Flummoxed. With the release of the Garmin chrono, I’ve tossed my LabRadar in the back of the shop and packed my MagnetoSpeed in the trunk for backup. I did a comparison test of the three chronos and they tracked well although there was a small but constant shift in the velocities across the three chronos. In that test, I noticed the velocities of my 6mm BRA (109 Berger Hybrids, 30.2 gr N150) were drifting higher over the session. I conducted subsequent large N tests in 4 separate sessions; the drift was still observed. Shooting conditions were mild and consistent across the sessions. Bartlein barrel never got more than slightly warm as my firing protocol was slow, a minute between rounds; 5- or more minutes between 5-shot groups. I conducted maintenance cleaning at 50 and 141 rounds and a deep clean down to shiny metal at 237 rounds. The velocity drift continued. In the session which started with the deep clean barrel, the velocity shifted significantly lower but then drifted higher. Across all my sessions, each 5- or 10-shot group produced terrific numbers with SD’s almost always under 5.0 fps, always under 7.5 fps. However, across the entire session string, the aggregate SD was much larger. I statistically tested the data and the trend was significant. I’ve included a plot of my data. The drift seems clearly related to carbon build up, but so quickly? Anyone experience MV drift over a set load? Ideas?
MV Drift: 6mm BRA
- Thread starter OMB
- Start date
How many rounds on the barrel?
I'm no pro...far from it. I have a buddy that is having issues with the same powder in a dasher (ran around the same velocity you're running) with 1500ish on it.
My first thoughts are the barrel is fire cracked enough to start fouling quicker than you guys are used to. And/or the powder is fouling more than you guys are used to.
My buddy has ran a dasher for years and ran n150 all last season I believe. So not sure why he'd all the sudden have issues but it's exactly what you saw. He couldn't put his finger on it because the gun hammered before 2 different matches and then he kinda chased his tail and couldn't figure out why his data was always off (prs shooter)
Right or wrong, I don't know...but I deep clean back to bare steel every 100 or so rounds. Thatll get me through a 1 day match. I know what my bore does from 0-100ish.
I'm no pro...far from it. I have a buddy that is having issues with the same powder in a dasher (ran around the same velocity you're running) with 1500ish on it.
My first thoughts are the barrel is fire cracked enough to start fouling quicker than you guys are used to. And/or the powder is fouling more than you guys are used to.
My buddy has ran a dasher for years and ran n150 all last season I believe. So not sure why he'd all the sudden have issues but it's exactly what you saw. He couldn't put his finger on it because the gun hammered before 2 different matches and then he kinda chased his tail and couldn't figure out why his data was always off (prs shooter)
Right or wrong, I don't know...but I deep clean back to bare steel every 100 or so rounds. Thatll get me through a 1 day match. I know what my bore does from 0-100ish.
Shooter13
Gold $$ Contributor
This ^^^^^
Nothing obviously wrong to me. My first two sessions were at 112 yards with no significant difference between the sessions: the weighted average CEP(90) was 0.279” (90% of my shots under 0.56”). The next four sessions were at 518 yards, again with no significant differences among the sessions: weighted average CEP(90) was 2.363” (90% of my shots within 4.72”). As a newbie and geezer, these are probably at my own limit. I don’t have a good round count but it’s upwards of 2,000.
I've seen this behavior in two different rifles, my 6mm BRA (Bartlein) and my .308 Win (Shilen). I've attached plots of my .308 data, comprising 472 velocities with two bullets (168 gr TMK, 167 gr Scenar) and N140 powder. In the plots on the left, each colored panel represents a different session at the range. The lower left plot, last panel was my F/TR data. This was the only session in which my barrel got hot. In all others, the barrel was not hot. For some panels, the dramatic drop between the end of one session and the beginning of the next is likely related to my Bryan Litz-inspired bore paste cleanings. Despite a scrubbed barrel, the velocites still drift up. The barrel is not worn with about just under 1,000 rounds, none hot. Scoped the barrel, and to my eye, nothing unusual there. My reloading practices are pretty standard: every charge is weighed, cleaned brass, necks neo-lubed, inline seater, etc.
urbanrifleman
Site $$ Sponsor
It appears the total spread over nearly 300 rounds in varying conditions was about 40 fps total.
I'm not really sure the expectation of the system.
I'm not really sure the expectation of the system.
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