Marushin Kar98 Problems

[T.Smith]

Well, I bought this gun used from a fella who just used it as a display piece (He was the only owner)

Anyway, after fixin' a few problems with the gun, I have discovered a main one which is really startin' to frustrate me. There is WAY too much hop-up.

Here is what I have tried so far.
-Used a different gas (I've tried Propane, an' Duster)
-Back out the hop-up screw
-Removed the hop-up entirely
-Rotated the barrel 180 degrees to see if it had anythin' to do with that
-Examined the shells for any abnormalities
-Tried a different weight BB (.34 an' .45s have been used)

All to no avail. The thing just won't shoot without flingin' up an' posin' a real danger to any low flyin' aircraft.

Any help would be MUCH appreciated

[DonP]

Have you inspected the fired BBs? Check them for a gash/slice/other physical distortion.

I have seen something like this happen before. Usually the BBs are hitting a bit of flash or other piece at the muzzle (like the flashhider if there is one) upon exit.

This might not actually apply to you. Hard to tell without seeing your gun but might give you a different direction from which to approach the problem.

[T.Smith]

Alright, I will be sure to check it out. So far though, the barrel looks as smooth as glass, an' there is no visible catches. I'm baffled, really :S

[T.Smith]

Update:

Well after ruling out all possibilities, I have set to work to make a "reverse" hop-up. Just for testin' sake, I've started with some heavy duty cyanoacrylate, an' if that proves to work, I'm goin' to be explorin' other, more permanent, measures.

Does anyone have any experience in these sorts of mods?

[T.Smith]

I have discovered that the problem lies with the bolt face itself. The 'top' of the face's nozzle is a bit deformed, allowing gas to vet out the top. This puts a harsh backspin on the BB an' causes my problem. Since bolts are not readily available, I had to find other methods of fixin' it.

Solution:

After a bit of thinkin' sessions with myself, I have come up with a solution. The hop-up mechanism allows for total reversal with a bit of machining (To allow the hop-up bucking to sit at the bottom) I have essentially created a reverse hop-up that is neither permanent or temporary (As it can be reverted back to it's original position with a few minutes of dissassembly)

Here is a rough sketch of what I have done. Not shown are the small holes I needed to drill in the stock an' a nearby piece to allow for clearance of the hop-down screw.

Now, I am in hopes of findin' a new bolt so this problem will cease all together an' I will be able to use this gun with it's maximum range (It loses a bit with the hop-down system, not much, but enough to be noticeable)