Scope mounting question

[Atroxus]

I recently mounted a Bushnell .22 rimfire scope on my Marlin model 60. I *thought* I had tightened the screws down pretty tight. When I sighted in last week at 50 yards my best 5 shot group was barely over an inch across. Today I took it to another range and was shooting at a distance of only 25 yards, and my shots were all over the place. By the end of the 200 round session all were hitting far right and low of point of aim. When I got home I realized that somewhere along the line the scope had slipped back far enough that the rear mount was completely OFF the end of the mounting rail. Anyone have any idea how to keep this from happening again?

The picture below shows the screws on the scope. I am wondering if I need a special screwdriver or driver bit for a drill to get these tightened enough? The widest screw driver bit I own still only made partial contact due to the big hole in the center of the head slot, so I tightened it as tight as I could without risking stripping the screw heads. Apparently it was not tight enough.

 

[Geno]

Use a good degreaser on the screws, and a small amount of blue Lock Tite on the threads. Be sure the receiver groves are also clean and dry.

Geno

 

[AKElroy]

Definately invest in a good screwdriver bit set for your firearms. Brownells has several good kits under $30.00; will save your screw heads & allow proper torque with a bit that EXACTLY fits your screw heads.

You might also want to hit the inside of your rings with a little fine sandpaper to rough them up a bit.

 

[CZguy]

Use a good degreaser on the screws, and a small amount of blue Lock Tite on the threads. Be sure the receiver groves are also clean and dry.

Plus one..............also invest in some gun screwdrivers.

 

[X-Rap]

I think you must have forgotten a screw, I can't see the 22 shooting a scope loose.
That set from Brownells will be some of the best money you spend on gun related tools, just save them for that purpose only.

 

[Atroxus]

I checked brownells and midwayusa but I could not find a screwdriver or bit that has that round part in the center of a flathead. I am 100% certain that I tightened both screws when I mounted the scope. A couple people on another forum stated it's because of the dovetail mount on the model 60 being "sucky", and suggested alternate mounting methods.

 

[CZguy]

I checked brownells and midwayusa but I could not find a screwdriver or bit that has that round part in the center of a flathead. I am 100% certain that I tightened both screws when I mounted the scope. A couple people on another forum stated it's because of the dovetail mount on the model 60 being "sucky", and suggested alternate mounting methods.

Well that's an easy one. Don't go back to that web site.

All of the suggestions mentioned above are good. Follow them and you will solve your problem.

Check out Rimfire central.

 

[AKElroy]

You also might want to try rings that provide a wider purchase to the rail; weaver makes a topmount ring set for .22 rails that look to be nearly twice as wide as those pictured. I use weaver topmounts for nearly every application. They are old fashioned, but they WORK.

I cannot see what you describe happening with a .22. It will absolutely happen with a spring piston air rifle, though. In fact, the .22 rails on most quality spring piston rifles have a set screw bridge stop on the rail to prevent this. Not saying you posted an air rifle issue in a rifle forum to get access to a broader breadth of knowledge--

 

[dmazur]

Here's a picture of a decent screwdriver set. It comes with a good assortment of bits (with parallel ground tips so they don't torque out like tapered tips...), and you can add 1 or 2 special bits easily if you have a rifle that requires something not in the kit.

http://www.brownells.com/.aspx/pid=22300/Product/OFFICIALLY_LICENSED_NRA_MAGNA_TIP_reg__SCREWDRIVER_SET

The bits are standard 1/4" hex bits so they will fit a 1/4" drive adapter, if you have a 1/4" socket set with a torque wrench. If you ever get involved with a rifle that requires screws to be torqued to a certain value, this will mean you don't have to buy a special torque screwdriver.

Re: the slipping scope, you shouldn't need a screwdriver that "matches that hole in the middle". It's there so the threads can go all the way through. If the threaded stud is all the way up into the slot, you may be tightening the ring against itself rather than clamping to the .22 rifle dovetail. Look for a "gap" between the loose part of the clamp and the rest of the ring. If you've run out of room, you need a set of rings that fits your rifle.

A more adventurous route is to file down the flat ring area behind the clamp...this doesn't alter the clamping surfaces, which have to be parallel. If you want it to be black colored again after filing, you can get a bottle of aluminum black at a gun shop. Buying a set of rings that fits is easier, but isn't free.

By the way, .22 scopes can usually be mounted/dismounted using a nickel as a screwdriver. I think you'll find that a nickel fits the slot just right. If you can't do it with a nickel, it's probably an indication of something else wrong.

Not that a good set of screwdrivers isn't a nice thing to have. You'll need something like that eventually. However, right now that might not be the solution...