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Thread: Sheared scope mount screws with 375 Ruger

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    Default Sheared scope mount screws with 375 Ruger

    Hmm, 375 Ruger, 1917 action / busted scope mount screws

    I added a steel recoil lug from an old Vz-24 to the laminated Boyds stock on my Remington made 1917 Enfield actioned 375 Ruger project because the recoil was denting the laminated wood.

    So off to the range I went today with some fairly snappy loads to see how they would group.

    This is a fairly light rifle for this cartridge and as a result you do know when you have touched off a round...

    I only fired 15 rounds today before the screws that hold the one piece mount to the action sheared right off. The front two sheared and the rear screw was still intact when I pulled off the mount. SEE PHOTO:
    So now I have to drill and tap the little buggers and try something much bigger.

    Actually I need to find somebody who is good at this sort of thing... I am likely to bugger them somehow...
    Any ideas????


    All used virgin Hornady brass, and federal 215 magnum match primer. All had a COL of 3.340 inch with no crimp. The barrel is a 22.5 inch long Shaw barrel with 4 grooves.

    300gr Accubond with 79.0gr H-4350 = 2,810 fps and a big group at 100 yards.
    270gr Speer SPBT with 80.0gr H-4350 = 2,860 fps and a 3/4 inch group.
    260gr Accubond with 81.0gr H-4350 = 2,918 fps and a 1.75 inch group.
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    Are those #4-40 or #6-48 screws?
     
    First donít be tempted to go to a higher grade of screw. I had one show up with hardened screws snapped off in it . . . Had to send it out to get them cut out by EDM because no tooling would touch them.
     
    If they are #4-40 go to #6-48, much stronger screws. Next is there anyplace to get a 4th screw in there, behind the front two maybe? Making sure it fits dead tight to the receiver will help a lot too, if one screw is pre-loaded sucking the parts together then its taking all the shock load. Need to spared that force over more screws as evenly as you can.

    Iím a long way from Homer but you can mail the action and mount if you want, these fine threads are easy to cross up if you don't have some way to guide the tap.
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    I think these are the smaller #4s. I need to get it up to you to have something more substantial installed. Maybe a different type of mount as well.

    Shaw opened up the magazine feed rails and I am not happy with their work. It does not feed correctly. I think they went too far... Although a different follower might help.

    How close are you to the Palmer Airport?
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    Iím in the approach pattern up on Lazy Mountain, I can meet you at the FSS or something.
     
    I think your one piece mount should be workable with some more bight to the receiver. If itís just three #4-40 screws Iím not at all surprised it didnít hold up to 375 Ruger.
     
    If you want me to play with feeding bring a full load of dummy rounds.
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    All of my Heavy recoil guns have 8-40 screws in the mounts. Brownells sells these screws for converting from the 6-40 size that you sheared off. An extra screw (4 total) would help also. I use a Picatinny type base. If you desire more room to give greater clearance for recharging the magazine in a hurry, you can use a two piece base. The 1917 action is a difficult action to put mounts on because the rear portion of the action was a cut down of the military receiver and each one was done at the whim of the guy cutting it down. I bet that if you changed to the 8-40s you would be OK. A thought comes to mind is if you are using Lead sled with a lot of weight on it, that could be the cause of the heavy recoil having such an effect on the scope and the mount. I know of folks who have broken stocks using these contraptions. The "old timers" used a stand-up rest so the body could absorb some of the thrust.
    Just a thought.-Craig

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    #6-40 screw on a scope mount would be somewhat unusual, #6-48 is the usual but #4-40 shows up on small caliber and older guns and #8-40 on heavy recoiling.

     
    Your point about the tops all being milled off different is exactly what I was getting at before. With the mount not sitting dead flat to the receiver one screw is being pre-loaded, doing all the work and taking all the recoil. When that one screw gives up the force all gets moved to one of the remaining two . . . Soon you note everything is loose and discover a broken screw, a boogered screw and a loose screw when you inspect.
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    I'm rather positive they are not #4 screws. Most likely #6's. Redrill and tap the holes to 8x40 once you get the broken screws out. I could do it for you, but like Andy, I'm a long way from where you are. That was a heavy scope for a big gun. Lots of mass wanting to stay put while the rifle accelerated to the rear. I see this once or twice a year. Heavy scopes on heavy recoiling guns will do the trick. #6 screws will usually do the job, but everything has to be good. If one screw fails, it will cascade down the line as the system becomes progressively weaker. 1917's are notorious for bad scope mounts, as there is no "standard" for the mounts on one.
    "A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise, and independence to the mind."

