Powder Burn Rates and bullet accuracy

[Veduci]

Can anyone please explain why I get different results among powders with varying burn rates? For example, my Savage FCV (204 Ruger) shoots great groups with either Benchmark (fast burn) or Varget (slow burn) but poor groups with either H4895 (fast burn) or CFE 223 (slow burn).

[stomp442]

In my experience burn rate has a lot to do with great loads. Although a you are trying similar burn rate powders there could be just enough difference preventing you from getting to the sweet spot. Take my 308 for example. I had read that Varget was the go to powder and I tried working up loads from start loads all the way to flattened primers and sticky bolt lift and it just wouldn't come together for me. Switched to the old faithful IMR 4064 and the rifle loves it half inch or better groups. Very small burn rate difference between the two but vastly different results on paper.

[missed]

I have run into the same thing. I have come to the conclusion that some rifles just have that sweet spot with the certain recipe. I have noticed with Varget and cfe 223 I had to slow the cfe load down and find that sweet spot with tenth grain where the Varget just didn't seem to matter. I finally got the cfe to shoot like the Varget it was just a lot more work.

[Veduci]

Missed, I also note that small changes in grains really matters. With Benchmark I get fantastic results in the 26.4 to 26.7 range, 1.5 centimeter groups. Not much room for loading error. Once i go above 26.7 to 27.0, then the group expands to around 8 centimeters. Going the other way, less powder, I hit unacceptable (2.5 centimeters) at 25.8 grains. Thus there is a narrow range of only 0.6 grains (26.1 - 26.7) that really groups. I guess that would be the sweet spot to which you refer.

[eddiesindian]

Can anyone please explain why I get different results among powders with varying burn rates? For example, my Savage FCV (204 Ruger) shoots great groups with either Benchmark (fast burn) or Varget (slow burn) but poor groups with either H4895 (fast burn) or CFE 223 (slow burn).

if that isnt the mother of all questions then I dont know what it is...lolo
At times i wish I was that madd chemist that could figure out the powder,s burn characteristics and get down to the natts ass of your question.
been asking myself that question for way too many yrs....you can go crazy being experimental with the after effect of putting serious dents in your wallet.
I love varget but Id be a real dumb ass to say its my "go to" powder... Ive got too many rifles to load for and they all have different appetites. Ive been able to find there sweet spots on all of them but theres one that to this day still eluds me....
If you find out the answer to the question?.........please lemme know..olololol

[82boy]

Can anyone please explain why I get different results among powders with varying burn rates? For example, my Savage FCV (204 Ruger) shoots great groups with either Benchmark (fast burn) or Varget (slow burn) but poor groups with either H4895 (fast burn) or CFE 223 (slow burn).

Because the rifle is out of tune, there is more than powder charges when dealing with powder changes. different powders may/will need different seating depth adjustments. You may also find that some powders preform better with different neck tensions. For example, in my 6 PPC N133 prefers heavy neck tension, and 8208 prefers light neck tension. If I try to use the heavy neck tension on the 8208 it will not shoot, but with light neck tension it will shoot equally well with n133.

Also powder will behave differently responding to the environment. For example, you may find one powder preforms better than another when it is sunny and hot and vise a versa, the other powder may out shoot the first powder when it is cold and rainy. Last thing to work with is primers, some primers brands work better than others in certain cases, it may be that you don't have the optimal primer in the case, and due to the changes in burn rate you may be on the verge of cold fire. For example I have shot a 6 dasher it would shoot great at 200 yards, with either a rem 7 1/2 primer or a 450 cci. Go out to 600 yards and the rounds loaded with a rem 7 1/2 would have 8 inches of vertical, where the cci 450 would shoot a group in the low 2 inch area.

Last off re-check your burn rate charts because h4895 is just below Varget and CFE 223 is right in the area of BLC2 and h380 which are much slower than Varget, and no were close to benchmark. To add benchmark is much hotter than Varget or 4895.
http://www.hodgdon.com/burn-rate.html