Ian_Gere
Retired Moderator
- Apr 1, 2012
- 6,417
- 2,050
I don't think you and I are talking about the same thing. Fair enough, if your intention is to scientifically compare shots with equal muzzle energy so that the only variable is the BB weight, so for eg at 1.14J a 0.2g BB has a muzzle velocity of 350FPS and a 0.25g BB has 313FPS - but these are figures derived from maths. To actually achieve these equal muzzle energies/velocities you could not simply load different ammo into the same gun and set the hop, because in the real world applying more hop to lift a heavier BB reduces the muzzle velocity more than simply the change in weight would suggest. I doubt many people have ever thought much about this because we expect to lose velocity when we use heavier BB's; what drew my attention to it was fitting a Falcon 455x6.03mm TBB with the Dual Point hop rubber...
It really struggles to lift .25's, so when I slide enough hop on (it's an AK: no clicks) to get the best range possible with flatish trajectory, the result is 5-6m less than I can get firing 0.2's... (is this the dreaded one gun phenomena conflated erroneously with fairies at the bottom of the garden, et al, a la Ed's comment above perhaps... read on and decide for yourselves).
...which made me think the whole process through again - I had thought about it a bit back when we were considering the alleged phenomena of 'Joule creep'. TBH I can't remember the complex reasoning of the discussion, although it is somewhere within these hallowed pages, but i do remember thinking that it didn't matter anyway because of the way in which hop up works - basically it is a brake designed to fail: if the brake succeeded the BB would be stopped completely (and some hop units can do this, much to the annoyance of a steady stream of noobs whom we meet here at their wit's end), but by only partially succeeding the braking effect is applied to one side of the BB resulting in backspin - but here is the point:
braking occurs
...and more hop on equals more braking. I just did a quick test on my chrono to illustrate the point: the average of 10 shots with no hop firing 0.2's was 353.45FPS vs 321.27 with hop set for max range flat traj. It's dark so I can't see to set the hop with 0.25's (it was left on set for 0.2's) But you all know this. So why is it difficult to swallow that applying more hop to lift heavier BB's reduces the energy those BB's carry as momentum, over and above the velocity lost by a heavier object given a similar impetus?There are other complicating factors also, such as how whatever imperfections there are in the air seal from piston head to barrel will behave differently under the changing pressure over the time it takes for the BB to exit the barrel and since this is different for different weights of BB, it is undoubtedly a factor*, just one which would need a pretty complex set up to measure. But hey, that just means that you really do need to experiment with your guns to find what works for you, as has been said.
*Simply changing the piston head to a dual O-ring type gives approx +20FPS / Modify Hybrid barrel & hop rubber combo can give +30FPS over and above whatever may be gained by changing a stock 6.08mm barrel to a 6.03mm TBB, so airseal and changes in its performance are significant.
But a blanket statement that 0.25's are better is not helpful. I agree that people do believe things which the evidence observed by someone else seems to disprove and otherwise sensible people have apparently witnessed evidence for things which just simply cannot be true** - maybe some of you remember the fad known as 'suckback' where it was believed by some that if you did not have sufficient air volume in your cylinder (because of vents) to make certain that the air was still expanding the whole time that the BB was travelling down the barrel, then in long barrelled AEG's when the piston was pulled back ready for the next shot the BB would be retarded by air being sucked back down the barrel. Well, you only have to work out the time the BB spends in the barrel compared to the cycle speed of the gearbox to know that this is impossible, but besides that, there are vents in the piston head which allow air to fill the cylinder from behind the piston head - but people wrote on forums and told me f2f that they had tested it with a chrono etc. You know what, I'm willing to believe that people would hallucinate better results with .25's because they believe they must be better in all circumstances.
There are different hardnesses of hop rubber: generally speaking the softer / lower the degree, the stickier the rubber and the stickier it is the less 'hop on' you need to lift any BB, but also the softer the faster they wear out, so if you have a high FPS gun you can use a harder rubber because you have power to spare, but this is also desirable because higher power guns wear their hop rubbers out faster. But most stock rubbers are made to work ok and last a fair while - a couple of years of average use, say once or twice a month skirmishing all day and a bit of plinking in between, and also bear in mind that, with the exception of Japanese guns, almost all AEG's are designed to be at least 25% more powerful than UK limits.
So going back to the beginning of this post, do you think that it is only funky hop rubbers such as Falcon Dual Point which can result in losing more power by putting enough hop on to lift .25g BB's than is made up for by additional range gained by conservation of momentum vs air resistance in denser BBs, or do you think that some guns downgraded to M100 springs with stock rubbers may suffer the same effect, bearing in mind that the difference or perhaps similar but not as extreme, so that what they gain from more weight is lost to additional braking? Perhaps you think as I do, that due to our UK FPS limits, if 0.23's were more easily available and cheaper, they would probably be a better choice than 0.2's or 0.25's for many UK guns, but in the absence of an overnight miracle, you should suck it an see...
**I wonder if you were referring to our conversation Ed when I said that I was getting 70m accurate for man sized target shots from my tac AK? I know. It sounds impossible, but I swear, @MCG The Gaol firing out of the window of 1 cell block, across the path through the main gates into the yard of the main block with the refectory etc in it, the entire length of that block to targets standing around believing they could not be hit by people 15-20m closer to them than I - not flat trajectory, but not walked onto target lobs either, aimed shots at an upward angle - approx 346-7FPS (using a Magic Box double O-ring piston head, lashings of CT-2 grease, unbranded ali O-ring nozzle, lonex hop unit, G&G green rubber, PTFE tape wrapped hop rubber, Madbull fishbone spacer, 6.04mm TBB (i had to downgrade the spring to some poxy shotgun spring i got in a job lot of parts because i was getting over 380 with an M100) and Blaster .25g BB's
she died about 15mins from the end of the day grrrr - but she shall return weyhey!
