O.A.L. and Velocity Questions.

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I know that load data from different sources may not agree on certain points.
But I have a couple questions regarding that issue involving my .41 magnum.

One book I use to load 2400 powder says at 17.6 gr. of powder I should be getting around 1200 velocity. On the Alliant website, they say with that load I should be getting 1400 velocity. That is a pretty big jump in numbers to me. I only found the Alliant reloading data today, and I am wondering if I should probably be more inclined to go by that since this powder is made by them? Another thing Alliant mentions is that is a revolver with a 5.8" bbl. whereas my book doesn't mention bbl. length. Mine is a 6 1/2 barrel. I guess barrel length will play a role in velocity too, but to what degree?

Now another thing I noticed is the oal is different. Alliance says O.A.L. should be minimum of 1.575, but my book simply says 1.580 maximum. The ammo I have been loading is usually between 1.575 and 1.579, but some of them have been as short as 1.570. What kind of tolerance is there on the over all length that is considered safe? Now, I have shot quite a few loads at the shorter length, and have had no problems, but I am still new at this.
So, how about some thoughts from you pros? Thanks!
 
too many variables to worry about the velocity between different guns. as long as you are crimping in the groove I wouldn't worry about oal. the slight differences won't be noticeable
 
Thanks, steveno. I am crimping the the groove good. As a machinist I know everything has a tolerance, and can only be off so much. I didn't think that ten thousandths would be bad, but wanted to be sure.
 
There are so many variables that if you are in the ballpark of their figures you are OK. Some use test barrels, some, like Speer, use actual firearms. Some use 4", some use, 6", etc. Some guns have a tighter barrel, some have gigger cylinder gaps, etc. If they fire a .41 Mag in a test barrel with no cylinder gap then they obviously will get better velocity than a real revolver of the same length barrel.

My 4" 686 (.357) gives as good velocities, and generally a tad more, than my Blackhawk (.357) with a 4 5/8" barrel because of differences in barrel throats and cylinder gap.
 
Unless you chrono your own loads, the velocity numbers you see in published data are little more than rough guesses at what your loads are doing. As others have noted, there are too many variables at work to think that a published velocity is what you are getting. Now, I don't chrono my own loads, as I don't have a chronograph. I don't really pay much attention to velocity. I have a general idea about the range I can expect with a given bullet weight, and leave it at that. I'm more concerned about how the load shoots -- meaning felt recoil and how accurate I am with the load. I'd rather hit what I aim at with a bullet going 1000 fps, than miss with a bullet going 1400 fps. But then that's just me. ;)
 
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