CZ 550 .308 Varmint bugholes at 100 but trouble at 500

[Thorbird]

My buddy has a new CZ 550 Varmint .308 with a 1 in 12 twist. Beautiful gun and impressive shooter. It is an easy 1/2 MOA gun, with many 1/4 MOA groups. He has shot great groups out to 400 with this gun. However, when he shoots at 500 with it, he is having consistent problems. We were shooting at 500 yards, and it was a windy day, with 10 miles per hour full value wind with higher gusts.

My friend was getting 2 shots about 1.5 inches apart in the 7 o'clock position, and then 1 "flier" about 7"-10" up at the 1 o'clock position, and then it kept repeating that pattern. 2 close and then the flier. He had the same problem about a week before at the same distance. He has tried a number of powder, and primer combos, but always the same bullet. The Sierra palma 155's seated 10 thousands off lands at about 2700 fps. On this day he was using Hornady match brass, 43.1 grs N 140 Fed 210 primers. He has been very consistent in his shooting and is a great shot. The rifle is not bedded yet, the barrel was not dirty or hot. Any ideas on what could be going on would be appreciated.

Thanks for any suggestions you might have.

 

[tsiero]

My suggestion would be to bed the rifle first and retest. Bedding the rifle if properly done will only improve the rifles accuracy.

 

[jo191145]

Besides the wind I have no opinion.

43.1gns of Viht 140 is the exact charge my Kreiger Palma barrel likes with the 155 Palmas. .012 jammed. I tweaked the load with BR-2's and received an occasional flyer no matter what. Four out of five were always .25 moa or less plus a nasty flier.

Tried a really old lot of Fed 215 magnum primers with that load and it came together nicely.

 

[Jumper]

I had a similar problem with my 25-06. The first shot would be POA the second would fly and the 3rd shot would again be POA. I tried many different component combinations, outside neck turned my cases etc ., but the problem turned out to be scope parallax. I adjusted my scope for least parallax and my groups have eliminated the "flyer".

 

[Thorbird]

Thanks jumper, I'll tell him to check it out.

 

[Forum Boss]

Run a borescope if you can find one. I experienced a gun that would do that. The culprit proved to be a factory barrel with one land that was shorter than the others. This caused shots to unpredicatbly spit out. Jerry Tierney had a similar problem with one barrel that had a damaged land about half-way up the barrel.

Back to my example, I was able to reduce the flyers by moving the bullets out to .025 off the lands. I would experiment with jumping that far or even more.

I've also see factory barrels that were not stress-relieved toss flyers like that it was heat-related.

Check the action contact in the stock and check the action screw torque. And make sure the scope mounts and rings are properly tensioned.