You don't say where/when/why you will be carrying extra ammo. It would help a lot to know what you're planning for...
1. Do you like ammunition on the outside of your shotgun? If so, how much and how is it carried?
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Most absolutely certainly yes for sure you betcha, I want a reload (or close to it) on any defensive long gun in the house. That way if I can manage to get hands on the gun, I have extra ammo too. I ain't exactly likely to have pockets or a belt on if I have to roll out at ohdarkthirty to repel boarders, ya know, and sleeping with a bandolier or any other means of carrying ammo is a nonstarter (if I have THAT much to worry about, we will be standing watch in shifts). "My" shotguns have six round SideSaddles, "our" guns have the four round versions- reason for that being my petite wife prefers a full length field style forearm on 'our' 870s to go along with the 12.5" LOP.
2. Do you have any favorite pouches or pockets, or other ways of carrying shells?
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Been a while now since I have carried a shotgun for serious outside the house work. When I carried for security (working gun show locations overnight etc) I wore a GI web belt and suspenders with holster/sidearm, two extra .45 magazines, and two or three 12- round GI shotgun ammo pouches. I usually carried buckshot and slugs segregated by pouch, and i always put an extra ALICE clip in the middle of each pouch to keep them from sagging on the belt. They are sorta like the one at
http://www.eagleindustries.com/ProdDisp.asp?PartNoID=112 except they use snap fasteners and not Velcro. You can see the cotton duck version of the GI pouch at
http://www.vietnamgear.com/kit.asp?kit=365 , the ones I have are GI, but are nylon sewn on the same pattern. When working 'dress up' security I used to carry a few shells loose in various pockets separated by type (buckshot or slugs).
Nowadays we always carry a shotgun on the road, and the 'war bag' that goes along with us is a vinyl-bottomed milsurp canvas bag, closed firmly with Velcro, with a shoulder strap (all from Cheaper Than Dirt). The middle compartment is wide enough to carry two 50-round boxes of 9mm at the bottom, with buckshot in 10-round boxes on top of that, and slugs in 5-round boxes in the smaller side compartments. The bag usually has 100 rounds of pistol ammo, 20-30 rounds of buckshot and 20-30 rounds of slugs. There's also basic first aid stuff, a flashlight, a large folding knife and a pair of FRS/GMRS radios in there too. Yes, it is a HEAVY little sucker.
3. Do you carry multiple types of ammo, and if so how do you carry each type to avoid confusion?
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Yes, 00 buck and slugs. The gun has 00 in the magazine and slugs in the SideSaddle. The magazine is always loaded one round down to allow for the insertion of a slug if needed when the excitement commences, any reloads after that from the SideSaddle will be slugs since that's all that is present. Otherwise ammo types are segregated by the carry method employed.
4. How much ammunition do you consider "enough", and what do you consider that amount enough for?
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What's in/on the gun (usually 7- 11 rounds) SHOULD be enough for anything that happens 'out of the blue' around Chateau Lapin. If it is apparent big trouble is in the offing, we are likely to not be here for the festivities if at all possible, or at the very least loaded for bear (along with everyone else in the neighborhood) if we do hang around. Out on the road away from home, the contents of the war bag should cover things sufficiently if anything approaching the predictable level of difficulty arises. As far as what's at home is concerned, I buy ammo that works for me in case lots and shortages are not likely to be a problem for a while.
YMMV,
lpl/nc