After experimenting with a few different cylinders, barrels and springs I am pretty sure that the optimal ratio for cylinder to barrel volume depends also on the strength of the spring (what fps you are going for). For example, I have a cyma SR25 with a full v2.5 cylinder and a 455mm 6.01 barrel ( ratio of about 2.4) . With the spring that is in currently it shoots 1.2J with 0.2gr bbs and 1.05J with 0.3gr bbs. This result is the opposite from what you would expect when looking at the ratios that 1tonne has calculated. What you would expect to see is more Joule output from the 0.3 gr bbs since 2.4 is closer to 2.27(optimal for 0.3s) than to 2.17(optimal for 0.2s).
When switching to a stronger spring I find the results calculated by 1tonne to be more accurate. Can anyone confirm this?
You are certainly correct, except for one thing, AEG buckings really suck.
Heavier BBs put more resistance on the piston going forward, and that leaves one easy place for air to escape, the bucking.
This is pretty much impossible to fix unless you go HPA or weight your piston as much as possible, and even then it is difficult to fix.
VSR-10 bucking lips on the other hand are thicker and much longer than AEG ones so they have the ability to seal much better, and they are usually backed by the chamber making it impossible for them to get pushed out of the way, which can happen with AEG buckings.
Also, AEGs and HPA engines don't have nearly as much loading force as a springer or most GBB guns, so they can't drive the nozzle as far into the bucking or into a tight bucking as well, making that air seal issue even worse.
Definitely look at weighting your piston somehow or getting an aluminum one, and try putting a thin layer of super glue around the lips of your bucking so it is tighter in the nozzle, and also look at trying a different nozzle and boosting the power of the spring on your tappet plate.
This should all help with you gaining lost power with heavy BBs, making your gun about the same as 1Tonne's numbers.
Give or take a bit of course due to air seal, piston friction, cylinder volume, barrel diameter, bucking type, chamber, and numerous other things, but it will definitely help you out.
Thanks for your reply but I don't think its an air seal issue since my fps is pretty consistent +-2 fps. Also if I put a stronger spring in the gun (M150) it shoots 2.05J on 0.2s and 2.44J on 0.36s which is in line with 1Tonne's results. It seems strange to me that the spring strength would have an effect and that's why I commented.
You can still have great FPS consistency even with an air leak, as long as the leak is pretty constant.
I guarantee that you do have an air loss, but it is probably better than most.
This could have to do with a few things, spring age, spring rating, spring quality, spring brand, and piston stuff.
I know for a fact that cylinder/barrel stuff is not linear and neither is piston weight/friction, so you probably have a little bit of that going on as well as your spring being different.
It's near impossible to duplicate a spring let alone years apart from the first one, so that definitely doesn't help with this since that can be a huge variable if you are getting weird readings.
Anyways, 1Tonnes stuff is obviously not perfect due to all the variables out there which simply can't be accounted for, but it's a great guideline for someone to begin with, and they can go farther with it if they so choose to dial everything in exactly.
Hey. Search did not help me so I hope someone in this thread can help me.
I tried to build my m4 as efficient as possible. 407mm barrel, full cylinder. Ratio about 2.3 using .32 bb's.
The result? Less joules than with 3/4 ported cylinder and 407mm barrell. Is it normal to lose fps with full cylinder?
Edit: After installing stronger spring the results seem to be better. Maybe it needed a little more push for it start making magic.