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Stock Bedding an Air Rifle

Stock Bedding an Air Rifle

One of the most important considerations in the performance of any rifle is how well the action fits into the stock. In the case of a pneumatic air rifle, it becomes even more critical as the air cylinder, which on the majority of PCPs runs along the inside of the stock, expands and contracts during its pressure cycle from 180bar down to approx. 100bar. This can have two effects on accuracy.

Marginal Inconsistencies

If the stock contact with the action is marginal, it can cause the inconsistent `flyer` that we all dread as the cylinder pressure decreases during use. If the contact is heavy, it can show up as a zero shift as the rifle is fired through its cycle. This will usually show up as a drop in trajectory as the cylinder contracts, in effect lowering the barrel.

With a lot of the modern metal stocks these problems will not apply, but anyone using traditional wood needs to be aware of the importance of bedding. It is a straight forward job to do overnight as long as a few simple precautions are followed along the way. At the very least it will give peace of mind knowing that it is one area that won`t need investigation should an accuracy problem occur.

A good bedding material that I have used over the years is Araldite Repair Bar (ARA400015), which is available in handy tubes from most car accessory shops. It looks like a roll of putty with the hardener running through the middle and only requires working into a ball for the chemical reaction to take place. This takes about 10 minutes to start going off; plenty of time to allow placement before introducing the action.

Proper Preparation Prevents…

Before that can be done, a few more bits and pieces and some preparation is required.

A piece of writing paper to be used as a feeler gauge between the stock and the action, a roll of clear tape, and some grease or Vaseline to prevent the bedding material from sticking to the action will complete the list.

The idea is to give the action a nice flat `bed` to sit on when it is tightened down into the stock, leaving the main air cylinder free floating from in front of the trigger block to the front of the forend. A lot of stocks only have one main retaining bolt which is forward of the trigger block and this can be a problem when trying to prevent the forward weight of the tube and barrel from dropping down onto the stock. Provided that there is enough room ahead of the bolt on the block it shouldn`t be a problem. If the action has a rear fixing bolt as well it really makes things simple.

In this case, the donor rifle for this article couldn’t have been more awkward, as it was Daystate’s Mk4 electronic model that had been married into a custom made stock with one fixing bolt and virtually no room ahead of it on which to bed the trigger block.

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The action was really marked and rubbed on the underside where it had been making contact with the stock and it was impossible to slide anything between the forend and cylinder due to the action falling forward and resting on the stock.

The owner had reported that it seemed to be very inconsistent and that the problem had only manifested itself after the fitting of the new stock. The electronic Mk4 is unconventional in many ways and apart from the fixing bolt mentioned above, it has a printed circuit board running the full length of what would be the trigger block on a conventional action.

This board is set on one side of the action and also prevents any type of bedding material from being applied in that area at the rear. I figured that provided the front was solid and the rear supported on one side it should be good enough to allow full support to the action with the front free floating. But how to support the front?

Plan of Attack

Just ahead of the trigger block is the regulator in the form of a dome shaped cylinder. This is covered with a thick plastic sleeve and sits slightly lower than the block. The answer to the balance problem was to sit this regulator on a bed of plastic metal so that the main fixing bolt set back behind it, pulled everything down and straight when tightened up. With the plan of attack decided and everything needed at hand, it is now time to get down to business.

The first thing to do is to ensure that the inside of the stock is de-greased to allow the plastic metal to bind well onto the wood. Some white spirit will suffice for this. Now the action needs to be protected at all points where it will contact the bedding material, allowing for it squashing and squeezing upwards and along the inside. This is where the tape comes in. I find that plain old Sellotape is just fine. Along the trigger block, up the sides and along the front and rear. In this case the addition of tape around the regulator unit cover was also used.

Once satisfied that all the right bits have been protected, a smear of grease or Vaseline on the taped areas will ensure that the stock isn`t welded to the action next morning! I say now if you don’t do this then you will really have a one-piece rifle!

Taking the Araldite out of the tube, a piece is cut off and worked by squeezing it until both strips are thoroughly mixed. This is now applied to the specific points along the inside of the stock where the action will sit (action void), allowing for some expansion as the action is initially pulled down into it.

Easy Does It…

Now it’s time to sit the action onto the bed and, with the piece of writing paper set between the air tube and the forend, insert the stock bolt/bolts and lightly pull down the action ensuring that the paper is free to slide back and forth for the entire length of the tube. Resist the temptation to keep tightening down. The trick is to stop just before the bedding material is fully compressed.

One more check on the paper sliding freely and now it`s time to stand the rifle up vertically to take weight off the action while the bedding material goes off completely. This really needs to be left overnight before any attempt is made to remove the action from the stock.

Once sufficient time has been allowed, the action can be removed and all the grease and tape removed. Now it can be full tightened down into the stock and the paper test repeated. If the job has been done correctly, it should slide freely from the forend to the face of the trigger block.

This means that the whole pressure tube is now effectively free-floating; eliminating any worries about zero shift or expansion/ contraction problems due to temperature or pressure changes. At the time of writing, the owner of the Daystate has not had the opportunity to check out his rifle but I can guarantee that any problems that may still be present are not caused by an ill fitting stock.
You know it makes sense!

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