Spring Gun Tuning

[Supermick]

Thanks to Hsing-ee for the following :-


Tuning The Older Springer

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ALL WORK DONE USING THIS INFORMATION IS AT YOUR OWN RISK - APPLY COMMONSENSE TO YOUR WORK AND SEEK ASSISTANCE FROM A QUALIFIED GUNSMITH IF YOU GET OUT OF YOUR DEPTH. Use a spring compressor and be careful!

If you want your old or new-to-you old spring-piston rifle to give you its best then you could try the following tune-up. It takes a bit of patience and elbow-grease and dosen't involve any drastic modifications but if you follow it carefully your rifle should shoot sweetly afterwards for a good long time.

The following is a basic tune for spring-piston rifles which was common in the late 1970s and early 1980s. The idea is to make the rifle as smooth and consistent as possible, and does not involve modifying the rifle in terms of piston weights, top hats, etc, that is for the more advanced airgunsmith. I used this on a Feinwerkbau Sport recently and it would cut 7mm groups at 25 yards from a rest, and in my 30 year old BSA Meteor which does 10ft/lbs and 20mm groups with a standard spring so it seems to work OK. The guide refers to a rifle with a leather washer, obviously don't soak the washer in silicone oil if it is of a synthetic material, just wipe a small drop of SM50 over it before assembly.

For the full works you will need:

new spring
new piston washer and buffers if fitted
new breech washer

Can of Dri-Slide (or Gun Slide from Chambers) or tube Molykote GN paste
Abbey LT2 molybdenum grease (J.S.Ramsbottoms has this)
Abbey SM50 oil (J.S.Ramsbottoms has this)

Solvol Autosol metal polish ( a car accessories shop like Halfords or a hardware store)
Methylated spirit or white spirit
Very fine abrasive paper
Cheap toothbrush (unused)
18” length of broomhandle
Couple of packets unused ‘J’ cloths or similar

The idea of the tune is to make sure the bearing surfaces are smooth and appropriately lubricated, with the aim of consistent mechanical action giving consistent velocities without dieselling and so giving good accuracy. The molybdenum in the Dri-Slide binds to steel giving a very slippery hard surface.

IT IS ABSOLUTELY ESSENTIAL THAT YOU CLEAN ALL THE PARTS COMPLETELY AFTER POLISHING THEM WITH ABRASIVE PAPER OR METAL POLISH. Use newspaper under the parts as you work and throw them out as they are soiled. Have a clean area to put your clean parts and don’t do ‘dirty’ work next to them. Be careful with naked flames and the hair-drier, the methylated spirit and the carrier element in the Dri-Slide ar e both highly inflammable. WORK IN A WELL VENTILATED ROOM OR WORKSHOP.

1. Place the new piston washer in a pellet tin or similar receptacle and pour over Abbey SM50 to cover it completely. Leave to soak overnight.

2. Disassemble the rifle, taking care to store small parts so they don’t get lost.

3. THE COMPRESSION CHAMBER

A. Degrease all the parts and the inside of the compression chamber using the meths. The broomhandle should have a 3” slot cut in one end so that a stip of J cloth can be slid in and wrapped round to give a cleaning head. Be very thorough, and keep using fresh strips of J-cloth until they start coming out completely clean. Check that the transfer port is clear by using a non-metalisc implement like a cocktail stick and examine carefully by eye. Use the toothbrush and methys to clean the threads that the rear cylinder block screws into. Dry the inside of the compression chamber using further J-cloth strips.

B. If you feel it necessary you can remove the sharp edges on the inside and outside of the cocking-slot. Pack the compression chamber with cloth and using a spatula or table-knife with the fine abrasive paper wrapped around it smooth the inner and out edges of the slot. Don’t overdo this, just remove the sharp EDGES from the slot. Degrease again and be meticulous about removing all the metal filings and abrasive dust using methys and J-cloths. Remove the packing cloth and degrease again until you are sure all the dust has been removed.

C. Using a hair-drier, warm the compression tube by blowing hot air inside and outside the tube body. When it is warm, pour a tablespoon-size amount of Dri-Slide into the compression chamber and roll the chamber around so that the liquid coats all of the surface of the chamber and also further back in the area above the cocking slot. Be careful not to lose all the Drislide out of the transfer port! The chamber can be left to dry for a couple of hours or overnight. Alternatively, rub in some Molykote GN paste onto the whole surface of the inside of the compression chamber.

