Pump Shotgun Capacity

[NJGF 375]

I am confused about the specs for shotguns.

 

I am comparing two Mossberg pump action 590a1 shotguns:

 

An 18.5" barrel model has an overall length of 39.5" and holds 6 shells (+ 1 in the chamber).

http://www.mossberg.com/product/590a1-7-shot-50776/

 

A 20" barrel model has an overall length of 41" and hold 8 shells (+ 1 in the chamber). It is 1.5" longer than the 18" barrel and 1.5" longer overall length.

http://www.mossberg.com/product/590a1-9-shot-51660/

 

Both magazine tubes seem to go the full length of the barrel. So how does adding 1.5" to the barrel length add 2 more 2.75" shell capacity?

 

The only thing I can think of is that the magazines have plugs to limit the number of shells but I am not sure why they would do this.

 

Thanks.

[checko 180]

The first link has a shotgun with an extension on the tube I assume is included. The 20 inch version does not need an extension

 

 

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[NJGF 375]

But in both pictures the tube goes to the end of the barrel. With an overall length difference that is only 1.5" how can this hold 2 more 2.75" shells?

[T Bill 649]

Very possible it is plugged to comply with ban states.  Some states do not care if semi-automatic or not.  The seven shot seems to be new this year.  The only other thing I can think of is because both have 3" chambers one is quoting 2.75 inch shells the other 3 inch.

[weekend_junkie 129]

But in both pictures the tube goes to the end of the barrel. With an overall length difference that is only 1.5" how can this hold 2 more 2.75" shells?

I'm doing the math and am equally confused. 7 rounds of 2.75" shells would be 19.25". That leaves 0.75" of extra space for a followers and compressed spring. I can't imagine how they expect to fit an extra shell in there.

[PK90 3,570]

If you have a shotgun shell, measure it. You will find that it is about 2.3" or there abouts. It becomes 2.75" when fired.

 

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[Vlad G 345]

Also don't assume they count the same way for various models.

[Njpigeon13 10]

The first link has a shotgun with an extension on the tube I assume is included. The 20 inch version does not need an extension

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I agree with this. It has to be something with it being a tube extension and the spring inside taking up room.