.410 chamber issue -- too small?

[lewis1914]

I bought a new Mossberg .410 SA over the weekend. I can't get any of my shells to chamber in it. I used a plug gauge to measure the chamber and the largest I can get to fit is .474.

I did a chamber cast and it read at .4751 a few hours after the cast. I think it was around .4746 shortly after the cast.

My reading of the chamber specs says that the chamber should be .4811 -0/+.005

Am I reading the blueprint correctly? Is this chamber too small?

[Polymath]

I had 3 different 410's up on my bench one day and they all had different size chambers. I slugged each bore too.
I found that if I want to chamber every round, the brass all had to be resized. Picked up a old MEC just for that. Problem solved. I found if the tight bores chambered fine then maybe it would fit in the larger ones but not the other way around. So every hull gets full sizing. I made a go-no go bushing to check as well.
I crimp the 2-1/2" hulls on the Mec but roll crimp the 3" hulls. I hand load the powder charges and the shot too as the size of the shot fails to drop from the tube. Load mostly #4 and #5 shot for hunting.

[Squid Boy]

I just had the same problem with a new to me 410 and even some factory ammo didn't want to go past the brass. My MEC only sizes down to .472" and they barely go in. I even bought a Super-Sizer because the MEC Tech said you could adjust it smaller. Not quite right because once the collet is all the way shut that's all you can get. It was only about 0.001" smaller set all the way closed. They just barely go in now. So I did two things. I made a sizing insert for a spare 12 gauge sizing bushing to size 410's to .468" and then took a Dremel and whiz wheel to the spaces in the collet sizer and that will now size to .468" also. It's a very nice Italian SxS hammer gun by a very small maker named Giuseppe Pirlo. He just passed away at 99. His workshop was around the corner from Beretta. I'd rather fix the ammo then mess with the chambers. Thanks, Squid Boy

[skeettx]

I used a NEW 3" 410 chamber reamer and reamed it to maximum. All problems went away
Mike

[jsizemore]

I checked this on SAAMI a long time ago. 3" chamber should be min. .4811 + .005. 2" chamber should be min. .4780 + .005. Both cartridges should be max. .477 - .009.

I had the same problem as you with hulls fitting a Mossberg 410 that shot 3" & 2.5". I have a MEC 9000 which has an adjustable collet sizer and a P-W 375 with a sizing shellholder. I size to .473-.474 to fit in the Mossberg. Much over .474 and the Mossberg will skip ejection on an unfired round.

You may need to wrap some Scotch-Brite on a dowel and polish the chamber to open it up. With some oil go slow and check often so you don't do too much material removal. Your other actions are to return the gun, send to Mossberg or visit a gunsmith.

Better than a too big chamber.

[Hogtamer]

chuck the last section of a cleaning rod in your drill and apply grinding compound to the brass bore brush. Check with sized hull as you go. Cheap and easy.

[lewis1914]

Thanks for the feedback. I decided to send the gun back to Mossberg as it was brand new and I have no idea what else might be wrong with it.

[W.R.Buchanan]

Thanks for the feedback. I decided to send the gun back to Mossberg as it was brand new and I have no idea what else might be wrong with it.

Good Idea!

Randy

[6pt-sika]

I bought a Belgian made 410 hammer gun with 30” barrels from a friend in 2022 at the Southern Side by Side . I bought it thinking it to be a 2 1/2” gun turned out it had 2” chambers . RST was or is still making 2” 410’s but I let it go .