D. When you are ABSOLUTELY SURE IT IS DRY, use a tightly-wound long piece of J-cloth on the broom handle, burnish the surface of the compression chamber thoroughly. A lot of the Dri-Slide will appear to come off, but it is leaving behind a layer so don't worry.

4. THE PISTON

After disassembling the piston, degrease it inside and out as above, using meths and J cloths. Polish any scratches on the piston body out using the fine abrasive paper, using a rotary action i.e. turning the piston on its axis and holding the paper still so the mark is polished out in a ring around the piston. Polish the whole of the outside of the piston with Solvol Autosol, particularly the back of the piston where it makes metal-to-metal contact with the cylinder wall. Use a J-cloth and to apply and polish off the Solvol. Carefully polish the surface of the bent (part of the piston which engages the sear) with Solvol on a J-cloth drawn tight over something flat and rigid (e.g. a small file). Degrease and clean with meths. Heat the piston up with the hair-drier and coat the inside AND the outside of the piston with Dri-Slide as with the compression chamber, except you don’t need to polish it in afterwards, just leave the coating as it is.

5. THE SPRING

Take a peice of the fine abrasive paper and place it on a very flat surface e.g. a suitably strong piece of glass or steel plate. Polish polish the flat ends on the paper until they are shiny. You can make this a mirror finish if you then polish the ends using Solvol Autosol on cloth stretched over the plate. Degrease and clean the spring carefully afterwards.

6. THE PISTON GUIDE

Degrease inside and out and polish out scratches using a rotary action using the fine abrasive paper and then Solvol Autosol to give a shiney surface. If you like, pad a vice and use a file to remove the sharp edges on the base of the guide. Degrease and clean as above. Make sure you clean the passage through the middle of the guide and get rid of any old grease and dust in there.


ASSEMBLY

1. Take the piston washer that has been soaking in SM50 and squeeze it dry using a J-cloth. Fit it to the piston, avoid getting any lubricant on the screw/bolt attaching it to the piston body. Smear a couple of drops of SM50 around the base of the leather washer (away from its face).

2. Take a lollipop stick and smear a stripe of LT2 grease about 1” in width around the back of the piston (trigger end), be fairly generous.

3. Fit the piston back into the compression chamber, easing the piston head into the chamber gently. It may be a little bit swollen at this point, but persist in easing it in and don’t use hammering or excessive force. Line up the cocking slot in the piston with the one in the compression chamber.

4. Using a small pad of J-cloth, apply a thin smear of LT2 grease to the outside of the spring and a generous layer to one flat end. Fit the spring into the piston with the greased end forwards.

5. Apply a liberal amount of LT2 grease to the outside and INSIDE of the spring guide and fit it to the end of the spring.

6. Smear a little LT2 grease on the threads of the back-block and use this to compress the spring and reassemble.

7. Reassemble the rest of the rifle using LT2 grease on all the main points of wear. Apply SM50 oil to the trigger by dropping it into the mechanism, allow the excess to drip out before reassembly. Replace the breech washer with a new one, and clean the barrel in the normal way. Make sure all the stock screws are tightened appropriately (not too loose, not too tight).


The rifle may be a little bit smokey the first ten or twenty shots but should then settle down to be very consistent. All that is needed in terms of lubrication after this is a drop of two of SM50 at the joints occassionally, and once every 1500 pellets or so a drop of SM50 ***BEHIND*** the piston washer, which can be done by removing the stock and putting the oil in through the cocking slot. Leather washers can take a long time to bed in, so I recommend doing alot of plinking, like two or three tins of pellets, before the gun reaches its peak. Then you should be able to shoot the rifle for thousands of pellets without doing anything more than slip a new spring in occasionally and a sparing use of SM50.

CAUTION: Do NOT over-lubricate. Stick to the amounts indicated here - less is more, especially with polished bearing surfaces.

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[Supermick]

Thanks to Rob M for the following advice :-


Making leather piston washers

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Hints on making a new leather piston washer:

I get off-cuts of sole leather from a cobbler's shop to make new piston washers.

It's good to make your own washers, with a few scraps of sole-leather you have all you need to keep an old-fashioned springer working for a lifetime! It's also satisfying to make the bits you need to keep your old guns alive. These methods can help with the manufacture of leather breech seals too if you should need them.

