Action screws loosen with temperature changes - bedding?

[Alistair]

Hi all,

A quick question on my rifle. My go to hunting rifle is an old .270win Tikka M695 with a pretty walnut stock which I rebarrelled fairly recently. The one in my avatar to be precise. It shoots great most of the time, printing 1.5" groups with factory softpoint and a little under an inch with homeloads. All good stuff.

Bu here's the issue. A fair bit of my hunting is consecutive days on red hinds in Scotland. 5 shots in a day and maybe 20 in the week is not unusual. I have found on 2 occassions now that over the course of the week, and in some cases over the course of a single shooting day, that the stock screws can work themselves loose, leading to zero shift and in some cases missed shots or time consuming re-zeroing. It could also end up in a miss or even worse a wounded animal.

Now I shoot the rifle a lot on the range and this is never normally a problem but it really seems to struggle with the combination of moisture, repeated cycles of temp change (wet and cold in the day, warm and drying out overnight) plus the vibrations and impact inherent in repeatd firings and lugging the thing over fairly rough terrain for 7 or so hours a day.

I don't really want to switch out the stock, its good wood, I like the aesthetic, plus it shoots, but it's getting to the point that I can't ever be truly sure that when I pull it out of the slip that I have a reliable, working rifle.

I check the screw torques before I zero and I try and keep on top of them every morning, but I'd like to explore a slightly more permanent solution. One option might simply be to threadlock the screws, but I'm also toying with the idea of bedding the stock.

Does anyone have any thoughts or advice on this, or should I just bite the bullet and get a synthetic stock for these conditions?

Thanks for your thoughts,
Al.

 

[PHOENIX PHIL]

Can't see where bedding will help with the problem. It's not bad to do and can improve accuracy. But the simpler and easier way is to the thread lock the action screws.

 

[450 Dakota]

I would have aluminum pillars installed and bed it. The pillars should help with the expansion and contraction of the wood. If they still loosen after that some blue loctite like Phoenix Phil said will stop it.

 

[Russ-F]

Hello Alistair,
For years I’ve habitually shot in basically the same variable conditions (similar locations even) as you have with wood stocked rifles & never had a problem with either the stock bolts nor bedding - I’m not diminishing your troublesome experience with that comment though.

All of my rifles had pillars at the bolt locations & very well seasoned wood. I think the pillar bedding played the key role though & most rifles had socket headed bolts which allow a decent torque to be easily applied plus the pillars can take the increased compression.

If your rifle doesn’t have pillars installed I’d suggest getting them done (it’s not expensive) - obviously assess the general bedding at the same time, I’d then change to socket head bolts (Allen or Torx) if you don't already have them & make sure they were nicely tight. A nicely polished & blued head on a socket headed bolt to match the finish of the rifle looks fine.

Regards
Russell

 

[Luvthunt]

I am a function before form guy—-so I would buy a synthetic stock use it for the week of hunting and replace it the rest of the time with the wood to look at

 

[Russ-F]

I am a function before form guy—-so I would buy a synthetic stock use it for the week of hunting and replace it the rest of the time with the wood to look at

A decent wood stock offers both form & function.

 

[Mekaniks]

Use a little Loctite or similar product on the bolt threads. Make sure to use the removal type and not the forever heavy duty style. If used properly it should keep your screws tight.

https://www.brownells.com/gunsmith-...liquids/248-threadlocker-stick-prod20762.aspx

 

[Alistair]

Cheers guys.

It seems loktite is the first option to explore.

The rifle isn't pillar bedded or anything at present I don't think, just the standard wooden stock and bottom metal, so I might explore this option as well.

It'd be nice to stick with the wooden stock if at all possible, so hopefully this'll resolve it. If not, it might be time for a synthetic.

Cheers,
Al.

