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FPS or velocity from gun to gun

 
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  #1  
Old 03-30-2013, 08:08 PM
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Join Date: Dec 2010
Posts: 78
FPS or velocity from gun to gun

I have a Model 7 in 243 and a Model 70 in 243 that the barrels seem almost identical. The same reload shoots under .4 in both guns. With barrels being almost equal, can I expect the same velocities from both guns?

Now, What if I move up 6" in barrel length and still shoot the faster burning 3031 that shoots so well in my shorties?

Here's what I'm getting at. If I see reloading data in a book or on the internet and the data is compiled using the same barrel as mine, can I expect fairly close velocity out of my identical barrel. I don't have a chronograph and am trying to figure out how to make an educated guess when figuring out my "come up-ins" for given bullets. I guess a $100 chronograph would be the best way though?????

Thanks for any advice,
B
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Old 03-30-2013, 08:18 PM
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Join Date: Dec 2011
Location: Michigan
Posts: 1,042
Re: FPS or velocity from gun to gun

They should be close - BUT - throat, twist, other minor differences can add up to make your velocities different. I am also a firm believer in gun gremlins, that make what appear to be the same (but different) equipment do unexpected things.

As far as determining velocity, I saw something interesting in a post on chronographs that I intend to try. Basically, the poster (my apologies I forget who to give credit too) will zero at 100, and then shoot groups a few farther distances. By measuring the drop at these ranges, he can use ballistic programs to back-out the true velocity. Pretty smart IMO.

Hope that helps!
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Old 03-30-2013, 11:15 PM
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Join Date: Aug 2003
Location: NC, oceanfront
Posts: 3,031
Re: FPS or velocity from gun to gun

Every barrel is unique, and few assumptions in pressures or velocities would stand up to actual testing.

Get/borrow a chronograph
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  #4  
Old 03-31-2013, 12:10 AM
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Join Date: Jul 2009
Location: Northern MN
Posts: 203
Re: FPS or velocity from gun to gun

VarmintH8R you hit the nail on the head, with todays ballistic programs and even the "free" ones a person that enters all the data in correctly will be able to make a reasonable estimation of their velocity using that method and when it comes to buying a $100 chrony over going to the range, the shooting day wins everytime..(more on the Chrony below)..

Before us backwoods "hillbillys" had or could afford chronographs we used bullet manufactuers drop tables to determine velocities....Guess what? when we aquired our first chronies we verified that our methods weren't too far off...

Now with todays balistic programs we not only can back up our chrony results with field drop testing...But we also can determine our velocities in absence of our chrony based solely on actual drops at known distances....That is providing we have and enter all correct information...

I am not knocking the $100 chrony because I have had two of them over the years...They can be as accurate as more expensive ones or give useless information depending on how they are set up...I have one set up permanently at my 100 yard range....It is mounted within a box which controls the amount of ambient light that enters the sensors...Bright sunlight is now directed away from the sensors and bullet path....When conditions are dark(overcast near dusk) I use two battery powered LED lights....But I still haven't mastered the sundown angle (I shoot west)....Direct sunlight gives the Chrony brand fits (probably others also)...

BeezleBub if you reload or intend to a chronograph will be a real asset when you start working up loads...The actual range data will be the real answer to your current question regardless if you acquire a chrono or not.

Good luck,
Randy
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  #5  
Old 03-31-2013, 04:38 AM
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Join Date: Dec 2010
Posts: 78
Re: FPS or velocity from gun to gun

Thanks guys. Midway has an F1 on sale now for $79. Think I'll give it a try. I've got about 20 pistol loads I'd really like to know the "speed" on and about that many rifle loads to test as well. Groups is what I strive for, but a tight slow groups isn't as good as ascreamin medim - small group when hunting. At least not in my head. Still, I'd like to know how fast my one hole groups are shooting... :-)

tks again,
Beelz
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