Cleaning side effect.

[big5ifty]

After cleaning my rifle, I loaded up a new batch of ammo and went to verify zero.

The zero group was terrible. From a half moa load to over four. I was, to say the least, very depressed.

This is the same day with the rude little c*nt on the range, so I was not in elevated spirits.

So I get home, and think about what I may have done wrong.

Now it just happened that next to me on the range that day was a young man whose rail worked loose, and he had come over to ask if I had tools, which I did, and helped him out with.

I thought about it a bit more, and realised that the problem has to be mechanical, not load related, because the rifle shoots anything to within one moa, which it did for me over and over during load development.

I rocked the scope from side to side, and the rail rocked with it. The front screws were loose, the one rear screw was loose, there was one tight rear screw holding the rail on.

In the past, I had used a clear epoxy to bed the rail. The Ed's Red contains acetone, and it penetrates between any metal surfaces. Some of it clearly found it's way into the the front chamber area, worked it's way up the front rail screw, into the second rail screw, and must have dissolved the release agent I used on the action when I bedded the rail, creating  enough of a gap to permit the screws to work loose under recoil. When I removed the rail, I had liquid between the rail and the front of the action.

I'm seriously considering using an acetone resistant epoxy to fix the rail to the action, after I get the rail screws bored out to one size bigger.

[oafpatroll]

I'm seriously considering using an acetone resistant epoxy to fix the rail to the action, after I get the rail screws bored out to one size bigger.

Those two things are bound to work. I did the same for the rail on my Mossberg seami auto 12G which used to work loose. Been fine for > 5 years of mainly warm slug and buck loads.

[Treeman]

what epoxy did you use ?
ABE epoxy 372 ? - it is everything resistant. I use spray and cook on one surface,nothing other side. Desemble after curing a few days and clean surfaces thoroughly before tightening up.
Lasts forever and a few days.

[big5ifty]

I believe it was the 372. The epoxy on the bottom of the rail did not soften at all.

There are two possibilities, and they may be concurrent :

1. the acetone mix worked it's way from the chamber up the second screw in the front, which is why I had liquid between the rail and the front of the action.

2. the screws were loose before I did the cleaning, which is why the solvent was able to flow where it did

I've had the problem once before where the rail shot loose. I then bedded it, and used blue loctite on the screws.

It's been somewhere around 150 rounds now, and it's loose again.

The scope is 1.2 kg, the bullet is 300 grains at just over 2900 fps. The screws are the normal 6-40 size, which is 3.5mm. Next size up is 8-40, which is 4mm.

The first thing I'll do next is replace the rail screws with something bigger, a lot bigger - like  5mm.

Then I'll clean the 372 off the bottom of the rail, and re-bed it with 372 again.

If it shoots loose after that, I dunno.

[Treeman]

I also glue my rings and mounts, they then need a good sturdy tap to separate.I have been using Bostic todate.I am not able to prove this works, but for me my troubles stopped about there.

I read somewhere that in europe some folk use epoxy on the rings and mounts.

[janfred]

When using blue locktite, or any locktite, make sure that the threads are oil and grease free. Failure to do so ensures that the locktite won't work.

[janfred]

414gates. Are you using countersunk screws for the rail?

[Treeman]

When using blue locktite, or any locktite, make sure that the threads are oil and grease free. Failure to do so ensures that the locktite won't work.

*************************
If not your locktite is worth breadcrumbs in a famine.

[big5ifty]

414gates. Are you using countersunk screws for the rail?

The current 6-48 screws are cap head screws. I will have the rail and action drilled for either 4mm or 5mm metric taper head. I bought taper head and cap head in 4 and 5mm metric, the taper head has a lower profile than the cap head, and will "grip" a bigger area of the rail.

If I look at the area of thread in the action holding the rail down, in a 4mm thick section, the 4mm screw gives me 75 mm squared of contact, the 5mm 102 mm squared. A 6-48 screw in the same section has 63mm squared of thread contact area.

I don't know of a good reason not to use 5mm screws.

[Treeman]

 I don't know of a good reason not to use 5mm screws.
[/quote]
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I have often wondered about this, but kinda just went the " must have a good reason' and moved on. Why do they use those little dental tools screws and threads?

[Ds J]

414gates. Are you using countersunk screws for the rail?

The current 6-48 screws are cap head screws. I will have the rail and action drilled for either 4mm or 5mm metric taper head. I bought taper head and cap head in 4 and 5mm metric, the taper head has a lower profile than the cap head, and will "grip" a bigger area of the rail.

If I look at the area of thread in the action holding the rail down, in a 4mm thick section, the 4mm screw gives me 75 mm squared of contact, the 5mm 102 mm squared. A 6-48 screw in the same section has 63mm squared of thread contact area.

I don't know of a good reason not to use 5mm screws.

Are the holes over or near the chamber?

Would the larger holes cause structural weakness to the action?

[big5ifty]

The one front hole is over the barrel thread.

The gunsmiths that I spoke to never once mentioned the action being weakened, they were all of the opinion that 6-48 is all anyone will ever need, and then they usually mention how they mount scopes to big bore rifles with those screws and there's never a problem.

[Ds J]

I doubt that it would make a difference.

The barrel and chamber take the pressure, and not necessarily the action?

[big5ifty]

The action will take the force of the recoil from the bolt lugs.

That force is perpendicular to the holes, so there is no force pushing in the direction of the hole itself.

The ability of a screw to withstand un-screwing when correctly torqued is related to the area of thread.  A fine thread of the same diameter can resist better than a coarse thread, but when the diameter of a coarser thread is increased enough, it exceeds the thread area of a smaller diameter, finer thread.

On the following link, Jon A gives a bit of math.

Link to opticstalk.com thread.