The ways that leather washers are affixed to the piston vary from manufacturer to manufacturer. Some are held on by bolts, hex bolts or machine screws, others are riveted on.

To make the washer, measure the diameter of the old washer (or the piston) then add twice the height of the washer to the diameter. Cut out a disc this size (approximately) from your leather, carefully use a sharp knife or fretsaw or similar. Find the centre of the leather disc, and drill a small hole there, then, with a nut and washers, fasten the leather disc to a bolt that you can hold in the chuck of an electric drill. Now you can use the drill as a lathe, and use some clean files and wet and dry abrasive paper to round the disc off perfectly and also make the leather thinner if necessary. It has to be "Wet and Dry" type abrasive, as sandpaper or glasspaper will shed bits of abrasive that might end up embedded in the leather, this doesn't happen with "wet and dry". If using a drill or lathe wear eye protection. Depending on how much reshaping you need to do, a dust mask might also be necessary. You can shape leather like this this easily by hand if you don't have power tools, but it will take a little longer.

If the leather has a shiny side, I usually remove the shine with Wet and Dry, as it is sometimes a paint-like finish applied to the leather and could have adverse effects on the eficiency of the finished washer. Some say that the shiny side should go on the outside of the washer where it contacts the cylinder wall, but washers made of raw unshiny leather soon develop a shine after a few dozen shots anyway.

Most leather washers are actually a pair of washers,a large rear washer that is formed into a cup shape, then a smaller front washer that fits inside the cup to minimise lost volume, so you will probably end up making two discs, one smaller than the other.

Fit the washer(s) to the piston, then fasten a jubilee clip around the washer to shape it into the necessary 'cup' shape. It's worth taking your time, tightening it up a little at a time over a period of a few hours. I spray the washer liberally with a little aerosol of stuff I got from a cobbler's shop called 'Leather Stretcher', which actually just softens leather enabling it to be formed into shape more easily. This stuff really helps, and makes the job much, much easier. Tighten up the jubilee clip until the washer fits easily into the cylinder. Spray it, retighten the jubilee clip until you are happy with the fit and shape, then leave it to dry and set overnight or for a day or two if you can. If necessary, any bits of leather that you feel need removing can be carefully trimmed off now with a sharp knife.

Don't worry if, at the moment, it does not look anything like the old washer: The last step in the procedure will shape it precisely to fit the piston and the cylinder. At this point, the washer might appear much thicker than the original, and have a large gap between the back of the washer and the piston, especially around the outside, but don't worry. The important thing now is that the piston can be refitted into the cylinder without the leather washer getting damaged on threads, cocking slots, etc.

Before refitting it, let some "Bisley Gun Lubricant", or "SM50" soak into it for a few hours, or overnight, this is a silicone oil that will not cause the leather to disintegrate over time, plus it contains molybdenum which will lubricate the leather in use. Let the Bisley Gun Lubricant soak well in, but before refitting it, you might need to dab it with a clean cloth or tissue if there is much silicone lube on the outside of the leather. Silicone lube is good for the leather, but no good where metals will be in contact with each other, so you don't want it dripping off the washer into the cylinder or smearing the cylinder wall, for instance.

Obviously, if you are going to put GN paste or moly grease on the piston, do that now. When you have finished reassembling the gun, let the gun stand for a few days with the piston at the end of the cylinder under spring pressure (as if it has been fired), so that the spring pressure can slowly form the washer to fit the cylinder perfectly. Avoid the temptation to fire it straight away! This last step shouldn't be rushed, as allowing the leather to gradually conform exactly to the shape of the cylinder, rather than slamming it suddenly into shape by firing the gun straight away, will increase its life and help to stop it disintegrating when it gets old.

If you do all this, and haven't made the washer too big or too small, you should have an efficient and long-lasting piston head washer... It may take a short while to bed in, but it shouldn't require any more lubricant for thousands of shots now. If you should ever want to relube it I recommend taking it out of the gun to do it, rather than putting silicone oil down the transfer port which could end up damaging the piston and the cylinder.

Even if you buy a pre-made washer, some of these tips should still be useful.

Hope this helps!

Rob M

[Bad Beagle]

I can vouch for this tuning guide - as a complete amateur I have followed it successfully see the review section Gamo Quickshot.

Big thanks to Hsing-ee.

