BSA Mercury - difficulties with power output.

[severnsider]

Hi. Just looking for some advice, please. Ref. a couple of posts in this thread http://www.airgunbbs.com/showthread....ditioning-tips

I replaced the innards of a .22 Mercury with the appropriate spring/spring guide/tophat/seals kit from Chambers and as stated in my post on the above thread, had to collapse quite a bit of the Titan XS spring to have any chance of getting the rifle back together. Even when shortened, the Titan spring was far stronger than the spring which was originally in the rifle, so I had high hopes for an improvement in power.

Anyway, all the horrible twang is gone, and the rifle is smooth to cock and fire, which is a good result. However, power remains low at under 8fpe (470fps). This is no better than with the original spring.

In your experience, is there anything else to look for? The piston and breech seals are new and undamaged, the replacement spring is significantly "stronger" than the original. My only thought was that perhaps the 'O' ring seal by its very design is likely to let air past (unlike the Weihrauch seals which, I guess, tend to seal more efficiently with pressure against them).

Just thought I would ask on here since some members have indicated that they have used a Mercury at close to legal limit. Any advice would be gratefully received!

Kind regards,

Mike

[jonny.c]

Get an ox spring cut one coil off should be perfect
or just ring bsa????????

[mrto]

Hi. Just looking for some advice, please. Ref. a couple of posts in this thread http://www.airgunbbs.com/showthread....ditioning-tips

I replaced the innards of a .22 Mercury with the appropriate spring/spring guide/tophat/seals kit from Chambers and as stated in my post on the above thread, had to collapse quite a bit of the Titan XS spring to have any chance of getting the rifle back together. Even when shortened, the Titan spring was far stronger than the spring which was originally in the rifle, so I had high hopes for an improvement in power.

Anyway, all the horrible twang is gone, and the rifle is smooth to cock and fire, which is a good result. However, power remains low at under 8fpe (470fps). This is no better than with the original spring.

In your experience, is there anything else to look for? The piston and breech seals are new and undamaged, the replacement spring is significantly "stronger" than the original. My only thought was that perhaps the 'O' ring seal by its very design is likely to let air past (unlike the Weihrauch seals which, I guess, tend to seal more efficiently with pressure against them).

Just thought I would ask on here since some members have indicated that they have used a Mercury at close to legal limit. Any advice would be gratefully received!

Kind regards,

Mike

Hi Mike,
You need to be sure that you have a correctly fitting 'O' ring.One that is not snug enough in the cylinder ie an insufficient amount of 'crush' to its circumferance may not seal properly and give low power and inconsistent results.Also are you sure that the buffer washer is in good condition and doing its job properly and that there is no play between the piston,buffer washer and piston head.ATB.

[severnsider]

Thanks for your replies. I'll measure the 'O'-ring and confirm that it is of the correct size. The buffer washer is in good condition - rubber with some compressive "give" (perhaps this is the problem?) rather than the replacement item which is a thick, hard fibre washer - and there is a small amount of play between the piston head and the piston which I thought was necessary to cope with minor misalignments and to make sure that the piston "skirt" is not forced against the bore of the compression tube? I don't wish to go down the OX spring route, but I could call BSA........ would anyone there still have knowledge of old Mercurys I wonder?
Regards
Mike

[Mr. Gen]

Cock and load the gun, dust the barrel/cylinder joint with a little talc - when you fire you will see if the seal is blowing.

HTH..

[Bolor]

Any spring you have to chop up is a no no in my eyes. Buy the original spring and having it shoot sweet. In the eighties ox springs were all the rage, now it's Titan springs. It's a fashion thing and I won't fall for it. Right I'm off shooting now, I'm just putting on my bell bottom dungarees

[gedfinn 2]

Hi. Just looking for some advice, please. Ref. a couple of posts in this thread http://www.airgunbbs.com/showthread....ditioning-tips

I replaced the innards of a .22 Mercury with the appropriate spring/spring guide/tophat/seals kit from Chambers and as stated in my post on the above thread, had to collapse quite a bit of the Titan XS spring to have any chance of getting the rifle back together. Even when shortened, the Titan spring was far stronger than the spring which was originally in the rifle, so I had high hopes for an improvement in power.

Anyway, all the horrible twang is gone, and the rifle is smooth to cock and fire, which is a good result. However, power remains low at under 8fpe (470fps). This is no better than with the original spring.

In your experience, is there anything else to look for? The piston and breech seals are new and undamaged, the replacement spring is significantly "stronger" than the original. My only thought was that perhaps the 'O' ring seal by its very design is likely to let air past (unlike the Weihrauch seals which, I guess, tend to seal more efficiently with pressure against them).

Just thought I would ask on here since some members have indicated that they have used a Mercury at close to legal limit. Any advice would be gratefully received!

Kind regards,

Mike

Hiya Mike, I had to highlight the above !
They use O rings to seal at 3000 Psi, They let air past, ?
If the breech seal is OK, Its 99% a too tight O ring piston seal , Unlike a " Parachute type seal " It doesn,t expand on to the cylinder walls
( As much ) Braking the pistons progress.

I am not saying its better or worse, Just that properly fitted , Which is generally loose , It,ll make 11 Fpe no problem ,
I might add, I had a Lightning with a " Loose piston seal "
It made the limit no problem, No reason to change it ?

Cheers, Ged.

[severnsider]

Mr Gen, Bolor, Ged - thanks for your helpful advice. I'm beginning to think it's a seal, rather than a spring, issue. Will investigate further.
Cheers,
Mike

[ggggr]

If it was mine, I would be looking at using an original spring. Not being an engineer or anything or being able to measure things for roundness etc I would try these things. A breech seal is a likely cause of loss of power so look at the gun and see if the barrel pivot looks loose or "eggy" and also if the barrel plunger is in good nick and the spring seems strong enough to keep the barrel locked up. You could try to pack the breech seal something underneath it to see if it makes a difference. Try to push a pellet down the barrel to see if there is any sort of blockage or tight spot. I had a Webley falcon that had a bent barrel AND some bits of pellet smeared into the rifling. If you have to strip the gun down then check that the piston or head are not tight in the cylinder. Check the spring is not too tight on the guide. Hold the cylinder and barrel to the light and see if the transfer port is in line with the barrel. You could try putting the piston and cylinder in water and test for leaks.
It is possible you have the wrong section O ring but I would give the gun 150 shots or so to bed in before trying anything.

[severnsider]

If it was mine, I would be looking at using an original spring. Not being an engineer or anything or being able to measure things for roundness etc I would try these things. A breech seal is a likely cause of loss of power so look at the gun and see if the barrel pivot looks loose or "eggy" and also if the barrel plunger is in good nick and the spring seems strong enough to keep the barrel locked up. You could try to pack the breech seal something underneath it to see if it makes a difference. Try to push a pellet down the barrel to see if there is any sort of blockage or tight spot. I had a Webley falcon that had a bent barrel AND some bits of pellet smeared into the rifling. If you have to strip the gun down then check that the piston or head are not tight in the cylinder. Check the spring is not too tight on the guide. Hold the cylinder and barrel to the light and see if the transfer port is in line with the barrel. You could try putting the piston and cylinder in water and test for leaks.
It is possible you have the wrong section O ring but I would give the gun 150 shots or so to bed in before trying anything.

Thanks, ggggr - all good advice. Breech seal and barrel lock-up all seem in good condition. Barrel is clean and straight. Will send a few more shots down it as you suggest.
All the best,
Mike