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My barrel doesn't like those bullets!

Posted by Marty on 11/19/2011
Have you ever heard someone say " my barrel ( or gun) doesn't like those bullets? Perhaps referring to a brand or particular weight of bullet. Well before it happened to me I used to think this was the product of some over- analizing reloader that had dual degrees in engineering and physics. Not picking on the educated but my black and white, concrete sequential, logical mind just couldn't see how high quality bullets with high ballistic coefficients could get such different results from the same barrel. Here are the specifics , Thompson Center Encore rifle systems, 280 Ackley Improved caliber, 24" Bergara barrel accurized by BellmTC in Oregon, a 26" MGM barrel, 139 gr Hornady SST bullets, Hornady 162 gr SST bullets. The ballistic coefficient of the 139 gr is .550 and the 162 gr is .625. And in the BC game higher is better. Bottom line we reloaded sample loads using data from Hornady 8th edition and Sierra manuals using IMR 4831, IMR 4350, RE-19, Big Game powders in combinations with those 2 bullets. As a rule the 139 gr bullet ALWAYS grouped better and the 162 gr ALWAYS grouped worse. By better I mean from an astonishing .494" group to 1 1/4" groups and by worse I mean 1 1/4" to 2 1/2" groups. How could this be? Our reloading conditions were very good and detailed, 2 different shooters alternating guns and loads. 2 different barrels, and all the accurizing tricks we knew. Our barrels simply don't like those heavier bullets. Well after alot of over-analizing , reading and research we found our answer . Rate Of Twist !!! Both our barrels have a 1 in 9" twist rate, and it takes more twist to turn the bullet faster to stabilize its flight. This was confirmed by email from Kurt Bellm at BellmTC. So don't throw out that inaccurate gun or barrel, find the bullet it was designed best to shoot! Thanks for reading. Marty