what the heck ?

[canyonhunter]

Bought a Savage LRH in 7 REM MAG, added a 20 MOA base Night Force scope the load that was 64.0 gr H4831SC with 180 Berger 180 gr VLD yielded 5/8 inch group at 200 yards with vol of 2837, today went to the range with another batch of reloads and could barely get a 2 inch group and the velocity averaged 100 fps faster and the group was around 2 inches, what the heck ?

 

[Barrelnut]

Same brass on both trips?

 

[canyonhunter]

same brass but new can of powder and new box of primers . exact same load and seating depth.

 

[Barrelnut]

If the new can of powder is not from the same lot, that could be an issue. Lot to lot variations can be a little crazy sometimes. This spring I started a new lot of H4350 that was about 100 FPS slower than a lot I was using the year before. I believe lot to lot variations can be about 3% at times. With the 7RM load running 2837 FPS that 3% difference in the lots would be about 85 FPS.

Same with the primers. Though I haven't noticed as much difference in lots, a brand change can make a difference of 25-30 FPS sometimes.

Might just have to adjust the load now to get back to that good node.

 

[moombaskier]

same brass but new can of powder and new box of primers . exact same load and seating depth.

You always need to work up a new load with a different lot of powder. My buddy just had to lower his charge 3 full grains for his 300RUM using Retumbo to get the same velocity and node.

 

[canyonhunter]

Thank you I will of course back off the load , I only shot 3 rounds and the last round blew the primer out of the case . The gun went straight into the case as soon as I saw that.

 

[Corey Schwanz]

I would venture a guess that the powder burn changed in the new lot (assuming it is in fact a new lot of powder). The downside of changing anything with your load is you have to re-check and adjust as needed. Hopefully, if you bring the speed back down 100fps to where you were before, the groups will tighten back up for you.

 

[Edd]

I think the variation between lots or variation for whatever reason will be compounded when using H4831SC with a 180 gr bullet in a 7mm Rem Mag.

I think the burn rate of that powder is too fast.

I would start with Retumbo and if I couldn't get enough of it in the case I would switch to H1000.