***Mods, posted this on "Build it yourslf" forum.   This forum may be more appropiate, sorry.

I recently got a new DPMS upper and in the near future I want to replace the fron sight base with a PRI Flip-Up model with the clamp screws.

I called DPMS to see what what the distance between the pin holes were. The guy I talked to told me there where no standards specs and they were just drilled in depending on who they got their fron sights from... WTF??? That sounds screwed up to me.

Next I called PRI and they said that their flip-up fron sights have 1 3/8" spacing between the pin holes. According to PRI this should be the mil-spec Colt front sight pin hole spacing. He was also agast about what the DPMS tech told me.

I then went to measure the pin hole spacing on my new DPMS upper. Believe it or not it was right at 1 3/8"!

I then measured the front sight pin holes on my pre-ban Eagle Arms upper. It was also very close at 1 3.5/8".

These two uppers were within 1/16" in difference!

So my question is how much variance is there in the front sight pin hole spacing? Will the 1/16" differnce be enough to not be able to put a PRI flip-up front sight on my older upper?

If there is a mil-spec standard for pin hole spacing what is it? Shouldn't all front sight be interchangable?

Next, what about the taper pins? Is there a standard pin size?

On a side note the guy I spoke to at PRI said that in next few weeks they are releasing a new version of the flip-up, screw clamp model. He said the current version required some filing to install because of the tapered pin holes. The new will have the clamp screws lowered a bit so that no filing will be necessary. This is good news to me!

Troy,

As always thanks for the good inforamtion!  If you get a chance could you measure the distance between the front sight pins on your Bushmaster a let me know what it is.

My next question is, if there are no standards how do we know the gas port on the front sight is in the correct location?  It would suck big time to install a PRI sight only to find out the gas port is now covered up... [abused]