I just picked up a new CZ Mallard 410. Being new it has a rather stiff action and for some reason, I'm thinking the top barrel is chambered tighter than the bottom, if I shoot high brass shells in the top barrel I have to crack it open w/ my knee. Using low brass in the top barrel doesn't require the knee just a good grip on the barrels and a good push. Of all the guys I hang around with at Seattle Skeet & Trap there are two very differant opinions as to what should be done. One thought is that I should leave the gun alone and as it wears in it will eventually start opening on it's own w/ high brass and the other is that I should polish out the top barrel to loosen it up a little. I'm sort of leaning towards "do nothing" and let is loosen on it's own.
What are your thoughts on the matter? Do I polish it out or not?
Thanks for your advise.

Are the high brass and low brass ammo two different primer mfg?

I'd tend to lean more towards the cocking linkage is not camming the hammer/striker back soon enough to take the firing pin pressure off of the fired case before the bbl rotation begins.

The firing pin is still down hard into the primer and the case is being dragged accross the pin. How deeply the pin is set into the primer (hard or soft primer) can dictate how much effort you need to open it.
It's a common problem is older doubles w/worn cocking parts. Changing ammo to one with a harder primer seems to 'fix' the problem as the firing pin isn't buried as deeply when fired so it doesn't take as much effort to open.

Just my thoughts..

Unlikely to be the chamber. 410s tend not to stick in chambers. Lube it and Shoot it another 500 times and see if it still needs help.

G'Day Fella's,

SxS-Boy, here is a quick check method, for you to try!

1) In good light, look into both barrels and look for any deep machine/tooling marks toward the rear of the chambers of both barrels!

If all looks to be OK here then.

2) After firing a High Brass round of ammo in the Under Barrel, extract it and then chamber this fired cartridge, in the Over Barrel! If it wont chamber easily, there may be a difference in the chamber size between the individual barrels!!!

Other than that, I would try other brands of ammo, to see if there is an improvement in function of them in this shotgun!

Hope that helps

Doh!
Homer

Thanks Guys

After now shooting 25 boxes of ammo through this gun here is what I figured out. first of all you three are all correct about what is happening and what I've discovered. 1st on the fired case of the top barrel there is definately a drag mark on the primer where the firing pin is pulled across the face. Secondly, putting a fired case from the bottom into the top it is really tight and heeds thumb pressure. it also won't open once closed on the empty and firing pin released. I also used 800 grit emery cloth to polish off the sharp surface of the chromed chmbers. Not just the edge but the 1st 1" of chamber. I am now reloading the high brass hulls using Fed.209-A primers and the gun does open w/o the knee but I do have to give the barrel a little twich while pulling down on the forend. I think everything is going to be OK. Now if I could just get this thing to shoot where I'm looking it would even be that much better.

Thanks for the advise. Joe