hi steve, i always have fun with these,i take it its the rubber ones you are fitting,i grind a bit off the face of the rear of the seal[ the bevelled end] and trial fit until the barrel can be just pushed down without too much pressure,dont over do it as they always settle a bit with use.i no longer buy seals for these ,i make my own out of neoprene car fuel line..cheers greasemonkey