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Thread: Drilling in 8x57R 360, case reaming & claw mount adjustment.

  1. #1

    Drilling in 8x57R 360, case reaming & claw mount adjustment.

    Some years ago, we were entertained on TV by a programme called University Challenge, a quiz game between rival teams. The quizmaster would always lead in by saying, "And now a question for six points..." This then became a catch-phrase here for any question out of the blue. So can someone earn 6 easy points by telling me how they go about reaming 9,3x72R cases that have been cut down to form 8x57R 360 cases? (or similar conversions where the cut down case is over-thick where it becomes the new neck).

    I have velocity on this Drilling up to 1833 fps (SD=7!), which may sound slow but actually, that's spot-on according to "The 8x57R/360 - Obsolete Old Favourite" by John J. Stransky in Handloader #139. Despite this, an unfired .318" dia. bullet will not fit inside any of the fired case necks. Having said that, there are no signs of pressure. All cases fall out of the rifle when it is held upwards.

    Should I outside neck case neck turn? I am set up to do this on a variety of calibres with an RCBS hand-tool and I'd just need a close fitting custom pilot - easy enough to make with a lathe. I figure it should be OK if I don't seat the bullet lower than the case neck was turned. Meaning, there would be a small thickness or lip left over around the position of the case shoulder/neck.

    If instead I would be better advised to case neck inside ream, (no lip), should I go for one of those expensive reamer/die set options such as RCBS/C-H etc., make where I ream the case vertically using my reloading press as the mount? Or perhaps use a trimmer adapted to horizontally case neck ream?

    I assume some of you guys must do this sort of thing regularly. What do you recommend?

    The next question for six is;

    When you adjust the opposing windage screws in a claw-mount post, are they generally of the same thread? If so, is it the case that one full turn of thread generally equals a certain amount of shift in POI at 100 meters? This Drilling is shooting a 5-shot group under 2". It would do a lot better if I slowed down as usually 2 bullet holes will touch in a group. I just need now to get it to regulate to the target bull. My thinking is that, perhaps all these older rifles with similar claw-mounts and opposing windage screws on a square post would regulate to some sort of rule-of-thumb that a quarter turn = x amount of change at 100m. However, the fly in the ointment might be that different scopes are different lengths, so that the amount of change of POI will vary. So in that case, is there some mathematical formula that perhaps divides the distance between the scope mounts into the distance to the target and then multiplies this by the thread pitch?

    Or do I just continue to do what I always have; give it a quarter turn or two and shoot it, note the effect and forget about thread pitch, mount separation distance and etc.?

    Thanks in anticipation.

  2. #2
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    Kiwi_bloke,
    The decision to neck turn or ream is strictly a personal one, each has its own advantages and disadvantages. You are already aware of some of the options, but there are others. Since you mentioned a lathe, I guess you either have one or have a friend with one. There is an article in the Dec.2015-Jan.2016 issue of MACHINIST'S WORKSHOP that addresses the very concern you have, and making the tools to allow reaming case necks. You may be able to get a copy of the magazine or the article from Village Press. You might try :subservices@villagepress.com.
    For my own 8x57R/360 I use original factory cases, but when I first started loading for it, I "mocked up" and fireformed a case from an original length 38-55 case. Such cases would be a little short (2.125" vs.2.250"[ trim length 2.238"]) but work fine if the bullets are seated out to the same overall length. These cases won't require reaming or neck turning. They are a little smaller in head diameter, by an insignificant amount, and depending on the particular rifle, the rim may require turning and/or thinning. Acknowledging this is a personal thing, I never did like trimming so much from good 9.3x72R cases, when other acceptable cases are available, often more available.
    As far as your second question is concerned, the threads are the same on the left side as on the right. That is the easy part. Harder is "how to make the adjustments. With some makes of mounts The screw "pushes" the scope, and in others "pulls" the scope (depending on whether the female thread is in the top or the bottom part). Many don't have any kind of "scale", but most have "witness marks" allowing you to see which direction the scope is moving. Because of the reasons you mentioned, adjustments have to be "cut and try". I have found that small adjustments move the bullet impact more than you would think. It is usually quicker if you "bracket" the target rather then "sneak up" on it. I hope this is of some help.
    Mike

  3. #3
    Hi Mike

    All good info. Thanks. I use a small tube cutter to initially take down the 9,3x72R cases to near the right length for 8x67R 360 and trim the remaining excess. I would imagine that inside reaming might in theory help eliminate fliers, though that doesn't seem to be a problem in this rifle.

    I hadn't thought about the push/pull effect of where the scope mount thread is. I've got them working smoothly but I don't think I ever pulled one fully apart so I never noticed that. I suspect the mathematical approach described above, when I measure the pitch of the thread, will be of some use and I'll give it a go. Bracketing would sort of work too. In the 1914-18 war, naval ships would fire a round short and then a round long and from those two then calculate exactly how to land the next one right on their target. So I guess it's a bit like that.

    Thanks again
    John.

  4. #4
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    John,
    If you insist on cutting off 9.3x72R cases, you might try turning the neck area before you neck them to 8mm. You might be able to eliminate the "step" you would have when turning the neck of a formed case. Just as a matter of information, I load mine to 2150 fps, but with a 170gr bullet( I use .321 and .3215"), I guess from your velocity that you use 196gr .318" bullets.
    Mike

  5. #5
    Just checked to remind myself and found:

    Thread is male on the twin screws. Adjustment is done by the screw head pushing against the scope base above, which is in a dovetail. I think most of them are like this?

    The range is 100 yards = 91.44 meters.
    The mounts are about 100mm apart, so that would divide 914.4 times into 91.44m
    The screw pitch is 0.75mm
    So 0.75 x 914.4 = 686mm.

