Dirty optic glass constantly... How to plug the chamber witness hole?

[ar15barrels]

Originally Posted by Carcassonne

You could try a heavier and lighter recoil spring so the barrel unlocks sooner or later than it is now.

Heavier.

The longer you keep the slide locked up, the more gas that will vent out of the muzzle end of the barrel, leaving less pressure in the barrel when the barrel finally unlocks.
The less pressure remaining after unlocking, the less gas that can come out the breech end of the barrel.

Eventually, too heavy of a spring will affect actual function but there is a range of a few pounds usually where a gun will cycle correctly.
The farther UP the weight range you can go, the slower the slide unlocks.

[shojivic]

I JB Welded the witness hole on a spare factory barrel. It may be too early to draw conclusions, but it does appear to have helped somewhat in reducing the "soot" on the RMR lens. I didn't have the time to shoot as many rounds to try and re-create the same testing regimen, but I'm cautiously optimistic. As I said before, I'm maintaining the factory recoil spring.

[Batman]

How many rounds does it take to get the sight dirty? The first step to solving a problem is to understand the problem. Right now, you're guessing it's the witness hole. I'd tape a piece of white paper to the front of the sight (have it go around the slide on either side and above the sight... You WILL cover the front sight, but that's the intent) and shoot enough rounds through (yes, I know it's a waste of ammo) to see what the pattern is on the white paper in front of the sight. If it's from the witness hole, it'll be a straight up black line pointing right to it. If it's all over the place, then it's probably powder residue from when the gun cycles, and blocking the witness hole won't do anything to help the situation.

[sitruc]

Originally Posted by shojivic

I JB Welded the witness hole on a spare factory barrel. It may be too early to draw conclusions, but it does appear to have helped somewhat in reducing the "soot" on the RMR lens. I didn't have the time to shoot as many rounds to try and re-create the same testing regimen, but I'm cautiously optimistic. As I said before, I'm maintaining the factory recoil spring.

I've noticed this happens on all my handguns w/ optics. My glocks, sigs, and CZ experience this and none of them have witness holes. The usual culprit is too much lube as it happens near the beginning of when I shoot as opposed to later. Little bit of oil + the carbon being sprayed as the case ejects = very noticeable black specks on the optic lens.

It doesn't help you now but may help in the future, but just some advice I've learned along the way: Have your rear dovetail sight re-milled to be in front of the optic. Once I had this done to my glocks, the front of the rear suppressor sight takes most of the grime instead.

I've also done some searching for aftermarket M&P barrels and they all appear to come with that witness hole, regardless of manufacturer. I am curious to see if the JB Weld holds and for how many rounds.

[sigstroker]

You lucky devils with Glocks.