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law unto

I think the chewing has to do with the various accents, some of which can be hard to follow. The young guy at the end sounded like he had a Cockney accent which can really swallow up consonant...

Yup, Ok we're gonna take this target here, it's coming from the top there
Bob, just give us one of those, would you please mate?
There you go..
Not too difficult, but you know....
Ok, take the...

yes.

It refers to an area where people shoot for pleasure. "Grounds" basically means open area or space.
Example: http://northamptonshootingground.com/

ounce and eighth.

Winchester produced fiber wad loads for fiber only grounds

it sounds like some sort of gun term, whatever was replaced by what is now, as he says, compulsory (I can't tell if that's the gun, the shot or what).

he actually says one ounces of shot.

1st voice: just try (mount?) it a couple of times see how it does fit at all
2nd voice: OK, the gun is empty
1st voice: perhaps first pop it up at my eye again

Caveat emptor.........

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And (I'd just like to point out that) Tanya's gun she's using here. The one she's using. (She's) opted for the automatic gun which is very - (is) actually ideal for women to shoot and also...