How to DIY tune a HW77K spring airgun: Part 1
Tuning a HW77K Weihrauch air rifle or other spring powered air gun beats shooting a rifle in the factory “default” condition, which by most standards is pretty basic. There are a few prerequisites that need to be followed prior to diving in and stripping your Weihrauch air rifle with the view to tuning it.
- Firstly, if you are a lousy shot, then save your time and money because a tuned air rifle will not make you a better shot and you won’t be able to blame the rifle…
- If the air rifle is brand new then I suggest that you consider shooting around 1500 shots through it to bed it in. This will allow you to develop a shooting profile, consistent grouping (be it good or bad) and muscle memory. This is important because it will give you a datum to compare your tuning to the original performance of your air rifle.
- You will need some basic mechanical aptitude and by that I mean you need to know one end of a hammer from the other…
Before you start on in, consider whether or not you feel you have the confidence and basic skill set to do a neat job. If not, then maybe you should recruit a mate who is more technically inclined, because tuning a HW77K needs a degree of competency. However, should you get stuck doing the tune-up, you can always call me, and I can talk you through it, even if you purchased your air rifle elsewhere…. hmmm.
Tuning a HW77K: tool requirements
Let’s look at what tools you will need here so that you do not get halfway and get stuck for lack of tooling.
- Metric Open end/ring spanner set up to 13mm.
- Ball Pein (aka Ball Peen) hammer 12 – 16oz (small to medium).
- Pin punches – Long Series 2.5mm, 3mm and 4mm will get you by.
- Metric Allen Key set to 6mm.
- Flat screwdrivers to suit the stock screws.
- A cradle of some kind to support the action and/or stock.
- Buffing machine (Bench grinder with Buffing attachment – see image below).
- Workbench (Kitchen Table/Dining Table would be nice when the wife is out shopping…) that is clean and covered with a cloth base to protect the rifle parts.
- Bench vice.
- Cleaning fluid – degreasing spray or mineral turps etc.
- Moly grease and a suitable oil.
- Several containers – 1 for parts to be cleaned, another for clean parts and a 3rd for tools etc.
Your workbench should be clean and covered with an old sheet or similar material to minimise stock scratching and making unsightly marks to the bluing. Do not use a blanket as it will leave fine strands on material sticking to oiled parts of your air rifle. You need a container for parts and good lighting as the bluing is easy to scratch and difficult to repair. Keep all your tools well clear of your air rifle as it is too easily mark your bluing or stock on some sharp edge of a wayward tool lying close by.
The buffing machine can be your typical bench grinder with the accessory spindle fitted to take buffing wheels. The images below show 2 buffs, the dark one is used for initial prep work using a fine compound like Autosol metal polish and the light coloured buff is an ultra fine cloth to finish the steel to a fine polish without anymore compound. I do NOT advocate using the bars of a compound often used with buffs as these can be a bit savage. Should you end up taking off too much metal (rather than just polishing it) it will prove to be an expensive exercise.
Fine Polishing Buff Very Fine Polishing Buff
Stripping the Air Rifle
Start by making sure the air rifle is not loaded or cocked – this may sound kind of elementary but “empty” guns have killed more people than smallpox… not literally, but you can see where I am going with this. Just check the damn thing.
With the Weihrauch HW77K, turn the rifle upside down in a cradle that will support it leaving your hands free. Then start by loosening (half a turn will do) the small screw behind the trigger guard, then the main spigot screw in front of the guard and lastly the 2 opposing fore-end screws. With all 4 screws loose you can then remove them from the rifle and place them together with the fore-end washers into a container. Separate the action from the stock and place the stock away from your work area leaving the action clear of all tools and crap you may have on the bench.
Using a 13mm metric open-end spanner, undo the spigot pin and spacer (numbered “1” in the image below) and place these in a container.
