I am in the process of drawing my wildcat at 10X actual size to see if it will completely "overwrite" the present 300WSM chamber. All indications are that it will, but not by much. The WSM case has a base datum diameter of .555 inches; the 300RUM parent of the wildcat has .550 inches at that point. That leaves .0025 inches of "questionable space" surrounding the base of the cartridge. My question is: What is the diameter of the reamer for a SAAMI 300WSM at .200 inches from the head versus what it is for a 300RUM? I need to use the very bottom of the chamber as is to save the time and expense involved in having the barrel removed, the shoulder set back, the thread extended, the barrel put back on and the chamber cut with the new reamer. My 10X drawing shows the .0025 inches as .025 inches, which is at it should be. I have continued the taper to the new shoulder, drawn the 30-degree shoulder angle and drawn the neck. The present chamber is just barely wiped out by a few thousandths. The lines of the case walls of the wildcat follow those of the 300WSM almost exactly for very, very nearly the entire length from head to shoulder. I am wondering if I can have the reamer cut to have a maximum diameter the same as the present chamber (SAAMI 300WSM) and have it work for the 300RUM parent case. Will the present chamber be "too big" to closely breech a 300RUM wildcat?

I wish I could somehow show the drawing. But the lines are very fine and not very dark...

home

Don't mess around with trying to draw the chamber and overlaying a drawing of a reamer. Make a chamber cast. You now know EXACTLY how big (or small) the existing chamber is. Then measure the reamer you intend to use. You now know EXACTLY how big (or small) the chamber will be. From there it's not rocket science to see how well your idea will work.

I'd go even one step further. I'd get some of the brass I intend to use and see what the EXACT measurements of it is.

Unless, of course, you are only interested in factory ammunition in a SAAMI chamber. For that, the tolerances you cited are OK, IMHO.

Ray

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Unless, of course, you are only interested in factory ammunition in a SAAMI chamber. For that, the tolerances you cited are OK, IMHO.

There will be no factory ammo for this wildcat. It's a 300RUM shortened to 30-06 length with a 30-degree shoulder commencing at 2.094"-- just a red hair above the 2.090" trimmed length of the 300WSM. Neck is .400" long. Diameter at the bottom of the shoulder is .536" according to my whopper drawing. Diameter of the 300WSM is .538" at its shoulder.

Is it asking too much of a gunsmith to exactly follow the contour of the existing chamber when cutting the wildcat? The new cut has to be exactly centered in the present chamber or it fails...

So where do I get the casting metal and how do I use it?

The gunsmith will have no trouble following the existing chamber. A reamer will naturally do that for him. The trouble will be if the reamer is smaller than the existing chamber. That's why it's important to know the exact dimensions of both the chamber and the reamer.

Do you already have the reamer? If not, you can have it ground so that it cleans up the existing chamber. But, at the risk of repeating myself, you have to know the dimensions of the chamber. Don't assume it to be max or min SAAMI.

As an alternate, the smith can set the barrel back enough to be sure that the new chamber will completely clean up, regardless of dimensions.

Maybe I'm not explaining this well enough???

Cerro-safe casting ingots can be bought at places like Brownells but it sounds to me like your not familiar with using a chamber cast. It may be better to furnish your smith with details of what you're after and let him do the figuring.

JMHO

Ray

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Maybe I'm not explaining this well enough???

Not at all. Any and all information I can get from those who have done it is priceless. I appreciate every word...

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Originally posted by homebrewer:
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You could just try it ,and it if doesnt clean up,set the barrel back and do it again.

I have heard of Cerrosafe casting metal for just this purpose. I see Brownell's has it for about 30 bucks per half-pound. I also see it melts between 158 and 190 degrees Farenheit. Seems to me it could be melted in a tuna can in hot water on your stove, then poured through a plastic funnel right into the plugged chamber. I'd do it but that price, plus the shipping, can be put toward other things...