Cylinder and barrel length question

[Glenn]

That and Mythbusters would foul it up somehow. I love that show, but I just got a new job by going on at length during an interview about how annoying it is to watch the them screw up.

[Sale]

Stealthbomber: There are other reasons for ports as well. One is that during the rearward motion of the piston, it moves more easily after passing the port (because thee BB is in front of the nozzle, and despite of the +-shaped aperture the flow is not optimum). This theoretically increases ROF and battery life. I have to agree with you wondering why on earth they would do it, but I guess they had enough reason to do it.

 

TM does not produce high end guns because they would be expensive, like Systema. They cut some corners to drop production cost, but you have to admit they produce stunningly stable quality and the gearboxes keep on running and running with little if any maintenance, if you don't tinker with them.

 

Glenn: The likely reason why you missed the discussion about excess air affecting accuracy is because the threads about ported or bore up cylinders usually contain "debate" like: "No wAY suCKbaCk is TRUE 'CoZ thE PisToN dOesNt g0 bACk sO fAST!"

[Tallbloke]

Sorry just been reading through I ok I find it hard to believe in some ways.

 

Your saying that every gun (lets take CA for example) has a different cylinder set depending upon the model of the gun. IE a Version 2 M4a1 cylinder set a m16 set a cqbr set etc etc etc for every different model. Rubbish. they will produce the version 2 gear boxes the same. Some may be slightly different (M16 length & the CQBR length) but overall they wont be specific models for each variation of gun as It wouldn't make business sense. Every gun you buy has a muzzel velocity of say 330-360fps...... hmmm wonder why there is a 30fps dead zone - esp if you loose 25fps by shorterning the barrel length..............

 

Chris

 

Feeling sceptic

[Stealthbomber]

Thanks for sharing.

 

Meanwhile, back on planet Earth, you'll find that airsoft guns are all fitted with cylinders which have holes in them to optimise the way they work.

 

They're not all different. There's about 4 standard types of cylinder and companies just fit the one which matches the other properties of a gun.

[Smoke 6]

Can anyone tell me on average how much power do you lose when you combine a mechbox with a non-ported cylinder to an inner barrel thats short, M4 length or so?

 

I recall losing about 25fps or so when I put a full cylinder in my M4. Is that about right?

 

Reason I ask: I want to be able to swap on/off a para length barrel onto my M249 MkII. But I don't want to be tearing down the mechbox each time to put in a ported cylinder, so I want to see how much fps loss I should expect when I run the short barrel.

 

Next  the bigger question:  Is there any adverse affects put on the mechbox, being as there's no chance of suckback (I'm not putting a ported cylinder on a long barrel rifle)?

 

Or will I be doing a semi-dryfire every time I run the short barrel (since its only using somewhat like 2/3s of the cylinder volume before the bb leaves and back-pressure is released) and putting added wear and tear on the pistonhead and cylinder head and the other parts?

 

Thx in advance for any advice, comments, warnings, etc

<{POST_SNAPBACK}>

 

Hey, it's Atomic from AO (sniper in the wicker VC hat).

 

 

Until some physics wiz comes up with the actual calculation, we can only speculate. Let me offer my perspective from a past career in manufacturing.

 

I would guarantee that the reason TM ports some cylinders and not others is due to excessive strain on the gearbox and subsequent failures (breakages). If you look at the higher end Systema cylinders, they used ported cylinders in the M4 kits, but not in the M16. It is probably because in testing they had more failures in non-ported M4 cylinders with heavier springs, and had to vent some of the air so that the piston did not pound the rest of the gearbox.

 

If my assumption is correct that the function of the ports is to prevent failure, then I would say yes, that using a smaller barrel will increase the wear and tear on your gearbox. However, another forumer answered on page one that he has found the wear and tear negligable.

 

I don't do many exotic mods to gearboxes, but is there a piston that has a cushioned face to lessen the damage? That way you could use the same cylinder with both barrels and not have to worry. May be worth investigating.

 

Good luck, I really don't have anything else intelligent to offer.

[Almighty]

In an old Japanese magazine article on the subject of optimum muzzle velocity relative to cylinder volume and barrel length.. it was said that the best combination is where the barrel bore volume is approximately 2/3 that of the compressible air volume in the cylinder. Anything more, or less, than that results in lower muzzle velocity (assuming constant spring power).

[Stealthbomber]

In an old Japanese magazine article on the subject of optimum muzzle velocity relative to cylinder volume and barrel length.. it was said that the best combination is where the barrel bore volume is approximately 2/3 that of the compressible air volume in the cylinder.  Anything more, or less, than that results in lower muzzle velocity (assuming constant spring power).

<{POST_SNAPBACK}>

Indeed. 2/3rds is a good rule of thumb to avoid suckback but you can get away with significantly lower ratios by using tightbore barrels and appropriately sized BBs.