6.5 CM High SD

[Andielouroo]

I'm a newb to loading 6.5 and running to some trouble with my first round of load development in that my velocities are all over the place. Shot a quick OCW yesterday and a ladder at 300 yards today and just for fun loaded 5 rounds to shoot for a group. The results are attached.

The gun is a 16.5" 6.5 with a SiCo Omega on it. I don't expect super high velocities out of the short barrel, and you'll see that the OCW loads started really low and worked into mid range loads. The ladder test today went just above book max. Next I'll load 5 nearer the max load to see if that makes a difference, but otherwise, I'm at a bit of a loss. My SD when loading .308 match loads is generally 3-5, so I'm fairly confident in my technique, which makes this all the more confusing. Maybe I need to try a diff primer? Go LR Magnum primer? Any help and suggestions are appreciated.

16.5" 6.5 CM
IMR 4451
CCI LR Primer
130 Berger Hybrid
Prime Brass
Loaded to .02 off the rifling
Using Magnetospeed v3

 

[Fursniper]

"If your weighing your powder to the 0.1 grain and you're SD'S are much above 10fps, try a different primer"

"The importance of primers can not be overstated"

"Primers matter a great deal!"

Bryan Litz, "Modern Advancements in LR Shooting"

 

[supercorndogs]

You need to get your distance to the lands and run a length test. This is place you can tune your SD.

 

[Supersubes]

Id consider moving to a faster powder, like varget or 4166.

 

[Deadshot2]

I've found two things that affect SD/ES the most. Number one is Case Prep. Case neck thicknesses need to be uniform both within each case and in the batch. If you have case necks that vary in thickness by .001" or so around the neck and from case to case in the batch, bullet release will be uneven. Annealing also helps insure that each bullet will take the same amount of pressure to get it started down the barrel.

Second, the percentage of case fill. I've found that each and every powder has a sweet spot for case fill. Some do very well around 90% case fill and others shine when at or near 100%.

A good example of both was my experience yesterday at the range. I was working up a load using cases I had meticulously prepared. First the necks were annealed. Then the cases were neck sized without the expander ball installed. Necks were expanded using a Sinclair Mandrel Expander Die which gave me a perfect .002" of neck tension.

When loading each and every bullet slipped into the case with even pressure on the handle (I seat bullets using a short handle on my single stage press so I get a better "feel" for seating pressure.

As I increased my charge weights the speed's increased proportionally but the SD's went through a cycle. Starting at an SD of 5 for my lowest load it increased to 12 then went down. SD went as low as 1.5 and that group was as close to a "bug-hole" as the afternoon wind would allow. The powder was RL-16 with a 147 gr Bullet and case fill was about 99% of useable volume.

When there is an ideal amount of powder in the case for that "burn rate" good things happen. Outside of that parameter there is no "harmony".

A famous Benchrest shooter considered Case Prep to be paramount. The rest was just matching powder to case volume and using the right bullet that utilized that amount of powder without excessive pressure.