What should be the minimal clearance between the scope bell and barrel? Mounting a new AO scope on my 17 HMR revealed that the knurled AO turning ring stands pround about 1/64" from the bell. Mounted, the bell is about 1/63" from the barrel and I can see light between the knob and the barrel. I can get a piece of news paper between them - barely. Is this too close?

Well - never mind - I ordered a new scope with a smaller objective - nice excuse ha ha

For the nil recoiling 17 HMR cartridge the clearance you had would have been fine. I don't know that there would be any measurable flex of the objective lens housing of a scope on a rifle under heavy recoil but to be sure that some clearance was maintained between the objective lens housing and barrel on a big kicker I would want a little more than just newspaper thickness.

If one really had to have a particular AO scope on a rifle where the clearance was thought too little it would be easy enough to carefully file off some of the knurling on the alloy adjusting ring and touch up the result. Carefully done it would not be noticeable.

I mounted 6x Kahles scope on my Schultz and Larsen rifle in low 26mm Weaver rings (could only get low rings in 26mm) but the objective lens was touching the tapered section of the barrel ahead of the receiver. A little judicious use of a file on this tapered section of the barrel, touch up the bluing and all was perfect. Used this combo for several decades of hunting with just minimal clearance of the lens to the barrel.

I won’t be filing the knurling off any of my A/O adjustment rings on my scopes.
I have a leupold with am A/O ring on a Sako 6 Ppc. It have the amount of clearance described by the OP and it works fine.

the real question is, after you've fired some rounds and the barrel gets hot, do you still have space?

I would be surprised if you'd have a problem with any rifle, let alone a 17 HMR.

Before I filed on barrel or scope, I'd be trying shims.

quote:

Originally posted by carpetman1:
Before I filed on barrel or scope, I'd be trying shims.

Thanks for the replies. I had 4 layers of electrical tape on the lower half of the rings to get it where it was. The AO knob is rubbery feeling so I think removing some of that accurately would be difficult.

The rifle is a Ruger 77/22 VBZ heavy barrel that I have 3 barrels for - 22, 17 HMR and a 17 Mach II. Currently I have the Ruger HMR barrel on it. I frequently use it with the Mach II barrel which is an after market barrel with a profile that is "pretty close" to the factory but a little heavier. So rather than lose sleep over it, I got a non AO side focus scope with a smaller objective. The AO version will be put to use on a rifle that I already have high rings for!