Suggestion for loading bore riders

[Potashminer]

So, I am putting together a "punkin chucker" - rifle will have a Hellqvist rear aperture sight, a nice sizeable front bead that I can actually see, and is destined for plinking and putzing away at things that are out to, say, 100 yards - I would consider 150 yards to be a very long reach for me with this outfit. Hoping that 4" groups at 100 yards might be achievable?

The cartridge is 9.3x57. The bullets are gas checked 285 grain Round Nose Flat Meplat - see picture below. I know I want the lube groove fully covered with the neck. I know I want the gas check at or above the junction of the neck and the shoulder. So that seems to still leave a lot of choice as far as actual seating depth. I have loaded 1,000's of jacketed rounds since 1976-ish, and some cast rounds, but none have that shoulder as shown. The nose section is very much smaller diameter than the rifling to rifling diameter - say .003" or so smaller.

I have not put the barrel into the action yet, nor have I received the dies to convert the 8x57 brass. For "optimum" results, where do I want that shoulder on the bullet to be, relative to the "lands" - do I want "jump" or do I want the cast bullet shoulder hard into (engraving) the lands? No clue yet if the later is even possible, until I get the rifle assembled - given the magazine length of a M96 Swede. Or, does it matter? I would appreciate hearing anyone's experience doing it one way or the other.

 

[just having some fun]

Cast ... the only way to find out is to load a test round with no powder and see

black marker test

you might have to aneal your brass, to size up ... do not over heat it

 

[just having some fun]

What powders are you going to use for your plinkers .... you might be surprised on what cast will do

 

[Peecos]

Welcome to the adventure. I’ve been on a similar quest for about a year now and have a M 98 and 96. Each has been very different in their path. The 96 I used PPU 8x57 brass, necked up with Hornady die and seated bullet to the case shoulder with a few different charges of Unique and voila 1” groups at 50 yards. I’m currently using cast from Jet Bullets but have a mold to try. The M98 was very different. Tight chamber and neck, used Metalvirken 8x57 brass which is quite thick. I’ve had to neck these up to.375, turn the necks to get rid of the old shoulder ridge, neck back to 9.3 until I can close the bolt and have been shooting jacketed as the cast won’t fit. Now that cases are formed to the chamber I think I can try cast loads.

 

[fingers284]

I would strive for much better results than what you "hope to achieve" at 100 yrds. I would consider 4" groups a failure...more along the line of sub-2" would be my goal and completely achievable with cast.
As for the driving ring positioning, When the BPCR copetitio0ns started to be a "thing" they discovered that the "Farmingdale Sharps" rifles with their very long "free-bore" couldn't compete with the custom chambered rifles with the short free-bore...even with the long pumpkin's seated far enough out to touch the lands. The theory was that the gap between slug wall & free-bore dia. was allowing the BP obturation to distort the bullet before it totally became supported by the rifling lands.
When Sharps moved to Montana, a contingent of BPCR competitors lobbied them to shorten the free-bore up considerably and they did...and never looked back as being a "go-to rifle" for competition.

I wasn't there nor have I ever competed in a BPCR event but that is what I read when researching the sport.

One thing I think that is completely do-able now with Powder coating would be to coat the slug nose up to be a bore-rider on any free-bore with a little experimentation...might be a bit of extra fiddling but that's what hobbies are for...aren't they?

 

[Potashminer]

Thanks for comments, fingers284. My "goal" is based as much on me shooting with a rear aperture and a bead front sight - will be new experience for me - so, no doubt rifle and load should be able to achieve 2 MOA - not real sure that the "nut behind the bolt" will be able to - the M648 receiver that I intend to use is drilled and tapped for that Hellqvist receiver sight, but was also D&T for scope bases, so quite do-able to mount scope to take time to develop 1.5 to 2 MOA groups with scope and then go for the 4 MOA with aperture sights!! I have an M8-12x Leupold, bought specifically to use for load development with various rifles of mine. Always want something else to "blame" poor results on, but will take full credit for any successes!!

I think I do understand the desirability to have the cast bullet snug into the free bore, as much as possible (actually a plus, I think, for jacketed bullets as well?) . As mentioned, this "bore rider" style will be new territory for me - two diameters on the bullet. So nose part can not be snug to free-bore, but maybe shows improvement when snug to top faces of rifling - rear diameter would be nice to fit well into free-bore, but also must be able to chamber in the first place. So, lots of opportunity for "fiddling", as you say. Long, cold winters here in Manitoba - should work out just fine!!! I planned to start with a Cerrosafe cast of the chamber, while I have the barrel free - just to know what has been cut in there. Bullet diameter, neck thickness, etc. all can be adjusted, but I guess positioning of that shoulder may become totally "theoretical", if the magazine length is shorter than the "leads" are...

The picture above posted by Peecos is about what I envision? Shoulder on bullet probably just starting into the free-bore; nose riding portion hopefully up into the rifling - as he mentions - that load does chamber in one of this rifles - case walls are too thick for another of his, but do not yet know how my own chamber was cut - have to sort that out first!!!