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Hello and thank you for your time,

I have a S&W pre-24 (1956) and a S&W 24-5 (Performance Center 2001). Both are 44 specials. Both are mint. They are not identical, but both have 6.5” barrels, 20:1 twists, 0.429 groove diameters, barrel-cylinder gaps < 0.0074, 0.430 chamber mouths, and their other chamber dimensions match SAAMI specs as close as I can tell with caliper and micrometer.

I hand cast 224 gr Anderton bullets with wheel weights and gas checks. Lubed and sized to 0.430. Used a CCI LP primer, and 5.7 gr of Universal. Neck tension and crimp right on. COAL 1.500.

I won’t go into further detail here other than to say that all factors for velocity were standardized when I shot the two guns with the identical loads minutes apart. The results shown below are not the result of chronograph error. They reflect some difference between the guns.

Rounds fired in this particular test = 8 per gun.

24-5 = mean velocity of 726 FPS and a spread of 25 FPS. These results met reloading manual expectations.

Pre-24 = mean velocity of 597 FPS and a spread of 69 FPS. 129 FPS below the velocities observed for the 24-5. No evidence of excessive blow back, case streaking, or leading or powder fouling on the frame around the forcing cone. Dead on accurate.

Here is my question.

If anyone has ever experienced such a large difference in velocities between two similar guns shooting identical loads under identical environmental conditions, did you ever determine the cause?

I am prepared to take this to a smith to get better barrel-cylinder gap measurements and maybe cast the chambers, but wanted to reach out to others first.

Thanks again!
 

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If the gaps are the same, I wonder if there's differences between the cones.

We're these averaged over several shots? Single data points are pretty worthless.
 

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No 2 guns will ever have the exact same velocity (or accuracy for that matter). Chamber dimensions, forcing cones, bore diameter, rifling depth, barrel/cylinder gap, free bore or a combination all affect velocity (& accuracy).
 

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All the above and it applies to all firearms no matter what the configuration of the chambering is. Even muzzle loaders.
 

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My experience is consistent with what others responding have indicated. Over about 40 years of chronographing I've seen all kinds of variations in velocity, extreme spread,etc. between same model and barrel length guns. This particular issue was discussed by Dave Andrews in Speer reloading manuals #9 and #12, "Why Ballisticians Get Gray". Three 6" Pythons were tested with a particular load selected for it's consistency. Velocity with the three seemingly identical Pythons was 1227 FPS, 1468 FPS, and 1477 Fps. Three S&W Model 19s with 6" barrels varied as much as 203 FPS....
 
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