    In other words, I can expect 686mm / 27" of change for one full revolution, if my maths is OK.

    I need 1.5" of RH adjustment. That's 1/18 of a full turn required. So I need to be looking at making just 1/4 part of a 1/4-turn.

    I'm sure it won't work exactly like this in practise, but at least it gives me an idea for the scale of adjustment needed, (i.e. only about 1/4 of what I originally had in mind).

    There are no radial lines in these screws, on the Vinzenz Urbas, Ferlach, Driling. However I notice that the screws on my Krieghoff have 16 divisions.

    I hope this helps someone in the same predicament.

  6. #6
    Sorry Mike, missed that post. Yes, good idea re the step. I'll certainly try it.

    New 9,3x72R cases are a lot easier to get here than .38-55 of any vintage. So don't worry, I'm not using up the last stocks of them. My 20 cases will probably last for some time and, of course, they get this old gun, (the data string suggests 1927), shooting again. No one even knew what calibre it was, when I purchased it. The bullets are 196-grain (.318"), as you correctly guessed.

  7. #7
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    Kiwi_bloke,

    On your cases you may want to measure the case thickness at the neck first to determine if it is in fact too thick. I have been loading a 12.7x44R lately and when the pressure is low the bullet is released but the case springs back or never expands and the bullet will not go in. There just isn't enough pressure developed to stretch the case out. I have seen this in several other calibers when working up low pressure smokeless loads.

    Thanks, Diz

  8. #8
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    Kiwi-Bloke,
    Diz makes a good point. While the cases in question were 9.3x74R, not 9.3x72R, I checked neck thickness of some shortened cases as part of a "discussion" with another board member. The increase in thickness was insignificant. To Diz's point, remember that the neck of most new cases have been annealed, and when shortened, the new neck may move to a harder area of the case. Consequently, the case may not fully expand with the first firing of a reduced load. Necking the shortened case to 8mm would work harden it even further. Reforming shortened cases is a common and often necessary procedure. As a matter of habit I anneal the necks of all my reformed cases, even if not shortened. Oftentimes they are still not fully formed with the first firing.
    Mike

  9. #9
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    Kiwi bloke, there is no general recipe for sighting in the windage adjustments of claw mounts. While in some, mostly older mounts, the adjustment screws push the scope as you describe, on many others, mostly newer ones, the screws pull the scope over. Then there are some old mounts with sort of a cross feed inside the rear mount… As the screws are usually of standard metric DIN sizes and threads, the amount of sideways movement of the poi depends entirely on the distance between front and rear mounts. At the least minute adjustments, say for an inch or so, even the torque you apply to both screws comes into the play. So IMHO it's all a question of shooting, doing some adjusting, observing the new poi and trying again.
    About case wall thickness and the need for neck turning/reaming: RWS cases, especially newer ones, feature a marked increase of wall thickness behind the neck. This makes them less desirable for any reforming that includes shortening or setting back the shoulder. Thinning the necks is nearly always needed. I myself prefer Sellier & Bellot cases for radical reforming, as these have a rather uniform wall thickness. I made my own 8x57R360 cases from 9.3x72R S&B brass. no need for neck reaming or turning. Here in Germany, not a single .38-55 or .32-40 case turned up for sale, even after several phone calls. So I drove the ten miles to the Kassel outlet of Waffen Frankonia and bought 40 new S&B cases right over the counter.
    Maybe you are struck with a chamber that is below modern minimum dimension standards. Before 1940 the Suhl and Zella-Mehlis gunmakers resharpened and reused their reamers as long as a factory cartridge would enter. If the thing stood firing the proof load everything was deemed ok. BTW, the CIP minimum neck diameter of an 8x57R360 chamber is 8.80 mm = .3465". If a chamber cast shows your neck being smaller, you have a real problem.
    Last edited by Axel E; 12-07-2015 at 05:54 PM.

  10. #10
    Hi guys

    I think you are all correct, each with different parts of the puzzle.

    So my question was initially to flush out from users of these rifles what Diz has just said; that such low pressures don't seem to open the case mouth enough. So that was my suspicion - now confirmed thanks.

    But also Mike I can see that annealing it might help change that too. I anneal case neck/shoulders in molten lead for a count of "5", by the way. It makes them a lot more flexible. I'll do that tomorrow and see how it helps. It just might work. I'm sure it's a good practise regardless.

    And yes, Axel, S&B cases seem to be better. I measured the case mouth and found the thickness, from reformed 9,3x72Rmm S&B cases, was quite a bit less than some ordinary Geco .243 Winchester cases I also had on hand. So these 8x57R 360mm necks aren't actually thick. That was a surprize too - but it agrees with what Diz said about low pressure.

    I do have measurements from a chamber cast and also a copy of Wiederladen with C.I.P. mx/min diameters, but I never thought to check that. So good point Axel. I do know that it was within the specification though. That's how I worked out what it was.

    Also, yes, just the torque on the opposing screw to tighten things up can make an impression on the POI in my experience. So I understand that any figures I arrive at on paper are just a rough guide, compared to actually shooting it. Still, they might stop me getting too carried away for the first adjustment. They also make me think about adjusting a Drilling with a short distance between mounts being more sensitive than a rifle with a much longer distance. Of course, when I adjust 1/16 turn and then shoot it and notice a certain change, I'll write that down for future use.

    So this has been a very useful set of suggestions all round.

    BTW Axel, to get some more 5,6x61 and 5,6x61R cases from Germany, it looks like I will have to pay 90 Euro just for the export permit. I would gladly drive 10km to Waffen Frankonia in Kassel to get them if I could. A friend has offered to bring them out for me, but I think that without the permit, that would only get them in trouble as they leave. It's getting a lot harder.

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