 

[Hogpatrol]

I go along with the suggestion to install pillars and then bed the action. Make sure the pillars are touching the action and not covered with bedding material. Check your barrel clearance to make sure there isn't some pressure being applied to it by the stock. With that work done, your problems with POI changing should be resolved.

 

[Longwalker]

I agree that pillars and epoxy are the solution. I have had several rifles modified in this way, and each time the changing point of impact issue was resolved and usually accuracy increased as well.

 

[Nhoro]

Can you check if the screws are turning and loosening or are they getting loose but have not turned. There are two possibilities: 1. The screws are turning themselves loose due to vibration (Loctite will fix this) 2. Screws have not turned but the wood has shrunk or shifted.
If the wood of the stock is changing dimensions that much, Loctite will simply lock the screw in place. The wood can shrink and the torque of that Loctite screw will decrease and you POI will shift. The screw wont shift but the stock will,if that makes sense. Glass bedding/pillar bedding will help because you will screw aluminium or glass against the action.

 

[ZG47]

I agree with epoxy bedding and pillars, as suggested above.

Beyond that, I suggest that you remove the butt pad and seal the end grain with multiple coats of thinned polyurethane varnish (spar varnish from the nearest chandler would probably be best).

Also seal the barrel channeI, any other inletted areas that do not get covered with epoxy bedding agent; and the checkering. A ‘hard’ tooth brush works well for the checkering.

 

[Dewald]

Alistair, i have a Tikka M695 6,5x55 as well, that has been, similar to yours, my go to rifle for twenty odd years. They are great rifles.

The bottom-metal however is plastic, with the action screws going through a tapered farrel/ washer that sits in the plastic. Over time this farrel gets drawn deeper into the plastic and your screws can bottom out. Also inspect the plastic bottom metal for cracks, which could cause trouble.

The easiest solution is to file 1mm of the end of each screw, and use Loktite to hold it in place.

Nothing wrong with bedding it, and pillars will prevent further compression of the stock and plastic bottom metal

If the bottom metal is damaged, you can replace it with an aftermarket aluminum one.

 

[lockingblock]

There are two solutions.

Optimal would be bedding in Marine Tex along with stainless pillars glued in. This is a 100% solution.

However....if you want a DIY solution, go to your auto parts store and buy a tube of blue lock tite. Clean the threads and put a drop on the threaded portion, then tighten to spec. It won’t come loose until you put a screwdriver to it. Don’t use red or purple. Generally, I have a gun rule that anything with threads should get lock tite....

 

[rookhawk]

Pillars and glass bed. What makes you think the screws are loosening via backing out? It could be compression of the wood under recoil, etc.

Threadlock isn’t the answer.

 

[rookhawk]

I'll give you a little more verbose response in an anecdote:

So many states in the USA have a slug-only, NO rifles allowed for hunting policy. That leaves us with a horribly inaccurate technology to use for hunting in many midwestern states. The proof has been consistent regarding their accuracy: the 3" 20 gauge slug is by far the most inherently accurate cartridge for slug hunting over long distances. The problem is that they have a recoil that is greater than most medium-bore safari rifles, not a boon for good shooting practices and long range discipline. (long range means 180-250 yards)

Add to that, there are very few "high quality" slug rifles out there and the ones that exist are $5000-$7000, double-triple marked up, and really not that great in the quality department. Thus, we have to build our own. We start with a Savage 220 bolt action slug rifle in 20 gauge and then strip it down to the action and barrel. We then toss away the worthless injection molded plastic stock and buy the only custom stock available: Boyd's plywood laminate stocks.

This is where the story comes back around to your issue/question. We found that to get accuracy, you need to torque the bolts to about 35-inch points of force. The problem is that the violent recoil compresses the stock and over a few shots from a rest/bench the bolts appear loose. Do we tighten them again and thread-lock them? NO. Reason: the wood is compressing under recoil, the screws aren't backing out. Next thing you know, you've smooshed/smashed/crushed/compressed the stock because you're just driving the bolts deeper. Eventually, they protrude into the action raceway and then you're dressing down the screws so the bolt will operate unobstructed.

