VFC Scar-L Inner Barrel problem

[philly0001]

I have put a madbull 6.03 inner barrel in my VFC Scar-L (Using VFC hopup and bucking). When I use a mid cap mag I get 10 foot drop shots. When I use a high cap I get great results. Sometimes it would jam but for the most part good preformance with a high cap. Would anyone be able to provide any suggestions on getting things working with the mid caps? You help is greatly appriciated. Mags I have used are Echo1 metal mid cap. 1 green label and non green label Magpul mags. FYI if i swap back to stock barrel everything works fine.

[MaciekA]

Originally Posted by philly0001

I have put a madbull 6.03 inner barrel in my VFC Scar-L (Using VFC hopup and bucking). When I use a mid cap mag I get 10 foot drop shots. When I use a high cap I get great results. Sometimes it would jam but for the most part good preformance with a high cap. Would anyone be able to provide any suggestions on getting things working with the mid caps? You help is greatly appriciated. Mags I have used are Echo1 metal mid cap. 1 green label and non green label Magpul mags. FYI if i swap back to stock barrel everything works fine.

This sort of thing can be caused by a bunch of different factors. There are a few checklist things you should do to narrow down the issue.

1. Make sure your hopup has sufficient tension from the spring on the front (whether it be a barrel spring or a hopup spring) to push it against the gearbox. It's possible that the new barrel has changed the dynamics of fitment between your bucking/barrel/hopup and that your nozzle doesn't make an adequate seal against the bucking during fire. The reason I mention the above is that if your hopup unit is able to move around a lot or at all when the mag mates with it, it is actually possible to push the hopup unit forward enough to create a leak. This is why you see mags that are out of spec with certain mag wells or hopup units feed and seal better when the bottom of the mag is gently pushed in the direction of fire, causing the feeder tube to mate with the hopup unit better and causing the hopup unit to sometimes tense back against the mechbox, which in turn causes the nozzle to have a better seal.
   
2. Related to the above, if you notice through the chrono that you are getting 30-60fps higher when you push the mag up and forward into the mag unit (causing the unit to move backwards), then this is a telltale sign you have this issue.
   
3. Next up, do the bucking lip test. Remove your barrel and hopup from the gun and turn it upside down so that the feeding tube is facing the sky. Then take a BB and feed it into the unit through the hole where the nozzle goes in. It should settle against the bucking lips. Now take a pin or screw driver or something and GENTLY (feathertouch) press on the BB. It should take a very minimal force to cause it to go into the barrel. By the way, make sure you haven't accidentally put the other end of the barrel against something that would create a seal or you will be confused as heck
   
4. If you can't get your hopup unit pushed back hard enough against your gearbox, try wrapping the front of the hopup with Teflon tape to add some springy volume to the front. It'll take a bit of experimentation to figure out how much you need to add, but in my experience "slightly too much" is perfect and really helps with the seal.
   
5. Try the velcro mod on your magwell or mags. Go get some adhesive velcro strips and put a short piece on the bottom rear of your magwell so that if you were looking at your gun's left side face-on, the mag should be rotated clockwise slightly as a result of the velcro mod.
   
6. Try to manually feed a BB into your hopup without a mag and fire your gun upside down. Does this always result in a reliable shot?
   
7. Make sure during all of this that you have your hopup completely off.
   
8. If you have a different bucking available.. try it. The bucking lip test might necessitate it. Before trying this option though, do the above hopup unit tension-against-mechbox tests.
   
9. It's unlikely this is the issue unless the interactions here are complex, but if you begin to suspect that your bucking is leaking compression, try the Teflon tape mod or the dental floss mod (see Maekiii's video on YouTube for how to do this) to tighten the seal your bucking is making. If a new barrel is causing compression problems, it can sometimes mean that its outer diameter is not sufficiently large to allow the bucking to create a seal in the hopup chamber. Note that this can cause your barrel+bucking to be harder to re-insert into your hopup unit, but this is kind of what you want. Take your time
   

I should also mention that if you do think you have a leak in the hopup/nozzle area of your gun, make sure that you don't keep firing BBs through it if something is still wrong in this area. If you create a jam in your hopup unit, you will get backpressure into your cylinder, and begin to shred your piston.

[SMIC4]

MaciekA's got it all covered from what I can see, but my guess is it's #1. The mid cap is probably pushing the hop up out of alignment and ruining the air seal between the hop-up and the nozzle. It might be a very minor misalignment (even if it's .05 mm) and you'll notice a significant drop in power.

Dry firing the gun a few times with both mid and high caps and listen to the sound of the air. Compare the sound it makes with a mid vs high. If you hear a nice poof coming out of your barrel and the mechbox isn't making any clanking sounds your compression should be ok. If no poof and you hear a clank, that means there's not enough air pressure building up in the cylinder causing the piston head to slam against the cylinder head! This is not a sure fire test for small leaks, but in your situation if the mags are causing a misalignment I think you'll be able to hear the difference.