I just finished  putting La Rue FF's on my 16in BM. I also installed a LR low profile gas block. My question is when I put the block on, it did not sit over the two slots that are in place for the FSB pins on the barrell. I made sure it could go back no further , then installed the set screws. Sine I also installed an A3 flat top, I made a small line(inside under were  the charging handle would be) on the A2. (were the gas tube came from.) When measured the tube(in the A3) is the same distance from the opening of the BCG to the gas tube  as the line is from the opening of the BCG on the old recciver. Just wanted to know if its normal for the set screws not to line up with the FSB taper pin slots. Is there any way to check and see if the gas tube hole is properly alligned to the barrell? Took everything out of the BCG and pushed it with my fingers only, back and forth. I did not have any trouble moving it back and forth nor did it have any problem slidding up to the locking lug's.  

It is ok if the set screws do not exactly line up. The pins and the sight base are drilled together and not usually in the same place. Just put flats or dimples where the new set screws hit the barrel, and it should be fine. You can measure and mark for gas hole alignment, but a good "eyeball" will do. The hole in the block is bigger than the hole in the barrel, so if close, it will be ok.

Thanks alot. Thats what I thought , just wanted to make sure.