June 11, 2022Editor – Many new barrels will deliver higher speeds with the same load after 100 to 150 rounds through the bore. Although the exact cause of this speed-up is not known, velocity increases (if any), will vary from barrel to barrel. This “speeding up” phenomenon can happen with any barrel, so be prepared. From the Sierra Bullets Blog
Article by Mark Walker, Sierra New Product Development Director
In a previous post I mentioned a few ways to tune your load to your barrel to achieve the best accuracy. Load tuning is a common task for people who have a new rifle or a different barrel. Both cases are new barrels that have not been fired much. The Speed Up Phenomenon after 100-150 rounds
Although your new barrel shoots great after you load it up, many shooters find that their rifle stops shooting as accurately around 100 to 150 rounds. This happened to me with a rifle. I was puzzled as to why it suddenly stopped shooting. I decided to pull out the chronograph and do another load check to see what was happening. Surprised, the velocity had increased by around 80 fps from the original velocity! After performing another ladder test and adjusting my seating depth, the rifle was shooting again. One theory is that the barrel will break in and the tooling marks on the throat of the chamber will become smoother, allowing the bullet to exit the bore with less resistance. This could lead to increased speed. Another possibility is that the throat area becomes more rough, which causes more resistance, which in turn increases pressure and thus more velocity. Although I’m sure there are others who know more about why this happens, it can affect your rifle’s accuracy. Experts confirm that barrel speed-up is common
Two well-known shooters have noticed an increase in velocity after using new barrels, usually after 100 rounds. Thomas “Speedy”, a Hall-of-Fame benchrest shooter and gunsmith, has witnessed barrel speed-ups through testing. Speedy’s borescope barrel inspections showed that the barrel lands were smoother. Jim See, a top PRS competitor has experienced barrel speed-up many time. He re-tunes his load at 150 rounds. Alex Lipworth and me documented this phenomenon four years ago. I have shared this information with all my customers. My son Mikee would shoot 100 rounds through any new barrels that we planned to shoot before we began load development. A shooting snail caught all the bullets when it was set up in front an indoor bench. It was a wear-in process, because the bore’s cut-rifled bore looks more like a button-rifled barrel. The lands have a more softened look than a buttoned bore. Speedy Gonzalez “Seen it [barrel velocity increases] too many times to count. My match barrels receive a ‘generic shot’ loaded for them. This has worked well in barrels of the past. I finish 150 rounds and fine-tune the load until the tube slows down at the end of its life. — Jim See
Similar Posts:Tags: Barrel Break-in, Barrel Velocity, Jim See, Speedy Gonzalez, Velocity
