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Hi all. I need help/advice. This is long. Please bear with me. I have a Ruger Bisley 45 Colt sixgun. I have a light practice load using the Mid-Kansas Cast Bullets 250 grain RNFP and 10.0 grains of Universal Clays. I have chronographed this load several times and the velocity has always been around 1050 fps. It is a consistent and accurate load. Today I was out shooting and chronographing some loads including this one again. It gave its usual velocity of 1050 average but I did get one reading of 1290 fps. Another load that I have chronographed in the past is using the Cast Performance 335 grain bullet with 22.0 grains of Lil' Gun. A few months ago it gave a velocity of 1250 fps and a few days ago I got 1200 fps. 21.5 grains of Lil' gun gave me 1210 fps a few months ago as well. That 335 with 21.0 gr of H110 gave me 1075 fps a few months ago. Well today I got some very high velocity readings with the CP 335. 10 shots of 22.0 gr of Lil' Gun gave an average velocity of 1340 fps with an extreme spread of 23 fps. 22.5 gr of Lil' Gun gave a vel of 1375 fps. Then I tried some loads with H110 and the CP 335. As mentioned I had tried this bullet with 21.0 gr H110 in the past and got 1075 fps. Well today I tried 21.7 gr H110 and got 1470 fps and 22.2 gave 1500 fps and 22.7 gr gave 1545 fps. These velocities do not seem right. I had expected about 1300 fps for the 22.7 gr charge based on some data I had received and based on velocites measured earlier with the lighter charges. Not only that but the case extraction did not seem any more difficult. Additionally the recoil did not seem to be the 40% greater that it would be if the velocity were actually 1500 fps instead of 1250 fps. So I do not believe I was getting velocities that high but wonder what the heck could have happened. I had the sky screens 15' from the muzzle like normal and I had the computer box well away from the muzzle because I have experienced wild velocity spreads caused from the shock of the muzzle blast. Have any of you shot similar loads and what kind of velocities did you get? Incidentally I use a Pact digital scale and set up my powder measure to give the exact amount of powder and check it frequently so I know I am not getting overcharges of powder. The group fired with 22.2 gr of H110 behind the Cast Performance 335 gave me a 2.0" group at 55 yards open sights from the bench. That is the best I have ever done at that range (even when I had my scope on). I tried for the first time today a piece of electrical tape with a small hole in it over my shooting glasses to give me an aperture and it really seemed to help. Thanks for any input you can give. Again, mainly I doubt seriously that my velocities were as high as the chronograph showed, but the velocities for the 250 gr bullet with 10.0 Univ Clays were normal except for that one shot. Mostly I wonder how could I get such a reading and not blow up my gun or notice the recoil if the velocity were actually that high and what kind of velocities are you guys getting with similar loads? Thanks, Brian C.
 

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Brian,

In looking at your post, I think perhaps a look at your chronograph itself might be in order!  Some brands of chronographs are very sensitive to atmospheric conditions, and with varying lighting can deliver greatly varying velocity readings, consistent for that session, but inconsistent with other shooting sessions.

When you are getting such readings, and questioning your chronographs reliability, a simple check is to run some good quality .22LR through the skyscreens as a control.  The .22's are very consistent when fired from rifles, and very predictable with quality ammo.  This makes a very inexpensive way to check the reliability of your chronograph readings for that session.

Brian, I really doubt that your ammo is producing such extreme differences in velocity, especially the H110 loads with the 335 grain bullet.  As you said, you would have noticed a change in recoil, a change in point of impact on your target, and a change in pressure signs when extracting fired cases.

Give the Chrono a lie detector test!

God Bless,

Marshall
 

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Its most likely chrono based like our good Mr Stanton has already diagonosed.
I'm sure your aware of this but I will mention it anyway, Ammo left in the sunlight will raise the temp of the ammo and you can see some wild velocity changes and if your sky screen spacing varies any it too can cause diff readings from time to time. Ignore this last part if your screens can only be placed the exact same time from setup to setup. I have a home made sky screen holder and found this prob untill I figured out what was causing it. Hope this helps. That was some fine Iron sight shooting. JSanders
 
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