Internal Transfer, FPS Loss
 

So, I’m having a slight problem with my new M4. All the upgraded internals were originally in a G&P M4. It was shooting ~1.3J or ~380FPS with a 0.2g bb. I since bought a VFC VR16 to transfer the parts to the VFC. However, after switching all parts and shimming to new gearbox, the internals have since dropped to about ~0.95J or ~320FPS with a 0.2g bb. No internals were changed, no compression issues. When nozzle is fully forward, there is no light down Barrel when a flashlight is used in feeding tube. Like I said, absolutely everything is the same. What could this be?

So let me get this straight you put the g&p internals to the vfc gun?

What parts did you swap and can u include specifics like barrel and nozzle?

Are they different inner barrel lengths?

If everything air seal wise ok, is piston traveling free? A tight binding piston will slow down, and you’ll loose power.

Should’ve left the VFC parts in there. G&P is not an upgrade.

Sorry for confusion. I had the G&P all upgraded with parts.
G&P aluminum nozzle, SHS Cylinder Head, SHS Cylinder Ported, SHS Aluminum Piston Head, SHS Piston, Guarder M120 Spring, SHS 13:1 Gear set, SHS Tappet Plate, SS’d 2 teeth, AoE corrected, etc. Also VFC Rotary Hop Up with Prommy 275mm R-Hop’d Barrel. Nothing has been changed other than motor. Same internals, same Hop Up, same Barrel.

It was shooting 1.3J in the G&P body and now 0.95J in VFC Body. Idk what is wrong

Sorry for confusion. I had the G&P all upgraded with parts.
G&P aluminum nozzle, SHS Cylinder Head, SHS Cylinder Ported, SHS Aluminum Piston Head, SHS Piston, Guarder M120 Spring, SHS 13:1 Gear set, SHS Tappet Plate, SS’d 2 teeth, AoE corrected, etc. Also VFC Rotary Hop Up with Prommy 275mm R-Hop’d Barrel. Nothing has been changed other than motor. Same internals, same Hop Up, same Barrel.

It was shooting 1.3J in the G&P body and now 0.95J in VFC Body. Idk what is wrong

It should be last I checked...

Swap the g&p nozzle with the stock vfc nozzle and tell us how it goes

This. Those G&P nozzles are fucking terrible. Use a plastic one like modify, guarder, systema, etc

I’m pretty sure I have a Retro Arms nozzle somewhere I can use. The guy upgraded the VFC and nozzle o ring is pretty well no resistance and leaking air. Not fun. But that’s doesn’t really say why the change gave me an FPS loss of 60 lol

I can change it out for a Retro Arms, what I have around, but air compression is great. Found the aluminum G&P nozzle to be great in my experience. But, doesn’t tell me why it gave me a 60FPS loss in the transfer of gearboxes lol

It's not the gearbox it's the nozzle length. You swapped out the gearbox but the length from the nozzle to the hop up unit might be different since you had a g&p hop up and switched to a vfc. Lots of these parts aren't a simple drop in when you're switching brands. This is something I learned a long time ago. Either use the same length nozzle or stick to the stock parts. +/-1 mm can cause a fluctuation in fps because the nozzle doesn't extend deep enough into the hopup rubber.

You didn't mention if you swapped the gearbox she'll either so I just pray that you're using the stock vfc she'll in the vfc gun because if the gearbox is +/- a few mm in position away or closer to the hop up unit that can also mean problems.

For clarity sake and my own sanity can you just confirm if the retro arms nozzle and the stock g&p nozzles are the same length? Can you post dimensions of all 3 nozzles with caliper measurements if possible?

I never switched the Hop Up... It is still the VFC Rotary Hop Up that I had in the G&P. As I said, nothing has changed in the transition from the G&P custom internals to the VFC. Only thing I switched was the shell, from G&P to the VFC one. The nozzle is the same as before, compression parts are same as before, nothing has changed in the transition between rifles.

Okay the explanation for what you had done was clear as mud until now.

When you swap parts and brands they will inevitably have different dimensions. Those miniscule differences in the gearbox dimensions can cause the differences in fps e.g. front of gearbox thickness where the hop up rubber sits, where the cylinder is seated relative to where the hop up mates with the gearbox, or even how thick the inside the gearbox is where the tappet plate pushes forward the nozzle. Definitely do not be surprised by this outcome.

I'm fairly confident its piston fit. If you haven't already, do this check https://youtu.be/v1i5rCMiueE