Few things i would like to know .

[No1_sonuk]

Re: Few things i would like to know .

Great maths but unfortunatly you have missed the point. Not sure how you would get negative pressure with out drawing the piston back....Never mind thanks for that.

I assume you're referring to the underlined part here:

Assuming the piston doesn't start to withdraw during that 0.00375 second period, no negative pressure would result. Even if it did, there's usually some excess pressure that blasts out of the muzzle behind the BB.

"It" in that part is not a reference to negative pressure, that's "Even if the piston did start to withdraw..."

But to answer your question:
If the cylinder capacity is lower than the barrel volume, the BB will get to a point where it will be effected by negative pressure behind it because the piston isn't moving. The moving BB would act like a piston, and because there is no positive pressure behind it, it's movement and "seal" will create negative pressure.
That's not likely to happen in an AEG, as the cylinder/barrel volume ratio is usually above 2:1.

[North West Outpost]

Re: Few things i would like to know .

Sonic you seem to have gone off at a tangent there.

I fully understand the fact that if there is more air volume in the barrel than availible in the cylinder you will get neg pressure. Due to atmospheric outside and a diminishing pressure pretty much sealed behind the bb, making a vaccum effect.

What I was discussing here was the fact that if the bb hasn't left the barrel befor the piston starts it's return backwards you will get a much stronger neg pressure. In super fast setups what I would like to know is how far in mm does the bb have to move befor the piston starts to move backwards. Lots of variables I know fps, barrel dia, bb consistency, piston head, cylinder, cylinder head components, hop up and follow through to some extent.

IE if you had a 590 barrel can you run it at 30 bb's a sec? No.

[No1_sonuk]

Re: Few things i would like to know .

Most, if not all, cylinder:barrel ratios would mean the piston is still moving forward when the BB leaves the barrel...

More important factors you didn't mention are the interaction between sector gear and piston.

If someone can tell me the maximum angle that the sector gear grips for, I can factor that into calculations and get a rough idea about theoretical max BB/s.

Assuming the sector gear has 180 degrees toothed, 30 BBs/second rate would leave the piston free for 0.016s before starting to pull it back. That's 4-5 times longer than the BB needs to clear the 400mm barrel @350 FPS (I can't run the 590 number right now, but it would still be plenty of time).

[North West Outpost]

Re: Few things i would like to know .

A couple of thing to try to work out would also be. Generally a very high speed sector gear would be short stroked by up to 3 teeth. Coupled with that the cylinder would be vented.

I was going to fit a gearbox together without the cylinder and spring to measure how far the piston moves during a cycle.

[No1_sonuk]

Re: Few things i would like to know .

Measure the length of the piston rack over the number of teeth on the sector gear. It'll be no more than that.

[No1_sonuk]

Re: Few things i would like to know .

Some numbers for you:

Standard Marui cylinder is 27.1cc (can't remember where that number came from)
590mm barrel:
6.04mm - 16.91cc - 1.60:1
6.03mm - 16.85cc - 1.61:1

BB flight time 590mm @ 350 fps (106.68m/s) = 0.005331 s
Theoretical max BBs through barrel, 1 at a time = 180.8 per second

BB flight time 590mm @ 300 fps (91.44m/s) = 0.006452 s
Theoretical max BBs through barrel, 1 at a time = 154.9 per second
Numbers are "theoretical" because they don't account for the need to accellerate the BB from rest.

30 rounds/s = cycle time of 0.033333 s
Assuming 50% teeth on sector gear, piston free time = 0.016667 s

Should be plenty of time.

[guard-sniper87]

Re: Few things i would like to know .

OI OI OI

im not on about suck back or back pressure or making my lipo runb in an m14 ,

im just after internal help as i never had one before and dont want to ruin in ,

also i do know that the longer the barrel is in some cases not all you have to get a quater or half ported barrel ,

please stay on topic or will be closed ..

only after info on the upgrades stated or different and better alternatives

[mark1989]

Re: Few things i would like to know .

In a full length m14 i've put in a 550mm barrel and it's still not poking into the flashider just for the record. Any longer and you'll need a silencer to feed it into. I have a Lonex 6.03 barrel, they're not bad but i'm not over the moon. I prefered the madbull ver.2 i had in my old aug. And please use .25s in it. All m14s deserve .25s

that's my opinion, also, if you're making big changes to the gb then i got all of the piston and cylinder parts and things from a website which drops supplies for airsofting. The ka mags on there are ok but if you've got a high rate of fire the spring is pretty weak and you might find it'll only feed every other shot. I did when using a 9.6v battery. The ones from a certain scottish website that rhymes with airsoft hurled are better in my opinion.

That's a few things i've noticed from recently upgrading an m14, hope at least some of it is helpful.