Velocity variation with my 6.5-284

[Greyfox]

I am curious if anyone has experienced this.
My load for my 6.5-284 is : 140gr VLD , 59gr Retumbo, Fed 215, Lapua brass, seating .075 off the lands, rifle 1:8 twist Cooper. Velocity 2965fps ,es 15 fps. I have reproduced this with different lots of Retumbo and with new or fired Lapua cases.

My buddy replicated the load except for a different lot of Retumbo and primer and used a Norma case. His weight of powder was checked and it is 59 gr on my scale. The Norma case capacity is .5 gr less than my Lapua. Testing in the same rifle, same chronograph, same day. The load is consistantly 60 FPS slower (2900) than my load with the same ES. Accuracy is the same. I haven't tried my load in the Norma case yet.

Could the variation be:
Different powder lot
Different primer lot
Different case
Combination of above

Any similar experiences?

 

[backwoods83]

My advice is to ditch the retumbo or the 215s or both! The coldest id use is H1000 at about 56grns with 210Ms or cci BR2s, I was getting 3021fps with 49.5grns Imr4350, norma case, br2 primer, 139 lapua scenar, 3.133" .008" in the lands 5shot sting from warm barrel had 2fps ES this was also a 30" barrel but the only diffence is you will lose some velocity, you may also want to move those bergers .050" closer to the lands.

 

[Boss Hoss]

This may not work for your gun but my go to load minus .3 to .7 grains in a couple of tubes is 215M, prepared Lapua brass, H4350 49.5gr and a 142 SMK. In almost every tube the ES is in single digits at 2935 to 2965 depending on the tube and the ambient.

 

[Greyfox]

Thanks for the info and response. I will try some of the recommendations. I was a hesitant to change my recipe since I get good consistancy with my personally loaded ammo. While my extreme spreads are a litttle high, my groups hold .25-.5 moa reliably out to 800+ yards. I was more interested in trying to understand if anyone had seen velocity changes(+60 fps) as I described by changing lots of powder. primers, or using different, brass, all other factors being equal.

 

[backwoods83]

Well to answer that question then yes, but for what I load I may get 5-10#s of powder from the same lot, and 2000 primers, you will notice it more with retumbo, but check the h20 capacity of the old and new cases as well as their weight. If you change one thing its usually a minor difference, if you change all four case, powder lot, primer, and bullet lot it can change drastically.

 

[Bart B]

I think you should compare each rifle's bore and groove diameters. It's easy to see 25 yo 50 fps difference between barrels using the same load. And there's been near 100 fps difference beween two folks shooting the sam rifle/ammo combination. It may not be the components used.