Guess the inaccuracy issue BSA Mercury

[TonyL]

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

Absolutely, evert.

And, like many, I'll often jump in on some of that banter. But it's usually amongst "known proponents" and always intended as fun and light-hearted, not serious critique.

I currently own three BSAs. Two are definite keepers - my 1906 LJ Underlever and my scruffy, tatty early Supersport that shoots very sweetly and is very accurate. My personal jury's still out on my Mercury S, though....sweet shooting and easy cocking. Accurate at the close ranges I've tested at (like genuine little one-holers at ten yards with Superdome and H&N Excite Hammer) but details like the "Mickey Mouse" (in my view) pivot bolt and poor finish on piston detract. All told, though, I'll probably keep.

[T 20]

I currently own three BSAs.

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

[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.

[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.

[T 20]

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.

Yes Bill, that's how the shims work.

The Mercury with the Weihrauch breech bolt arrangement just had the stock recessed for the bolt head, not the full semi circle of wood removed as on a Weihrauch.


All the best Mick