BSA Mercury, Friction in the Piston

And Finding The Most Accurate Pellet For a 70's British Springer

Out in the woods testing the .22 BSA Mercury.

I have done a far bit of tinkering with the .22 mercury, but i know it needs a little more. It's knocking out RWS Superdome's at 10.5 ft/lb then slowly dropping down to 9 ft/lb, this i'm sure is down to the tight fit of the rubber O ring piston seal. 

The new piston seal O ring below is a bit over sized.

 I've read that it's a common problem that the piston seal can be a little oversized when new, and i did have to use some force to push the piston into the compression chamber with this one. Most people usually put a tin of pellets through to wear the piston seal down, but i reckon in this case i would need nearer two tins of pellets before any wear is noticed on the O ring.

Repeatedly putting a 1000 pellets through the Mercury would get a little tedious to say the least.

My other option would be to dismantle the rifle yet again, and use wet and dry to wear the O ring down, i would need to turn the piston in the lathe and apply the abrasive to give it even wear, 

It doesn't look over sized when fitted on the piston head , but believe me it is.

Then i would size the piston now and again till it was just short of a sliding fit, so once the ruff edge of the seal had smoothed out after reassembly it would fit perfectly. 

I would rather avoid going through this rigmarole again.

My only concern for the rifle is for the thread on the breech block getting damaged with all this taking apart and reassembly, i also have a concern for the spring compressor because of the mighty preload.

These were good value and sorts out the problem of the scope rail dovetails being set too forward on the compression tube of the Mercury.

A 1970's .22 BSA Mercury has a barrel that is 5.6 mm as opposed to 5.5 mm that is more prevelent now a days, and the older pellets that were a tad wider are not available any more. Eley Wasps in the blue tin are sized at 5.6 mm but are crap compared to how they used to be, 

No 2 5.6 mm Eley Wasps are not the pellet they used to be.

i have found that RWS Superdomes fit just as well in the breech and are infinetly more accurate. So with this in mind i reckon it would be best to see how the rifle performs after i put a tin of Superdomes through it, at 7 quid a tin it sounds like the fun option to me and i usually take a second rifle with me when i go down the woods.

Accuracy

   I have found the Mercury shoots most consistantly with a light hold and supported by my off hand just in front of the trigger guard, from personel experience most springers are more accurate for me if i support them at where they balance and this is where the Mercury balances out. The trigger breaks lightly and cleanly with no first stage travel so it's easier not to pull any shot of target, both my BSA Meteor and the Webley Hawk have similar triggers to this so i reckon it must be some British thang.

Ready for the off.

Testing the accuracy in the woods means i can't test from a bench rest, but the results will be more indicative of how it will perform in a hunting situation. The rifle was sighted for 28 yards and i will test at 15 yards and 30 yards, and with the shelter of the woods i don't have to worry about wind effecting the results.

Resting the rifle, uncocked and unloaded, while i go of to check the target.

Using the large cardboard boxes that were left over from Christmas presents as targets i took Scatterbone down to the woods and paced out 15 yards, 

Handy large cardboard box left over from Christmas, inside is foam packing and a piece of ply wood, after a few tests i can stick targets to it with the Gaffer tape i always carry around with me. As i say," If counceling won't fix it, Gaffer tape will."

i shot from a sitting position with my back against a tree while holding the rifle lightly with my off hand supported on my left knee. Out of AA Diabolo's, Falcon Accuracy Plus, Eley Wasp's, and RWS Superdomes, i found the Superdomes to be the most accurate in the 5.6 mm barrel of the Mercury. 

RWS Superdomes in any caliber are the best all rounder in my opinion.

At 15 yards 6 shots came inside the size of a two pence piece with the Falcon's coming a close second, the Eley Wasp's were all over the place thinking i had lost my mojo but then the the Superdomes did it again.

I'm pretty happy with these results, cleaning the barrel and perfecting my hold will improve results no end.

I tried to test the Mercury out to 30 yards but it was pretty windy even in the shelter of the woods, with the wind push the pellets two inches over to the left. I managed to do some shots compensating for the wind and managed to get on target, but as it was i was well chuffed with the results of the 15 yard shots. Having put just over half a tin of pellets through the Mercury since i last tinkered with it i have found the best hold for me, being happy with that i reckon i should just put an other couple of tins through it till it beds in and the velocity rises and settles down. I really would like to keep this air rifle as the surge and recoil are quite mild and as a .22 it carries a lot of knock down power down the range, and above all it looks bloody sexy for an air rifle.

TTFN

Wing Commander Sir Nigel Tetlington-Smythe.   

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, The Final Stages

For now.........

Sweet looking air rifle

When last i wrote a blog i had just finished fixing up the BSA Mercury, and left off with popping in the breech seal. However i realised i had forgotten to order one, just missed it out on my order from J Knibbs. So in goes another order for a Titan XS mainspring for the Weihrauch HW35, a flip up red filter for my gun lamp, and two generic BSA breech seals, I got two as i have a BSA Meteor which would benefit from a new one as well.

