I have always wondered why some wads are more suitable for tapered hulls and some for straight walled hulls. It must have something to do primarily with the ignition of the powder and how tightly it is sealed in the base of the hull. So a better seal could be achieved with a tapered hull and it will result in a hotter load--at least in the first few inches? Thanks! Gil

Gil
I always beleived that hulls that had a seperate tube and base required a straight wad to match the tube. A cast case or forged case allow taper to ease extraction from the mold. I also think the base was formed like a hemi head to promote uniform combustion.
Just my thoughts
bill

I believe the answer is the inside taper of the hull. Federal, Fiocchi, etc. are said to be "straight walled". Winchester AA, Remington STS etc. are "tapered wall". So, wads are made with slightly different diameter at the base to make a good gas seal for the two different types. Not sure the basewad makes a difference to the wad, they don't touch for any load I've ever done. I'm so sure I think I'll head down to the loading bench to mike a couple different wads!

http://www.claybusterwads.com/index.php/product-by-style/by-style-winchester/3

The 'insert' referenced would be the basewad.

Reifenhauser was the father of the plastic shotshell. He invented a way of work hardening and extruding a plastic tube that was both thin enough and strong enough to make a shotgun shell.

Those shells are still with us today as the 'Reifenahuser tube', are straight walled, and require a base wad of some type. The design of the shape of the combustion area and the internal volume varies considerably from brand to brand.

The 'compression formed' shell was devised by Winchester in the early 60's as another way to skin that cat and is made in a die. The shell is one piece with the exception of the head. The taper strengthens the base and improves the thermal efficiency of the shell. Remington STS and Gun Club are still one piece tapered shells. The AAHS is a hybrid of sorts and gets some of it's taper from the basewad.

All shells gas seal best and work the best with wads designed to match their internal dimensions. Other wads can be used and in fact many of the 'lower pressure' loads you see published rely on poor fitting wads. Powder migration can be a problem in such cases especially with fine grained powders such as ball powders. Flake powders mitigate this to some extent. It's still a dubious practice in my book.

What do you mean by "thermal efficiency" and why does it matter to the soon to be dead duck?

It acts as insulation and shapes the combustion chamber for optimum. This isn't by accident, it's the result of experiments leading to final optimum design.

Ever notice how tapered shells use less powder than straight cases to do the same work?

Shotgunj, the short answer to your question is, No. But that's why I asked. I'm a pretty casual shotgun reloader, primarily for hunting. I can't see how insulation could matter, but I can accept that a shaped charge may. I thought the taper was merely a design for manufacturing efficiency, as it is with brass cases for rifles and pistols.

I'd be interested to see some apples to apples comparisons of the shaped charge case vs. the straight wall case.

Shaped base wads were used before plastic shells were invented for the same reasons.

A shell is a heat engine, and anything that contains heat and keeps it from escaping aids performance.

Looking at Federal data vs. Winchester data for common loads in the Alliant loading manual shows that using Red Dot for example with the same primer and the 'correct' wad for the hull the difference is about one grain.

The straight wall cases have a larger internal volume. Think of the difference in the wed area of a piece of .308 brass vs .45ACP. Basically the same exterior dimensions. The Federal Gold Medal hull has slightly more internal capacity than a AA or STS. Because of that with the same load it would have lower pressure and lower velocity. With fast burning powder the AA and STS are more efficient. They are designed for target loads. The Gold Medal hull optimizes with slower burn rate powders and has more potential to do work with the larger internal capacity. If you use a Federal wad in a AA because the wad is for a straight wall case it may create a minor bulge in the case wall. If you use a wad for a AA hull in a straight wall case the smaller diameter of the bottom of the wad mat allow some powder types to migrate past it and on ignition it may not completely seal the gasses behind the wad when the powder burns. So in summation the AA and STS type hulls were designed for peak efficiency with target loads. The straight wall cases will be less efficient with target loads but have more potential to load heavier payloads at lower pressure on a top end hunting load.

Sort of.

The Gold Medal is an optimized target load thus the name.

The base wad is quite a bit different than Federal field loads and the case capacity is less than Federal field loads or Federal promo target loads such as 'Top Gun' or 'Estate'. Federal uses two piece wads especially designed for the hulls as target loads in those cases. You can bet the powder charge contains more energy regardless of powder RQ for those loads.

The internal capacity of the FGM is still larger than a tapered case and in spite of the base wad it still takes more powder to do the job.

Mark II, just a few nights ago, I measured the volumes of the CF Winchester AA and a Cheddite shell using flax seed. Maybe that was the wrong medium, but it was handy and it settles very easily and uniformly. I could not find any differences, much less any meaningful differences. I'll try that again with some other medium.

I have been loading the Claybuster CB1138 12 equivalent to the WWAA12R in clear, low-brass Cheddite hulls with Longshot powder. I don't see any powder migration past the cup. Those wads were supposedly designed with 1.25-1.375 oz loads in mind which seem like hunting loads to me. Maybe that is why they fit better in a straight case, but in any event, those are my observations - and they do pattern beautifully.