Spec Size for a 12 Gauge Shell


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numaone
December 16, 2009, 05:35 PM
My 870 express had a failure to cycle after firing. It was the first time this occurred, and was after 350 shots. The forearm was locked forward after shooting. To clear it, I needed to pop the barrel off. This occurred 6 times in 150 shells. Twice, the shell wouldn't come out of the barrel and I needed to use a long rod to knock it out of the barrel.

We were shooting Federal Value Pack 12 Gauge and Winchester Universal 2 3/4 inch shell and 7 1/2 shot. I had used these before with 0 problems, which is what's confusing me.

I took two of the shells that got jammed and they measured .815 and .816. What's the spec size for a 12 gauge shell and the tolerance.

Thanks,
Numaone

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Warhawk83
December 16, 2009, 05:42 PM
According to Chuck Hawks and Wapedia, the bore of the barrel is 0.729''.

http://www.chuckhawks.com/12gauge.htm

oneounceload
December 16, 2009, 05:45 PM
and they measured .815 and .816

Is that the diameter of the fired hull? (I'm assuming so, but we know what assume means)

Winchester Universals have a poor history of FTF and FTE issues with their steel bases that expand upon firing but do not contract, resulting in hulls that stick etc.

First thing - try some good target loads - Winchester AA or Remington STS and see if the problem still exists. If not, it's an ammo issue - if yes, then you might have an extractor issue

Standard bore dimension for a 12 can vary from the OLD standard of .729 to an overbore standard of about .745....Remember that is the bore and not the outside diameter of the hull

rcmodel
December 16, 2009, 05:49 PM
Minimum 12 ga chamber is .798" at the front near the forcing cone, and 812" at the rear near the rim. Manufacturing tolerance would make most chambers slightly larger then that.

There is no spec for a fired shell as far as I know.

There are known problems with some of the bulk ammo being sold now.

It expands tightly in the chamber and doesn't contract enough to let go after firing.

Never was a problem back when shotgun shell case heads were made out of brass instead of steel like the cheaper ones are now.

And shotgun chambers were polished smoother then a baby's bottom.

rc

RandKL
December 16, 2009, 05:59 PM
Polish your chamber with some ScotchBrite pad and a power drill. If that doesn't fix it permanently, leave the smooth plastic hulls alone and go for ridged ones.

OneOunce, pretty much all common shotgun ammo these days has steel bases. The brass color is only a wash for tradition's sake.

r

oneounceload
December 17, 2009, 10:13 AM
OneOunce, pretty much all common shotgun ammo these days has steel bases. The brass color is only a wash for tradition's sake.

On the cheap promo loads, I agree. The higher quality target loads, meant for lots of reloading, still have the brass heads - what allows you to use a magnetic stick to pick them up is the magnetic metal in the primer. (just checked it in my garage)

RandKL
December 17, 2009, 12:14 PM
On the cheap promo loads, I agree.

What sort of hulls are you using, OOL? I don't think I've seen a real brass base in at least a decade or more.

rich

oneounceload
December 17, 2009, 01:00 PM
My 28 gauge AA and STS appear to be all brass - no magnetic properties at all.....same for my 12 and 20 gauge AA hulls. I don't have any 12 or 20 STS at the moment. Now the gun clubs have steel, but the resize easy enough in my MEC Jr.

ArmedBear
December 17, 2009, 01:06 PM
Get one of these, and you can check any shell, really quickly:

http://www.mecreloaders.com/order/OrderItem.asp?PartNbr=1008486

After I got that thing and used it to adjust the sizer on my press, I have never had a single feed problem with my handloads. If I get commercial ammo that I have questions about, it takes very little time to test a whole box.

MAX100
December 17, 2009, 01:55 PM
You also need to know the chamber diameter of your shotgun.


GC

ArmedBear
December 17, 2009, 08:43 PM
If the shells are to spec, and they don't feed, the chamber needs to be resized.

You don't size shotshells to your chamber, unless, of course, you're stuck on a desert island with nothing but one shotgun with an out-of-spec chamber, a Mec 77, and a bunch of reloading supplies. Under ordinary circumstances, a chamber that doesn't work with shells that are properly sized is known as "defective.":D

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