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300 Win Mag Muzzle Velocity Inconsistent

 
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  #1  
Old 05-24-2011, 12:38 AM
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300 Win Mag Muzzle Velocity Inconsistent

Worked up a load for my T3 Tikka 300 Win Mag with a stainless steel light weight hunting barrel. The rifle also has a muzzle brake. After doing some preliminary ladder testing, (we don't do ours exactly like the article on this website recomends, we are developing long range hunting ammunition, were happy with .75 moa) we found that H4831 SC at 73 grains with CCI No. 200 Large Rifle Primers, Winchester Nickel plated brass topped off with a 178 grain HNDY-AMAX, was definately getting us the accuracy that we wanted out to 500 Yards. Are range isn't further than 500 Yards so we can't shoot past that. However the only issue we have with this load is that it vairies as much as 150 FPS. Now we were restrained by time so we were trying to get done, so maybe the scorching hot barrel had something to do with it, but then again maybe not. Every bullet was seated at .50 of an inch off the lands, and all of the cases had been neck turned and trimmed to .001 of an inch. At 500 Yds 72-74 grains of powder ( in half grain increments 5- Shots total) all hit in a 3.5 vertical by 1.5 horizontal group. At 500 it obviously won't make a difference, but when we want to shoot 700-1000Yds, I think it will. Any thoughts or ideas?????
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Old 05-24-2011, 07:39 AM
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Re: 300 Win Mag Muzzle Velocity Inconsistent

Try moving your chrono at least 18 feet out from the muzzle. I suspect you are getting interfearence from the muzzle blast or a faulty chrono. 150 fps should show more than 3 1/2" at 500 yards.

Jeff
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Old 05-24-2011, 08:29 AM
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Re: 300 Win Mag Muzzle Velocity Inconsistent

Quote:
Originally Posted by Broz View Post
Try moving your chrono at least 18 feet out from the muzzle. I suspect you are getting interfearence from the muzzle blast or a faulty chrono. 150 fps should show more than 3 1/2" at 500 yards.

Jeff

+++1

The numbers don't add up. SD should be less than 40 ft/sec to end up with a total vertical spread
of 3.5 " at 500 yards.

If groups are 3.5 X 1.5 @ 500 yards you have a good load to work with and it sounds like the
chrony.

J E CUSTOM
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Old 05-24-2011, 10:40 PM
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Re: 300 Win Mag Muzzle Velocity Inconsistent

Thanks guys, I'm new to using a chronograph, I think we had it at about 10 feet!!! That explains a-lot...I'm guessing because of these inaccuracies that I will need to shoot again with chrony at 18 feet, and then redo the drop data.
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Old 05-25-2011, 08:33 AM
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Re: 300 Win Mag Muzzle Velocity Inconsistent

Quote:
Originally Posted by Prairie Dog50 View Post
Thanks guys, I'm new to using a chronograph, I think we had it at about 10 feet!!! That explains a-lot...I'm guessing because of these inaccuracies that I will need to shoot again with chrony at 18 feet, and then redo the drop data.

If you have your screens set at 4' between the front screen and the back screen use the 4', times
4 or 5 to get 16 or 20 feet and then you can calculate Actual muzzle velocity by the velocity drop
between the screens (If you have a proof screen) Example: 5 ft/sec loss in 4 feet x 4(16') = 20
ft/sec more than chronograph velocity. (Note : this is not exact because velocity loss starts at
the muzzle but it is very close).

This will make your drop tables as accurate as possible but you still need to shoot at range to
verify actual drop.

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