I just received my Knoxx NRS stock/forend for my Remington 870 and i gotta say it looks pretty sharp. When i removed my factory wood stock there was a little metal washer/spacer between the stock and the receiver. When i put this piece back on along with my new Knoxx stock there is a gap between the receiver and stock ( approx 3mm). when i put my new Knoxx stock on without the washer/spacer, my new stock fits snuggly without a gap against the receiver. Should i use this washer/spacer or not? I like the snug fit without the washer, but i do not want to sacrifice structural integrity. Thanks ahead of time!