Walking impact

[rstreich]

I shot three 20-shot strings with my 6BR today in a club match. In all three strings, as the barrel heated up past a certain point, it started to walk the bullets straight down. It went about 1.5 minutes in all. No cleaning between strings.

The rifle is a BAT SV with a 26" HV taper.

Other than stress in the barrel, what might cause this condition?

 

[treeman]

if there wasn't much wind maybe it was the mirage from the heat coming up from your barrel??

 

[rstreich]

Nahh, it's not a bad thought, but this was way too predictable. The winds were light, but pretty active. I could see the effects of barrel mirage pretty clearly when it would wiggle around the deflector and into view--fuzzing out the view in the process. I can't say with absolute certainty that barrel mirage wasn't the cause, but I think I would have had a lot more bouncing up and down going on as the mirage came and went with the air currents.

 

[Travelor]

Sounds like bedding is causing stress on the barrel that is "relieving" itself as the barrel heats. Check and see.

George

 

[rayjay]

Your bore is probably curved significantly. This means that there is less metal on on one side of the bore hence uneven growth as the bbl gets hot. It does sound like your bbl is indexed so the curve in the bore is in the vertical plane.

 

[SlowpokeRodriguez]

Something else to consider is how long the round sat in the chamber. When the chamber heats up and the round is also in the chamber heat is transferred which increases pressure when the powder is ignited. Have seen that problem too many times during matches.

 

[olympian]

This is a different situation altogether, but this is common with some of the thin barreled,older military) rifles, e.g. Mausers, that buddies and I shoot. After six, seven, or eight rounds, or less depending on the load, I have seen the point of impact drop a foot or more at 500m. These barrels are not stress relieved or bedded. It is all about the heat with these.

 

[rstreich]

I talked it over with my gunsmith and gave the manufacturer a call. I'll send the barrel back to them. If it is a bad barrel, well, it was bound to happen sooner or later.