What is notch there for?

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>>34141154
Better pic

>>34141170
Space to move around without slamming into the slide during cycling.

>>34141198
I don't know of any other gun with the deeper cut there like that.

>>34141198
If that were the case, the notch wouldn't need to be there. It could just be a step.

I'm tempted to think it's a manufacturing defect, as if somebody programmed in a pass with an endmill wrong or included a z movement where they shouldn't have. It would probably still pass a go/no-go test, or at least be within tolerance for the height of the step.

Is this present on other FN 509s? Ideally we would be comparing samples with drastically different serial numbers to avoid being within the same batch.

probably the locking lug.

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>>34141154
>notch
D-delet this, before it's too late

>>34141414
see
>>34133683
>>34134895

>>34141365
I was thinking this might be the case.

>>34141365
>>34141483
The firearm cycles fine but if I go to unload it, it snags or snaps like there is a hang up disengaging the barrel lock up or ejector somehow, only does it when pulling back on slide if there is a round in chamber.
Is this normal?

>>34141154
just looking at it could be something to do with lockup maybe. It could enhance barrel to slide fit for more accuracy or maybe it could delay unlocking

>>34141524
Firearm type?

>>34141524
There should be a snag in that case, since you've got a bullet partially forced into the rifling. All handguns do this.

>>34141154
Is this a S&W barrel?

>>34141568
Cool, it's just very pronounced. Gun does function fine.

>>34141558
It's much 509, like the gun a lot just curious about this mystery notch.


BTW, I called FN and they had no clue what I was talking about.

>>34141568
Actually now that you mention it, I do have it loaded with some long ass ARX ammo that was on sale. If it is from rifling being engaged, I could totally see this ammunition highlighting the effect.


Thanks all,
not too worried just figured if anyone could solve the mystery it'd be /k/, going to assume >>34141365 is correct and going to sleep.

>>34141365
Thats not the case. No one is going to use a tiny ass endmill to rough out the chamber end. They are cut with inserted carbide roughers and endmills while being held in a fixture.

Its probably clearance for slide tilt and move over the barrel under recoil
a similar feature is present here:
https://www.youtube.com/watch?v=jF3FTICtjNQ

>>34142677
I don't understand why it would act as clearance, though, since the inside of the slide is flat and there's a raised feature immediately in front of the notch that the slide would have to clear anyway. Maybe it's there as an undercut, to allow for cleaner engagement between mating faces. Maybe in case of debris buildup?

>>34142677
The 509 is the gun in the OP and I don't see that cut in the video you linked when he shows the guns at the end.
I'm going to go find one at a gun store today and compare with mine.
Will let you know

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>>34142677
>>34144408

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I don't know if it is used for clearance, but it defiantly shortens the required length of the ejection port. It should work mechanically identical to any other modern barrel with no cut.

All it does is push into the grove of the ejection port. The barrel then has to overcome mechanical resistance of the slide delaying the blow back. You can dress the gun up how you wish, but the mechanics are still a purely blow back design.

>pic related uses locking lugs instead of a cut in barrel.

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>>34144472
>I don't know if it is used for clearance, but it defiantly shortens the required length of the ejection port. It should work mechanically identical to any other modern barrel with no cut.

never mind I'm retarded and got almost no sleep. That is just a normal barrel.

>pic related browning's improved design

>>34144472
Yes but I've never seen it recessed. Compare >>34141170 to the top barrel here >>34144417
It's the same make and model.
Most guns just have a 90 degree "L" shaped cut. So the questions:
>is this a manufacturing defect?
>if so what problem could it cause?

>>34144516
You might see stress cracks after 1000 rounds. That's it.

>>34142939
> Maybe it's there as an undercut, to allow for cleaner engagement between mating faces.

I was looking at it again. It holds the slide level with the front edge on the chamber end. you are correct

>>34145813
>>34142939

Well I called FN and they don't know what I'm talking about.
I've driven around to 5 gun stores today and nobody has one in stock.
Hopefully you're correct but nobody knows.

>>34147319

what model fn is it? I've got an fnp45 laying around

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>>34147438
509
I really like the gun. Shoots nice, cycles fine but I just want to know if this is as per blueprint. It being an undercut for cleaning mating surfaces makes a lot of sense. However, I haven't found a second 509 to compare it to and you can't see it here >>34144417

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Finally got back in town and checked owners manual

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>>34148232

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>>34141154
>notch

SUMMONED
U
M
M
O
N
E
D

>>34148232
>>34148249
Wouldn't worry about it looks like that there is a feature and not a lemon or some shit.

I am mighty curious as to if its for delaying unlocking or improve accuracy, not to mention how the area will handle wear.

>>34148670
The thing is it shouldn't have anything to do with unlocking, since that's what the cam controls.

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>>34141524
>>34141568
>>34141732
The snag was the ammo, check this out

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>>34150351

>>34148689
Just what do you think is locking?
The barrel is locked into the ejection port of the slide. That cut is right at the front bearing surface that the slide is pushing against.

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>>34150351
>ARX

>>34150359
>PDX


ARX ammo doesn't correctly in the 509.
It's fine in my sp-01.

>>34150369
In lieu of a diagram, have the worst descriptive writing I can hurriedly create.

The flat faces in front and behind the locking block are the locking faces, but the top front corner is the critical one for locking. The notch in front of the block would not affect that without anything going in it. The unlocking process is started as soon as the cam hits the raised portion of metal sticking out of the frame, upon which the barrel is forced down and out of the way. In this case, the slide will clear the chamber block when the front, highest corner is brought lower than the inside top face of the slide. In this manner, the notch would be inconsequential, because it is lower than anything else on the barrel. In other words, there's no clearance to provide for unlocking that wouldn't have to be addressed in the design of the barrel cam.

However, if the notch were not present, and debris happened to get on top of the barrel in the place it would go, the pistol would be unable to go into battery. The notch may have been included to be a place for such hypothetical debris to mush into, out of the way.

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>>34151313
>guns are now designed specifically to pass autistic youtubers mud tests
>fn creates a gun with one garillion rounds of testing
My face when the garillion rounds were spent trying to pass MAC's torture test.

Anyway, the seems like a good idea for debris clearance and a general cleaner mating surface. I'm sure we'll find out soon enough.

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>>34141154

>>34148326
NOOOOOO

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>>34151706
You get twice the barrel life with that feature.

>>34151762
This, it's like rotating your cars tires.

>>34148326
Serious question though, what's the notch for?

>>34141154
Minecraft.

>>34151774
A corner like that which fits against a shoulder so perfectly leaves no way for dust/grit/carbon/belly button lint to migrate out. On the notched design, it's two flat surfaces engaging eachother with room between them for stuff to get scraped away to. It's a good thought.

>>34151966
I meant on the knife.

>>34151313
Very reasonable answer. Call it the "shit shelf"