Thread: Scope mount screws

Hi all.

I need some help please...

Picked up a second hand 300 WM last week with Bushnell scope mounted on a 20 MOA rail.

Took it to the range Saturday and had to bore sight then got onto the 100m range and ended up with a sore shoulder before I was satisfied with grouping. When i picked the rifle up to take home I realised the scope had come loose. The screws mounting the scope to the rail were the culprit and I went o tighten them when I got home but they appear to be screwing all the way through the screw hole without tightening. They aren't stripped, I just don't think the screw head is the correct width?

ChatGPT tells me there are a couple of different standard screw sizes, is this likely to be my problem? Any recommendations on correct hardware to use?

Appreciate the help in advance.

Steel or alloy rings?

If alloy - I would guess the thread is flogged out in the base.

Good question... Will have to have a look when I get home.

So you are saying the screw head is passing right through the clamp plate that secures the ring to the rail/base? Might be a good time for a photo just to confirm.

If this is the case, and the screw head is too small for the rail it might be a case of someone grabbing the wrong hardware at some stage and then slapping it onto the rifle before selling it. If this is the case, it might just need a washer under each screw head to take up the extra room in the hole.

Also when refitting the rings, push each one fully forwards before tightening the locking screw fully as this is the direction the scope wants to go under recoil. If the scope has room to move that might be enough to start everything loosening. I would check that both rings are fully forwards, you might need to lightly screw the rings on then release the cap screws on one of the rings. Push the still tight ring forwards and lock it down, then push the other one forwards and lock it down and then retighten the ring cap screws.

Rings are very much a you get what you pay for item.
Do you know what brand they are Toyah.
If they’re junk rings you might be trying to make a silk purse out of a sows ear, especially if ‘bubba’ got to them first.

If a manufacturer doesn’t publish torque specs for their product or they require lapping, then don’t have too higher expectations for them.

Yeah, if it needs lapping something isn't right from the get go. Making a hole bigger is often not the best idea.

Have you tried inserting the screw directly into the threaded hole without the screw going through the hole in the clamp?, This will tell you if the hole is stripped or if the clamp is holding the screw clear of the threads.

The other thing than might have happened is that the first few turns of thread are stripped, so the screw can't get purchase initially, but if you look into the threaded screw hole it looks fine. This is highly likely if the mount (and threads) are alloy.

As others have stated, photos will assist greatly.

Have posted some photos. The threaded hole is good as is the thread on the bolts. As per the photos, the head of the screw is passing through the inside of the bracket.

Maybe it is the wrong bracket for the rail?

Originally Posted by Toyah

Have posted some photos. The threaded hole is good as is the thread on the bolts. As per the photos, the head of the screw is passing through the inside of the bracket.

Maybe it is the wrong bracket for the rail?

So it's the bolt that attaches the rings to the base which is the problem, easy fix buy some better quality rings.

Looks like alloy mounts and they are flogged out at the place that clamps to the rail. Best answer be to get some new rings

At first glance it looks like the bolts are either the wrong diameter head size (too small) or are missing a washer. At any rate they should not have pulled through the body of the ring like that. It seems any further diagnosis is now only of post mortem value.

As fawkes has stated. Time for new rings, preferably rings of better breeding.

Little washer would fix that it seems

Thanks all for your help.

Yeah someone has "upgraded" the original allen head screw to a torx head screw with a smaller and ill-fitting profile.

I would look at replacing the rings - as what you have is likely going to only cause headaches going forwards.

On rails like that fitted to Rem 700 actions there are a few things that should be checked when plumbing everything in. With the rings being replaced, it would be a good time to do this. When you have the rings off, remove the rear screws holding the rail to the action, and see if the rear end of the rail has any form of gap between it and the top of the action's rear bridge. Also, remove the front screw from the front of the base and see if it comes loose as this screw can bottom out on the barrel shank if it is too long and only be along for the ride. If this is all good, screw the rear screws back in and tighten and then remove the last front screw and see if the front of the rail has a gap under it. If either end is floating and you tighten it down it's stressing the receiver and putting a bit of misalignment into the works which isn't ideal. Can be sorted quite easily, but need to check for it first!