fseaman
Well-Known Member
ugg. you win tarzan.
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Rebated rim cartridges for precision
- Thread starter fseaman
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Sorry didn't take the time to read the whole thread. If I did, I may learn something!And 284 based chamberings are quite successful in "F" class.
That is not the original purpose of the thread. It is a discussion of the pros and cons of rebated rims.
So far the pros are the increased capacity and surface area. Pedantic waring: PSI is a portion of the pressure formula. How many SI does the cartridge have? That is surface area in inches.
Cons so far have been bolt drag. That is a new one for me and really really gets to why I postulated the question and the "weak" 284 cartridges but that perceived weakness being applied to all rebated cartridges is how we get a little digging deeper into perceptions are reality. Until they aren't.
I will be more careful and read everything before I post an answer. Thanks for keeping me on my toes.
Been so busy the past two months with a litter of NINE new Great Bernese Pups and new Kubota Tractor and implements that I have not been in the shooting/GS world.
Well the bolt face size is one reason with the rebated case, and I guess I'll keep quiet and leave the responses to the experts.
Thanks much!
Len
fseaman
Well-Known Member
You're good man.
Some of the "experts" are replying without reading and that is disappointing. They be acting like some "noob asking dumb question".
What prompted me to ask the question was "experts" seeming to take a dump on all rebated rim chamberings.
I have had only success with my rebated rim rifles so was wondering what "issues" there were.
fseaman
Well-Known Member
There are gems of knowledge in this thread from those that know much more than I do and for that I am thankful. It was hard fought to get it.
MagnumManiac
Well-Known Member
Albeit true that a rebated rim DOES take more force than one at the same size as the body, psi force is determined by the diameter INTERNALLY of the case, not the size of the rim. As Alex Wheeler pointed out. (Very glad I am no longer a member of that forum!)
The RUM case is substantially rebated, but it appears no ill effects are contributing to primer pocket expansion.
It is my belief, and many others, that what DOES determine primer pocket expansion is web thickness, the thicker it is, the longer the case resists expansion.
Winchester (old blue bag) has some of the thickest webs, as does Lapua and RWS.
This makes a difference.
Cheers.
The RUM case is substantially rebated, but it appears no ill effects are contributing to primer pocket expansion.
It is my belief, and many others, that what DOES determine primer pocket expansion is web thickness, the thicker it is, the longer the case resists expansion.
Winchester (old blue bag) has some of the thickest webs, as does Lapua and RWS.
This makes a difference.
Cheers.
Alex Wheeler
Well-Known Member
Rebated rim has 2 downsides. Primer pockets dont hold up as well and mag feeding is slightly less reliable. Not huge issues but they exist.
fseaman
Well-Known Member
Hi Alex,
You have far more experience than I do and I am intrigued by "pockets don't hold up". The feeding or as @bigngreen says, bolt drag, yup I understand that.
I am heavily vested in 404 Jeffry based rebated rim chamberings. The only chambering I have had enough cycles on is 300 WSM. I have gotten nominal 15 firings from a fairly stout load. Sorry I can't be specific, I have not "recovered" my load data from a move 5 years ago.
Is 15 cycles in the "pockets don't hold up" realm?
Are you referencing more toward the 284 based than the 404 based?
Do you think Weatherby's update to the 284 based "RPM" will address the "pockets don't hold up"?
HRM Johnny
Well-Known Member
Tag
300 Wsm, 7 saum, 284 shehane, there are the most popular cartridges you'll find in a typical 1000y benchrest competition. All rebated rim. It has nothing that'll affect the "precision" of the rifle system. Getting them to feed well is no issue either. Run a hawkins hunter mag setup, or choose a hawkins m5 bdl with a wyatts center feed box, tune the feed lips properly and they run like butter and still get 3 magnum rounds down in the box. If you run a standard bdl VS the m5 version, you'll only get 2 rounds down into the mag box.
MagnumManiac
Well-Known Member
I agree with the feeding issue, but only when the action wasn't designed for that cartridge in the first place.
In all of my F-class shooting, we can't load the magazine, so feeding issues are moot there anyway.
Cheers.
RichCoyle
Well-Known Member
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.
They must work well, the 6.5RPM is a Weatherby designed case, it's a stretched 6.5x284. They already offer it on the 6lug mk5. Shouldn't be too tough to get it running!
MagnumManiac
Well-Known Member
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.
