Longsroking the .22 BSA Mercury

After fitting a brand new Titan XS spring to the Mercury, I discovered that the recoil was a little fierce, so I thought it would be a good idea to take it apart and nip a few coils off. I also thought I would have a go at increasing the swept volume, as this had been recommended on some of the airgun forums I have read. As it stood, there was far too much preload, and when I fired it I could not follow through as the scope view bounced all over the place.


So there came a day when I had the house to myself, what better time to set about tinkering with a rifle! Out came the screws that held the stock on and the action was placed in a vice protected by an old glove.

Don't want to scratch the bluing any more than it already is.

Then I set about unscrewing the trigger housing with the use of an old metal bar.

Any old bar will do the trick.

Remembering the preload, I jammed a large heavy piece of wood behind the trigger unit so it wouldn't go flying through the shed wall when it came loose as I undid the rest by hand.

Just got to be careful here.

There was still a far too much preload. I could see 2 or 3 coils coming off this one.

That came off with some force all the same.

Moving back to the kitchen table to remove the guide rod, spring and piston. I first removed the cocking linkage guide so the the linkage could be removed from the piston.

As the cocking linkage is articulated, you can remove the guide to slip it out of the compression chamber with out removing the barrel.

Once the piston was removed, I could straight away see one reason for some inaccuracy - the buffer washer I had made up out of rubber washers had flattened and was rubbing along the compression tube. Just as well, that was the piece to take out to shorten the piston and long stroke the compression chamber.

Pin is out, piston head removed.

With the piston head removed by tapping out the pin, the washer was removed. Now I had to see how much of the front of the piston cocking rod had to be removed in order for the head to sit on the piston body.

See how much needs to come off the end of the rod.

It was no more than 2 or 3 mm as there was extra space in the piston head for the rod end to sit in, so a quick grind down on the lathe soon removed the excess.

After the grinding of the rod, mmmm shiny.

Next I took out the Dremel, (well, actually a cheaper copy made by Draper), which had the bits and bobs I needed to carry on with the job.

The Draper, which is cheaper than a Dremel, and the piston body after the rod has been shortened.

Using the Draper and a cutting disk, I then set about extending the cocking slot in the piston body, because with the buffer washer removed, the piston would slam into the cocking linkage if this was not done.

Extending the cocking slot.

I removed about 4 mm and smoothed it off with a grinding stone, making sure it was even so that both bars of the cocking linkage would connect with the piston slot. I thought it best that if I was shortening the piston by 4-5 mm that I should only lengthen the cocking slot by no more than that, that's how thick the buffer washer was.


Now I had to drill a new hole for the pin that connects the piston head to the piston body, this is most likely strongest if done at 90 degrees to the original.

Lining up where to drill hole.

I lined the head up with the body and marked off where the pin would go through. First I used the Draper to grind a center for the drill, then with a battery powered hand drill I started to drill a 3.5mm hole.

Grinding new hole for the pin.

I found I was getting no where fast as the post was hardened metal, however I did find some sort of metal grinding tool in the Draper parts and that did the trick nicely.

Strange grinding head that beat the drill bits.

The hole now completed and not crossing paths with the original hole, I tested it all lined up with a darts head, which it did nicely allowing me to tap the pin in.

The finished article.

With the piston completed, I applied the appropriate greases to the seal (abbey SM50) and base on the piston (abbey LT2), then inserted it into the compression tube which I had cleaned and polished up. With the piston fully inserted I tested to see if there was space for the cocking linkage, which when pressed flat along the compression tube was about 2mm.

It's dark in there, but there is a gap.

There would be more than this as there is a steel spring plate that holds the cocking linkage against the linkage guide, also the spring stops the linkage interfering with the mainspring.

Steel spring plate that holds the linkage up.

I have a belief that the preload shouldn't exceed the swept volume. This is not proven by me but picked up from articles i have read by people who know their stuff. So with this in mind I decided to remove 3 coils, which i did along with shaping the last coil on the mainspring.

With some Abbey LT2 grease smeared liberally over the spring, spring guide, and washers, the rifle was placed in the spring compressor along with the trigger bock, in the jig I had previously designed for it.

