Go back to old barrel & stock hop unit on the shorter 220-ish barrel
coz barrel length can REALLY alter crap I just discovered.....
just got through testing about a dozen springs and interesting results.....
Also I noticed no real difference which way round the springs went either ??? which is a bit unexpected
You are supposed to fit spring with tightest coils at spring guide end to allow easier starting on irregular springs
and it is supposed to make a difference or lower fps if it goes back to front (tight coils at piston) - NOPE
For the record these springs were tested on a APS UAR that is supposed to have a full stroke 410-ish stock barrel
Some were std regular or linear or same crap coil spacing & others were irregular springs but no difference seen on either ???
(also worth noting the m100 fitted to UAR from TWG was hitting a bit over too 348 - 355 so a bit over its official 328 rating)
Also tested the old cm515 spring which was 400-405fps on 380mm barrel and it gave 405-410fps so kinda about right on 407mm
Also the Element M105 used to give me 350fps on a CM18 with a 275mm barrel with AoE done but stock spring guide
(probably hit 365fps with spring guide is my gut feeling)
But 1 - maybe 2 of these (found another in a bag of old springs that looked same) was hitting 390 to nearly 400fps on UAR
if I fitted spring guide to CM18 and expected 365 - that is still a 25 to 35fps increase on the longer barrel in UAR
Going by a list of figures n crap from these springs tested it does seem to indicate there is joule creep as barrel gets longer
(Well don't know if it is exact same joule creep as some gas guns get lifting heavier 0.25's bb's at similar or close fps to 0.20's)
But fps does seem to rise the longer the barrel gets showing an increase in Kinetic energy - lol
God I love that word and had to squeeze it in somehow coz you always see that kinetic energy crap being used in spring/fps posts etc....
What is odd that my gun was able to stay below 350 previously but piston seal might not have been 101% perfect
plus I did recently change bucking as it showed a slight nick looking where the lips where - so this may explain some stuff
(same spring, different pistons but still short stroked 2 teeth - rof has dropped a smidge but now using all bushings & bit heavier piston weight)
Anyway.......
Springs tested - most I haven't got a bloody clue wtf their ratings are/where:
440 fps - same both ways
432 fps - same both ways
425 fps - same both ways
* my gut feeling these 3 could be m120's hitting say 30fps more on longer barrel *
410 fps - cm515 spring so sounds about same/similar fps in UAR (same both ways) - might be a m115 ????
390 - 395 - Element M105 - irregular spring but same both ways ???
385 - 390 - Element M105 - maybe - well looks very similar and probably chucked in spring bag coz unsure if 105 or 115 spring
* could be rated a m105 but might be a smidge over / worn m110 *
380 - 385 - same both ways
380 fps - same both ways
* these could be used m105 or over rated m100 ??? *
(one of these came out of a used broken G36c I'm lead to think)
340 - 345 - same both ways - Hmmmm, this could be a m95 or so spring and could come in handy later........
325 - 330 - this could be a m90 or m95 slightly worn spring......
The last 2 springs are quite possible lower springs than m100's if the Element M105 is anything to go by
These might show a small minor increase if installed say in an AK47 with 455/469mm barrel ????
So these might save me a major headache when I downgrade my cm28a AK's perhaps
(would be good to get somebody like Ian's experience on this though)
Think Sp00n had an L85 & R85 thingy majig and had to drop in a m90 or m95 spring in there (stock barrel length of 510mm me thinks)
as he was too hot to use .25's at around 310fps (aprox 350 on 0.20's - ah to hell with it - KINETIC ENERGY
Phew......
Now I still gotta rip my box apart - pull spring out, and test this mofo that hit 385/390 even though it is short stroked 2 teeth
and then when tested in UAR try and get something 30-35 less perhaps, I'll try 30 is my gut feeling atm.....
Getting back to your own problem it seems that the 50 fps increase is half tbb & maybe half barrel length increase
Though you say you tried the old barrel I think - so the mystery deepens if you put back all the stock stuff
though the flat hop has probably pushed it up a smidge but jeez......
I'm really sorry I do not have a perfect solution other than complete stock barrel & hop,
clean barrel and wait for a bit of fps drop before doing any further tweaks - not what you wanted to hear
but just a little alteration can make a big difference I have just found out and can increase fps but so much it places us over site limits
Damn Kinetic Energy bollox
But atm my hunch, and that is all it is btw seems to show that there "might" be a 20-30fps increase when you extend barrel lengths by 100mm
This could equate to say about 8 to 10% increase in fps per 100mm but tbh this crap & my findings has proven only one thing
Trying to work out rough expected fps is a major guessing game as so many factors can alter $hit
Think I'll cancel my degree in airsoft mathematics for now coz as soon as I find something that works
another curve ball gets thrown at me and knocks me on my ar$e that I feel like an England Rugby player atm
edit/update thought or conclussion based on f*ck actual knowledge but here we go.....
G&P gun has 215mm barrel so to ensure it has a bit of oomph they bung in a m105 or maybe m110 to compensate for fps lost
You fit in 300mm which bumps it up to normal fps level of 350-360 but coz tbb it goes up a further 15-20fps
this might explain where the hell that extra 50fps came from
this is all duck speculation and end of day it don't change $hit that its running hot
but might shed some light or idea wtf all these weird figures are coming from maybe
I'm off to get some Nurofen coz I got a major headache and my own crap to sort out still