Friday, 10 January 2014

BSA Mercury, Friction in the Piston

And Finding The Most Accurate Pellet For a 70's British Springer

Out in the woods testing the .22 BSA Mercury.

I have done a far bit of tinkering with the .22 mercury, but i know it needs a little more. It's knocking out RWS Superdome's at 10.5 ft/lb then slowly dropping down to 9 ft/lb, this i'm sure is down to the tight fit of the rubber O ring piston seal

The new piston seal O ring below is a bit over sized.

 I've read that it's a common problem that the piston seal can be a little oversized when new, and i did have to use some force to push the piston into the compression chamber with this one. Most people usually put a tin of pellets through to wear the piston seal down, but i reckon in this case i would need nearer two tins of pellets before any wear is noticed on the O ring.

Repeatedly putting a 1000 pellets through the Mercury would get a little tedious to say the least.

My other option would be to dismantle the rifle yet again, and use wet and dry to wear the O ring down, i would need to turn the piston in the lathe and apply the abrasive to give it even wear, 

It doesn't look over sized when fitted on the piston head , but believe me it is.

Then i would size the piston now and again till it was just short of a sliding fit, so once the ruff edge of the seal had smoothed out after reassembly it would fit perfectly. 

I would rather avoid going through this rigmarole again.

My only concern for the rifle is for the thread on the breech block getting damaged with all this taking apart and reassembly, i also have a concern for the spring compressor because of the mighty preload.

These were good value and sorts out the problem of the scope rail dovetails being set too forward on the compression tube of the Mercury.

A 1970's .22 BSA Mercury has a barrel that is 5.6 mm as opposed to 5.5 mm that is more prevelent now a days, and the older pellets that were a tad wider are not available any more. Eley Wasps in the blue tin are sized at 5.6 mm but are crap compared to how they used to be, 

No 2 5.6 mm Eley Wasps are not the pellet they used to be.

i have found that RWS Superdomes fit just as well in the breech and are infinetly more accurate. So with this in mind i reckon it would be best to see how the rifle performs after i put a tin of Superdomes through it, at 7 quid a tin it sounds like the fun option to me and i usually take a second rifle with me when i go down the woods.


   I have found the Mercury shoots most consistantly with a light hold and supported by my off hand just in front of the trigger guard, from personel experience most springers are more accurate for me if i support them at where they balance and this is where the Mercury balances out. The trigger breaks lightly and cleanly with no first stage travel so it's easier not to pull any shot of target, both my BSA Meteor and the Webley Hawk have similar triggers to this so i reckon it must be some British thang.

Ready for the off.

Testing the accuracy in the woods means i can't test from a bench rest, but the results will be more indicative of how it will perform in a hunting situation. The rifle was sighted for 28 yards and i will test at 15 yards and 30 yards, and with the shelter of the woods i don't have to worry about wind effecting the results.
Resting the rifle, uncocked and unloaded, while i go of to check the target.

Using the large cardboard boxes that were left over from Christmas presents as targets i took Scatterbone down to the woods and paced out 15 yards, 

Handy large cardboard box left over from Christmas, inside is foam packing and a piece of ply wood, after a few tests i can stick targets to it with the Gaffer tape i always carry around with me. As i say," If counceling won't fix it, Gaffer tape will."

i shot from a sitting position with my back against a tree while holding the rifle lightly with my off hand supported on my left knee. Out of AA Diabolo's, Falcon Accuracy Plus, Eley Wasp's, and RWS Superdomes, i found the Superdomes to be the most accurate in the 5.6 mm barrel of the Mercury. 

RWS Superdomes in any caliber are the best all rounder in my opinion.

At 15 yards 6 shots came inside the size of a two pence piece with the Falcon's coming a close second, the Eley Wasp's were all over the place thinking i had lost my mojo but then the the Superdomes did it again.

I'm pretty happy with these results, cleaning the barrel and perfecting my hold will improve results no end.

I tried to test the Mercury out to 30 yards but it was pretty windy even in the shelter of the woods, with the wind push the pellets two inches over to the left. I managed to do some shots compensating for the wind and managed to get on target, but as it was i was well chuffed with the results of the 15 yard shots. Having put just over half a tin of pellets through the Mercury since i last tinkered with it i have found the best hold for me, being happy with that i reckon i should just put an other couple of tins through it till it beds in and the velocity rises and settles down. I really would like to keep this air rifle as the surge and recoil are quite mild and as a .22 it carries a lot of knock down power down the range, and above all it looks bloody sexy for an air rifle.


Wing Commander Sir Nigel Tetlington-Smythe.   

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