So how do you explain this?

[1911 guy]

I'll just echo what everyone else has said. Mechanically centered does not mean sighted in. There's a thread stickied in the rifle forum to figure exactly how much to drift it. That's when you use a caliper, not to simply center it on the slide.

 

[phil dirt]

I could do that and probably will, but I am more interested in this particular issue as a mechanical interest/curiosity.

I owned a Glock so long ago I don't even remember what model it was, only that it was a 9MM. When I took it to the range, I was appalled to discover that in order to get it zeroed, I had to push the rear sight so far to the right that it was hanging over the side of the slide. I took my Glock back where I bought it, got my money back, and bought a new Sig 228. I realize that a lot of people like their Glocks, but in my 50+ years of shooting pistols, I've never had a pistol that was anywhere near as out of tolerance as that one was. Because of that experience, I've not yet gotten interested enough in Glocks to try another one. But I've still got the 228. However, your Glock doesn't sound like it needs much adjustment. As others have said, move the rear sight a few hairs to the right and be done with it.

 

[22-rimfire]

"Evidently some people think a hand gun should dead on POA right out of the box. HA!"

Evidently you never had one shoot this poorly as compared to the other Glocks you have owned. I installed a new higher rear sight. Didn't help much. Pretty much thru spending money on this lemon.

 

[vaalpens]

I decided to shoot the G22 from 2016 first. The sights on this particular gun are Warren Tactical 2 dot sights. I place my target out at 7 yds. Fire 10 rounds of 165 grain 40 s&w, fmj, Estate ammo. All the rounds were hitting in a tight group, but everything hit an inch left of my POA. I knew my sights were dead center because I used a digital caliper to center the rear sight.

My suggestion is to test your gun from a rest at 20+ yards and then make the adjustment. The adjustment based on your 7 yard test should be: 1/252*6.49 = .025" (error ∕ distance x sight radius = correction needed). Even when you drift the rear sight .025" to the right, it will probably still look and measure center for you.

 

[exbrit49]

Just had a real good belly laugh at this post. It would seem that many of the respondents know nothing about the mechanics of sighting in a new firearm and the reasons it is required.
Just wondering if any of these folks ever stopped and wondered why the sights are driftable?
As one respondent wrote "Evidently some people think a hand gun should dead on POA right out of the box. HA!"
I have owned many handguns and have never had one shoot to POA, I have always had to tweak the sights. The mechanical tolerances will very rarely put the POI AT POA. Just too many variables, including the shooter. Drift the sights where they need to be, like the rest of us have to do and then go out and enjoy shooting it.

 

[Tirod]

The OP has discovered exactly what gunmakers, gunsmiths, and accuracy shooters have known for quite a while - you can install the sights perfectly aligned to the OUTER dimensions of the barrel, but it really has nothing to do with the INTERIOR bore and the dynamic placement of shots fired.

Just because a barrel bore doesn't exactly duplicate the outer circumference doesn't make it a lemon. It does, in fact, make it entirely normal and it's the reason why sights have been adjustable since the invention of guns. The first barrels bored proved to the barrel makers that their skill at getting them concentric wasn't as exemplary as they wished. Since then things have gotten a lot better - for the most part it's only bespoke shotgun makers who actually bend the barrels to change the point of impact.

Think about that for a minute.

The custom of the day and still practiced to this day is to literally put the barrel in a vice and then bend it in the direction needed to get the shot group placed. On shorter thicker barrels that was much more difficult, so they simply moved the sights to align the point of aim to the point of impact.

One other important factor in aligning impact to aim is the muzzle - where the barrel touches the bullet last on exit. Given two identical barrels shooting identical ammo, having the muzzle identical is nearly impossible. That alone can cause a bullet to vary it's path on exit creating a measurable difference. The simple solution for one far out of tolerance is to recrown it. Hopefully the results improve, but their is no guarantee. How the round chambers can also make a difference, as the leade - the portion of the barrel in front of the brass where the bullet engages the rifling - can cause the bullet to line up coaxially, or not - which results in the bullet nose being off axis and that results in it being tilted on exit at the muzzle. It has to stabilize in that flight path which can result in a consistent impact off the point of aim. Reaming the chamber often corrects that.

There's a lot more to it than just the sights sitting on the outside of the barrel. As was discovered long ago.

 

[420Stainless]

The explanation is that there are many other factors that could cause the POI to be different. If both sights are perfectly centered in the slide then: Is the slide slightly warped or machined in such a way that the center of the front of the slide is not in perfect alignment with the center of the rear of the slide? Is the barrel perfectly aligned with the slide? Is the bore of the barrel in perfect alignment with the outside diameter of the barrel (if solely this problem, then you should be able to swap the barrels between the two and the problem will shift to the other)? Is the slot of the rear sight perfectly milled in the center of the sight body (did you center the slot, or measure to the outside surfaces of the sight body)? Is the dovetail slot for the rear sight perfectly perpendicular to the slide?

Probably other factors that I'm leaving out, many discussed earlier in the thread. It could be any one thing, or it could be an accumulation of several things being ever so slightly off.

 

[Walt Sherrill]

Two guns that came down the assembly line one after the other aren't necessarily going to shoot to the same point of impact when using the same point of aim. As noted above, just because the slide and sights look the same, it doesn't mean the barrel inside the frame locks up the same. They can look identical, but they won't be.

The rear sight should be moved in the direction you want to point of impact moved to. (If the point of impact is low, you need a higher rear sight; if it's high, you need a lower rear sight.)

Adjust the rear sight. Use the Brownell's Sight Correction Calculator to know just how much to adjust the sight. Note: if you click on the pop-up wondow it can disappear on you. If that happens just minimize the current window to find it again. Here's a link: http://www.brownells.com/GunTech/Sight_Correction_Calculator/detail.htm?lid=13093

 

[FROGO207]

So I start my handgun sighting in process with a laser sighting device that I insert and center in the bore. Then aim it at a target at the distance I want the handgun to shoot POA. Next set the sights and laser dot to the same point. Remove the laser and shoot some ammo and see how close you actually are. Tweak to match from there. Not that difficult IMHO.

The one big advantage of buying a used handgun is somebody has already adjusted POA mostly for you already.

 

[RecoilRob]

When the slide blank is put into the CNC machine it's possible that yours went into the fixture maybe .010" canted/twisted. The machine would faithfully cut everything according to the programming but that initial blank tweak would mean that all surfaces cut at that station are going to be skewed a bit. Not enough to matter but I understand you wanting to figure out what is up with it. You replaced the barrel and sights so about all that's left is the slide itself. If the hole in the front is tweaked to the left and the breech-face that same amount to the right...it'll shoot left a bit. Comparing your other guns measurements to the gun in question might show this offset, but even if you find such a thing trying to get Glock to admit that it's a problem will be another thing entirely. That IS why they make the sights adjustable...to allow for fine tuning after machining. Good shooting!

 

[Acera]

..................................before I blame the gun.

You have got to rethink your position. There is nothing wrong with the gun. It's sights are made to be moved to get correct for you. Everyone in this thread has suggested drift the sights and be done with it. Your gun is not the problem, don't let the thought of that eat away at you. You seem to be way overthinking a very small (and insignificant to many) issue.


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