So last week I found a nice 27-2 6" at the local fun store so it came home with me. I hopped on line and found the best deal on some 357 fodder to use before I get my reloading set up. I ordered 200rds of geco 158gr 357 mag. These particular ones are made in Hungary. I loaded up the first cylinder after a through cleaning and fired all six rounds ammo seemed good definulty had some magnum pop to it.

Then came the problem I opened the cylinder to eject the rounds and ended up having to beat the rounds out of the cambers all 6 were completely stuck. All 6 had flattened primers and I put the rest of the ammo aside.  How could factory ammo be overpressure like  this? any body else have this problem? Every use this ammo? I don't want to use it in a classic smith but I don't have any other 357 to try except an sp101 and I'm not to keen on that idea.

It does say quite clearly on the box that it makes Ispc major power factor but I'm not familiar with what that means.

If the previous owner shot a lot of 38's out of it ( as most do) you develop a ring of fouling where the case ends making loading or extracting 357 difficult. Clean chambers throughly and make sure they are bone dry after. Oil in the chambers can cause a sort of hydraulic seal and increase pressures and difficulty extracting

Did you fire any other ammunition?  It could be as captain127 says and you have a bad fouling ring in the chambers from shooting shorter cartridges.  I would try it with other 357 Mag ammo, that might help you figure it out.  How thorough was your cleaning?

IPSC uses power factor as part of it's scoring system.  The sport rewards shooters for shooting a handgun with more recoil with more favorable scoring.  Power Factor is basically the momentum change of the bullet or total recoil impulse.  For IPSC that is calculated by taking the bullet weight in grains, multiplying it by the velocity in feet per second, and dividing that by 1000 to make the value more tractable.  IPSC Revolver division Major power factor is 170.  So if that ammo makes IPSC Major it had to have a velocity of at least 1076fps.  Fast but certainly no where near max pressure for 357 Mag with that bullet weight.

I fired some 110gr Winchester white box and some reloads that were 158gr and 14.0 of 2400 I had from last time I reloaded 357. All functioned fine dropped out of the cylinder with ease and no flattened primers. Only the geco had any issues or pressure signs. I just find it hard to believe that factory ammo could be that out of spec...

Obviously it wasn't a very good deal.

Geco is supposedly quality ammo

What did the primers look like?

flattened completely...

Flat primers alone are not always a good indications of pressure in a revolver.  If there is a bit of room in the headspace a primer will back out of a case slightly and then when the main charge goes the case will be driven back onto the primer against the recoil face.  This will leave a flat looking primer that was not caused by pressure.  Use to get that all the time with 40 S&W in my 610.  The primers would be flat with a small bulged ring around the side where it filled in the primer pocket bevel.  But I know my loads where well below max SAAMI.  Now if the primers are cratering or extruding into the firing pin hole that is a good (bad) pressure sign.

If you're not experiencing stuck cases with your other loads I'd toss the rest of the Geco and chalk it up to a bad lot.

Normally I'd pull the bullets and salvage the brass but I'd be suspect of this brass.

I experiment with reloads and have had primer flow to the point, where there is not just a flattened primer, or cratered firingpin hole, but barely a firing pin indent to be seen. I attribute hard extraction, like in binding, to rough chambers or residue build up.

As a reloader you can take care of that easily, bell some .357 cases and push them into the chambers after soaking the cylinder in any good cleaning solution. That should scrape lead and carbon out without too much hassle.

I have the same issue with this ammo in one of my GP100s

That's what I wanted to know if it was just me. I have decided to not shoot the rest of it for now.

Did you shoot all of your how many rds if so?

Well, shucks.
Now I'm a little nervous about the 1000rd case of Geco .357 I bought from SG Ammo a couple months ago. Bought it for my 6" 28-2 and a possible future .357 levergun.

Guess I'll see how it goes. And will probably report back, if I remember to do it by then

I think I have one or two boxes left. I'm not concerned about safety... I feel that the ruger is plenty strong. It's really just a nuisance when they all bind up

As already noted, the prior owner shot a butt-load of .38 Spl. I had this in a Python that wouldn't even allow .357 to fully seat. It had to go back to Colt to be reamed.