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Posted: 6/3/2008 5:07:02 PM EST
I need to purchase a rear buis for an upper with a non F-marked front sight base. Are there some that will work and some that won't, or do I have to buy a taller front sight pin. Will the YHM-9680 rear buis work?
Link Posted: 6/5/2008 9:49:57 AM EST
Pretty much all rear BUIS are the same height. I don't know of anyone who offers different heights for the F and non-F FSB, so you'll have to use the different height front sight if it doesn't work. The YHM should work fine - it's one of the best less expensive folding BUIS.

Note that there are FSBs that are the F height but aren't marked F. You might want to measure or shoot it before you change anything.

Link Posted: 6/5/2008 11:37:18 AM EST
You will be able to zero with just about any rear. The front may need to be adjusted a tad more than if it were "F" height, however there should be plenty of elevation on your front sight as is. Worse case is to get a taller front sight post from Bushmaster if you find it needed to zero.
Link Posted: 6/5/2008 11:46:39 AM EST
ARMS 40L works fine on my 6520 converted to flattop with the non-F marked FSB and stock front sight post.
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