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Old August 30, 2014, 10:14 PM   #1
SpringOWeiler
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Counter Bore Question

Does anybody have experience with deeply "inches" counterbored rifles? I'm building a pistol caliber bolt rifle and I don't want to deal with the tax stamp for a short barrel so I was was wondering if there were any tests on barrels with about 4" of essentially free bore at the muzzle end. Accuracy results?
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Old August 30, 2014, 10:26 PM   #2
Mobuck
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Don't know what round you're planning to use but I've found 16" of barrel is still advantageous even with a 9x19mm.
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Old August 30, 2014, 11:22 PM   #3
chris in va
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I'm not sure what purpose this would serve.
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Old August 30, 2014, 11:38 PM   #4
SpringOWeiler
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Because I want 12" of rifling and need 4 more inches of barrel length. SBR is not an option.
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Old August 30, 2014, 11:46 PM   #5
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Sounds like a waste of 4" of fps to me. If you want a 12” barrel cut it off at 12” and add a 4" flash suppressor permanently affixed. That's what they do with AR-15 rifles, bug it's usually just a 2" flash suppressor.
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Old August 31, 2014, 01:34 AM   #6
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No point in doing so. It's just a waste of barrel length, and a great way to introduce undesirable variables.

Chop the barrel where you want it, thread it, and permanently install a muzzle device (brake, comp, suppressor, whatever...).
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Old August 31, 2014, 04:16 AM   #7
Bart B.
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Bloop tubes have been used on rifles for many years with great success. It increases sight radius to make the front sight appear sharper and better in focus:

http://www.accurateshooter.com/gear-...om-norm-houle/

https://www.google.ca/search?q=bloop...w=1187&bih=552

Anschutz made .22 rimfire match rifles with them; did very well in the Olympics. I've seen 'em on some high power match rifles 10 inches long. While one changes the resonant frequency of the barrel, it's still very repeatable from shot to shot so accuracy's not impaired.

I don't know where folks get the idea that adding anything to the muzzle will add another variable. All barrels, with or without something hanging onto their muzzles, vibrate with the same frequencies and harmonics thereof depending on their material, shape and length. It's the same for every shot fired. Adding something to the muzzle will change the frequencies it vibrates at, but they'll be at the new frequency for every shot thereafter. There are no variables in that new frequency; the physical properties of the barrel and its attachments don't change from shot to shot.

Just counterbore the barrel back as far as you want to the diameter the barrel can withstand. It'll work the same as bloop tubes and not come loose.

And you want 12 inches of rifling? Why? Starting from the breech face, chamber mouth or where to the end of it?
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Last edited by Bart B.; August 31, 2014 at 11:29 AM.
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Old September 1, 2014, 10:35 AM   #8
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I have a featherweight 270 Win barrel on a pre 64 that someone must have fired a round through it when there was mud or something in the bore. The bulge was within two inches of the muzzle. Would always get a flyer.

Gunsmith reamed the last two inches to remove the rifling. So I have a rifled smooth bore rifle!

I have only put a Lyman 48 on the thing, it is very handy, but since the front is a bead, can't say it is a target rifle, it shoots around 3 MOA at 100 yards. But the group is round. Can't say it is a velocity champ.

Code:
Pre 64 M70 
		
100 grain PSP Remington Factory
	21-Jan-03	T = 48 °F
		
Ave Vel =	3055	 
Std Dev =	66	
ES =	165	 
Low =	2982	
High =	3147	
N =	7	
		
		
130 grain Nosler BT 55.0 grains H4350 wtd R-P cases WLR OAL 3.30"
	24-Mar-04	T = 70 °F
		
Ave Vel =	2839	 
Std Dev =	33	
ES =	123	 
Low =	2784	
High =	2907	
N =	19	




I have buds with bloop tubes on their AR 15 actioned 6.5 Grendels. These guys assemble the rifle each match, shoot outstandingly with the things.

I don't trust bloop tubes, but the guys around me shoot good scores with the things.

Last week, an AMU shooter next to me shot a perfect small bore prone score, with irons, and his rifle must have had two extra feet of bloop tube. It did not hurt that his eyes are great, he probably sees with naked eyes, what I see through a scope!
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Old September 1, 2014, 08:45 PM   #9
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I'm not understanding how having a long amount of rifling missing would not affect accuracy.

Couldn't the expanding gases push past the bullet before it exits the muzzle, or at least push the base unevenly?

Just seems that a bullet with the ability to wobble inside the bore would be detrimental... If not, where's the limitation? Surely, a couple inches of rifling and two feet of counterbore wouldn't cut it...
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Old September 2, 2014, 07:55 AM   #10
Bart B.
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Gas flow and direction around bullets in bloop tubes is very repeatable from shot to shot. If not, how do such things allow rifles to win matches and set records? If it wasn't, their poor effect on accuracy would convince top ranked competitors not to use them.
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Old September 5, 2014, 05:02 PM   #11
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Thanks I'll look into the bloop tubes.
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