.410 shotgun reloading

The rim of the .410 cases differs with 0.1mm from the rim of a 303. Would it be possible to convert a Lee 303 case holder to accept the larger shotgun primers?

And does one use shotgun primers in blown out 303 cases, or are they converted for shotgun primers as well?

I'd be interested to find out if shotgun primers are required at all if using 303 cases. Unless rifle primers were massively overpowered it would be nice if you could just use those.

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I have and it worked just fine, blew cases out, reloaded using .303 shell holder and Lee primer tool, large rifle primers.

The rim of the .410 cases differs with 0.1mm from the rim of a 303. Would it be possible to convert a Lee 303 case holder to accept the larger shotgun primers?

And does one use shotgun primers in blown out 303 cases, or are they converted for shotgun primers as well?

I had both, thinking back now, I think I had those drilled, but I am so sure that I also have received as is with shotgun primers, bought like that.
Never thought of a .303 case holder, suppose there will be something that fits from some caliber or wildcat

Glad Ds J saved me from this rabbit hole! Have had a quick look about and have found a number of old references to large pistol primers being used. Given the charges at play for shot shell loads that sounds like a win.

The rim of the .410 cases differs with 0.1mm from the rim of a 303. Would it be possible to convert a Lee 303 case holder to accept the larger shotgun primers?

And does one use shotgun primers in blown out 303 cases, or are they converted for shotgun primers as well?

I'd be interested to find out if shotgun primers are required at all if using 303 cases. Unless rifle primers were massively overpowered it would be nice if you could just use those.

The rim of the .410 cases differs with 0.1mm from the rim of a 303. Would it be possible to convert a Lee 303 case holder to accept the larger shotgun primers?

And does one use shotgun primers in blown out 303 cases, or are they converted for shotgun primers as well?

https://www.somchemreload.com/search?c=12&f=294

When I get a chance I will make a quick video parts and use of each. Yo u need to go to engineering supplier and buy 2 non shelf sized bits or know someone who has a workshop with odd size drill bits.
You also need a hole punch for punching wads out of foam leather paper whatever, this can be bought but sometimes its easier to have it made.
A block of very hard wood 100 x 100 mm +, a sheet of 2 mm = steel 50 x 50 mm +, a dowel that fits in a case tightly (sand part of one that almost fits down to fit - piece 3 x length of cas). Then lastly (I think) its a steel bar that fits in the primer pocket (Cut a good tent peg and round edges off). You will also need a piece of hardwood broom handle thick 100 long, cut and finished square - you might replace this with a polypropylene cutting board later.

The metal sheet is screwed and glued to the wooded block after a hole drilled through the metal and wood the wood hole shell OD size, and the metal hole is the size of a unfired case.

Odds and ends would be a wooden/rubber hammer, some sizing lube, wad material, some form of glue, measuring spoons.

You take a shot case and put it over the steel plate on the block over the hole, use the tent peg rod to knock the primer out, you can do this with a hammer or I preferred a piece of scrap wood.
You then turn case over push it as far as it goes through the metal hole, it will stop at the metal around case base(which you have lubed like a rifle case). Use the broom handle piece and a small hammer to tap case level into metal hole - it really just slides in. You can even use flat of palm as a hammer.
Turn block over use dowel that fits into shell to tap shell out the block.

Inspect shell inspect it well and place it back through metal side hole. Put a shotshell primer over the primer hole and using the broom handle piece and a wooden hammer tap the dowel and the primer slips in.
You can for more safety, cut that poliprop cutting board into a 4 finger wide strip and put that over the primer and then give it a tap or two to push primer in. The board method just diverts any AD directly away from operator.
I have never had a AD when tapping in, x a 1000.
You now have a primed case.
Next you build the cartridge.

Its sunday early now, so I am off to make wors with my new wors stuffer 8)

From reading on the US forums it seems that reloading for .410 is quite a bit cheaper than 12 gauge. However , that is the US.

What is the purpose of the different parts?

Powder charge is self-explaining. Then comes a wad to keep the powder compressed and separated from the shot. Does it get glued too?

What is the wad cushion for?

How available is lead shot, or does one cast it?

Imagine degrees og "bang" Starting at lighting petrol in a can "wooompf!" to a 300 Win Mg with no suppressor. Pretty much same thing with effectiveness directly related to crack of the bang.
When you load and seal using wax it sound very "bwaam" and is visually ineffective and lame. When you seal using wood glue on top wad you start getting a proper ignition and velocity.
When you get to know a few things and use things like Egg Glass and Liquid Silicon or even epoxy and a compressible, you start to equal or exceed shop bought ammo.
Problem is I have, had no way to measure pressures etc. So I could only gauge primers and sound, luckly, the shot gun primers come loose very early in the pressure resultant series of events.

If you start loading 410, you will always be eyes open for new, better wad material and wad cushion possibilities. You will start noticing almost any agent that glues, cures or dries, like shellac for car gaskets or cold glue for wood, trying gasket cement and silicon sealer, cable glue and things like layering thinner wads.
Its a whole world of experiments, the drawer of stuff I promised you is one dresser draw full of useables and possibles.

... you need more pressure build up than you think in the beginning.

Is this to ignite the powder charge properly?

And what happens if the pressure is too low? Any chance of an exploding barrel, or does it rather result in a underpressured blow-out with the shot falling in the dust ahead?

The reloading is easy, the finding the right propellant is not. S265 was the closest i got to success. The next hard part is getting the resistance of the overwad correct, this will be an ongoing matter of experimentation, you need more pressure build up than you think in the beginning.