We can then continue the strip down the air rifle by first releasing the loading arm from the fore end detent by pushing in the button beneath the front of the barrel. Then select a 3mm pin punch or one close to the pin diameter which is just forward of the bridge mount which is attached by the 2 fore-end stock screws. In the image below it is numbered “2”. Cradle the action over a couple of wood blocks covered with towelling and tap through the pin. You can then lift the loading arm and disengage it from the action, placing it well away from the rest of the air rifle action.
When looking at the action of the HW77k Weihrauch Air Rifle cast an eye over the pins and you will see on one side the 2 pins that hold the trigger group have a recessed flat on one side of the action where each pin is located. This is the side you insert the pins when putting them back and this is the side they get pushed out of (pushed out from the other side).
The blued pressed metal slide is known as the anti-beartrap (“3”) which is designed to slide between the trigger pivot and action the moment the loading arm is released. The idea is to stop some clown from pressing the trigger when the loading arm is down in the loading position: this could result in some painful fingers if they are putting a pellet into the barrel at the same time. Don’t worry, it’s been done I know.
Next tap out the 2 pins (“4”) holding in the trigger group and put them aside in a container. This will allow you to remove the trigger group from the action. While the image below does not show it, the safety catch should be removed at this point together with its compression spring.
You should now have your rifle stripped to the following as shown in the image below.
Once you get to this point, clean everything away on your bench as you will need to pull apart the action next. Cleanliness in tuning a HW77K does not stop at keeping the rifle clean. If you want accuracy and longevity in your HW77K or any air gun for that matter, keep your pellets clean too. The best way to do that is with a Pellet Pouch and not your grubby pockets.
I can’t stress this enough, and that is to work in a clean and well-lit environment with tools and other miscellaneous bits and pieces well away from your air rifle as marking it is just too easily done. For those of you who are familiar with pulling down air rifles, these points may seem a bit lame or even basic. However, I can assure you from the phone calls that I get, there are a large number of air gun owners who know nothing about stripping down an air rifle.
The next thing we need to do with the HW77K is unwind the trigger housing from the main body of the action. You should find this very tight and may well need to put a close fitting spanner end into the trigger group recess. When doing this, find a large spanner with a thickness very close to that of the trigger group, place it deep into the slot, then while holding onto the main body, strike the spanner so that it twists the trigger housing in an anti-clockwise motion. Once the trigger housing starts to move, I suggest that you undo it by hand while watching how much thread is still left in the housing. Once you get down to about 4 or 5 threads left (looking through the loading arm channel under the main body), it is time to place the air rifle down and fasten a clamp across it from the barrel end to the trigger housing end.
Do NOT unwind the air rifle trigger housing all the way by hand as it may fly out the end with a terrific force and if it hits you, it won’t do you any good at all.
On 12 Fpe air rifles the spring compression is such that you can, with some common sense, undo the trigger housing while pressing down while unwinding – this is done with the air rifle facing upwards at 90 degrees and you holding down the trigger housing while you unwind it. However, in the interest of getting you to safely unwind the two housings, I would prefer you to do it this next way as it is safer.
The safe way to disassemble a springer
I use an Irwin sliding clamp as pictured and lightly oil each pad then tighten it gently holding the barrel end and trigger housing in the centre of the clamping pads. This is easily accomplished when laying the components down flat. Once you have taken up the slack in the sliding clamp and have applied a bit of pressure on the air rifle you can unwind the rest of the action without it flying apart.
I also put the rifle together using the reverse of this clamping method. See the Irwin clamp that I use, it has a 920mm opening and works very well. I purchased it from Bunnings for around $36 I think.
Tuning a HW77K part 1, the air rifle components.
Once you have separated the housings you should have the following on your bench that will require cleaning, inspecting and then polishing before being re-assembled.
Now you have got this far, the next thing we will move onto is Part 2 of this tuning article following: that will cover inspecting, actual polishing and assembly options pertaining to the Weihrauch HW77K air rifle. A lot of what I have here also applied to other airguns even though I am targeting tuning a HW77K Weihrauch.
Author: Ian McIntosh, Gunroom