some of the old original ones were pretty round nosed, based on the German Catalogue pictures Jspencer posted some time back with very little bore riding portion.   makes for a lighter bullet and for 200 yard paper punching they may have worked fine if the rest was well centered and sealed the groove diameter well enough.  If you are shooting longer ranges, higher velocities, and making a longer nosed bullet to get more mass weight, you might want it bore riding for support.  you need to consider the interrelationship between the case length to the mouth, case mouth OD & ID vrs actual chamber diameter and bullet base dia.  also factor in the actual edge of the case mouth to the leade taper to the actual rifling length and how the length and diameter of the stop ring will fit.   The stop ring does more than just keep the bullet form dropping into the case.  I'd think a stop ring that was groove diameter plus a bit and long enough to be a solid contact fit between the case mouth and the beginning of the throat would be desirable---especially if your bolt gun can "cam" the ring into the throat.  You want to get a good seal between the case mouth and the chamber wall.   Id fire-form a few cases several times before settling on a final bullet base OD.

My suggestions,

1. Make the base band only .317/.318. What ever size you can reliebly get started in the case mouth.

2. Make the band above it .315

3. Make the aft part of the stop ring .318

4. Make the stop ring .322

5. Make the fore part of the stop ring .315

6. make the area forward of that (bore riding) .300

7. Remember that the alloy can change your as cast diameters.

8. I would also suggest that you neck size (no longer than the area behind the SR) the case so that you know the fit and that the bullet is straight, for sure. The neck has taper and the base band can be loose, back of the mouth.

The above will give you the least amont of distortion, fit the inside of the case as well as possible and still seal the barrel reliably.

With a bullet like this, the next thing to do is lengthen your case until it will just let you bolt close with what ever pressure you feel is right.

8.15x46R chambers are usually a little long and if you don't use a stop ring, the case can be somewhere around 1.94 long. So, make up some cases in .010 increments and see how long a case you can chamber. Make sure you give the case mouth just a very slight chamfer or the stop ring can go inside the case.

Frank

Guys,

This is the 1st I've heard of a stop ring bullet.  After reading this thread I'm very curious?  I realize the bullet is designed to seat in the case down to the stop ring, but what advantage does that offer?  Also, what determines the stop ring diameter?  Inquiring minds need to know.

Wayne

Apparently the Germanic way of cartridge shooting /reloading evolved divergently from the American style as muzzleloading offhand target shooting evolved into breechloading cartridge. 

American target shooters who were seeking ultimate accuracy moved from fixed ammo via "breech-muzzle loading" to "breech seating" the projectile separately form the charged case.

I wish I knew more about the whys and wherefore of the germanic target shooting practices.  Maybe sometime BiggiH can enlighten us on their old-time practices.

From what I have found, it seems that with limited firing points, shooters would rack their arms between shots, load and fire in their turn, re-rack and wait for their next shot.
  Some of the old turn-of-th-last-century US matches ran that way too.  That old NY national schuetzenfest article I linked to a week or two ago describes some of the match practices that way.

From the old catalogues is looks like they bought their swedged lead bullets and did not do their own casting like we do.  They did not do cartridge re-loading they way it has evolved here.   A few cases that could be de-capped and re-capped on site with simple tools. primers, a box of "store-bought" bullets, and propellant.  (I have heard of premeasured powder in paper tubes, referred to as "straws" being used)  By having a stop ring it simply kept the bullet from falling down into the case when it was inserted into the charged case.   That avoided having to have some sort of some sort of seating/crimping die and press on hand.
I wonder if there might not have been some sort of legal restrictions on reloading arms or having powder and primers in ones home in that place and time.  The shooting seems to have revolved around established clubs and facilities with the guns kept at the clubs and shooters taking their sights home with them.

Swiss shooters seem to have simply used government issued fixed ammo for their military/target rifles

Frank,  I tend, perhaps in error, to differentiate between  benchrest accuracy and offhand accuracy.   Think of like a theoretical accuracy and practical accuracy.  
If we compare a 200 yard score target,  we have BR shooters who fairly regularly shoot 250/10X  scores which figure to about 3/4 MOA or less.   the best 10 shot 200 yard off hand was a 241/5x by Jim Feren back in 1993 which must amount to around a 1 1/2 MOA.  

I agree that most of the original rifles will probably shoot more accurately with carefully designed bullets that are breech seated than with stop ring bullets-----if you are shooting an 8.15x46r chambered rifle in benchrest matches and trying to compete with full-blown bench rest rigs and shooters. 

  But to my mind that is not what these rifles are purposed for.  They are offhand rifles by design (and a PITA to shoot "off the bags"; and I think the margin of error inherent in the bullet design is more than  outweighed by the shooters own induced-angle-of-dispersion anyway.

Wayne,
While I would agree that these rifle where built for OH only, I wouldn't agree that you should settle for poor accuracy. The only thing you will get with that is the lucky shot that went the near opposite direction of your flinch and the law of averages should cancel that out. You can't get a true evaluation of your skill w/o that .75 moa accuracy. If you shoot a 200 average or higher, I don't think you'll want a 2.5 moa rifle and I think that's about all a stop ring will do at best. 

As far as Jim Feren goes, he wouldn't settle for any less accuracy than the best BR accuracy. He would not even shoot a DST rifle OH because of the slower lock time.

I've shot mine off the bench a lot and all I need to do that is to have a high front rest. I've only shot mine BSed and wouldn't consider shooting it with a SR bullet. I think you could get much better accuracy shooting a fixed, well fitting bore riding bullet, with a taper on the next two bands and as little in the case as possible. You can also shoot longer bullets in the common twist rate of 14.17 (360mm). 1.12 would be my suggestion. I shoot a 1.03 long bullet at 1300 and will be trying 1.19 long BSed bullet next.

Frank