Hull differences in loads

[358Scout]

I've been trying to come up with 7/8 oz 12ga load for shooting International Trap. Having done some calculations on the Federal steel based and Winchester AA hulls along with Clays powder and IMR 700 this is what I found.

If everything equal, pressure levels differ between the two hulls. Further, I cut a Winchester AA and a Federal in half and guess what I found?
I expected to see the Federal with a slightly different base but not true. They look exactly the same.

I then looked at the wads. The Grey wad made for 7/8 oz is the same size as the pink wad which is made for the 7/8 oz to 1 oz loads.

I don't understand how this difference in chamber pressure of to 900 PSI is derived - why should i use two different loads if the hulls are the same?

 

[blaser.306]

Hulls

Winchester, wether new two piece or old one piece are a tapered hull as the federal are a straight hull , from my experience I have found that the federal hulls tend to require slightly larger powder charges to get the same kind of paterning . Also if you look at the federal componant wad you will find that the base end obturation cup is larger than the one for a tapered hull making for a better gas seal as it travels down the bore giving more eficient powder burn . Overall lenghth of the grey 7/8 wad and the pink 1 oz wad will be the same however the " leg " section will be slightly longer .

 

[beretta boy]

blaser.306 ... right on the money !

 

[jacky]

Blaser beat me to it but really was that a test because I am sure you knew that already.
I shoot with a fella who was on Team Canada for international trap. He shot nothing but Federal. I am sure he played with Winchester but I know he used primarly Federal.

For Trap I perfer Federal hulls but Blaser is right in that Federals work better with slightly larger powder charges. I found that 700X was not ideal as Green Dot or Promo. Promo in a 1oz load and Green dot in a 1 1/8 oz load ( I don't shoot tha one anymore) wroked great. I used 700X in a winchester hull and grey wad and it was really good too but I like Federal better.