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American Handgunner Nov/Dec 2009 - Page 40
electing barrel length is often a major problem for the average shooter. The vast majority select middle of the road length barrels but the trend of questions about length often revolve around extremely long barrels for both pistols and rifles. The expectation of what a long barrel will do versus a short barrel is often unrealistic in both velocity and accuracy. Having spent thousands of hours and hundreds of thousands of dollars with a large variety of calibers and chronographs, I’ve come to some general conclusions. The final assessment? The the more I know the more unanswered questions I have. For example, in revolvers, single shot pistols and rifles the length of the barrel is of little or no consequence ballistically in hunting guns. The barrel length will not make any difference to anything you shoot. Excessively long barrels may be counterproductive to accuracy and velocity. Yes, there are “fast” and “slow” barrels and in some cases I can see the reason, but in most I can’t. Types of rifling, chamber dimension, throat and other factors all contribute. As an example I had a .308 in a M-70 with a hammer-forged barrel 20" long and developed a few excellent sub-sonic handloads. Putting that ammunition in an Accuracy International cut-rifled barrel 26" long stuck the bullets in the barrel about 16" from the bolt face. Testing one ammunition through a half dozen .308 rifles with new or nearly new barrels I found about 340 fps difference between the fastest and slowest barrel. One ammunition gave its highest velocity in a 16.5" Ruger. As I understand it, SAAMI bore dimensions define the minimum “swept” area of the bore, which is the minimum area of the bore, but not the maximum. Any type of rifling matching the minimum swept area is acceptable. The bore and grove dimensions for a micro-groove barrel and a cut-rifle barrel will vary quite a lot. All factory loaded ammunition should be safe in any factory barrel. Not so with handloads. A load “worked up” in one gun may be dangerous in another. 40 The LongVs. Short Of It S Cartridges in photos are .300 “Whisper,” .308, .30-'06, and .300 Win Mag. J.D. Jones HANDGUNHUNTING TIPS, TECHNIQUES AND POLITICALINCORRECTNESS Any Consistency? I i n checking dozens of .44 Magnum revolvers I have yet to find a S&W 8.375" barrel to give any more velocity than a 6" S&W. And, assuming reasonable barrel-cylinder gaps some 4" guns may even be faster than some 6" guns with some ammunition. In the .300 Whisper, generally the same subsonic ammunition will be about the same velocity in a 10" and 16" barrel with the 14" length being slightly faster and 20" substantially slower. In high velocity ammunition the velocity keeps increasing past the 20" point. n testing 17 different .308 factory ammunitions through a Encore 15" barrel and a middle of the road in velocity Winchester 22" barrel on the same day, the velocity difference in 150 grain was 5.29-percent; in 165 grain 5.13-percent and 180 grain 4.18-percent. The highest velocity difference recorded was a 180 grain at 7.03-percent (186 fpd, with most between 100 and 150 fps) and the lowest a 180 grain load a -.56-percent. In 150 and 165 grain ammunition the extreme velocity spread was less in the 15" barrel. The reverse was true in 180 grain ammunition. In general a .30-'06 in the same comparison will show a little more difference and a .300 Win mag a little more difference. The greater the case capacity, normally the greater the difference. But, a 10-percent difference will include most of it. Lets say you have a rifle with a realistic 400 yard maximum killing range. Deduct 10-percent velocity going to a 15" length in a pistol and you have a 360 yard gun. In the .50 Peacekeeper with 650 grain bullets and a 110 grain powder charge, the velocity difference per inch between 24" and 30" was an average of 17 fps per inch — not much to worry about in anyone’s book. For more details on the load charts, go to www.americanhandgunner.com and click on “Web Blast.” rifle realities * WWW.AMERICANHANDGUNNER.COM • NOVEMBER/DECEMBER 2009