I am using change mesh to change my guns ,but my guns go messy

here is the gun: http://server6.theimagehosting.com/image.php?img=Kuvat�mmis.png&public_view=1&album=0&fullsize=1

And here is it messy: http://server6.theimagehosting.com/image.php?img=Kuvat�mmis-1.png&public_view=1

the pictures don’t show up on that shitty site…hint:photobuck, or imageshack!
ps:sorry for the rough language, i’m in a bad mood!

Real
http://img409.imageshack.us/my.php?image=kuvatmmiskh6.png

with change mesh - messy

http://img128.imageshack.us/my.php?image=kuvatmmis1te0.png

If I understand well, it’s a Centre problem
Before parenting try to replace your object
If the problem its still there, enter Edit mode and move/rotate the vertices
until they reach the desired position
Not a very good solution
Post a .blend if possible
Bye

oh, i have parent the gun and its great ,but if i use replace mesh then it will go ugly