What issue is causing this?

[Don Fischer]

I think the first course of action should be to clean the gun! Next check the bedding. Next don't try to save on ammo sighting in. Thing like what yu have right here blow that idea all to h*ll! Take thing one at a time. Scope is probably tight because you seem to have some decent groups, well semi decent. But could be a loose scope I guess, I've never had one. If it's bedding, I doubt, I read that horizontal stringing is generally caused by a high spot in the barrel channel that the barrel is bouncing off while vibrating. If the stringing is vertical then possibly a bind in the action. After that is checked, few minutes, before testing any loads, clean the barrel. Might not be dirty enough to do any harm but then again it might and unless you know it's clean, you don't have a clue what's gonna happen. Something I read about cleaning the barrel, don't over clean it. Seem's an overly clean barrel will require fouling shot's to get going again but a barrel that is not sanitary won't require the fouling shot's. Start at the beginning and end at the end!

 

[antelopedundee]

Good video from Jeff for scope base bedding

Kind of a neat looking Picatinny base. Never used a pickem tinny base so I ordered one like in the video, the 0 MOA version. Got it today. Would be nicer if the bubble was between 2 lines, but ya gotta be able to lift the bolt and clear the base soes you'd need RH and LH versions to accommodate a wider level. The bubble is kind of hard to see snugged away under the eyepiece so unless you got a critter that's not gonna bolt it may not be of much help in the field. Depending upon the objective diameter of your scope low rings could be a decent fit.