RTO and Star Crimps on Shot Gun Carts - Interchangeable?

[stevef]

Hi
I reload my own .22 hornet carts at the moment but I'm about to start reloading my own .410 3 ins carts and have a question that may be obvious to experienced shotgun cart reloaders:
If a plastic cart is RTO, does it have to be RTO when reloaded and the same question for star crimps, can you swap between the two crimps or do they have to remain the same?
many thanks
Steve

[slowcoach]

Hiya, better to trim slightly a used star crimp in my experience if converting to roll top.

Roll tops can be converted easier to star depending on the tool.

A star does close easier back into a star as the plastic has been 'trained' if that makes sense but with a star it is very critical to get the shot height just spot on as too much the star will bulge and too little the star tends to collapse and drag the outer case in with it.

Takes a bit of trial and error to produce a tidy star crimp but roll overs usually come out fine first time for that factory fresh look

Cheers John

[Junes1]

It's taken as read that a RTO opens more easily than a star crimp and so creates less breech pressure so I would go from a star crimp to a RTO but not the other way. A RTO also gives more volume inside the case which in a small gauge like the .410 is always useful.

[david1123]

My method for RTO'ing a star is to iron out the creases. Using a tool which fits in the drill press and snugly into an empty case fire him up and iron out the creases as best you can with some flat bar. Not ideal, probably get some rejects nor will the cases last for many reloads either.

[powderburner]

The main difference between a roll and a star crimp is the amount of case it uses..

Star crimps take up slightly more than half the diameter of the case, typically around 10mm mm for a 12bore. Roll crimps only take around 3mm.

There is a danger if you recycle a star crimp case to roll crimp without shortening it, you will end up with an overlong case. This could lead to overpressures if the case is pressed up against the front of the chamber. As far as I am concerned, you should always shorten a star crimp case if you are going to roll crimp it..

[stevef]

Hi
Thank you all for the insight and direction, I'm much happier to try both crimps!
Regards
Steve

[Junes1]

The main difference between a roll and a star crimp is the amount of case it uses..

Star crimps take up slightly more than half the diameter of the case, typically around 10mm mm for a 12bore. Roll crimps only take around 3mm.

There is a danger if you recycle a star crimp case to roll crimp without shortening it, you will end up with an overlong case. This could lead to overpressures if the case is pressed up against the front of the chamber. As far as I am concerned, you should always shorten a star crimp case if you are going to roll crimp it..

How can a case be overlong? A case is measured by its overall length not its crimped length.

[powderburner]

How can a case be overlong? A case is measured by its overall length not its crimped length.

Apologies, I was thinking about this the wrong way.. you are perfectly correct, the nominal cartridge length is actually the chamber length, which is the critical dimension.

I suppose the point I was trying to make is that case length for roll and star crimp is different. The roll take less case to form and the assembled cart is longer if you use a crimped case. Normally you would make up the difference with wads etc or you make up a shorter length assembled cart if you star crimp..

[Junes1]

Apologies, I was thinking about this the wrong way.. you are perfectly correct, the nominal cartridge length is actually the chamber length, which is the critical dimension.

I suppose the point I was trying to make is that case length for roll and star crimp is different. The roll take less case to form and the assembled cart is longer if you use a crimped case. Normally you would make up the difference with wads etc or you make up a shorter length assembled cart if you star crimp..

I load 20gauge mostly and found that 65mm cases with a RTO work nicely for 70mm recipes that are based on a star crimp. The components seem to fit quite nicely.
It should be noted that reducing a recipe into a 65mm case by just using a smaller wad and the same crimp as the 70mm recipe is likely to raise pressures significantly because there is less space inside the shell for the gases to expand in to before the crimp opens. It can mean 100s of bar extra