Draw a line on the shoulders of a case, where do the lines intersect? Some lines will intersect way out in the throat, while some intersect back in the case neck. PO Ackley referred to these intersecting lines as the "interference point" stating that when the Interference Point is back in the rear of the neck, this is where a lot of converging gasses and powder is "Blasted". As the interference point is moved back in neck vs being out in the throat, throat(barrel life) increases.
Years ago, I shot tens of thousands of p. dogs. 1000-1200 rounds of centerfire per day was the norm. We put a lot of wear on barrels. We started playing with Ackley Improved chambers back then, along with which powders reduced throat wear and which powder ate up barrels.
First thing we learned was that the 243 Winchester at up barrels at a much faster rate than the 6mm Remington, shooting the same powder, with slightly more powder in the 6 Remington, and shooting the same 85g Sierra bthp.
Recently, I wanted to try another experiment. I was forming 6 XC cases from lapua 308 Palma brass with the small primer pocket. When formed, the neck on the case was .400 long. I ordered a neck reamer, already had uni-throater. I cut the neck in the chamber to .410 to allow for a .400 long neck, then throated it .147 to shoot the 107g Sierra match king and the 105g Berger vld hunting.
900 rounds later, I only had .007 leade growth...nothing short of amazing shooting 400 rounds with R#17 and the balance with H4350. Accuracy was some of the best that I had ever shot in my life, and I shot registered Benchrest for a while.
So, my conclusion on this single example was that with a longer neck, interference point way back in the back of the neck, barrel life was greatly increased. I put 900 rounds on 30 of the Lapua cases of which I am still shooting 13 of those cases. I found an accuracy node with the 105g Bergers at 3250 on that 31" 8T barrel, but realized that I was killing my brass with that load after 5 firings with the R#17 at 3250.
The 6 Remington and the 6 XC have very long necks compared to many other cartridges without alteration, and I would consider the longer necks a plus.
Years ago, I shot tens of thousands of p. dogs. 1000-1200 rounds of centerfire per day was the norm. We put a lot of wear on barrels. We started playing with Ackley Improved chambers back then, along with which powders reduced throat wear and which powder ate up barrels.
First thing we learned was that the 243 Winchester at up barrels at a much faster rate than the 6mm Remington, shooting the same powder, with slightly more powder in the 6 Remington, and shooting the same 85g Sierra bthp.
Recently, I wanted to try another experiment. I was forming 6 XC cases from lapua 308 Palma brass with the small primer pocket. When formed, the neck on the case was .400 long. I ordered a neck reamer, already had uni-throater. I cut the neck in the chamber to .410 to allow for a .400 long neck, then throated it .147 to shoot the 107g Sierra match king and the 105g Berger vld hunting.
900 rounds later, I only had .007 leade growth...nothing short of amazing shooting 400 rounds with R#17 and the balance with H4350. Accuracy was some of the best that I had ever shot in my life, and I shot registered Benchrest for a while.
So, my conclusion on this single example was that with a longer neck, interference point way back in the back of the neck, barrel life was greatly increased. I put 900 rounds on 30 of the Lapua cases of which I am still shooting 13 of those cases. I found an accuracy node with the 105g Bergers at 3250 on that 31" 8T barrel, but realized that I was killing my brass with that load after 5 firings with the R#17 at 3250.
The 6 Remington and the 6 XC have very long necks compared to many other cartridges without alteration, and I would consider the longer necks a plus.
