Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen?

[GrizzlyDemon]

My M4 is currently having some work done on it. It's an 11.5" M4 CQB with a KAC QD suppressor mounted, in which I covered up a tight bore running almost to the end of the silencer. I also had to replace the stock ported cylinder with a full one to maximise air flow and all that good stuff. After realising that barrel length doesn't give you more range at all, I decided to have the barrel cut back down to the rifles original CQB length of 292mm so I can take off the silencer for CQB or put a tracer unit on etc, but it still has a full cylinder inside as far as I know. I don't have the money to have him open up the gearbox again and put in a ported cylinder, something I should have thought of before I said cut the barrel back, but the guy working on it says that it shouldn't really be an issue and that if I stick to semi or even short bursts on auto I shouldn't notice any difference. I trust what he says, as he's never let me down before and his work is very good but I'd like another opinion. I've heard that a full cylinder with a short barrel can put stress on the gearbox or make it lose fps. I have an ASG Ultimate Reinforced gearbox/meshbox inside it, and don't really want to lose much fps as its firing at 330-340 with .2's and I use .25's so the fps is already in the high 200's/low 300's.

-Grizzly

[dave38x]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

If you hold the trigger down and empty the entire mag it still wont make a difference to feeding or anything like that.

I expect you will see a significant loss of FPS though. I have a 363mm tightbore in my M4 (14" barrel length) and it currently chronos at 335. When I put a mate's 9" barreled upper on it that drops to 290fps, so I'd expect to see an even greater loss.

That loss is due to the barrel length, not the cylinder volume (which some say might reduce accuracy due to lots of air blasting out of the barrel behind the BB - I've yet to see any "accuracy" problems with my AK beta which has a 3/4 ported cylinder and a 150mm barrel).

[GrizzlyDemon]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

So since my barrel is 11.5" then I can expect it to drop around 20 fps or so? Its still at the shop, I'll get the guy to chrono it and tell me what the fps is. Not sure I like the sound of that tbh. What about accuracy and range? It was very nice and accurate before hand and its just had an A+ hop up bucking installed so the range should be even better than it was before, which was a good 150-180 feet of effective range.

[dave38x]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

More like 50 fps drop.

Range is entirely hop related (because it's how much spin can be applied for how little FPS loss), accuracy probably won't suffer too badly so long as the barrel is cut down properly (IE on a lathe)

[GrizzlyDemon]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

So I might as well just get it sorted while its there then, with a ported cylinder and a more powerful spring.... god damnit there goes my new sight I wanted in time for the nae :/
So all I'm looking at is fps drop? the un ported cylinder won't have much effect?

[dave38x]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

It shouldnt - the high rof 9" barreled weapon im using uses an almost completely unported cylinder and an m120 spring. It shoots fine

[GrizzlyDemon]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

The spring it had in it was a m100 spring with a couple coils cut off to be right under 340. Also had the AoE corrected too. I just hope it doesn't effect it too much as I really don't want to spend MORE money on it. If the performance isn't acceptable to me I will though, its just annoying that I didn't think of the cylinder before I said cut it down. I'm not even getting a tracer unit for at least a month, I should have kept it as it was for the time being

[dave38x]

Re: Cut barrel down from 440mm to 290-300mm with un ported cylinder. What will happen

ah well, it's the way of airsoft!