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barrel length vs. powder usage

 
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  #22  
Old 12-22-2013, 12:32 AM
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Re: barrel length vs. powder usage

Michael Eichele

I too have done the same thing, unburnt or partially burnt powder scattered on the ground or stuck into the (very close) target. Even in pistols. I think that is a very clear sign the powder burn rate is way slow. I cannot see how a load can be accurate with powder pouring out the barrel unused.

MontanaRifleman

Conventional wisdom says if RL17 @ 85% loading density is getting 3150fps and Retumbo @ 99% load density is only 3100fps, then RL17 is too fast and Retumbo is too slow. This assumes that RL17 is @ Max pressure and Retumbo is not. You did not mention your apparent pressure levels in these two loads so I assumed.
Therefore something in between RL17 on the fast side and Retumbo on the slow is the "optimum" powder.

From Hodgdon's 2013 Loading Manual with 145 listed powders, RL17 is @ #115 and Retumbo is @#138 giving a total of 22 powders between those two. There is clearly other choices. First choice in my book is RL19 because RL17 did so well. But closer to Retumbo are three powders that I favor personally; IMR 7828, RL25 and H1000 - which holds great favor with a majority of subscribers to this website. That being said I would pursue H1000 to achieve pressure "Maximum" and I'll bet the top velocity and excellent accuracy are sure to follow.

In the early '70s when I started reloading, chronographs were thousands of dollars and you got one shot through each pair of tin foil screens. The velocity was a combination of lights that illuminated as you rotated a switch. In other words we could only guess. So the rule of thumb was, "Use the slowest powder that filled the case and still developed maximum pressure and that would be the highest velocity." When I bought my first Shooting Chrony in the '80s I discovered we were either lucky or right.

Since I'm not that good at the Craps Table in Elko.....

KB
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  #23  
Old 12-22-2013, 01:04 AM
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Re: barrel length vs. powder usage

KB,

I agree the RL17 load is too fast as I like 90% capacity or better as a general rule of thumb. However the Retumbo load was what I considered a max working load at 72 gr and at ~ 99% capacity which is an ideal load in my book. I did run some at 73 gr but thought it was a little too close to the edge for me based on signs.

I did not get a chrony until about 95 when I got a Prochrono and that is when I first knew my actual (or close) velocities. Until then I just used measured drops to 300 yds and guesstimated velocities. No range finders back then and not much shooting past 300.
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  #24  
Old 12-22-2013, 12:54 PM
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Re: barrel length vs. powder usage

Retumbo has in recent years become my go to powder for my heavy bullet, large capacity LR hunting loads in 6.5x284 through 338 Lapua. While other powders work, I find that I get high velocity, low ES, low pressure, filled cases, and excellent temperature stability. I see no problem with burn rate effects using my 24-26" barrels. I believe Hodgdon did change it about the time they started labeling their powders as "extreme", claiming broad temperature stability. My loads at that time had to be reduced 2-3% by weight to develop the same velocity. They did something to change the formulation. It' seems to pretty consistent since then.
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