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Old October 26, 2013, 12:52 PM   #1
Kimbercommander
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Test Barrels VS Real barrels?

The question is does anyone know how to figure out muzzle velocity without using a Chrono? I have a 26" barrel but all the data i have found for a .300 win mag is with a 24" test barrel. I just picked up some factory ammo that is shooting really well for me and im trying to figure out the speed without breaking my bank for a Chrono. The round is a the Federal Fusion 180 grain. Has a B.C. of .485 and the info i have for it is 2960 for a average muzzle velocity. The reason im asking is i was shooting right at a half inch with this load. This REALLY suprised me but when i started looking for info on this round i couldnt find much. Thanks for any help and or info. All is welcome.
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Old October 26, 2013, 02:10 PM   #2
big al hunter
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It takes a bit of math but... if you sight in at 100 yards then shoot a few groups at 200 or 300 yards you can compare your results to the ballistic charts. That will get you close, but it won't tell you if you have severe deviation in velocity though I doubt you will have any.
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Old October 26, 2013, 04:11 PM   #3
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You could try this method of using a computer and microphone:
http://arxiv.org/ftp/physics/papers/0601/0601102.pdf

Looks like fun.
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Old October 26, 2013, 05:32 PM   #4
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Chonographs today are much less expensive than they used to be.
Claimed velocities for factory ammo are often rather optimistic & modern reloading manuals claim higher velocities with lower charges of powder than in their older manuals.
If you really don't want to buy one , they can be hired or loaned.
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Old October 26, 2013, 09:41 PM   #5
Kimbercommander
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Thanks for the answers and info. I think im just going break down and buy one. Im looking at 2 right now. One is a traditional Chrono and the other is a magnetic Chrono. Anyone have anything pro/con for these? Both are from Midway.
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Old October 26, 2013, 09:58 PM   #6
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It's a good call , chronos' can tell you much more than simple velocity.
I have only used optical , so can't comment personally on the magnetic units.
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Old October 26, 2013, 10:48 PM   #7
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For an overbore cartridge like the .300 WinMag, I'd not be at all surprised at a 100 ft/sec improvement for 26" over 24".
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Old October 27, 2013, 08:11 AM   #8
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SAAMI's tests on barrel length versus muzzle velocity showed that bullets in the velocity range the .300 Win Mag shoots them, there's about 30 fps change per inch of barrel length.

It's not unusual to have a 24" barrel shoot the same load's bullets out 50 fps faster than a 26" one because its internal dimensions are smaller. So, if you're comparing barrel lengths to velocity changes, the only difference has to be the barrel length; that rarely, if ever, happens with two different rifles. Otherwise, all sorts of variables can cause incorrect results.
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Old October 27, 2013, 09:11 AM   #9
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Longer barrels only yield their maximum benefit if you are loading especially for them. Most my barrels on my overbore rifles are 26" and 28". I have a couple of 30". To truly capitalize on the 30" you usually have to stray away from published data and go into powders slower than what the manuals publish data for.
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Old October 27, 2013, 09:15 AM   #10
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Every barrel is different and will produce varying velocities from "identical" factory ammo.

No way of knowing (unless they specify) the length of the barrel as tested.

"Trajectory validation" can also be used to determine your MV as big al mentioned.

Zero at 100, then take it out several hundred yards. Your drop (assuming reasonably consistent loads) will tell you what your MV was.

Validating trajectory is routine, it's rare that charts or ballistic programs are accurate at longer ranges and need to be "tweaked"- in my experience.
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Old October 27, 2013, 12:48 PM   #11
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Agree chronographs are nice. Don't know if you check the ballistic table here

http://www.federalpremium.com/produc...le.aspx?id=663

Be interesting to compare tables and see how they compare to what your getting.
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Old October 27, 2013, 01:18 PM   #12
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tobnpr says validating trajectory is routine, it's rare that charts or ballistic programs are accurate at longer ranges and need to be "tweaked"

I've used Sierra Bullets software with several of their 30 caliber HPMK's shot from .308's and 30 caliber magnums to get longer range sight settings from "shooting boresight" set on the sights. Once setting the atmospheric conditions and muzzle velocities in the software to what was observed at the range, sight settings based on bullet drop was not off at 300, 600, 800 and 1000 yards by more than 1/2 MOA.

"Shooting boresight;" determined by shooting from position at 100 yards to get initial sight settings, then correct the sight elevation setting for bullet drop at 100 yards plus sight height above bore axis. Using an optical collimator to see the results, the line of sight was never perfectly aligned with the bore axis after doing this.
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Old October 27, 2013, 01:44 PM   #13
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I have checked a few of the online ballistic mumbo jumbo sites online and so far nothing that really matches what im shooting. I use a App on my phone but its always off by a bit. I know I need to just buy a bunch of this ammo and make a drop chart for it at the range. Only reason im stuck on this ammo is it shoots better then the hornady's did for me.
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Old October 27, 2013, 07:28 PM   #14
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The software is pretty good if you have enough know points of impact to plug in.
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Old October 27, 2013, 08:34 PM   #15
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Go out and buy a $100 chronograph. They may not be as accurate as the more expensive models, they are more prone to errors in situations where light is less than perfect, but are accurate enough for what you want to do. Lots better than just guessing.
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Old October 27, 2013, 09:43 PM   #16
Kimbercommander
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I will be ordering a Chronograph off Midway for about 115 bucks on the first. That way I can fire 20-40 rounds thru it and get a average for that ammo brand. I would hope most would agree 40 rounds will give me a well rounded average for that ammo.
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Old October 28, 2013, 07:47 AM   #17
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I don't think you need that much. 5 rounds would tell me what I needed to know.
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Old October 28, 2013, 08:02 AM   #18
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I agree with jmr40, 5 rounds is good enough.

The average of them will be a few fps different than the average of 10, 20 or 40 shots. Depending how consistant you hold the rifle against your shoulder, that often produces greater spreads in average velocities than your load has when fired from your rifle hard fixed in place when shot.
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Old October 29, 2013, 10:55 AM   #19
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I'm not sure how far your max distance will be your shooting . The fact your shooting fussion ammo tells me your hunting and 500yds is likely max . I ran some quick numbers through my ballistic calc and I see a likely 2" difference in drop at 500yds . So we are talking 1/2 moa difference . I'm thinking if you shoot well , your still going to have a good hit on what ever your shooting - out to 500yds . I have two ballistic programs and a chrono . I have never been able to get them to match perfect . There's almost always a 1/10 to 1/4 moa difference out to 300yds and gets to about 1/2 moa at much longer ranges . Thats close enough for me .

Your going to want to dope your rifle in real world conditions . That way you will know what you and your rifle can do . For me I would not want to base a 500yd shot on game just using a ballistic calc .

If you base your velocity's on what Bart and Art said . Give your self another 30 to 100fps . That should get you very close at any distance and you can dope the rifle from there .
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