I am installing new front sight pins on a standard front sight and can not get them to go in..
I ordered DPMS taper pins and the upper is a Double star.
The pins go about half way in then mushroom out and will not go any farther.
Everything is lined up with the holes.  A friend pounded the old pins out to try to fix a lean in the front sight that caused my rear A2 sight to be adjusted all the way out for windage.
I am thinking maybe the front sight pins I ordered from Brownells are the "oversized"
I cant mic them at this point because they mushroomed out and I had to pound them back out.
I had them in right but they will not budge.  Used a punch and hammer.

Are you sure the pins you removed WERE tapered ?

What was your plan for repositioning your front sight?

The pins on my Doublestar upper are straight pins. I don't think taper pins will work too well in it.

There are a number of companies out there who use taper pins that are not hardened.  Those are a PITA to work with.  I tried removing the taper pins on a CMMG barrel to check the gas port because of an undergassing issue, and the pins just squished like butter.  I ended up having to drill half way through them then used a thin punch to remove them (this had the effect of pulling them out rather than pushing them.  I reinstalled using Colt pins which I know are hardened and they worked perfectly - I was able to drive them in hard with no deformation.

Try a different set of pins.  Make sure they are hardened, and do not cheap out on them.

You and your freind are messing up.

Doublestar barrels do in fact use straight pins.
Lets hope you did not foul up the FSb pin holes.

I would have checked for any gap in the index pin slot. If there is a very small shim/spacer will fix this problem.