1st time loading .30-06 & with GC'd lead in my M1917.

[Walstr]

21gr IMR4198 (I think, more shooting to verify), 150gr Wide HP, GC'd from BT Bullets, Inc. This was the 4th group of 5 shot & a real surprise using orig. battle sights.

[foesgth]

Interesting vertical stringing. Do you get that with other ammo in that rifle? 21 grains isn't much in a 30-06 case. I wonder if you could be having problems with powder position in the case? I have read a bit about Dacron filling on this site, that might help.

[runfiverun]

it's velocity variations doing it.
I see it with faster stuff like 4198-H-322 real bad.
a grain [grain and a half] of Dacron fluffed up from powder to case neck, and a grain reduction in powder will fix it.
probably tighten up the groups some too.

[Shiloh]

6:00 hold or center hold. With center hold I get stringing with the '03.

Shiloh

[Scharfschuetze]

What did the other four groups look like? If the other four groups are similar, you really are doing quite well with that old 1917.

As noted above, its very easy to get vertical stringing with 1917 or similar sights. Some factors that will lead to vertical stringing are: the lighting is bright or indistinct, the front sight is shiny, or focusing between the front sight and the target on different shots. Of course old eyes (presbyopia) do not help either if that's the case. It is for me now. I must admit though that aperture sights are my favorite sights for almost any type of shooting.

For a more distinct aiming point to take the possibility of sighting errors out of the equation, I would spray paint your paper plates flat black and then place it against a white or tan background and shoot a six o'clock hold. I buy regular bullseye centers in bulk so they're pretty cheap that way. They make for a much more precise aiming point for iron sights.

Don't forget the action to stock bedding, tightness of the action screws, or the bedding of the barrel in the long forend either. 1917 Enfield barrels were often made in the haste of war. It is not uncommon for some of them to start walking their rounds away from their cold bore zero as they heat up. Of course that's more common with full power jacketed bullet loads that heat the barrel up more than cast loads.