Same gun, different output !

[gedfinn 2]

Hi, I have just read a thread on piston washer sizing !
I have a well used Bsa lightning, It has a Gas ram which I have pumped up to give an output of 11.6 Fpe. ( .22 )

I know nothing about piston sizing, but when I took the piston out, The parachute seal looked OK but was a loose fit, Looser than I would have expected ?
The gun shoots VERY well & has a great trigger , ( All the reports on these say they are not so good )

I have made a silencer for it, & its pretty quiet, put it up for sale soon as I am finished with it, & 2 gas rams .22 & .177.

But this is my real point, I loaned the Gas Ram to a mate of mine, He has a Lightning also & said it fired well, However he was only getting 11.2 Fpe,??
His gun is in nice condition, better than mine, Same pellets, Etc.
He checked his & mine, His was still 11.2 & mine still 11.6 Fpe

I can see a problem for the gas ram or indeed spring makers if 2, almost identical guns can vary so widely,
Thats probably why the ram outputs are low !
Cheers, ged.

[junglie]

I've chronoed 3 lightnings & a supersport over the last year & they varied from 10.5 to 11.5 ged . I think it's down to quality control at bsa, the supersport(brum built one) was the scruffiest , had a square section spring fitted heavily greased, but shot much better than the rest & had a decent trigger on it too! I still have a test target in me shed I shot a clover leaf 10 shot group at 20m measured, all were .22 cal & the bore sizes varied quite a bit too ?

[gedfinn 2]

I've chronoed 3 lightnings & a supersport over the last year & they varied from 10.5 to 11.5 ged . I think it's down to quality control at bsa, the supersport(brum built one) was the scruffiest , had a square section spring fitted heavily greased, but shot much better than the rest & had a decent trigger on it too! I still have a test target in me shed I shot a clover leaf 10 shot group at 20m measured, all were .22 cal & the bore sizes varied quite a bit too ?

Well thanks for that Junglie, Mine is the old one, Brummy, Maybe thats the answer,
I also fired my mates with a spring in, ( Not for me ) Its graunchy, noisy & makes more noise when fired, I never fired mine with a spring in, as it came with a Ram, glad ?

But back to the piston seal, Mine is rather loose ( As I said ) I am guessing, but I imagine when it sets off on its journey down the cylinder,
Its not actually compressing until the seal itself " Parachutes "
This especially with a Ram fitted would accelerate faster ??? More kinetic energy,

Another thought is ! , A Parachute type seal is good, But when it gets near to the end of the stroke, Its, its own worst enemy IE the pressure is braking the piston on the cylinder walls !
This doesn,t happen with an O ring seal which is 100% efficient,
I wonder if !!!!! Ha ha, Cheers, Ged