Parts back in line and greased up.

Titan XS are really stiff springs and even with 3 coils removed there was a fair bit of preload, so when the spring compressor started creaking and broke, I wasn't really that surprised!

Bugger! Broke the spring compressor!

I remembered it straining last time I worked on the Mercury and should have strengthened the screw housing then, but by supporting the trigger block and jig with one hand it still managed to work and I was able to give the trigger block that 180 degree turn so it would catch. Quick as you like it was out of the compressor and tightened by hand until the final touch, that involved the vice and the bar so everything lined up nice and tight.


With the cocking linkage slotted in and the spring plate in place, I screwed the linkage guide in place, then the stock and scope were finally fitted and the gun was ready to be tested.

Start putting her back together.

The recoil is nowhere near as harsh as it used to be, in fact it's quite pleasant to shoot now. I am finding that with using .552 Air Arms Diabolo fields, I can usually get sub inch groups at 20 yards with the odd flyer, though I am refining my hold again as I have been using pnuematics a lot lately and my springer shooting tecnique has slipped a bit.

Yet again I didn't get around to putting a top hat and slip washer in the compression tube and piston, but it seems to be performing very well as it is. Apart from the odd flyer which as I said is down to my hold, it is a mighty fine air rifle indeed and i'm pretty chuffed with the results so far.

I believe that the spring was too fierce and was causing too much air to choke at the transfer port giving harsher recoil. I have also read that some other people also increase the diameter of the transfer port when long stroking, so i'll have to see if it's worth doing at some point in the future. For now i'm going to be finding the best pellets to use with this air rifle, as these older British ones do have a slightly larger bore of 5.6mm.

TTFN

Best wishes, Wing Commander Sir Nigel Tetlington-Smythe. 

BSA Mercury Rebuild

I think the BSA Mercury is a beautiful looking air rifle with the way the trigger block curves down from the back of the piston cylinder to meet the wooden stock, The chequering on the pistol grip, The short cocking linkage slot in the fore stock, and the slightly raised cheek piece. That's why i thought it would be a good idea to get her back to her former glory, so with a Titan XS main spring, piston washer seal, and a breech seal from J Knibbs i was on my way. 

This air rifle was given to me with a severe bend in the barrel at the breech block where it had obviously been fired with the barrel left open though this was an easy fix with a vice and a metal tube, and the forks that held the breech were very loose which again was fixed with the use of the vice. Also some one had put a spring from an SMK B2 in it and the breech seal was worn, which is what shall be adressed in this blog

BSA Mercury ready for working upon.

I removed the stock by removing the two cross head screws on the fore stock then the long flat head bolt at the bottom of the pistol grip, this is recessed into the grip and runs diagonally through the grip and screws into the trigger block.

Stock removed, note the long bolt that that goes through pistol grip.

To remove the trigger block i held the compression tube tight in a vice using leather to stop the vice scratching and gouging the cylinder, then there is a hole above and in front of the trigger guard in the block which an iron bar is inserted to give leverage in unscrewing the whole unit. As it came to the end of the thread i pressed a large block of wood behind it to stop the preload on the spring sending the trigger block flying,as it happens there was only two inches of preload which felt quite loose and the trigger block was  caught safely.

The hole in the trigger unit above and in front of the trigger guard is for using an iron bar for leverage

Then the cylinder, breech, and barrel were taped into the spring compressor to have the cocking linkage, spring, spring guide, and piston removed in a tidier enviroment than the work shed, basically the dining table in the kitchen

The spongy two inches of preload of the old spring.

The spring guide slipped out with two washers at it's base, one for supporting the spring and the other goes between the back of the spring guide and the front of the trigger unit. these keep the guide straight as the piston rod needs to pass through the guide and into the trigger unit, there it connects with the sear in the trigger unit which i had wrapped tape around to stop any pins falling out. Then the old spring came out, which seemed okay but the whole of the compression cylinder was in need of cleaning and lubrication.

