go a bit more on N570, and can get more velo out of R26 too. It shoots good here so i'm good with it. I will probably have UM get me a different reamer for my next one, but it doesn't take much time to turn necks. And you only do it once.

 

[RockCreekGuy]

Just to add some content to the thread I ran some QL #s. Berger publishes good information for bullet dimensions and I put the boat tail ogive at the neck shoulder junction to determine the cartridge length below. Max case capacity was adjusted to ADG's published data. Charge weight was manually run up to reach Maximum chamber pressure. Barrel length was set to 20" as everyone seems to be running these short but I added data above the screenshots for a 26" barrel as well. I realize running to max at a long length forces you into pressure during seating depth testing but it's apples to apples between a few cases at least.


N570 @ 26" runs 3,327fps 43fps/inch ave



Retumbo @ 26" runs 3,254fps 38fps/inch ave



N570 @ 26" runs 3,371fps 44.8fps/in ave



Retumbo @ 26" runs 3,304fps 39.6fps/in ave



N565 @ 26" runs 3,240fps 37fps/in ave N570 case is full long before pressure



IMR 7828 @ 26" runs 3,254fps 36.5fps/in ave

 

[RockCreekGuy]

It's a 20" Bartlein with a Scythe-Ti. I corrected my earlier post, it's ave velo is 3292 w/ 69.5 gr. N570. Before I turned necks this load was prob. max. I can go a bit more on N570, and can get more velo out of R26 too. It shoots good here so i'm good with it. I will probably have UM get me a different reamer for my next one, but it doesn't take much time to turn necks. And you only do it once.

My version of QL doesn't have the 7PRC, so I grabbed the 7RM SAAMI, adjusted case length to match the 7PRC, gave it a COAL to put the boat tail ogive at the shoulder neck junction, adjusted case capacity to ADG's published case volume and ran N570 up to pressure of 69.54gr on a 20" barrel. I'm still learning how to use it. I've long wanted to work with someone well acquainted with QL as there must be factors for powder burn rates that can be trued to make this match our measured velocities. I'm getting 3,146fps out of my 300 RUM on 94.4gr N570 and this is well over 130fps what QL says I should be getting. I've seen lots of posts out there of people running the 6prc with great success but it sure seems like the case fills faster than pressure can be reached with our popular magnum powders. I'm still tempted to want to go with a larger case.

This combo @ 26" runs 3,383fps 45fps/in ave

 

[GoatPackr]

@RockCreekGuy

With the modified case to resemble the 7 PRC what did QL say for 26" 7 twist with N570? That's what I run.
Curious how close it would be.
Oh 90HHT for the bullet if it list those.
I have run a few 108 ELM also.
How picky would groove caliber be with QL settings. A quick check and Ace list a .236 and .237 and I see you are at .243.

 

[RockCreekGuy]

@RockCreekGuy

With the modified case to resemble the 7 PRC what did QL say for 26" 7 twist with N570? That's what I run.
Curious how close it would be.
Oh 90HHT for the bullet if it list those.
I have run a few 108 ELM also.
How picky would groove caliber be with QL settings. A quick check and Ace list a .236 and .237 and I see you are at .243.

To my knowledge QL doesn't account for rifling twist. Otherwise that exact N570 data is in my post above... 3,383 fps @ 26".

 

[khuber84]

@RockCreekGuy

With the modified case to resemble the 7 PRC what did QL say for 26" 7 twist with N570? That's what I run.
Curious how close it would be.
Oh 90HHT for the bullet if it list those.
I have run a few 108 ELM also.
How picky would groove caliber be with QL settings. A quick check and Ace list a .236 and .237 and I see you are at .243.

243 is groove depth, 237 and 236 are bore diameters. Always go 237.

 

[Axlrod]

My version of QL doesn't have the 7PRC, so I grabbed the 7RM SAAMI, adjusted case length to match the 7PRC, gave it a COAL to put the boat tail ogive at the shoulder neck junction, adjusted case capacity to ADG's published case volume and ran N570 up to pressure of 69.54gr on a 20" barrel. I'm still learning how to use it. I've long wanted to work with someone well acquainted with QL as there must be factors for powder burn rates that can be trued to make this match our measured velocities. I'm getting 3,146fps out of my 300 RUM on 94.4gr N570 and this is well over 130fps what QL says I should be getting. I've seen lots of posts out there of people running the 6prc with great success but it sure seems like the case fills faster than pressure can be reached with our popular magnum powders. I'm still tempted to want to go with a larger case.

This combo @ 26" runs 3,383fps 45fps/in ave
View attachment 810666

When I was looking for starting loads for various powders in QL, I used the 6mm Arnold w/ 75 gr capacity and a 20" barrel. 69.5 Gr N570 is 3280 fps. So the data is real close.

 

[GoatPackr]

Otherwise that exact N570 data is in my post above... 3,383 fps @ 26".

Wow!! So about 45 fps more per inch of barrel added? That's a little better than average. I think people usually figure 25-35 fps per inch.

That's close to what I was getting with a 108 ELDm. Similar powder charge. Think I still had more room with those.
I've got 71 grn in under the 90HHT and it's full not compressed. I could definitely vibrate and get more in but it's shooting good at 3560 fps.

 

[GoatPackr]

The neck clearance was tight on fired Adg brass, so I turned the necks.

How did you figure necks were tight? What made you decide to turn?
Mine was probably made with the same reamer as yours and I'm running ADG

 

[Axlrod]

How did you figure necks were tight? What made you decide to turn?
Mine was probably made with the same reamer as yours and I'm running ADG

Reamer print shows .279" neck, my fired brass were .279". Couldn't fit a bullet in a fired case. Not enough neck clearance. Now my fired cases are .277"