Rebated rim cartridges for precision

[med358-boise]

deleted

 

[fseaman]

Sometime next year I will know empirically how a rebated rim works on an old Weatherby Mk V six lug action. A Pac-Nor 7mm barrel will be here early next year. The ADG 7 Nosler brass will be turned down to fit the .470 bolt face.

Are you willing to share your cartridge design? For parent case, I am not familiar with something called "7 Nosler". Do you mean 28 Nosler?

(repeating know information for reference) Since Weatherby now makes the 6.5 and .338 Weatherby RPM where RPM stands for Rebated Precision Magnum. Function with rebated cartridges is known to work. If your design is based on a 375 Ruger or 404 Jeffery, it may get harder.

so

If your design is similar to any of the rebated rim chamberings in the 6 lug you'll be good. Worst case, get mag box for the next closest chambering and have the bolt stop groove lengthened. I think I have a belted magnum in my 6 lug inventory (not sure, it's late, safe is locked ) If there is a belted magnum chambering for the 6 lug that the OD of the belt is close to your base OD and the COAL is similare, the mag box for that cartridge may bey your friend.

 

[med358-boise]

These folks don't seem to have a problem with it. This list is from 2020 and the2018 list was basically the same.

Cartridge Selection in F-Open Division

In addition, Matt produced an interesting listing of cartridge/caliber types for the F-Open division. This is helpful because cartridge choice is unrestricted in the F-Open class. By contrast, the F-TR division is limited to .223 Remington (5.56×45) or .308 Winchester (7.62×51). You can see that the .284 Winchester (and variants) currently dominate F-Open.

 

[fseaman]

Yes, due to the internal diameter above the web, more psi is exerted over the primer pocket and the sides of the web diameter is reduced for the extractor groove, this allows more brass movement outward either side of the pocket.
Unless the web is beefed up, read this as thicker, and the walls of the case are radiused from the web, then it will expand more laterally.
This is why primer pockets loosen in Norma brass prematurely.

Cheers.

Thank you sir!

I'm gonna restate with reference to my "favorite" rebated rim parent case, the 404 Jeffery and it's offspring. Please tell me if my restating follows your description and the logic there in.

With it's deeper/thicker web and more gradual internal radius the more recent chamberings based on the 404 parent may not experience the "weak primer pocket" endemic to the original 284 Winchester.

So

Painting all rebated rim chamberings with the sins of the original 284 Winchester may be "over exaggerating" and applying faults to a completely different parent design.

Correct?

 

[fseaman]

Cartridge Selection in F-Open Division

It may be just that event but do you know of anyone using the 7mm WSM?

The shoulder is pushed 0.037 and the neck is only 0.243. It seems the original spec was for a 9 twist so a build would need to be 7-8 twist for the heavies it can throw and throating to match.

 

[MagnumManiac]

With it's deeper/thicker web and more gradual internal radius the more recent chamberings based on the 404 parent may not experience the "weak primer pocket" endemic to the original 284 Winchester.

Whose brass have you sectioned to say this?
Original 404 Jeffrey brass has no rebated rim or extra thick webs, it ran the same pressure as 416 Rigby, Gibbs & many Nitro Express pressures around 38,000-40,000psi.
It has nothing to do with "weak primer pockets", it is the thickness of the web and internal shape of the brass that causes the amount of expansion in primer pockets.

Making blanket statements regarding brass expansion is incorrect.

If we take Norma 300RUM brass, compare it to ADG or Peterson, then results with the same pressure will be vastly different.
Same goes comparing WSM brass brands, I had my 25-300WSM web grow so much that it resisted sizing causing clickers after 3 firings.
My 6.5-300WSM did the same thing with Norma brass. This stuff costs $192AUD for 50 pieces…is it value for money? I think not, but it is the ONLY brass here always in stock.
Winchester brass was the best, but due to its hardness, normal sizing dies weren't cutting the mustard and body dies were needed to overcome the issue.
A wide case head actually has thinner webs, look at 416 Rigby cases, the expansion line is closer the extraction groove than RUM brass.

Oh, I section EVERY brass manufacture I have to see web thickness and shape of said case after determining volume in CC's.

Cheers.

 

[med358-boise]

It may be just that event but do you know of anyone using the 7mm WSM?

The shoulder is pushed 0.037 and the neck is only 0.243. It seems the original spec was for a 9 twist so a build would need to be 7-8 twist for the heavies it can throw and throating to match.

I do not know of any 7mm wsm users. Berger publishes this list every so often ( IIRC the 2015, 2018 and this one in 2022) I am always impressed by the 284s dominance. My understanding is the Southwest Nationals is a pretty big shoot so I would be surprised if other F-Class competitions looked different, but curious to see other information. Also note, that the KMR, Shehane, & Wheeler are just various 284 win improveds; so were are really talking about 69 out of 97 shooters are using a 284 or minor wildcat thereof.

We also have the 284 chambered in levers and autoloaders, so I am skeptical that there is a practical issue with a rebated rim for feeding as opposed to theoretical. Granted, the winchester 100 was not know as the most reliable autoloader but that malady was across all chamberings not just 284 sins.

 

[eshell]

Yes, due to the internal diameter above the web, more psi is exerted over the primer pocket and the sides of the web diameter is reduced for the extractor groove, this allows more brass movement outward either side of the pocket.
Unless the web is beefed up, read this as thicker, and the walls of the case are radiused from the web, then it will expand more laterally.
This is why primer pockets loosen in Norma brass prematurely.

Cheers.

Thank you for your explanation. I think I need more coffee though.

FWIW, I have used Norma brass in several calibers, including 6.5-284. While it seemed to be well made, I found it to be soft, both showing early pressure indications (case head expansion, ejector marks) and loosening primer pockets, when compared to other premium brands like Lapua. I don't use it for anything any more.

 

[Alex Wheeler]

Cartridges index on the feed rails off the case body. So the bolt has less purchase on a rebated rim. The rebated rim sees more pressure because of its reduced area. On a case like the 284 primer pockets loosen up pretty easy. The magnums have enough brass its a non issue.