The cocking arm linkage is articulated and once the cocking linkage guide and screw pin that connects it to the breech were removed, could now be removed and the piston could be slipped out the compression cylinder. The guide is held on to the cylinder by two cross head screws and holds a plate in place against the cylinder for the cocking linkage to slide against, it also has two tabs that fork out either side at 90 degrees for the fore stock screws. Where it connects to the breech there is a spacer washer that keeps the two walls of the linkage firm and tight, this is an easy one to loose if your not careful so i kept a watchful eye and it fell into my hand as i removed this end.

Old crumbling washer on the piston.

The piston head is held on to the piston body with a pin and a washer keeps the whole assembly firmly in place, but in this case the washer was well squashed and crumbled apart when the piston was removed. So i removed the the O ring piston seal and  cleaned all the parts with wet and dry and white spirits, then OOOO wire wool and white spirits , then with some kitchen towel i dried it out and removed any crud, and finished off with a final polish using Autosol on any parts that make contact with the compression cylinder.

Piston head and body cleaned and polished showing the holes for the pin

Luckily i had some tap washers that would fit the piston if i drilled the middle out to 10mm, however one was not thick enough and two was to thick.

Making the replacement washer

So i drilled out one and slipped it in place the after drilling another i managed to grind and file it to the correct thickness, so in the end one and 1/3  was just the right thickness to replace the washer. Some people have gone without the washer and drilled a new hole at 90 degrees to original hole further back,you have to grind down the end so the piston head fits but this does give you a tad more swept volume.

The new shiny smooth O ring seal below with the old tired one above.

The replacement O ring seal slipped into place on the piston head easily, comparing the old and new one showed me the original was worn and had streached with time and use.

I removed the compression cylinder and filed away any sharp edges, then went through the same cleaning and polishing routine i used on the piston.  Though this time all the materials  were clipped on to a slit in the end of some 6mm aluminium tube and wrapped around the end so i could get right down to the transfer port, looking at this made me think it quite a small diameter for a .22. The whole of the inside of the cylinder was shining bright when i had finished as i spent much more time and effort doing this part, it was then taped back in place on the spring compressor with some blocks at the breech support to bring the end of the cylinder over the end of the compression tube bed.

The preload of the Titan XS  spring, all 34 coils of it. In the fore ground is the old SMK spring.

The new Titan XS spring has 34 coils where as the the old SMK spring has 31 coils and was compressed a fair bit, this presented me with over four/five inches of preload which would surely test my DIY spring compressor. Also the curved shape of the trigger block meant that the end was off center for the threaded bar on the compressor, this was sorted by building a housing from two pieces of wood and some metal sheet. With the trigger block in this jig i could compress the spring while presenting the trigger block to the cylinder at the correct place and angle, once presented half a turn once the threads started to bite would hold the trigger block to the compression cylinder. Giving me time to remove it from the spring compressor and screw it into place with the use of the iron bar, though the last bit would need for it to go back in the vice and finish off screwing it together.

Trigger block in it's jig and compression tube just hanging over it's bed. I had to compress the spring by hand a bit so it would fit in the spring compressor.

Applied Abbey SM50 to the O ring seal and some Abbey LT2 grease to the last inch of the piston,then this was slid into the compression cylinder. Followed by the spring with both the ends polished, i had dabbed LT 2 grease over the front half of the spring then taking a cloth i spread it thin and evenly by wiping down and around the whole length of the coils, then LT2 grease was applied to the ends or the spring and the outside of the spring guide and both washers. The jig supporting the trigger block was lined up and placed  behind the rear washer with the threaded screw bar of the compressor directly on the back of the metal sheet at the back of the jig, this would allow me to turn the trigger unit 180 degrees when the spring was compressed enough so the threads would bite.

It took a couple off attempts to get it right in the end, and the spring compressor held together with the force of all the preload though i could see the poor thing staining. Once it was together the articulated cocking linkage was greased at the hinge, at the breech block on the screw pin and spacer washer, and on the tabs that go into the cocking slot and moves the piston so it cocks. The metal plate was slipped under the cocking linkage and the guide screwed back onto the cylinder, and then the stock was screwed back on leaving only the breech seal to be replaced.

