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Old 11-30-2016, 01:43 PM
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Custom build bbl length



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I could use a sanity check with regard to my thinking towards bbl length for a new bolt action rifle I am having built. Here are the particulars:

1. Deer Hunting use, out to 400 yrds, from tree stands, box stands, walking jump shots of opportunity, woodland, swamp, farmland, mountains, everywhere.
2. Shooting primarily 140gr, 7mm boat tails in front of @57 gr of IMR 4350 (which gets me @2900 fps out of a 22" bbl i already have).
3. Want a 20" bbl on this new build, to aid in handyness. I know that I will loose some muzzel velocity, but Im guessing it would be less than 50fps, and not significant out to the 400 yrd mark. Havent figured out what the add'l drop could be yet though.

Am I way off in my thinking on this so far? My current 22"bbl configuration with that load gives me a solid 325 yrds of point/blank zero well within a pie plate target diameter. I only need to use a range finder and facter bullet drop the last 75 yrds out to 400 with my current setup. Would like to maintain at least a solid 300 yrd point/blank range with the 20" bbl.
I'm gonna try some 120gr loads too.

Last edited by 284wahoo; 11-30-2016 at 01:58 PM.
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  #2  
Old 11-30-2016, 04:36 PM
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Look out for increased muzzle blast/flash. My Dad had a 22" bbl put on his 243, because the 19" was blinding when shooting at dusk. Couldn't see anything for a couple minutes after firing at dusk/early morning......

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Old 11-30-2016, 05:20 PM
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I think your choice is between 24" and 26" for a 7mm RM. You can load it a little lighter and extend the life of your barrel, if you don't want the extra free velocity.

With a #2 Sporter Contour, you will save all of 2.5 oz going to a 20". Going up to a 24 adds about 2.5 oz. Going to a 26 adds 4.5 oz. Strikes me as a small amount of weight. You will probably get 150 fps going from a 20 to a 26".
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Old 11-30-2016, 06:47 PM
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I gained 100 fps going from 26 to 30 inch barrel. I am guessing that you will loose a lot more than 50 fps going form 24 to 20. Nothing to prove it Look on rifleshooter.com blog and he has some barrel tests where he cuts off 1 inch at a time

David
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Old 11-30-2016, 07:33 PM
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The load is 284 Win, loaded long. I would be going from 22" bbl down to 20". More for the shorter bbl maneuverability than any weight loss. Even 2" can make a diiference when in tight quarters.
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Old 11-30-2016, 08:40 PM
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If you cut a 22" barrel to 20" you'll probably lose about 50 fps. You'd have to sight in about .3" higher at at 175 to be .4" lower at 300.
With a different rifle and a different barrel, there might be more difference in velocity, or there might be none at all. 2900 fps with a 140 out of a 20" 284 doesn't sound impossible.
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Old 12-01-2016, 06:44 AM
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Quote:
Originally Posted by 284wahoo View Post
I could use a sanity check with regard to my thinking towards bbl length for a new bolt action rifle I am having built. Here are the particulars:

1. Deer Hunting use, out to 400 yrds, from tree stands, box stands, walking jump shots of opportunity, woodland, swamp, farmland, mountains, everywhere.
2. Shooting primarily 140gr, 7mm boat tails in front of @57 gr of IMR 4350 (which gets me @2900 fps out of a 22" bbl i already have).
3. Want a 20" bbl on this new build, to aid in handyness. I know that I will loose some muzzel velocity, but Im guessing it would be less than 50fps, and not significant out to the 400 yrd mark. Havent figured out what the add'l drop could be yet though.

Am I way off in my thinking on this so far? My current 22"bbl configuration with that load gives me a solid 325 yrds of point/blank zero well within a pie plate target diameter. I only need to use a range finder and facter bullet drop the last 75 yrds out to 400 with my current setup. Would like to maintain at least a solid 300 yrd point/blank range with the 20" bbl.
I'm gonna try some 120gr loads too.
If you are willing to accept some ballistic compromise of the round's potential, there is no reason you shouldn't be able to obtain the use you want from your rifle in that particular configuration. I think what you're describing is performance similar to, or exceeding, handloaded 7x57 ammo, which (if 120 years of record keeping and literature can be believed) is no slouch on medium-sized game.
All that said I would have a hard time not sticking a 24"-26" barrel on it just because of the cartridge's design. But that's just me.

Good luck.
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Old 12-01-2016, 07:59 AM
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Quote:
Originally Posted by 284wahoo View Post
The load is 284 Win, loaded long.
Sorry, I forgot that. The 284 is a much more civilized round than the 7RM. I have a 6.5 Remington Magnum barrel on order for my Remington 700. It will be 28" finished.

Last edited by Ron AKA; 12-01-2016 at 08:01 AM.
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  #9  
Old 12-01-2016, 09:17 AM
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My huntin buddies who shoot the same load are incouraging me to go the 22" minimum route too. I'm pondering. More handy handling on one side, 50fps loss of muzzel velocity on the other side. 22" would be the max length in this build. If I were to rebarrel my first build next, I would go to 24" on that one.
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Old 12-03-2016, 10:40 AM
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How ‘bout a magnum contour or a bit fatter, cut to 20” making it even stiffer and so it’s better suited for your purposes, as you desire. Buy it an adequate supply of the best brass available, and have ‘em spec it a chamber reamer nearer to the case body and neck OD of your brass, and only .0005” over bullet diameter in the throat. Then fetch it custom Whidden die set whose internal dimensions will have been determined accordingly.
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