R10 low on power..

[rhyslightnin]

The BSA reg can be very prone to temperature fluctuations, much more so than a HuMa or Tench reg. There are lots of other reasons for a rifle to drop MV in the cold but it really shouldn't be more than about 0.5FtLb off what the gun is doing in "normal" ambient temps. Although the weather is a bit unseasonably cold here in Manchester we're probably only 4 or 5 degrees colder than average for this time of year and the cold snap will be over soon.
Try bringing the gun in the house, let it warm up for at least an hour and chrono it while still warm if possible (a cardborad box with a few Argos catalogues or phone books makes a decent pellet trap that's fairly quiet to use in the kitchen if you are allowed!).
Although BSA's aren't normally over-lubed at the factory any lube (oil or grease) that has crept or migrated into the hammer assembly will be thicker in the cold weather slowing hammer strike and reducing MV.
A strip, clean, degrease and re-lube may be all you need but remember to chrono at room temp (20 degrees C) as that is the temperature the police and the forensics laboratories will chrono at, if you set a gun for 11.5FtLb at 1 degree ambient it will certainly be close to or over the 12FtLb at 20 C.
If the gun has developed a "power curve" then you could try fitting new O rings to the regulator (make sure you don't disturb the pressure adjustment), which may cure it but the BSA reg design tends to limit itself (lowering MV) when filled over 200 Bar. You will also need to check that the BSA reg doesn't "spike" (cause a rise in MV) around the 100-80Bar fill pressure area. This is a common characteristic of the standard reg. Make certain that if your reg "spikes" it doesn't take you over 12 FtLb.

Ok.. testing today and it's shooting 290-350fps with 14grn sniper lites.. just changed the prob oring and that didn't change anything so what next? I'm a bit loathed to spend on it as I want to sell it now anyway

[Shed tuner]

Ok.. testing today and it's shooting 290-350fps with 14grn sniper lites.. just changed the prob oring and that didn't change anything so what next? I'm a bit loathed to spend on it as I want to sell it now anyway

It sounds like the reg is leaking through, so the hammer is seeing twice the pressure it's supposed to. Take the reg apart and replace the seals yourself, or accept that you'll be selling the gun for a fair bit below to allow for the cost of the repair.

[rhyslightnin]

It sounds like the reg is leaking through, so the hammer is seeing twice the pressure it's supposed to. Take the reg apart and replace the seals yourself, or accept that you'll be selling the gun for a fair bit below to allow for the cost of the repair.

A new huma is £100 so I'll advertise it for £430
Thanks JB
Rhys