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Well, based on Marshall Stanton's suggestion, I have now tested some loads using No. 9 in 45 Colt.  My loads consisted of a 265 gr. SWC GC in Starline brass w/ WLP primers (std and mag).  I began with a start charge of 18.5 grains of No. 9 and worked up to 20.5 grains in 1/2 grain increments.  The loads burned very cleanly w/ just a little unburned powder left in the barrel after each string.

I fired these in 10 shot strings over my chrono on Saturday with the temp around 70 F.  My 5.5" Bisley-Vaquero was used for all testing.  My results are as follows:

Charge     Avg FPS    E. Spread    Std. Dev.
---------     ----------    ------------    ------------
18.5          1084           80.19          21.70          
19.0          1078 ?      112.10          39.37  
19.5          1124         131.10          44.28
20.0          1130         151.90          47.06
20.5          1131         101.40          27.80

All cases extracted easily and showed no obvious signs of excess pressure.  However, the velocities I got are much lower than I expected and as you can see there was very little change in velocity for each 1/2 powder increase.  Also, the extreme spread numbers are a lot higher than I am used to getting from the faster burning powders I use.  I also rans a test using the same components listed above except w/ 2400.  The same 18.5 to 20.5 grain range of powder was tested and yielded similiar results, except slightly lower velocities were reached.

What could my problem be?  Could the B/C gap on my Ruger be too large and is allowing too much gas to leak out?  My Ruger doesn't seem to exhibit this same "shooting slow" characteristic with faster powders like Titegroup and Universal Clays, so I don't know what is going on.

Any ideas guys?
 

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Hi Mark,
I have a fair amount of experience with AA-9 powder but none with 45 Colt's so take this with a grain of salt.  

I pulled out my Accurate Arms reloading book and referred to 45 Colt for Ruger's & T/C's.  Though they do not list loads as hot as yours, the velocities you gave fall into line with theirs once you take away for their sealed breach and longer barrel.  

AA-9 is such a easy burning powder that the high extreme spreads are a real surprise.  When I get such high extreme spread numbers out of the blue (as I recently did), I check what is different with the brightness of the sky.  Chrono's hate direct sunlight or even too much reflected light.  My father always taught me to look for the simple solutions first.  Maybe you could try repeating the test when the sun is lower in the sky or with an overcast that will diffuse the sunlight.  I got caught with this problem 3 weeks ago with a higher spring sun and all my testing was rendered useless for that day.  The other trick is to take along a proven low es load to compare your results with in the same shoot.  

I'm sure the 45 Colt shooters can give you more cartridge spicific insight than I can, but maybe this will help a bit anyway.  

God bless....................  Bill M
 

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Try turning your Chrono sidewats ,away from the sun. Or build a box and a opaqe plastic cover for it. Good Luck.
 

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Good advice!  Check out the chrono situation, then if the data still points as it has, toward the large es figures, perhaps a change in primers would make a difference!  Although some of my most consistent loads use the same WLPP that you've employed, primers can still make a whale of a difference in load performance.

Keep us posted!

God Bless,

Marshall
 
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