[franktheferret]

Good stuff Mick, but for a final degrease, I like to use Iso-propyly Alcohol. You can't easily get it these days, but ordinary Surgical Spirit is pretty good. It absorbs water much better than commercial-grade meths, and with no powdery residue.

Alan.

[Paul Hudson]

I get my IPA from Maplin. They have a store a short walk from where I work, but they also do mail-order if you're having trouble finding a supplier.

Maplin website

Paul.

[Hsing-ee]

Just make friends with a nurse, they use gallons of IPA in hospitals - they don't trust the staff with 70% ethanol because they know they'll just drink it, and IPA is used as a convenient surface steriliser.

[Steve1]

Morning fella's just passing through

If you want to give you're spring a quick, thorough cleaning then you can follow the following[small] guide, heres what I do. First, you need an un-used toothbrush, the longer the better but it does not matter as long as it's unused. Two might be better, as you will see later.

Of course, it is better to work outside, but prepare a clean surface so the greased spring does not attract unwanted dirt or bits of sawdust, whatever may be around, you get the idea.

T-Cut Original or similar. The point here is not to shine, just to restore the surface of the spring, remove any grit and gunk. You could do the full polish with power-tools but I'm mostly speaking of general once-every-so-often maintanence, not power cleaning a really old spring which needs more care

If you have two brushes you can use one to apply the T-Cut evenly over the spring, and clean it throughly with the brush head. You could re-use this one later if you have an alcohol based cleaner to clean the brush.

Once any residual T-Cut is cleaned off the spring you can apply some grease of you're choosing to other brush, or re-use the other one. Apply a nice even amount, like a stripe across the brush head as though you are brushing you're teeth with it.
Now gently with the brush, stroke along the inner and outer length of the spring a few times, not too much or inevitabley you'll wipe it all off, again you get the idea. But be gentle you don't want to splatter it everywhere and spoil you're new wooden picture frame on the wall. This is much easier because theres an even amount of grease across the spring, a nice consistant layer and no sticky globs where you couldn't reach with your little finger. And only takes five mins'. Yee-haw

Also, as pointed out by Supermick, you could re-finish the ends of the spring where the spring guide and piston spacers meet in the cylinder. Although this would be better done beforehand, or you may be in a sticky situation with all the grease everywhere on the spring.

Thanks and good day/morning, happy shooting!

[matthu61]

Sounds a bit overdoing, why just not put the spring in a bucket of thinner. All grease and residue will come out in no time!

[franktheferret]

Fine, if you have a bath of thinners handy, but IPA is preferred, as it doesn't strip ALL oils from the metal, as thinners will do.

[danche]

Another good tip which I do to my spring guns, is to go to a hobby shop and buy some steel shim then cut it to fit inside the piston, get a steel washer to fit inside the piston. crimp the end of the shim, insert it into the piston, put the steel washer in, then insert the spring inside

What this does is to give extra smooth cocking, and also cuts the recoil down slightly, and makes the spring noise quieter. It's amazing the difference it makes

[danche]

Another quick tip for sping guns

Get some internal draft excluder, the foan one that goes around internal doors, take the action out of the stock and put some of the excluder every where the action touches the stock, and fit the action back

It makes a little shock absorber between the action and the stock

[frank]

Good stuff Mick, but for a final degrease, I like to use Iso-propyly Alcohol. You can't easily get it these days, but ordinary Surgical Spirit is pretty good. It absorbs water much better than commercial-grade meths, and with no powdery residue.
Alan.

Acetone will absorb the water even better and degrease everything in sight but
it's quite volatile also wouldn't tend to use it on some plastics etc

[Jamie Norton]

Isopropyl alcohol is generally available from pharmacies. It is also volatile (no smoking!) and will evaporate pretty quickly if you leave the lid off.

[deadeye dick]

Isopropyl alcohol is generally available from pharmacies. It is also volatile (no smoking!) and will evaporate pretty quickly if you leave the lid off.

No you cant it is not available to the general public, my wife gets it because she lectures and teaches nails and beauty but I have tried to get some without success I believe you can buy it in the USA over the counter

[neralcm]

Just bought a litre of the stuff from an electronics store, about £11 also available in a spray can (can't spell aerosol). Ideal for degreasing as it leaves no residue. Used it on my 97 to fit a V-Mach stage 1 kit, struggled a bit with heavy deposits but did the job.

Stuart