When i cocked the gun i could straight away feel the extra effort needed for the new Titan spring but it was still easy effort, linkage and internals moved smoothly and made no noise. Putting a Wasp No 2 pellet into the breech i locked it back an took a shot, there was no twist or kick to speak of as the piston slammed home which was a definate improvement. I will have to knock up a slip washer and top hat in the fonley lathe when i get some delrin bar, but for now its just a matter of prising out the old breech seal and pressing the new one home.

I did have a lot more pictures for this blog but before i had chance to move  them over the computer stopped working, so it had to be re booted and anything put on since it was last saved two weeks before was lost. But some were moved over to the blog before this happened so it wasn't a total loss, any way i'm sure i'll be coming back to the Mercury some time in the future so i'll get some better pictures then.

TTFN

Wing Commander Sir Nigel Tetlington-Smythe. 

   

  

Stripping the Diana/Original Mod 16

The Mod 16 is the small one above the BSA Mercury.

This is an old smooth bore junior air rifle, and it only shot a pellet two inches down the barrel when i first got it. Letting some synthetic oil soak into the large leather breach seal and piston seal and letting it soak for a day got it firing, inch groups at ten yards on average. Still not owning a chronograph i could still tell it was well short of its full power, so why not strip it and see what could or needed to be done to improve on this.

Checking out Chambers exploded chart and spares list i could see that a lot of parts were obsolete, but my bodging skills are improving nowadays. To take the stock off two flathead screws on the fore stock and one screw which held stock, trigger, and housing were removed. 

One of the two front stock screws

The rear screw is one long screw that screws into a circular bolt with a flathead driver fitting, the trick with this was to take an old flathead screwdriver and grind the middle out leaving two flatheads spaced far enough apart to grip the round bolt leaving the long screw to undo freely. Out came trigger, trigger spring that rests in a hole in the stock, and spring cylinder and barrel.

The rear stock bolt/screw that holds a lot of stuff together.

I pulled the tight fitting metal end cap off and and the spring guide retaining pin fell out, as the metal spring guide had two tabs that twisted into small slots at the back of the spring cylinder. The spring was worn so pushing the back of a screwdriver into the end of spring guide and giving it a twist i slipped the tabs out and out came spring guide, spring, and piston.

Using a rod i  wrapped some wet and dry dipped in white spirits and thoroughly cleaned the inside of the cylinder, then removed all residue with kitchen towel. Using the same method i polished it with OOOO wire wool and cleaned it again with kitchen towel, then finally gave it a really good polish with Autosol metal polish making sure to clean it out a good four or five times. This method was repeated with the piston and the spring was given a good clean with white spirit and a kitchen towel and each end polished, i slightly roughened the leather piston seal with wet and dry and let some Abbey SM50 soak in for a few hours.

Adding some more Abbey SM50 to the side of the piston seal and Abbey LT2 grease to the last inch of the piston i carefully slipped it into the cylinder, two metal washers either side of small rubber sink washer lightly smeared in LT2 grease were placed in ahead of the spring also lightly coated in LT2 grease. Spring guide also greased was pushed back in with the back of a screw driver and the tabs locked into their slots, then the pin was replaced and the end cap tapped back on with a mallet.

It took a couple of attempts to line up stock, trigger and spring, and the cylinder body together and slip the screw through but it was no biggy, the rifle actually dents wood with Hobby's instead of slightly marking it now. 

See the trigger tension spring behind the trigger?

I can't really justify spending much money on the Mod 16 just yet, the price of a replacement spring for this rifle is the same as one for the BSA Mercury and that is a wicked air rifle. But it was fun doing it and its got a little more poke to it now, and hopefully should do better groupings at ten meters now its had a clean and relube.

TTFN

Wing Commander Sir Nigel Tetlington-Smythe  

 

Tuning the Norica Quick

Seeing as i was passing on the Norica to my mate i thought i would give it a bit of a tune up, besides i needed to drop the trigger pull a bit as well so kill two birds with one stone. Also it would give me a chance to see how the spring compressor would work out, i reckon there must be some preload as it is quite heavy to cock.