 When i gave the original Mercury breech seal a close inspection i could see why it needed replacing, one half of it looked liked it had been filed flat so one side was flush with the breech face and the other side protruded a smidgen to where it should seal. 

Worn old breech seal

When i placed a cigarette paper over the breech to see if any air escaped when fired, it didn't just move it, it shot into the air, and that was with me gently holding the paper to the sides of the breech with my fingers.

Ready to replace

The generic breech seals are made from a firm rubber and are white, where as the original is a black harder harder material, but that may be because it has aged and hardened. 

Two new breech seals, i have a Meteor as well.

It's a folded over circular seal with a small slit on the inner fold, and the fold is the side of the seal that faces the outer side of the breech. The old breech seal had to be prised out and as it was so old it came out in small pieces and crumbs, most definately well past it's sell by date.

Oh crumbs!

Though once removed and cleaned the new seal just slipped in easily and straight away i could tell the differance between the old worn seal and the new one, standing just past flush from the breech face and making a perfect seal around the transfer port. 

New breech seal fitted

Cocking the rifle and loading the pellet then taking the shot i could hear the pellet hit the back stop with a lot more force than it had done before. Though i would like to point out that according to a very well known and experienced airgun tinkerer (known to some as T20) reckons that most Wiehrauch breach seals would fit even better to Meteor's, Airsporter's, Mercury's, et al, and give you an extra 1/2 ft/lb as they are made from tougher stuff and are a tad longer. Anyway read his blog 'Air Gun Tech' and you can see for yourself that him and his buddies know their minerals, it all makes sense to me, sort of.

I also made an order to Uttings for a 6x40 AO Nikko Stirling scope and a set of Accushot high profile off set mounts, the mounts arrived but i would have to wait another week or so for the scope as they were out of stock.

Lots of bit's that come with the scopemounts

Scope mounts in the box

I have discovered that after buying loads of economy scopes in the past that it's best to spend a little bit more, though you don't have to break the bank doing this. 6x40 is a good hunting magnification and Adjustable Objective is pretty handy for guaging the distance of your target, and being a little short sighted i can use a scope with AO with my glasses on. However they didn't have any in stock several weeks later, so i reordered a 3-9x40 AO Nikko Sterling and i can just leave it on x6 mag for hunting

Ready to fit the scope

The one piece off set mounts are crucial for BSA Mercury's and any other BSA with the curved trigger unit, as the scope rails are set to far forward for most people to use comfortably with normal mounts. In this case i  mounted an AGS 3-9x40 scope and with the off set facing backwards found it sat just perfectly for my head an eye to line up, two hex bolts clamp the mounts to the scope rails and two smaller hex scope stops screw down to add extra support on the top or the piston cylinder. The Accushot mount came with three allen keys and one spare hex bolt in each size, this was handy as i had a one piece mount with a striped hex head so i popped it in there. The hex head was a little thicker than the others but it does the job fine, and now i have a spare one piece mount for one of my other springers.

Out in the back garden i sat down at 27 yards from my target and trap and took some test shots with .22 Eley Wasps No2's, The scope was fairly close to the POI but the shots were stringing vertically and some went left or right which showed me this rifle would need at least half a tin of pellets to settle down and a very gentle hold, though when i tried some .22 RWS Superdomes i found the grouping was a hell of a lot better but still not upto anywhere good enough for hunting. Most Super domes fitted snuggly into the breech though some were looser and deep seated themselves. However i could feel the wasp's click in snuggly, but they can be seen by eye that they all differ or are slightly deformed in some cases, and would explain why I found this a little odd as old BSA barrels are 5.6 mm and Wasp No 2's are made for this and they just did not perform that well, where as the super domes that fitted deeply where falling into roughly 2 inch groups which was without a doubt an improvement.

With the new main spring and lube this rifle slams the piston home with force but there is no buzz or twang which is a bonus, but for a smoother lock cycle it is in need of a top hat and a slip washer and 3 or 4 coils removing. I feel this air rifle is now performing close to if not a little above factory specks, but give it a bit of running in to settle the spring in and short stroke the piston and its going to be a corker of an air rifle which is not so hold sensetive.

I mean, i shoot at a dot on a piece of paper and my shots appear to go all over the place, but if i place a few bits of 1 x 2 inch wood on the shelf in front of my back stop and i miss one every 5 shots. So it seems i can hit an inch size object better than i can group an inch circle on paper, and that's at different ranges to boot. Now that's all well and good out in a field of rabbits where i originally learn't to shoot well, but i have to garrentee i can do that with whatever air rifle i am using at the time in order to make a clean kill. Most of my air rifles will allow me to do that out to 45 yards in some cases, but with this rifle as it is now i wouldn't like to take the chance, even at 15 yards.

 It would appear that i still have a lot of work to do on this lovely little Mercury, and as this blog is all about my learning curve with working on air rifle dynamics and the improving of my knowledge of said objects. Then it would stand to reason that i will be squeezing a few more blogs off this gun.

TTFN

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.