Servicing a 70s Mercury - Spring Choice

[james_stan]

Hi All

Thank you for allowing me to join this forum - 1st post.

My kids are now of an age where there would like to to try some air-gunning in the woods
at my brother's farm - mainly targets I think but their desires for game (rabbits etc..) may overtake them.

I discovered my brother had kept the family Mercury in his gun case after all these years and he gave it to me.
It still has the BSA 4 x 20 scope on it but no open sights (those could be anywhere..) I think it's either
a MK2 or Mk3 I cannot spot a serial number anywhere but I have not yet at least removed the stock.

I thought I would start by refreshing it with Chamber's SK020 service which includes a new standard main-spring
but is it worth considering an alternative (e.g. Titan)?

Any other hints and tips gratefully accepted by this novice.

Regards

James

[CapitalBee]

Protek supplies do a drop in replacement spring for the BSA airsporter / mercury. I'd check their website out.

[Zomboid]

For my Mercury I used a Titan XS. I removed about 7 or 8 coils off it and then put a couple of the Titan power washers behind it. For .177 it puts out about 9.5ft lbs - the velocities almost match the factory figures.

Rest of the stuff was from Knibbs - piston o-ring, buffer, breech seal etc...

[junglie]

my advice is don't put a titan spring in it, nowt wrong with the standard bsa springs.With a titan it'll be hard to re-assemble & harsh to shoot + may well be over the power limit unless you cut the spring down & re-finish the ends.

[Phil Russell]

Piston O ring is a BS212 or if that is too tight a fit, one from a Meteor BS210 will often be fine.
Buffer washer can be made from a 3/4" tap washer or a leather disc; it is not essential to have an original. Breech seal can be made from urethane tubing (or other slightly pliant tubing) 12mm od x 8mm id x c 4mm deep.
If you can make or source these bits you save a lot.
Cheers, Phil

[Zomboid]

my advice is don't put a titan spring in it, nowt wrong with the standard bsa springs.With a titan it'll be hard to re-assemble & harsh to shoot + may well be over the power limit unless you cut the spring down & re-fininsh the ends.

You have to cut the spring down. There's absolutely no way a full one will go in and make the rifle nice to shoot. I assembled mine by hand by clamping the trigger assembly unit onto a low lying clamp and then used body weight to compress. Taking 7 coils off was enough to get a decent amount of preload without over doing it and making the firing cycle too harsh.

Nothing wrong with standard springs but the last one I had for my 635 didnt have enough compression on it - no idea why. Came from Chambers who are certainly trustworthy. Went with Titan in the end because I've used them plenty of times without fault - but you do have to shorten them.

[junglie]

You have to cut the spring down. There's absolutely no way a full one will go in and make the rifle nice to shoot. I assembled mine by hand by clamping the trigger assembly unit onto a low lying clamp and then used body weight to compress. Taking 7 coils off was enough to get a decent amount of preload without over doing it and making the firing cycle too harsh.

Nothing wrong with standard springs but the last one I had for my 635 didnt have enough compression on it - no idea why. Came from Chambers who are certainly trustworthy. Went with Titan in the end because I've used them plenty of times without fault - but you do have to shorten them.

Thats your opinion & if you'd read my post properly I did say you'd have to cut a titan down, I find them harsh even cut down correctly prone to buckling & overpriced.apart from a batch in the late 80's to early 90's that were overtempered & prone to break I've never had such problems with the standard bsa merc/airsporter springs & have fitted them to many makes of airgun if they fit correctly. Also not all people have an angle grinder or the skills & knowledge to cut down & compress a coil with a blowlamp & correctly re-grind the ends.

[hawkdriver]

Hi All

Thank you for allowing me to join this forum - 1st post.

My kids are now of an age where there would like to to try some air-gunning in the woods
at my brother's farm - mainly targets I think but their desires for game (rabbits etc..) may overtake them.

I discovered my brother had kept the family Mercury in his gun case after all these years and he gave it to me.
It still has the BSA 4 x 20 scope on it but no open sights (those could be anywhere..) I think it's either
a MK2 or Mk3 I cannot spot a serial number anywhere but I have not yet at least removed the stock.

I thought I would start by refreshing it with Chamber's SK020 service which includes a new standard main-spring
but is it worth considering an alternative (e.g. Titan)?

Any other hints and tips gratefully accepted by this novice.

Regards

James

as far as i remember the serial number is stamped on the underside of the breachblock, next to the cocking link, starts with a z , hope you see this.

[ZAKDINGEL]

as far as i remember the serial number is stamped on the underside of the breachblock, next to the cocking link, starts with a z , hope you see this.

bsa serial number dates (z mk1 1971-1973)---(za mk2 73-74)--(zb mk2 74-78) (zc mk3 78-85) Hope this helps you

[leetrenchard]

Rebuilt mine with standard chambers spring and.seals, shoots v sweetly at 10.5 in .22

[TonyL]

Hi James,

And a very warm welcome to the forum.

A most splendid resource and with many knowledgeable, helpful folk.

And welcome to the fun and rewarding hobby of springer tinkering.

Personally, and as many above, I'd go for the standard spring. Sources for all the parts you'll need (some mentioned above) are Protek (yes, there's a spares section on there), John Knibbs, Chambers and TR Robb.


If you were ever to need to shorten a spring, there's an excellent article in the March issue of Airgun World on this very subject.

[james_stan]

Thanks again. I found the serial number too - it's a ZB..

[Airsporterman]

Stick to the standard spring (nos) if you can obtain one, there used to be a member on here who had a supply of them (sorry I haven't read through the thread if this has already been covered) in my experience, any other spring fitted to these old BSAs tends to spoil them, makes them harsh to fire, makes them inconsistent and less accurate, in all, are generally not an improvement on the standard spring without a lot of messing around shortening/removing coils etc!
Just my view! (I have removed a few dreaded 'aftermarket' springs and the like from old rifles and replaced them with standard springs in the past)

ASM

[Rellum]

Rebuilt mine with standard chambers spring and.seals, shoots v sweetly at 10.5 in .22

Ditto nothing wrong with Chambers stuff if a little expensive