Could we not devise a simple way for a bolt to grip a rimless case uniformly enough to actually headspace the case against the bolt face?

This would allow the development of many straight rimless cartridges, most notably,on the '06 case. The simplest approach seems to me to involve "retainers" that squeeze into the extractor groove as the bolt face enters the chamber. At this point the extractor would hold it in a position suitable for impingement from two other points on the bolt face/shroud. This impingement could be initiated on entry, and then clamped as the bolt is dropped.

A "straight rimless" case can headspace on the case mouth (like a 45 acp).
Good luck!

A claw extractor does that to some extent. Hatcher did some headspace experiments with a M-1917 rifle and found that past a certain point the extractor was controlling headspace, not the depth of the chamber. He also found that is made little difference to have a massivly deep chamber, other than weird looking empties.



To have the extractor hold the cartridge tight against the boltface would mess up feeding. You need a little tollerence to allow the rim to feed up into the bolt.



If you were meaning springie or pivoting stops that slip in front of the rim you may have something. Maybe use three pivoting spring loaded stops placed radially around the chamber. The most obvious problem I see is putting cuts in the receiver. A second issue would be making those slots line up with slots in the barrel. Seems like if you ever ruptured a case those hold back devices would come out of the rifle an make dangerious projectiles. Sure seems like a belted case is a better solution. Basically your straight '06 case is close to a 405 Win. Why not rework the magazine and bolt for 405 and be done with it?

Chambering a rimless, straight wall cartridge involves some pretty tight tolerances. You can get away with it using pistol cartridges like the .30 carbine or the .45 Winmag, but when you get up to rifle size, reliability goes out the window.



Any type of feeding needs some sort of resistance against the cartridge for the extractor to slip into the extractor groove. If you vary too far from the Claw/Sako/Remington styles, you will end up with a rifle that has such close tolerances that is won't feed factory ammo. For safety purposes, the cartridge needs to headspace on a fixed object. The extractor may be holding it in place prior the firng pin striking it, but you don't want any possibility of that cartridge moving forward after the pin hits.

How's your .458 Winmag pistol shoot, Kurt?

While the idea would in theory be workable, the rims on rimless cases are not consistent enough in thickness to be reliable as a means of controlling headspace. That's the first problem. The second is that, once the striker is released, there is nothing to hold the bolt back against the locking lug seats unless some provision was made in the design to do this. Regards, Bill.

it's been done... i THINK it was cooper rifles that came out with a SUPER SUPER high pressure rimless that basically has a collet for a bolt head and a super locking breach...

it's not cost effective

jeffe

Just a off the wall idea, how about somthing like the extractor/ejector system on a Stevens "visable loading repeater". It seemes to me that they might be able to hold on securly enough to a rimmless caseing.