FNS 9C shooting low and left after recall repair

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Does anyone have an explanation for why poi would change after the recall work, other than something to do with trigger pull? The only variable seems to be the trigger mechanism, on a gun that was accurate before the recall. (Unless I'm showing my ignorance.)

My conjectured: In modern striker-fired guns, the striker/sear interface is between/across the frame and the slide, and may influence how the barrel is being aligned in the slide (where the sights are mounted). Something changed with the striker/sear interface as part of the recall. That changed how the barrel is sitting in the slide. The bore is no longer aligned with the sights.
 
ATLDave said:
My conjectured: In modern striker-fired guns, the striker/sear interface is between/across the frame and the slide, and may influence how the barrel is being aligned in the slide (where the sights are mounted). Something changed with the striker/sear interface as part of the recall. That changed how the barrel is sitting in the slide. The bore is no longer aligned with the sights.

I don't understand this comment, and I don't usually have difficulty in grasping what you're sayings -- so maybe it's just me this afternoon.

The striker assembly is typically located in the INSIDE the REAR OF THE SLIDE and in the striker-fired guns I own -- several -- there doesn't seem to be a way for the striker to affect barrel alignment.

In all of the striker-fired guns I own the barrel's position is controlled by stops in the frame and how the barrel interacts with the slide and frame as it moves forward and back. It would seem that about the only time the striker assembly could affect the barrel is when the striker is released and then it's really just hitting the primer, I don't think that would affect barrel position.

Changing the striker assembly itself shouldn't have any effect on how the barrel and slide lock up. (In that sense, I don't see how the striker assembly is really all that different than the hammer and firing pin (and firing pin return spring) in their respective abilities to affect barrel position.

Maybe I've just misunderstood the point you're making; perhaps you can explain it differently?.
 
The striker/sear interface is applying force to the slide when it is cocked/tensioned. I am conjecturing that this force is, perhaps subtly, changing how the barrel and slide are coming to rest in relation to one another.

As denoted by my use of the word "conjecture," my confidence level that this is correct is low! I'm just trying to spitball an explanation that would fit the available facts, and takes as given that this is not fundamentally a marksmanship issue (as reflected by tight groups, albeit off centered - it is pretty rare IME to see poor marksmanship result in such a consistent error that there is a tight group off the aiming point).
 
"..and possibly parts of the trigger assembly."

that wasn't mentioned before. in the striker a burr inside or on the rim can cause grittiness with the spring (reflected on the trigger) but you said the trigger is actually better and the difference is negligible, however, there's possibly something else..

..problem is I don't recall exactly how these particular pistols work,..but..

these have a hinged trigger safety on the lower half of the trigger itself forming part of the trigger. as I recall there's a protrusion of sorts that's applied against the frame or perhaps someplace else(don't recall exactly where), if this geometry has changed perhaps it's of interest to the issue. i'm not say it's for sure but depending where that protrusion works it's at least of interest.

( on a related note, but not necessarily the problem, when some people complain of grittiness in the trigger, it's sometimes because their finger has not pushed that lower half well enough).

also, ALTDave could be right.
 
ATLDave said:
The striker/sear interface is applying force to the slide when it is cocked/tensioned. I am conjecturing that this force is, perhaps subtly, changing how the barrel and slide are coming to rest in relation to one another.

As you said, our comments are all just conjecture. Mine might just be a "scientific wild-a$$ guess. :)

The striker/sear may be applying force to the slide, but that doesn't mean the slide and barrel alignment is affected by that force. But the movement required to change the point of impact is not trivial.
  • If the gun is shooting 6" low at 20 feet, the barrel would have to drop roughly 1/8th of an inch to cause that much error. (That was determined by using the Brownells Sight Correction Calculator -- which indicates the amount of sight change needed to get POI back to the POA.)
Generally, the only slide and barrel movement likely as the bullet is moving down the barrel is horizontal until after the bullet has left the barrel. (There can be a trivial amount of recoil-induced barrel rise) but it really is trivial The bullet leaves the barrel with most guns after a mere fraction 1/10th an inch (or less) of slide and barrel travel.

To get a lower point of impact, the rear of the slide would have to be moving UPWARD or the front of the barrel must be moving downward (or a combination of both) before the bullet leaves the barrel. Is there enough space for either one to move that much with only a fraction of an inch of slide movement? Is slide to frame fit or barrel to slide fit that loose? And would striker-induced force transfer be enough to do that?

If the top of the slide wasn't so flat, you could put a coin on the top of the slide and see what happens when the striker is released while dry-firing.. Wonder what a ball bearing would do, when the striker is released as the gun is dry fired? It would be interesting to see if it rolls forward.

I suspect something else is affecting the LOW LEFT results, but I don't have a clue as to what that might be.
 
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