Curious diagonal stringing

[Tom A Hawk]

I have been working with my latest build, (.54 Isaac Haines, 38" swamped Rice) to identify the most accurate load and I'm seeing a strange diagonal stringing effect with increased powder charge. 80 grains prints low, right. 90 grains prints slightly higher and left about 15 degrees. 100 grains prints center, slightly high and 110 grains prints high, left and again on the same 15% angle. Total spread about 5 inches. I've not seen this diagonal effect with other rifles and am puzzled as to the cause. Something relating to bullet rotation perhaps.

 

[Jaeger]

Is it possible that it's related to your gun barrel getting warmer with each shot instead of 10 grain increments in the powder charge?

 

[Tom A Hawk]

Is it possible that it's related to your gun barrel getting warmer with each shot instead of 10 grain increments in the powder charge?

I don't think so. 100 grains still shoots center, next time out with a cold barrel.

 

[dave951]

One possible cause- torque from the inertia of the bullet engaging the rifling. It's well known in modern high power handguns. If you watch a show motion video of one being shot, you'll see it will always flip up to one side

 

[Phil Coffins]

Do you left handed?

 

[Tom A Hawk]

Do you left handed?

I shoot right handed and the barrel has a right hand twist. Again, I have a number of other rifles and only see changes in elevation with powder charge with those.

 

[Frontier's]

I have been working with my latest build, (.54 Isaac Haines, 38" swamped Rice) to identify the most accurate load and I'm seeing a strange diagonal stringing effect with increased powder charge. 80 grains prints low, right. 90 grains prints slightly higher and left about 15 degrees. 100 grains prints center, slightly high and 110 grains prints high, left and again on the same 15% angle. Total spread about 5 inches. I've not seen this diagonal effect with other rifles and am puzzled as to the cause. Something relating to bullet rotation perhaps.

Like this?

 

[LME]

I have been working with my latest build, (.54 Isaac Haines, 38" swamped Rice) to identify the most accurate load and I'm seeing a strange diagonal stringing effect with increased powder charge. 80 grains prints low, right. 90 grains prints slightly higher and left about 15 degrees. 100 grains prints center, slightly high and 110 grains prints high, left and again on the same 15% angle. Total spread about 5 inches. I've not seen this diagonal effect with other rifles and am puzzled as to the cause. Something relating to bullet rotation perhaps.

shoot five shot with different loads, then pick the best one to use. If it doesn't group with any load something is wrong with the rifle or you?

 

[Tom A Hawk]

Like this?

Very similar but a little steeper angle. Maybe 5 oclock to 11 oclock.

 

[Rifleman1776]

Which charge gives the best groups? Find that set sights accordingly. The gun torque theory is, to me, very plausible considering a light barrel, large bore and heavy charges.

 

[Tom A Hawk]

Which charge gives the best groups? Find that set sights accordingly. The gun torque theory is, to me, very plausible considering a light barrel, large bore and heavy charges.

Thats the plan but was curious regarding the cause.

 

[SDSmlf]

Just to check the box, have you slotted the pin holes in the barrel tenon to allow for stock movement? I had a gun that would change POI as it warmed up, either from the sun or from shooting. Lengthened the tenon slots and the vertical stringing went away. Your issue sounds different, but an easy one confirm and take off the list.

 

[Tom A Hawk]

Just to check the box, have you slotted the pin holes in the barrel tenon to allow for stock movement? I had a gun that would change POI as it warmed up, either from the sun or from shooting. Lengthened the tenon slots and the vertical stringing went away. Your issue sounds different, but an easy one confirm and take off the list.

Thanks. I have not. The underlugs were simply dilled for pins. This is something to consider.

 

[Flint62Smoothie]

Harmonics … have seen it before.

Just also make sure that your barrel pin ‘holes’ are filed or jewelers saw cut to be ‘slots’.

 

[SDSmlf]

Just to check the box, have you slotted the pin holes in the barrel tenon to allow for stock movement? I had a gun that would change POI as it warmed up, either from the sun or from shooting. Lengthened the tenon slots and the vertical stringing went away. Your issue sounds different, but an easy one confirm and take off the list.

Thanks. I have not. The underlugs were simply dilled for pins. This is something to consider.

Honestly, more of a ‘must have’ rather than a something to ‘consider’ item. I like to elongate the holes in barrel tenons up to an 1/8” in each direction, particularly with a longer barrel. I have been using my guns in both hot humid weather (the Carolinas) and near zero F cold (upstate NY) for years, and the stocks do move.

 

[Tom A Hawk]

Honestly, more of a ‘must have’ rather than a something to ‘consider’ item. I like to elongate the holes in barrel tenons up to an 1/8” in each direction, particularly with a longer barrel. I have been using my guns in both hot humid weather (the Carolinas) and near zero F cold (upstate NY) for years, and the stocks do move.

I'm convinced. Will have to disassemble and work on the lugs.

 

[SDSmlf]

I'm convinced. Will have to disassemble and work on the lugs.

It may not solve your stringing problem, but if it doesn’t, at least you’ll know it’s not the cause. I remember reading that some old guns with no slots in their tenons had fore-stocks pulled apart by up to an 1/8”. Pretty sure I read it in one of Shumway’s books.

 

[Tom A Hawk]

It may not solve your stringing problem, but if it doesn’t, at least you’ll know it’s not the cause. I remember reading that some old guns with no slots in their tenons had fore-stocks pulled apart by up to an 1/8”. Pretty sure I read it in one of Shumway’s books.

Good memory.

 

[SDSmlf]

It may not solve your stringing problem, but if it doesn’t, at least you’ll know it’s not the cause. I remember reading that some old guns with no slots in their tenons had fore-stocks pulled apart by up to an 1/8”. Pretty sure I read it in one of Shumway’s books.

Good memory.

That sure looks like what I read, but believe I have more than one of Shumway’s books and not sure which one he said it in, although I bet he stated in multiple books. His statement just left an impression years ago, and the +/- 1/8” slot is just something I have done since. Might be time to go through the ‘library’ and see what I have forgotten. I know the bride points out plenty of things I have forgotten, but that’s a different topic.

 

[44Bro]

Two things come to mind. First, is the bore straight with no internal wander? Second, smoke the barrel and look for a high spot in the stock channel. A wandering bore set at an angle will cause the walking shots with greater recoil. A high spot in the barrel channel will cause a differing harmonic node on bullet exit.