I was wanting to know why when I roll my boilies on a boilie tray a small hole comes in the center of them and I have to finish rolling them by hand?I use a gun and trays I bought off the internet.I have tried different size nozzles on the gun also.

several factors come in to play here.
first is dough consistancy. Too dry, even just a bit will cause that 'hole'. Too sticky will too if suasage is too big ea expanded.
Second is wether or not your dough 'expands after leaving the nozzle from your gun...most doughs will, so you have to gestimate that in your nozzle cutting to size.
You can try spraying some anti stick cooking oil on your rolling table, that will help a bit but it does make the table more sensitive to the sausage size.
Some doughs you have to roll as quick as possible out of the gun and some need some drying time, so don't squeeze all the dough out of the gun at first and try that sausage, then a second one with some drying time and you'll find it all makes a difference.
Finer ingrediants help and the courser the dough the more difficult to roll in most cases.
All in all alot of variables that kinda force trial and error on you..
Good luck and i wouldn't be too worried about that hole..it'll catch just the same...Last carp i interviewed said they don't care..

for some reason it posted it twice...prolly my error. sorry about that.