Guess the inaccuracy issue BSA Mercury

[TonyL]

Mine has three shims under the bolt head. Some parts diagrams show four. When I was to first work on mine, when ordering the parts I ordered another shim but the gun didn't seem to want to accept that extra one so I re-built with the original three. When cocking and re-closing the barrel I see that the entire nut and bolt rotate.. It's one of the areas I want to address on the next fettle. I have been told by someone that the number of shims used isn't a definite number and that the factory used varying numbers depending on the fit and tolerances between different guns? Anyone else come across this? I've also wondered whether the tension from the detent latch and spring have anything to do with this?

[evert]

I've also wondered whether the tension from the detent latch and spring have anything to do with this?

That is perhaps the biggest issue with the lockup system on the BSA breakbarrels, the chisel tends to bind on the pin.
On some guns it is necessary to increase lockup tension with a few washers under the locking spring, and this of course increases the problem.

[TonyL]

Mmmmm........thank you, evert.. Scratches head..

[trajectory]

Interesting comments about the barrel bolts for BSA's of this era. The 'simple' bolt solution has often been the way to compensate for the forks opening up but if the bolt rotates then at first it sounds like its a candidate for having a lock screw fitted to prevent it happening. However if it is locked would the lack of rotation cause excess wear on on it in one spot by the barrel latch, maybe increasing the chance of vertical allignment / consistency issues. (hence loosness & needing to pack the latch spring?) Do you think that it might be better to allow the pin freedom to rotate instead or just watch out for wear to the bolt & replace as needed?

Reverse choke on BSA barrels is a new one on me.....how the heck does that happen?

[eyebull]

Reverse choke on BSA barrels is a new one on me.....how the heck does that happen?

Should imagine it's where the barrel is pressed into the breech block by a company that doesn't care much about what they do.

[trajectory]

Should imagine it's where the barrel is pressed into the breech block by a company that doesn't care much about what they do.

.....goodness knows.

[Phil Russell]

I am now of the opinion that this is not a 'guess the answer' thread but the search for an answer. In other words, the OP does not have a clue what is happening and is hoping to get inspiration from here.
I was hoping that the OP had found the answer and was going to tell us in order to broaden our experience / knowledge.

So, come on .... what's the answer?

Cheers, Phil

[greenwayjames]

Should imagine it's where the barrel is pressed into the breech block by a company that doesn't care much about what they do.

The barrel isnt pressed into the breechblock on any BSA springer.

[evert]

The barrel isnt pressed into the breechblock on any BSA springer.

It is brazed, and that can cause distortions too.