Cylinder question

[sdzx10]

I just received a complete mechbox for my m4 from Evike and the one they sent me isn't ported. I've read a few forums that say you'll lose fps by using a non ported cylinder in a short barrel gun and was wondering if any of you have had any experience with this. Thanks for any input

[GrimWulf]

In a ported cylinder, the cylinder hole leaves the cylinder unpressurized until the piston has passed the hole. Once the piston has travelled past the hole, the piston head seals with the cylinder for the remaining length of the cylinder. This means less TOTAL volume of air travelling through your barrel. On the other hand, with a non-ported cylinder, the piston head seals as soon as the sector gear releases the piston. This means a larger volume of air being forced through your barrel.

Now, why is this distinction important? (Please remember that the following is a generalization, and may NOT be true in ALL cases.) If you use a Non-Ported cylinder with a short barrel, the piston head will seal as soon as the piston is released, and before the the piston has completed it's cycle, the bb will have already left the shorter barrel. If the bb is already out of the barrel before the piston has a chance to complete it's cycle, then a good portion of the kinetic energy bound up in the spring is wasted. The closer the spring is to full decompression, the faster it travels thanks to momentum. At about 2/5ths of the way through the cylinder, the spring reaches a peak or sweet spot, in it's momentum. This is the point at which the piston is travelling as fast as it possibly can. You gain a noticeable fps advantage here because the air is being compressed at a faster rate against the bb down the length of the shorter barrel. Remember that the hole in a ported cylinder is there to leave the cylinder unpressurized until the piston and piston head are at the peak or sweet spot (the sweet spot being right past the end of the hole) of the momentum created by the spring but allowing enough air volume to be left in the cylinder to fill the barrel and thus fire the bb. All other things being equal except the cylinder, if you were to use a Non-ported cylinder on a short barrel, while you would have a greater total volume of air passing through the barrel, (about 2/5th's more air) your bb would already have left the barrel at a lower fps, and the extra 2/5th's of air would exit the barrel AFTER the bb has left and the bb will be traveling at a lower fps because the spring has not reached that "sweet spot" yet.

The use of a Non-Ported Cylinder is recommended with a longer barrel because before the bb can leave the barrel, the entire barrel must be filled with compressed air, which requires a larger volume of air, so you will need the piston head to make the seal with the cylinder as soon as the sector gear releases the piston.

I know this was a bit technical, but this was the easiest way I could think to explain it, without simply saying:
Long Inner Barrel = Non-Ported Cylinder
Short Inner Barrel = Ported Cylinder

I hope this helps.

[Straightshot]

What is considered long and what is considered short?

I'm wondering what my M4 is with the silencer on it now.

[sdzx10]

Thanks grimwulf. One other question for you. I'll probably just machine a port in the cylinder myself so my question is should I put it in the stock location or can I move it a little further down. Ive got a tight bore on it so I was thinking if its a smaller bore it needs less volume maybe I could move it down a little bit.

[sdzx10]

What is considered long and what is considered short?

I'm wondering what my M4 is with the silencer on it now.

                                                                                                                       Does your inner barrel go through your silencer? If not then it would be short

[Straightshot]

                                                                                                                       Does your inner barrel go through your silencer? If not then it would be short

Yes, that's why I want to know estimated lengths

[GrimWulf]

Alert...Alert...What I am about to post is an opinion and in no way constitutes actual facts, this is just my opinion from experience...lol

M4 length (360mm-370mm) and below is what I concider "short"

Anything above M4 length I would concider "long"

As to adding a port to a non-ported cylinder, I would just go ahead and get a ported cylinder rather than risk damaging the one you have now. The inside of most cylinders are deburred and polished to a mirror like finish that is going to be hard to achieve without special tools once you have cut out the port. I hate to tell you this bud, but the cylinder in that gearbox is a cheap uncoated brass cylinder. You will be much better off spending the $13 on a new Systema Cylinder. Here is a link to one I think you would be happy with that should suit your needs: http://www.airsoftgi.com/product_info.php?cPath=31_52&products_id=3378

You also might be able to find someone who has one laying around somewhere that they might be willing to trade or just give to you. You never know...lol

[Straightshot]

Alert...Alert...What I am about to post is an opinion and in no way constitutes actual facts, this is just my opinion from experience...lol

M4 length (360mm-370mm) and below is what I concider "short"

Anything above M4 length I would concider "long"

That's cool, it's an educated opinion.  I think my barrel is about 300mm.  May have to look into this.  Any guess what type of fps increase going to a ported cylinder would create?  I'm guessing a stock CA M15A4 CQB Compact Seal does not have a ported cylinder.

[GrimWulf]

While I have not been able to find a good review on the internals of your gun, I would assume, based on the CA's I have opened up, that it should already have a ported cylinder, but again, I couldn't tell you without actually looking at it. You should be able to take the upper receiver off in about 10 seconds and find out though.

Here is a video on how to take down your gun bud:
Complete M15 A4 Compact CQB disassembly

[Straightshot]

While I have not been able to find a good review on the internals of your gun, I would assume, based on the CA's I have opened up, that it should already have a ported cylinder, but again, I couldn't tell you without actually looking at it. You should be able to take the upper receiver off in about 10 seconds and find out though.

You assume I have the skills to do that  .  Although I was a mechanic in the Navy, I have not worked on internals of airsoft guns, and do not trust myself.  I did replace the inner barrel though.

[GARRETT]

Every CA M15A4 I have opened has a ported cylinder. So unless it has been modified, you should be ok.

[GrimWulf]

You assume I have the skills to do that  :'(.  Although I was a mechanic in the Navy, I have not worked on internals of airsoft guns, and do not trust myself.  I did replace the inner barrel though.

If you replaced the inner barrel, then you should know how to get the upper receiver off. You had to remove it to access the hop-up and barrel. Once you have removed the upper receiver all you have to do is look at the side of the gearbox and you will see the cylinder. Watch the above video, it is simply a matter of removing the front body pin and pulling off the front end and receiver, while pulling back slightly on the charging handle...

[Straightshot]

Every CA M15A4 I have opened has a ported cylinder. So unless it has been modified, you should be ok.

Sounds great.  My M4 just has weak range.  Maybe it needs a better bucking.  The original is about 3 years old now.  I don't know.  Would the next level spring take the fps above 340?  I'm not sure what the stock spring is in the M15A4 though.

Have I hijacked this thread?

[GrimWulf]

Yes a little bit, but it's ok...no one is going to be put in a silly hall of shame for it...lol. I would say though that we try to keep this topic on Cylinders and if you have any other questions about your gun bud, start a new topic and ask away!

BTW guys, if you are uncomfortable about working on your gun, there are plenty of people around the SC area that are more than willing to work on them for you. Don't hesitate to get in touch with them!

[Dominum]

Remember that my price(s) come with a free "tutorial" LOL, in other words, if you have me work on your gun you are always encouraged to watch and learn for yourself!

Yeah, after three years I'd say you might want a new bucking. Did you lengthen your barrel by much without replacing the cylinder? What does it chrono now? Springs go up in increments of about 30 FPS, with the occasional 15 FPS in between.