Hull Ultimate Twenty Shotgun Cartridge Review 

As for the Powder at 18.8 grains and 28gram loads, it's most likely the Aquila L, also manufactured by Nobel Sport for Cheddite. All the Aquila powders look like the A24. The chronograph at that close range with fibre wads doesn't work properly a lot of the times as it measures the fibre wad speed and not the actual shot speed. For Fibre wads you should place the chronograph at least 1.5m from the muzzle, recommended is 2.5m for Fibre wads, 1.5 for plastic wads.I have the same Caldwell chronograph.

I believe the internals are just the same as the High Pheasant Extreme 28g 5 which is a Continental size so U.K. 4.5

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