In short, not a winnable game. The solution is to glass bed at minimum, pillar bed if possible. That way, the barrel and bottom metal are compressed precisely and they are resting against metal pillars and the entire surface area of acri-glass. This is the road to accuracy. You don't want threadlock because its not the problem nor is it the solution for most applications. You need to lock down the bearing surface of the action and screws permanently. To do this, you need something harder than the stock...like pillars and acrylic-fiberglass compound.

To close the loop on the anecdote of the slug guns: we then had to glass bed actions, get steel picattinny rails because the aluminum ones damage under recoil, exceptional rings and scopes to handle the "africa level" recoil. A better bolt knob to throw those sticky spent 3" hulls. A good custom trigger instead of the lousy accutrigger. All-in, you're at $2500 to have a gun that shoots as well as any $300 rifle, yet that's what we must do to hunt in some states.

Now try to build that gun at 50lbs of recoil in a manner that a 8-10 year old child can use it to go deer hunting...not an easy undertaking!

 

[Hogpatrol]

@rookhawk, What sort of Boyd's stock and how much torque was applied to "smoosh" that wood.
I have a Boyd's laminate and that wood is harder than Chinese arithmetic. Aside that, can you use a smokeless muzzleloader?

 

[rookhawk]

@rookhawk, What sort of Boyd's stock and how much torque was applied to "smoosh" that wood.
I have a Boyd's laminate and that wood is harder than Chinese arithmetic. Aside that, can you use a smokeless muzzleloader?

35 inch pounds on the bottom screws of a boyd's laminate gun stock will actually CRACK the stock if it is a savage two-piece bottom metal. You must glass bed to provide a way to spread the load across a larger bearing surface, otherwise you'll just keep cranking down screws, firing shells, compressing wood, and then crank down some more.

I've built 8 savage 220F custom 20 bore slug rifles, all with boyd's stocks, all with this circumstance. (in a variety of colors of laminate and styles) There just isn't that much material inside a boyd's for savage action rifles to allow you to torque bottom bolts to the correct tension and have them hold.

So back to the OP, glass bed or pillars + glass bed is the way to go. Threadlocker is a bandaid but doesn't cure the disease.

 

[cagkt3]

35 inch pounds on the bottom screws of a boyd's laminate gun stock will actually CRACK the stock if it is a savage two-piece bottom metal. You must glass bed to provide a way to spread the load across a larger bearing surface, otherwise you'll just keep cranking down screws, firing shells, compressing wood, and then crank down some more.

I've built 8 savage 220F custom 20 bore slug rifles, all with boyd's stocks, all with this circumstance. (in a variety of colors of laminate and styles) There just isn't that much material inside a boyd's for savage action rifles to allow you to torque bottom bolts to the correct tension and have them hold.

So back to the OP, glass bed or pillars + glass bed is the way to go. Threadlocker is a bandaid but doesn't cure the disease.

Still a good idea to threadlock after bedding, or does it not matter?

 

[rookhawk]

Properly torqued screws don't move. So threadlocking is to hold something that ought not move at all. I feel its treating a symptom, not a problem.

So lets say that instead of threadlocking, you use a miracle technology and the bolts are welded/permanently fused at correct depth. The metal never moves again. Then a month later after shooting the gun, the entire action and bottom metal wobble...what happened? The stock was compressed by the recoil or swelled/shrank due to humidity. Back to the same solution, glass bed or pillar+glass bed the stock so the dimensions and bearing surfaces of the stock as it meets the bottom metal and the receiver NEVER MOVE. If they never move, and if the action is properly torqued to 35-45 inch pounds, it should always stay that way. Thread locking suggests bolts spontaneously jar loose, but short of metal stretching, what causes that? Answer: Wobble in the bearing surfaces, compression/changes to the stock.