Preload is from the start of the wider trigger slot

The first thing i did was to check out the exploded view on Chambers http://www.gunspares.co.uk/shopdisplayproducts.asp?id=24977&cat=Quick, this makes life so much easier. Two plastic tabs either side of the fore stock revealed screws facing diagonally up into the cylinder block, and two screws on the trigger guard the rear one connecting stock to cylinder removed the stock. The safety latch was connected on to the trigger guard, pushed in place by the cocking linkage when cocked. The trigger unit held a nut for the rear screw and two pins held it in place to support a washer, spring guide, and the main spring. The rear of the trigger unit protruded from the cylinder by one millimeter and when pushed flush removed the two pins, however the unit could only be removed by pushing the washer and guide unit forward and slide it forward and out the wide long slot in front of it.

spring and washer pushed forward and trigger unit slipped out forwards

Handy device for removing trigger block and then letting spring and all free

I made a tool from two fat lengths of ali bar bolted to a half inch length of copper pipe which i hammered square, the bars would then fit between the outsides of the trigger unit and the inside of either side of the cylinder. With the cylinder supported on the spring compressor by using parcel tape of all things, i was able to wind the washer and guide forward two inches so i could tease the trigger unit out through the slot. Unwinding the pressure off the spring soon started to become a little alarming as the compressor was fully unwound and still under tension but i could push this by hand and slip it off, it would seem that this air rifle has four inches of preload and six if i included pushing it forward for removing the trigger unit.

Held down by loads of parcel tape

Handy device being slipped between trigger block and cylinder walls

I removed the guts or the rifle which was pretty dry except for a spot of oil behind the nylon piston seal, it all seemed in pretty good nick apart from where the piston had rub a little on top of the cylinder. however the end of the main spring had not been ground flat, and the sharp ends had left a ring of tiny marks on the top hat and the metal washer on the inside of the spring guide. The mainspring itself was in near new condition but where the sharp edges had nicked the tophat and washer there were minute flecks of metal scattered about, the piston was heavy with an inner sleeve which was a tube with cocking and sear latching cut into the outer layer.

Spring as it came out of rifle

Both ends ground down flat and polished

Right then, what did i do? Oh yes now i remember. First off i ground down flat both ends of the spring and gave them a polish, then  sanded the washer and tophat with wet medium then fine wet and dry' then polished with OOO wire wool the tophat, spring ends, and washer that all connected with each other. I then cleaned out the piston cylinder with white spirits and wire  wool on the end of a piece of dowel then polished and cleaned out any old crap left in there with a J cloth on the same dowel. Mmmmm shiney smooth. The piston was polished before the seal and at the end, and all deburring was done with my trusty Dremmel.

Heavy polished top hat and piston seal

this is one heavy piston i can tell you

Putting Abbey SM50 oil around the base of the piston seal and Abbey LT2 grease of around an inch at the end of the piston i slipped it back into the cylinder, LT2 grease on the end of the tophat and slipped that in the piston, the spring was then liberally coated in LT2 and then inserted making sure both ends had a tad extra grease applied was put in, then the spring guide and washer was smeared with a little extra LT2 grease and popped into the main spring.

Just some handy shit to have around for tuning

Before reversing the whole process of using the special tool to slip the trigger unit back into the slot in the cylinder i used the Dremmel to grind the sharp edges off the sear and piston, but only a little as i did not want to mess it up big time. Carried on putting the Norica back together and put the scope back on, which with the stop on it should not interfere with its previous POI.

spring pushed back in so trigger block can be replaced

Out in the back garden and took a five shot group, though sometimes i perfer a ten shot group. Anyway the trigger pull was down and there was most definately room to take more off, and the grouping was tighter and three inches above point of aim which means that it is now putting out more power. The rifle was also not so hold sensative, which i would call a successful tune indeed. What more could you ask for, i am indeed one happy little marsupial.

As i said i could lighten the trigger some more, but i shall leave that up to my mates discretion . Me personally, i would take it down a lot more but then i am used to being spoilt on Record triggers

TTFN

Best Wishes, Wing Commander Sir Nigel Tetlington-Smythe DOA OBE MBE FOAD