Weird Front Sight Question

[usp_fan]

I posted this queston on another forum also, and I could really use opinions,

I've got an interesting puzzle I'm trying to solve. Recently I slightly modified my Springfield Mil-Spec. I changed the sights to the Yost-Bonitz Rear, and the Trijicon stake on front sight. The heights of these two replacement sights are very similar to the old sights they replaced.

Prior to the replacement, the pistol shot very close to POA = POI.

My pistol now shoots low by about 5" at 25-30'.

Using the formula in another thread here, to adjust the poi, to match my poa, I'd need to remove just under .1" from the front sight! That's a lot of material, and would leave me with not much more than a stub for a front sight, and no tritium vial.

One thing I noticed: After staking the new sight to the slide, I cleaned up the inside of the slide with my dremel. Even so, the bushing was a very tight fit, whereas before, it had been easy to insert and turn.

Could the protruding material from the sight tenon be exerting enough downward force to cause the pistol to shoot that low?

Said another way, could the force of the material against the bushing cause it to force the barrel into a lower orientation or force the slide upwards (increasing the front sight's height)?

I plan to relieve the area some more and restore the bushing's fit to it's previous state. I'd appreciate some opinions on what's going on here.

Thanks,

--usp_fan

 

[HSMITH]

By chance you aren't using the dot on the front for your precision sight picture are you? The precision sight picture will still be the top of the front sight and the top of the rear sight. Just a thought.

Yes, the tenon could be flexing the barrel down. Grind it down and shoot the gun again. 5" at 30 feet is a LOT of error, if the replacement sights are proportionally the same height as the originals and you are using the same sight picture the POI shouldn't change.

 

[NVMM]

Sight Height Calculator

This might help.

usp fan said, "The heights of these two replacement sights are very similar to the old sights they replaced."

A few thousands in front or rear sight height makes a difference!

http://www.brownells.com/aspx/NS/GunTech/sight.aspx

 

[usp_fan]

HSMITH:

Yup, Same sight picture. I actually thought about that too. So I paid attention and eliminated that as a variable.

NVMM:

I did measure these sights before install with a caliper. I don't remember the variation right now, but I do know that it was in the same direction and same proportion for both the front and rear sights. I remember at the time thinking, "I may have to file the rear sight a bit".

I am reloading some 200grn lswc in .2 increments up to max. I will test fire this weekend after making sure none of the sight tenon extends into the slide to interfere with the bushing.

I'm hoping I'll be able to ID a load that shoots to POA. If I get lucky, it'll be the max load which should duplicate my carry load.

Thanks for the suggestions,

--usp_fan