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Radius on rear ring of Mod 98 large ring

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05 March 2008, 19:38
butchlambert
Radius on rear ring of Mod 98 large ring
What are the 2 radii on the rear ring of a large ring 98?
Butch
05 March 2008, 21:20
aleaddict
Butch --

From Mark Stratton's book, the radius on top is 0.547", which ends on a 34* angle on either side. Kuhnhausen might have some different measurements but I'll have to take a look and get back to you later.

-- ale
05 March 2008, 21:46
butchlambert
Brian,
I guess that I better get Mark's book out. That sounds about right. A .500 radius guage was close. I need to make some scope bases for my Banner Mauser in 9.3x62 while waiting on Lilja for a barrel for my 6.5x47Lupua.
Butch
06 March 2008, 00:15
Jim Kobe
Set the action up in the mill to facilitate measuring. With a dial indicator from the middle (highest) portion of the rear bridge, measure an equal distance from the center toward the sides of the action and move your table up until you get the zero again. This gives you the chord length and the height and is all you need.

Next, to get the radius, use this formula:

R=chord(squared)+ 4times the Height(squared) divided by 8 times the height

I just did this the other day on an FN.

The formula is in the Machinery's Handbook


Jim Kobe
10841 Oxborough Ave So
Bloomington MN 55437
952.884.6031
Professional member American Custom Gunmakers Guild

06 March 2008, 02:24
aleaddict
Thanks for that formula, Jim. I can't wait to use it for my Mauser projects. Here's a numeric expression of the same formula you described:

R = [C^2 + h^2(4)] / h(8)

Good stuff!!
06 March 2008, 06:07
Craftsman
Butch

In Stratton's class I used a simple approach. I inserted a mandrel that was a slip fit in the action. Then measured from the top of the rear bridge to that mandrel with a dial indicator. Adding that measurement to the known radius of the mandrel gave me the total radius. Of course it works on the front ring as well.


Craftsman
06 March 2008, 06:37
z1r
Once I'm done surface grinding the action I measure the distance from the top of the bridge to my mandrel then add half the diameter of the mandrel. That gives me my radius.




Aut vincere aut mori
06 March 2008, 07:09
butchlambert
I'm gonna make chips in the morning. Freddie, if you are close, stop by. Unless something comes up, I will give a report tomorrow evening. Mike, what you and Craftsman said is so easy and why didn't I think of it. Jim, you think I got that far in college math?
Butch
06 March 2008, 07:25
z1r
Butch, The sides of the bridge are really flats. The angle depends on what you grind them at. In original form most are about 30 degrees.




Aut vincere aut mori
06 March 2008, 07:55
butchlambert
Mike,
I think that is pretty close to what I have. I will double check before cutting chips. I had to do the ones on my Pierce receiver 3 times before they were right. I sure hope the first time is a charm on this. I got my Pierce receiver and forgot this project. I am back on it as I have a long wait for the barrel on the Pierce.
Thanks Mike
Butch
06 March 2008, 18:36
Jim Kobe
By the way, if you keep the width of the base at about .700' you won't need the flats. I havee also found the flats on some Mauser receivers to be different angles from one side to the other.


Jim Kobe
10841 Oxborough Ave So
Bloomington MN 55437
952.884.6031
Professional member American Custom Gunmakers Guild

06 March 2008, 18:48
z1r
quote:
Originally posted by Jim Kobe:
I havee also found the flats on some Mauser receivers to be different angles from one side to the other.


That's why you surface grind them.




Aut vincere aut mori