Guess the inaccuracy issue BSA Mercury

[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

[Zomboid]

Worn pivot? Nearly new?

True, but they did stop making the Mercury 30 years ago!

[Geezer]

Paging @Hsing-ee

[Hsing-ee]

Poor technique is the answer! It's about three times the effort to shoot well compared to a 77. Thanks for all the suggestions, going to stick with my HWs.

[TonyL]

Hey Al!

Where have you been?

There's a Bash happening this weekend. You coming?

[TonyL]

Poor technique is the answer! It's about three times the effort to shoot well compared to a 77. Thanks for all the suggestions, going to stick with my HWs.

I recently did a little more work to my S, Al. It was already grouping nicely (certainly up to the 10 yards or so down the garden), but I'd wanted to address one or two areas......

I fitted a new breech seal.

Added a little more spring preload. When I ordered the WW kit for it back in 2020 I asked Will for a weaker than usual spring due to ease of assembly and due to expected duties (short range down the garden). But although it shot very smoothly and accurately the power was just a tad lower than I'd wanted. Ridiculously low cocking effort, though.. I had asked Will for some extra preload washers at the time of order so proceeded to fit. It's now doing a (still pedestrian) just over 9ft.lbs, but is very smooth, accurate and still has very, very low cocking effort.

The trigger, although generally not too bad, had become sometimes inconsistent in its break point. I was going to strip the components out of the trigger block, thoroughly clean and lube. As it was, just a simple re-oiling of the pivot points and contact surfaces seems to have done the trick.

I decided not to address the barrel pivot bolt rotating as mine didn't seem to be the only one showing this trait.

At just over ten yards it's doing five shot groups barely more than a pellet's diameter using the cheaper H&N Excite Hammer.

As always, a nice, soft, repeatable hold and not gripping the rifle pays dividends and at these shorter ranges, this one is certainly delivering. I'll see how it fares at longer ranges at The Bash this weekend.

And remember Rod Linton's pellet & rifle tests back in the day and the Mercury's outstanding performance with (I seem to remember) Milbro pellets in .177? Or were they Marksman.

[Big Seth]

Marksman produced a 4.5mm group, best result of any rifle/pellet/caliber in the entire "test"- hilarious😂. I had a nut and bolt mod done on my Mercury pivot back in the day. It was forever having to be nipped up due to rotation on cocking.

[T 20]

On the last .22" Mercury S I serviced for someone, I basically just polished all the internals and deepened the O ring groove to give less crush on the O ring and reassembled it with it's original spring.
The first shot over the chrono was exactly 600fps with a Superdomes --- I was quite chuffed with that considering I'd only spent a total of £4 on parts as I fitted HW80 breech seal to it.

On my own .22" Mercury MK4 rat gun I long stroked it a tad by removing the buffer washer and moving the head back on the shaft and redrilling the pin hole at 90 degrees to the original hole.
This allows me to use a shorter spring for the same power output as the S above.



All the best Mick

[TonyL]

I've thought for some time that the long stroking route will be the way to go one day, Mick. As recommended by your good self and a fair few knowledgeable others.. Possibly also give the cylinder and piston to Nick to have a play with and set the crush perfectly. I could then be tempted to have a play with a thicker piston sleeve and a TX III spring.

[T 20]

I've thought for some time that the long stroking route will be the way to go one day, Mick. As recommended by your good self and a fair few knowledgeable others.. Possibly also give the cylinder and piston to Nick to have a play with and set the crush perfectly. I could then be tempted to have a play with a thicker piston sleeve and a TX III spring.

I have a spare piston here that I machined a new head for that takes a 28mm Diana piston seal, Tone.

I don't think I ever tried it in a Mercury but if you want to have a play you're welcome to it.

[TonyL]

Thank you, Mick.

I think Pete (look no hands) has been down this route before?

I might pass on your most generous offer for now due to lack of tinkery time......it's taken well over two years to get round to opening this one back up to just perform those simple, quick little recent tweaks and I still have a few others to start that have been waiting for their fettles for years......like the twangy old school little 50, that 35 I bought from Nick, 18Wheeler, years ago and the 55.

Taking you up on your fine offer would seem to be greedy and over-indulgent and take that part out of the "pool" when you might need it for a future project. But thank you again.

Shall I drive over this morning and kidnap you for a Bash visit?

[TonyL]

Poor technique is the answer! It's about three times the effort to shoot well compared to a 77. Thanks for all the suggestions, going to stick with my HWs.

Hey Al!

Where have you been?

There's a Bash happening this weekend. You coming?

And great to finally get to meet you at the weekend, sir.

[T 20]

And great to finally get to meet you at the weekend, sir.

It was also a great pleasure for me to finally meet up with Alistair yesterday when he dropped off my new project gun, it's just a shame that our timetables didn't allow for more Boinger chat.



All the best Mick







.

[TonyL]

Yes, my only regret was that we only talked pretty briefly on the Saturday. I was hoping to get to spend more time with Alistair on the Sunday but hadn't realised that he wouldn't be there as he had other items on his itinerary.. Next time, hopefully?

What's your new project rifle then, Uncle Mick?

Ah, I've just spotted your thread on the "other" 35, Mick.

Will have a look-in now.