tipping bullets

[Dave]

I am a 300m ISSF competitor here in Sydney. I use two 6mm BRs, both with 1:8 twists, and I find that my bullets tip at the target. Berger 105, Lapua 105 and 107 MK. In examining other shooter's targets I find that their bullets tip also. But it would appear that I am the only one concened about it. Accuracy is superb, but I am concerned that the BC must be lowered if the tail of the bullet is hanging out in the airstream! Has anyone else noticed this phenomenon? I have just tried the 90gr Lapua and all shot holes are perfect. But the wind deflection of the 90gr is approaching that of the 308, so little is gained. Can anyone comment?
Dave.

 

[jb1000br]

what barrel?

crown perfect?

If hart barrel,have you measured ACTUAL twist.

Hopefully HBC chimes in here.

JB

 

[KHGS]

It would seem to be a case of understablisation at the distance tested. remember that long for diameter bullets often take some distance to "settle", this distance will be longer if the twist rate is close to the edge. I would suggest that you check the twist integrity, it will only need to a little longer than it is supposed to be, to creat your "problem". True 8" twist should be fine with the bullets you are using, even at sea level. All things being equal, the crown is the most important bit of your barrel.
Keith H.

 

[RCole]

Dave
The problem you describe is a long held question that I have had for some time.I shoot both the 107 and 105 at 300 yds and 600 yds. I have always suspected that the "long VLD" style bullets were not quite "asleep" at 300 yds, though I have seen numerous posts on this forum that purport to great accuracy at 300 yds with these two bullets.
I had a custom 6mm bullet maker build 500 107 flat base bullets and 1500 boat tail, more correctly a mini boat tail) bullets for examination and testing. Thus far I have shot the mini boat tail,MBT) bullets at 300 yds and 600 yds. The 300 yds testing have shown the MBT bullet to be very accurate indeed.The 600 yd testing showed the same as well. The 600 yd string that I shot with the MBT was a 22 shot clean with 13 or 14 X's. The 3 inch spotter that was being used had 11 6mm holes in it, its replacement, needed because the first spotter was shot to pieces) had 5 6mm holes in it.I was impressed to say the least. I would not shoot the MBT on a windy day at 600 yds as is is not near as "slippery" as the 107 or 105. The 300 yd testing showed the same conclusion. I shot so many spotters and "golf tees" out that the target crew simply began to mark my target with white pasters.
The testing on the 107 Flat base bullet is still ongoing and will only be done at 300 yds. I am hoping it too will be useful at the 300 yd line .
Both bullets are ideal with long throated chambers. When all testing is done, I will report back.
RCole

 

[Dave]

Both my barrels are Maddco, and I think those of fellow shooters are the same. One crown is 11 degrees and the other is recessed. I have measured the twist, as well as possible with a cleaning rod, and and they are both 1:8. I seat the bullets with land contact twice as long as wide. Earlier I worked up loads from the bullet jam position, but found that off a bit was best.

I feel the tipping is actually the air spiral described by Dr Mann relative to unbalanced bullets. He also stated that all spitzers are tippers, but settle and produce round holes at 100yds.

Tungsten bullets open up a possibility, with a 105gr no longer than a 68gr, but this is going to extemes! I could, of course, move to a 30 WSM and gain the deflection advantages of the 6mmBR, but I suspect barrel life would be very short.

Thanks to those who have replied.
Dave.