Horizontal Stringing

CHAIRMAKER

Experts,
I recently aquired a Remington Model 7 CDL in 22-250, 20" lightweight barrel with a 14" twist. I have bedded the action and floated the barrel. So far accuracy has been quite good (usually MOA or better) with Hornady 53 Gn. HPs using RE-15, and with Hornady 55 Gn. spire points using RE-15 and H-4895. However, when shooting Nosler Ballistic Tips in 55 Gn., I am getting pronounced horizontal stringing in the groups, often 2" or more at 100 yards. I am only shooting 3 shot groups and am allowing the barrel to cool completely between groups.

I have tried several different powders and charge weights as well as varying seating depths.

I am using Norma brass, Federal 210M primers, H-4895, RE-15, Varget, RE-19, IMR-4064, along with RCBS Gold Medal bushing dies.

Is it possible that the Nosler is too long (.810") for a 14" twist? The HPs (.710") shoot fine. This rifle seems to have a very long throat, in fact, I cannot seat the HPs near the rifleing and keep the bullet in the case.

Any ideas?

Thanks in advance.

MIKE WISKEY

light weight barrels like this USUALY like some 'up pressure at the forend tip (your rem. probably came this way, you removed it when you 'free floated' the barrel).

nononsense

CHAIRMAKER,

Mike's suggestion is a good diagnosis for short, skinny barrels. They have a tendency to move around even when we think we have allowed the barrel to cool. The smaller diameter barrels tend to have more stresses in them and move more quickly than a larger diameter barrel does and don't show up as fast. The common temporary solution is to use a small shim under the barrel at the end of the forearm such as a matchbook cover or something similar. This upward pressure can sometimes be the just the thing for getting your barrel back on track. A more permanent solution after testing is to create a pad of bedding compound that is the thickness of the original shim.

In general, most horizontal stringing is due to wind and our lack of awareness of it at various ranges. This is the single largest factor for horizontal stringing.

Less noted is the lack of balanced tightening of the rear windage screws on those types of scope bases. Too often we tighten one side thinking that this will combine to tighten the opposite side when in reality the opposite side has a tiny bit of looseness which can be magnified over time by continued shooting. Check BOTH sides of the windage screws.

In what might seem to be a more esoteric solution, we should be much more aware of the position of the bag supporting the butt of the rifle when we're using the bag as means of support. Too many times, we just accept the position of the rear bag from shot to shot. We should pay close attention to the fact that the rear bag needs to be in line with the barrel when we shoot. Check it after every shot and reposition as necessary. Misalignments in the rear bag and the barrel will contribute to horizontal stringing.

If your load for the 55 grain Nosler BT is a pinch lower than the books suggest, you could be experiencing some horizontal. These bullets benefit from being fired at the upper end of the pressure curve especially if you have a 1:14" twist rate. The length of these bullets puts them on the edge of stability with the 1:14" twist so additional velocity can be a benefit. But be aware that the most obvious indicator of instability is the shape of the bullet hole in the target and not horizontal stringing. Instability and wind can show a combined effect of horizontal stringing.

Remember that there is more than just the one accuracy node in any barrel/bullet/velocity combination.

Best.

Mobuck

You might be getting some pressure on the side of the barrel from the forend when the barrel warms up. Might also be technique. The shorter, lighter barrels tend to bounce away from anything.

konamtbiker

http://www.6mmbr.com/verticaltips.html

Good Luck.