Cartridge setback

[wpod]

I've read on here about setback, a cartridge developing a shorter C.O.L. from rechambering it several times.
So I experimented.
The firearm is a Beretta PX4 9mm.
The ammo is Federal HST 124gn.
I loaded 10 rounds into the magazine and chambered a round using the slingshot method.
I then removed the magazine and emptied the round out of the chamber and replaced it to the top of the magazine.
I repeatedly chambered the same round 30 times.
I then measured the C.O.L. of all 10 (factory new) rounds.

1.099 (rechambered)
1.134 (thought I was onto something )
1.101
1.098
1.098
1.100
1.099
1.100
1.098
1.099

It appears in my case, with this ammo in this firearm, I don't have an issue.
Not trying to disprove anything. Just sharing the answer to something I've been curious about.

Next I'll do the same with the wifes 92fs.

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[Junkie]

I'd suggest measuring the top round before you chamber it.

[wpod]

Or move the one longer cartridge to the top.
After rechambering 30 times it was within the average of the Virgin rounds.

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[alfred1222]

I've never tested it, but setback is an issue for me. Using Winchester white box HP in .40, over a 6 month period of clearing and then then rechambering it, we had significant setback in the top round

[wpod]

I don't carry my reloads. I don't recall their C.O.L. (not home at the moment). They are set to just clear the barrel throat.
I'll have to try my experiment with them.

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[FeuerFrei]

Isn't set back more of a problem with some cartridges and not all?
30-30 lever gun comes to mind.
Magnums in 357 or 44 under recoil the bullet can come loose (move forward) and lock up your revolver.
I remembered that 9mm and 45acp head space on the case mouth and as long as the bullet is firmly pressed into the case mouth (OAL to spec) without brass deformity the round will drop into your chamber and drop out just as easily.
So that makes a perfect fit from mag to chamber and nothing to head butt the bullet causing setback.
It's been a long while since I reloaded ammo but that is about what I remember.
Safety caveat. Only setback bullets I ever saw has were factory OEM and so they got tossed. I have seen hand loaded ammo that was not properly seated or no crimp applied and more than a few were ones I did.

[ExtremeX]

Before I knew what setback was I had some Remington UMC that I chambered a bunch of times... the first two rounds in the mag were extreamly sort... you didn't even need a set of calipers to tell.

I never fired them but I do look out for setback. Its something to take note of.

I can see a couple thousands of setback on my reloading just from 1 chambering.

I'm sure it depends on the gun, and ammo.