Rebated 300WSM

R

Rflshootr

Member
Has anyone ever tried rebating the rim on a 300 Win short mag to fit a 308 boltface?
I'm thinking about installing a barrel on my bench gun but have a 308 b.f. to work with.
 
Haven't tried it but I'll give you some dimensions to work with. The inside of the case near the web measures about .465 on a WSM. The small diameter of the extractor groove on a .308 case is around .41. For that area between these diameters, the web material is the only thing that will be containing the pressure. I could pretty much guarantee that brass is going to flow backwards into that groove. Couldn't guess how much or how fast.
 
If you were to ask this question on the gun smiths forum, they will tell you open the bolt face. Or buy a new bolt. Don't think it would be safe!

Joe Salt
 
There is no question it will work. The question is under what operating pressure? People chamber 338 Lapuas in Rem 700's and they too "work". In a rebated 7WSM is there any performance gain over a 284 Win? Can it even operate at those pressures? I don't have those answers. Haven't tried it. I only pointed out the math.
 
Sounds to me like the Oat Meal in the case to take up the space the powder doesn't fill! Doesn't end well. the case is fat to begin with so why would you wan't to make the back end smaller were all the pressure is going. But who am I? Have fun with you'r endeavor.


Joe Salt
 
Wayne Shaw said:
I would do it in a heart beat.
Click to expand...

Joe you pick a strange comparison as a 284 has a rebated rim. There is about .090 difference between the outside diameter at the web and the extractor groove on a 284 Lapua case. I don't really understand how the outside part of the rim where the extractor grabs has anything to do with strength inside the case. Although there are a lot of things I don't understand. I find this discussion really interesting because I was thinking about turning my 300 Norma mag rims down so I could shoot them in my Bat reg mag action. To my thinking I would be worried more if I had enough rim left for the extractor to grab.
Stephen
 
sdean said:
Joe you pick a strange comparison as a 284 has a rebated rim. There is about .090 difference between the outside diameter at the web and the extractor groove on a 284 Lapua case. I don't really understand how the outside part of the rim where the extractor grabs has anything to do with strength inside the case. Although there are a lot of things I don't understand. I find this discussion really interesting because I was thinking about turning my 300 Norma mag rims down so I could shoot them in my Bat reg mag action. To my thinking I would be worried more if I had enough rim left for the extractor to grab.
Stephen
Click to expand...


I am attaching a picture to help you visualize what I was describing. The case on the left is the WSM, and on the right would be the rebated WSM. Now imagine a high pressure load. We know under high pressure the base diameter over the web on a conventional case like the WSM will grow. In the rebated case under the same pressures, the brass has no choice but to yield to the area of least resistance. I would wager that would most certainly be in that little step closest to the bolt nose in front of the extractor groove. I drew that step at .160 from the bolt face since most of the bolts I have are .155ish in depth. If that brass yields at all it could end up touching the bolt nose. If you rebate the step a little deeper for clearance it will be weaker yet.

Yes, the .284 is rebated, but it's the inside diameter of the case that is important to relate to the small diameter of the extractor groove. The inside of a .284 measures about .410. I'm sure we could rebate this WSM to PPC head size or even .222 and it will "work". At what pressures? Again, I don't have a guess.
 

Attachments

  • rebated wsm.pdf
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Something else for you to consider. Load for load this case will produce a given amount of force in the form of bolt thrust. The rebated case has only 75% the surface area of the original WSM. If you have an ejector plunger, it will start imprinting the case head at a lower load pressure with the .308 bolt face.
 
Stephen,

Since your scenario is different I drew up another comparison. I do not have data on the Norma case but here is what a Lapua would look like. In the left upper cross section is a 338 Lapua. You can see it is MUCH heavier in the web than the WSM case shown in the left lower cross section. In the right upper cross section is your Lapua case rebated to a magnum bolt face. In the right lower cross section is the WSM case rebated to a .308. There is actually more material between the extractor groove and the inside of the case on the rebated lapua than there is on the standard WSM. I don't know if the Norma is the same.
 

Attachments

  • rebated lapua.pdf
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I've only rebated a 473 case to fit a PPC boltface. The tool I made doesn't create a step, it just continues the upper bevel.

Rebate_head a.jpg
 

Attachments

  • Rebate_head.jpg
    Rebate_head.jpg
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rebated case head for wsm

I enjoy reading this forum there is usually a lot of good info here my two cents worth short and to the point by a bolt that is correct these cartridges is not worth eating a bolt you are asking for trouble i do not care what anybody on this forum says negative about my responce i do this for a living i understand what you are trying to acheive but it is not practical at all.
Stan
 
Thanks again Joe I'll have to measure my case. I am one of those people shooting Lapua bolt face in a remington action. I have a Tubbs bolt and he forgot to mention it was not safe when I got it. Some seem to think that way.So far all the boom has stayed where it is supposed to. I am just exploring my options.
Stephen
 
I know you guys are talented, but I've got a bad feeling about this, the case has a lot of pressure and would not like anyone to eat a bolt. The other thing it reminds me of is a fat punch with a nice point, so when its hit with a hammer were is all the force going. The Oat Meal thing I seen what that does!

Joe Salt
 
Just to clarify MY position, I have no idea what anyone is trying to build here. I only shared my knowledge of case strength and design. My earlier statement of "There is no question it will work" was meant with a heavy dose of sarcasm. Anything will work right up until if fails. I don't know what the oat meal and eating bolts conversation is about. I must have missed something.
 
Joe you don't need to clarify anything to me. I really appreciate your time with the drawings. They helped me see exactly what you meant. I am not a person to dismiss opinions from Knowledgeable and respected people. There are many on this site willing to share. Thanks again.
Stephen
 
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