Guess the inaccuracy issue BSA Mercury

[junglie]

Unfortunately humour isnt always that easy to convey in text, I should have put a strategic smiley somewhere in that post
Another factor is that long term banter context may be a little too internal between a few members to be picked up by all.
And I'm not a native english speaker, which may complicate matters even more.

The point is that many members on here have a tone of "friendly banter" which may look rude to some that havent followed it over time.
But its all usually friendly meant

Your english is better than a lot of the natives here evert.

[pajj]

Your english is better than a lot of the natives here evert.

I wouldn't argue with that.

[TonyL]

I've just had a count up, Tone --- for some strange reason I seem to own 22 BSAs.

2 Prewar under levers
7 Meteors
1 Merlin MK2
1 Airsporter MK1
3 Airsporter MK2
1 Airsporter MK4
1 Airsporter MK6
2 Airsporter S
1 Mercury MK2
1 Mercury MK4
1 Mercury S
1 Lightning MK1


And I don't use any of them --- in fact the last time one was fired was by Chippendale at a Boinger Bash 3 years ago when he wanted to try an Airsporter S.



All the best Mick

Better to have and not use than not to have, Mick.

[billsnibby]

My experiance FWIW in case it may help someone...

My "S" breech had some play in the jaws which I thought may affect accuracy, and although it could not be felt with the barrel closed (latched-up), I felt that the play would mean the breech may not latch-up in the same position every time leading to inaccuracy.

The breech bolt rotates with the barrel in the jaws as someone described earlier in this thread, and the latching wedge moves easily. I attempted to reduce the play by tightening the breech bolt with the the latching wedge depressed and the cocking lever disconnected from the breech so it was free to move.

The "S" breech jaws seem quite substantial, and tightening the breech bolt with the latching wedge depressed so it didn't put a load on the breech bolt didn't seem to make a deal of difference to the play. Although unconvinced it would make any difference, I also tried with two of the original four bolt head shims removed; no difference as suspected.

To reduce the play I managed to wiggle (engineering term?) an 0.1mm thick shim washer on each side in between the breech and jaws which has removed the play and still allows the barrel to move freely.

HTH and Best Regards,
Bill.

[T 20]

My experiance FWIW in case it may help someone...

My "S" breech had some play in the jaws which I thought may affect accuracy, and although it could not be felt with the barrel closed (latched-up), I felt that the play would mean the breech may not latch-up in the same position every time leading to inaccuracy.

The breech bolt rotates with the barrel in the jaws as someone described earlier in this thread, and the latching wedge moves easily. I attempted to reduce the play by tightening the breech bolt with the the latching wedge depressed and the cocking lever disconnected from the breech so it was free to move.

The "S" breech jaws seem quite substantial, and tightening the breech bolt with the latching wedge depressed so it didn't put a load on the breech bolt didn't seem to make a deal of difference to the play. Although unconvinced it would make any difference, I also tried with two of the original four bolt head shims removed; no difference as suspected.

To reduce the play I managed to wiggle (engineering term?) an 0.1mm thick shim washer on each side in between the breech and jaws which has removed the play and still allows the barrel to move freely.

HTH and Best Regards,
Bill.

Hi Bill.

Yes it would seem that the breech pin is free to revolve on the S as there's nothing locking it to the action compared to a Weihrauch.

I thought the breech bolt on the mercury S was adjusted by removing or increasing the number of shims shown as W098. :-

image.jpg

I just put a bolt with locknut through my Mercury MK4 breech --- it works better than it looks.

Possibly the best fix for a Mercury breech I've seen is the fitment of a HW35 breech bolt and nut.



All the best Mick

[TonyL]

Ah, as I'm not alone in the rotating pivot bolt department (sounds almost like a chronic medical condition, doesn't it?), that'll be one job to do that I'll not bother doing. The HW style bolt fix would be the ideal solution, Mick, but far beyond my capabilities and equipment level.

[maximus]

I don't think the pivot bolt on my Mercury S rotates but I did end up sliding one HW shim between the barrel and breech because I ran out of adjustment on the bolt. I converted my lightning xl tac to a Diana breech bolt and added a pair of HW99 shims in as well. This required the breech to be widened a little to accommodate the shims. Good neat job when done though.

[TonyL]

Useful input as ever, Maximus.

This is turning into quite an epic thread.

But where IS Alistair?

[greenwayjames]

Bowkett copied the HW hinge bolt arrangement on various of his air rifle conversions in the 1980s. The 12 ft/lbs Meteor conversion included this and the total conversion cost was £23.50. It was also offered for many other break barrel airguns including the Mercury. He bored out one side of the breech jaws oversize and threaded the other about 9/32" fine thread. A bolt to suit was made, one end threaded and case hardened and a locking screw provided. When the correct tension was acheived the locking screw was tightened to prevent rotation of the bolt. This would make the barrel pivot bolt work like a cam and give varying points of impact
Just like the HW system but with a locking screw rather than a nut.

[junglie]

My 635 magnum bolt rotated but didn't affect accuracy , funnily the one on my challenger dose not. Also greenway james in what universe does a round bolt when rotated act like a cam? I'm no engineer but would really like to have that statement explained....

[billsnibby]

Hi Bill.

Yes it would seem that the breech pin is free to revolve on the S as there's nothing locking it to the action compared to a Weihrauch.

I thought the breech bolt on the mercury S was adjusted by removing or increasing the number of shims shown as W098. :-

image.jpg

I just put a bolt with locknut through my Mercury MK4 breech --- it works better than it looks.

Possibly the best fix for a Mercury breech I've seen is the fitment of a HW35 breech bolt and nut.



All the best Mick

Hi Mick,
I think I made a schoolboy error: now realising that the shims under the breech bolt head effectively shorten the unthreaded part of the bolt so if its nut was bottoming on the bolt threads before closing up the breech jaws sufficiently to reduce the play (which I don't think it was in my case), I should have added breech bolt shims rather than removing some!

I'm happy with the shimmed breech as it is now, but I may try a schnorr washer to fix the bolt and stop it rotating. However I don't think it's a big problem as someone else has said. I imagine that rather than the bearing surface being between the bolt and breech, its between the bolt and breech jaws.

I assume fitting a HW breech bolt to the Mercury required its stock to be relieved as it it on HW's?

Best Regards,
Bill.

[BTDT]

But where IS Alistair?

Good question, Tone. After all, it's not as though Ali has previous form for starting a 'firework' thread - light the blue touch paper and retire to watch the fun.

[TonyL]

Quite, Jim.

[look no hands]

Good question, Tone. After all, it's not as though Ali has previous form for starting a 'firework' thread - light the blue touch paper and retire to watch the fun.

That's why I haven't replied a much as usual, I felt Alistair's attention seeking had flared up again

But as par usual some interesting replies have come about because of it.

Pete

[maximus]

Good question, Tone. After all, it's not as though Ali has previous form for starting a 'firework' thread - light the blue touch paper and retire to watch the fun.

He could well be in BSA pellet testing hell like I have been over the last few weeks! It started with my mercury s which involved spring changes and all sorts only to yield what I already thought, that it only shoots super domes well. Then I moved on to my Airsporter s 177 which has never really shot anything well but I discovered it liked Bisley magnums, a result (if you like 177' at 22 velocities!!) This sparked a pellet buying spree to try other heavy pellets. Over £100 spent but no joy in finding another pellet it will shoot! Ah well at least the pellet collection has expanded, could be money in the bank the way things are going up!