Re: Barrel speed up patterns an experiences.
Posted: Sat Mar 11, 2017 2:55 am
I'd heard about barrels 'speeding up' before, but had never put much stock in it. Due to the PITA factor of setting up optical chronographs, along with questions regarding their consistency from session to session depending on setup similar to those voiced already... I normally only chronographed loads once they were pretty much 'done' and shooting well. Usually that was a couple hundred rounds down the life of the barrel, and I never saw any meaningful change until late in the barrel life when things started to slow down as the lands eroded more and more.
More recently, I was getting ready to break in a new Bartlein #9 HV barrel for one of my FTR rigs, and thought that since I had a LabRadar now... I should try chrono'ing as many rounds as possible during load development. People I'd talked to had indicated that they would not be surprised if the barrel took as many as 150-200 rds to stabilize, and would not consider doing any serious load development before that. That didn't sit well with me, to say the least! The first 30 rounds or so showed bullets moving consistently, if slowly (200.20X @ 2600 fps) for a given load. Over the next 50 rds, the velocity seemed to 'jump' up to about 2635-2645 for that same load, and stayed pretty consistent over several trips to the range. At that point, I decided to call it good and commence load development.
FWIW, the LabRadar units, while *awesome*
are not totally immune to some setup issues. Due to some local constraints that prevent me putting the chrono out just in front of the muzzle, I have to use the Doppler trigger rather than the acoustic one. Typically my setup is pretty consistent... but one range session, the LabRadar ended up much closer to the rifle (not as much offset) than ususal, and the velocity numbers were off... not a lot, but about 20-25 fps slower than normal. The next range session, with the same load, and the chrono moved back out to where it usually sits, and the velocities came right back to where I expected them to be. Hindsight being 20/20 and all that, I probably should have adjusted the offset value in the LR config when I had it closer, but it didn't occur to me at the time :/
HTH,
Monte
More recently, I was getting ready to break in a new Bartlein #9 HV barrel for one of my FTR rigs, and thought that since I had a LabRadar now... I should try chrono'ing as many rounds as possible during load development. People I'd talked to had indicated that they would not be surprised if the barrel took as many as 150-200 rds to stabilize, and would not consider doing any serious load development before that. That didn't sit well with me, to say the least! The first 30 rounds or so showed bullets moving consistently, if slowly (200.20X @ 2600 fps) for a given load. Over the next 50 rds, the velocity seemed to 'jump' up to about 2635-2645 for that same load, and stayed pretty consistent over several trips to the range. At that point, I decided to call it good and commence load development.
FWIW, the LabRadar units, while *awesome*
are not totally immune to some setup issues. Due to some local constraints that prevent me putting the chrono out just in front of the muzzle, I have to use the Doppler trigger rather than the acoustic one. Typically my setup is pretty consistent... but one range session, the LabRadar ended up much closer to the rifle (not as much offset) than ususal, and the velocity numbers were off... not a lot, but about 20-25 fps slower than normal. The next range session, with the same load, and the chrono moved back out to where it usually sits, and the velocities came right back to where I expected them to be. Hindsight being 20/20 and all that, I probably should have adjusted the offset value in the LR config when I had it closer, but it didn't occur to me at the time :/HTH,
Monte