SIG 552 - BBs not firing

[Fly 9]

Hey guys,

I've got a TM SIG 552 that's having some problems. When using the standard lo and standard hi-caps, along with the MAG brand mids it doesn't seem to fire, all I get is a soft thud sound and a back-up of bbs. Is this a hop-up problem?
It's one of those problems that kind of comes and goes but I'd prefer if it just went and didn't come back. Initially I thought maybe it might be a feeding issue and, if so, would it be possible to fix it with a complete hop-up referb?

Anyway, any light that can be shed would be appreciated.

Thanks.

[SlippGun]

Take a look down your barrel ( I mean removed from the gun) and see if the hopup unit is distorting the shape of the bucking. This sort of thing was happening with a friend's broxa, so I took checked out the barrel, and when you looked down, you could see that the bucking was being squished into an oval, instead of being nice and circular, meaning the bbs were jamming up on that point.

So, I then trimmed a bit off the bucking at the 9 and 3 o'clock position, and the gun feeds now. There likely is another sort of solution to this, but I didn't get a chance to try anything. The broxa's bucking was extremely soft, so I don't know if a stiffer bucking would be better.

I tested the gun with the hopup trimmed against my stock broxa and it had the same range and accuracy. If you wanted, I am sure you could teflon tape around the bucking.