New 363mm barrell not working.

[Chopper92]

Hi all,

 

just installed a new madbull 363mm tight bore barrell into my UMP with the intention of increasing the range. I have since created a new problem with the gun since swapping out the old smaller barrell(half the length of the new one). Which is the fact the BBs seem to be firing out the barrell fine but then after about 15 spiralling very noticeably into the dirt. The arc on them is simply outrageous. had the hop out, re-installed it etc etc... and all seems to be together perfectly.

Yet cant find the problem for this. Any suggestions ?

 

Is it something other than the hop up and barrell which could be effecting this?

 

Cheers

[Hef Legend]

Things to look at:

 

Hop Bucking, damaged/deformed

Ammo being used

Using a longer barrel could be the issue, something to do with the volume of air matching the barrel length.

[Spatch]

Standard barrel length in the umps from memory is around 200-205mm so you've almost doubled the length, this as her has said could be some of this issue vs the cylinder volume, I would also suspect the massive under hop is something to do with the hop rubber, either a small rip/damage or you've mis aligned it when reinstalling it so it's not operating correctly and applying no spin

[Sitting Duck]

put old barrel back - keep clean n 0.25's

hopefully will be back as it was

 

use longer barrel in M4 should be better suited I reckon

unless you wanna start changing cylinders around for correct volume ratio malarky

[BrightCandle]

Not all barrels have the same dimensions around the lip before the hop window, so sometimes what will happen when you change barrel is that you pinch the hop rubber and it causes more restriction than it should. I suggest manually testing it outside of the gun and confirming that the BBs can be dropped in the hop properly and they get to the top (the lips aren't in the way) and that then it takes "normal" force to get the BB through the hop unit into the barrel and it then rolls out freely. If it doesn't then a quick check of the barrels side by side might show you the difference around that window and you may find you need to grind some material off to get a good fit or perhaps a different bucking with narrower shoulders.

 

You are also going to get cylinder air issues as I suspect yours is ported to accommodate the shorter barrel it had initially. So you need a new cylinder at this point and get the air volume back to a reasonable ratio. Given all that you should get the gun at least working. Then you'll find the range is identical because barrel length != range. Range is a combination of FPS and the hop units effectiveness, so in practice the way to go about increasing range is improving things like your air seal, air volume and consistency in general and then having a very effective hop like an R Hop in there.

[Chopper92]

Okay so to properly increase the range ill have to look into getting a new cylinder? how would i go about checking if its the right one to give the correct air volume ratio?

also will look into getting a new hop as the one that comes standard with the gun is pretty naff anyway. In terms of firing the gun is firing fine, just with the new barrel its firing 'hot' and getting this insanely stupid arc

[Lozart]

Can I just ask - why have you put a rifle length barrel into a sub machine gun in the first place? Surely the whole point of the UMP is that it's a nice, compact weapon for moving around in restricted environments, putting a dirty great long barrel in kinda defeats the whole point of it, surely?

[BrightCandle]

Can I just ask - why have you put a rifle length barrel into a sub machine gun in the first place? Surely the whole point of the UMP is that it's a nice, compact weapon for moving around in restricted environments, putting a dirty great long barrel in kinda defeats the whole point of it, surely?

 

I think Op answered that, they believed a longer barrel was the key to extra range. Its not really true in real guns (a 14" M4 v a 20" M16 is only a small decrease in muzzle velocity) and its certainly not true in airsoft either. There is lots of bad advice out there, we have all seen it.

 

The answer is that the extended barrel requires a cylinder that is 3/4 ported. Rather than replacing the hop put your effort into something that is likely to work - R hop it and you will mostly remove the whole problem with a terrible hop unit. You will probably then find your airseal isn't very good but that is a whole other problem.

[Chopper92]

Can I just ask - why have you put a rifle length barrel into a sub machine gun in the first place? Surely the whole point of the UMP is that it's a nice, compact weapon for moving around in restricted environments, putting a dirty great long barrel in kinda defeats the whole point of it, surely?

The longer barrel hasn't affected this at all it has a folding stock and suppressor on it anyway, therefore the suppressor covers the extended barrel and then can always fold the stock in for better maneuverability. just wanted a bit more for those mid-range engagements.