What causes vertical stringing ?

[Spencer]

I have a new mosin nagant with which I was getting good accuracy with hungarian steel case ammo of uncertain bullet weight. I finally got my loading gear and loaded a selection of powder charges all with 150 grn hornady bullets. I get best accuracy but with perfectly vertical stringing with 39grns of IMR 3031. When I take the loads up to 43 grns of 3031 the vertical stringing disapears but the groups open up.

With 150 grn bullets and 39 grns of 3031 I get 1" groups with my No4, I was hoping I could do the same with the Mosin, and probalbly could if I could cure the stringing problem.

Anyone know what the problem might be ?

Thanks

 

[p-17]

Check the bedding first. Also check the barrel. It sounds like the barrel could be heating up, expanding, and causing pressure somewhere. Vertical stringing is a very common problem and bedding/barrel pressure is usually the culprit.

 

[Umbakrail]

Here is a link that may help you : http://w w w .6mmbr.com/verticaltips.html

 

[roberti11]

Stringing

Given that the stringing is vertical and resolves by changing the powder charge I would bet that it is bbl harmonics (See Below), try keeping the same bullet, COL, and varying the powder charge, but in smaller increments as shown in the picture.
Hope it helps.

 

[ben hunchak]

If you have isolated the problem to be the ammo.....the problem could be inconsistant case neck tension, you know how sometimes one bullet seats easier or harder than the next.