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    Plus you can see in the photo of the mount, that the screws are "weaver" style with the bevel on the bottom of the head, while the mount is a redfield, which takes flat bottom fillister screws. That is a problem right there, with only a minor portion of the bottom of the screw head bearing against the base.
    "A strong body makes the mind strong. As to the species of exercises, I advise the gun. While this gives moderate exercise to the body, it gives boldness, enterprise, and independence to the mind."

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    Unfortunately it was the only scope that had rings on it that was not doing anything that particular day. It is a 30mm tubed Boone and Crockett model 4.5 x14 Leupold.
    This rifle would be more than happy with a 1.5 x5 Leupold, although the accuracy with the 270gr BTs and the velocity suggest it could easily be a 300 yard gun... Assuming I can keep a scope on it....

    Since the eye-ball doctor told me to stop shooting heavy recoiling rifles, I have no idea what I will do with this gal once she is all done...
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    I am not good with looking at screws and telling which number they are.
    I am measuring the broken ones right now. They are 0.132.5 to 0.135.5 of an inch or about 3.45 mm in diameter, I think that makes them a number 6 screw. Although the broken ones in front are 0.132.5 and the one in back is slightly larger. Plus somebody buggered up one of the screw holes in the front receiver ring at some time in the past.
    .
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    Andy-Please pardon my typo-you are right about 6-48 being standard. I do not think that I have ever seen a receiver with 4-40 screws used to mount any sight. I am currently working on a Remington 30S. The sight mounting screws for mounting an Iron sight on the receiver are 6-48 as are the sight mounting screw holes on Pre-war Model 70s. That being said, we can probably agree that 6-48 is usually the standard screw to mount sights on American rifle actions. That being said, a few years ago the folks from Safari Magazine did a very interesting three part test. They got hold of a Weatherby in .460 WM. They took the muzzle brake off and went about testing several different so called "Dangerous Game" scopes to see how they would hold up. They had several "volunteers" to do the shooting and allocated 80 rounds to the testing of each scope. The gun was topped with a Redfield one piece base. I don't recall exactly but it was during the testing of the first or second scope that the two front 6-48 screws ripped out of their holes and scope sat in a position where it was pointing at the top of the mountain. They then got a new mount and used 8-40 screws. The rest of the test went just fine. What they found was that several of the scopes that they tested were too heavy and momentum from their weight made them fail. I just wish that I had kept the article. I took that as good advice and my guns in .375 H&H and above now have 8-40 scope base screws. The last thing that you need is to be ready to fire the second shot at a Cape Buffalo and find that your scope is no longer firmly attached to your rifle. I am too old to see Iron sights without wearing My Knoblok's with a special iron sight lens.

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    Yes thatís a #6 screw. Definitely the lighter the scope the better but mounted well I think that scope will stay there if its what you want. The biggest trick is getting the mount to fit to the receiver well and getting your threads good and squire with the correct screws.
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    The important factor that many miss - esp. in D&Ted military guns - is having the bottom of the base tight against the top rear of the receiver ring. The rear of the cut-out on the base for the receiver ring will then take the recoil instead of the screws. It is worthwhile to add a bit of steel filled epoxy at that point to ensure positive contact and then your screws should never shear off regardless of size.

    With weaver style bases and many rails you don't have this advantage. If I recall the two piece Redfield style bases still have the shoulder - it is an important feature.

    Quote Originally Posted by ADfields View Post
    Yes thatís a #6 screw. Definitely the lighter the scope the better but mounted well I think that scope will stay there if its what you want. The biggest trick is getting the mount to fit to the receiver well and getting your threads good and squire with the correct screws.
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    The screw holes and threads are buggered now.. So bigger screws are in the near future. I inherited a few odd things when I obtained the action.
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    The screw holes appear to be somewhat to the rear of where they should be located.

    If you place the base in position and slide it as far forward as possible are the screw holes off-set to the rear? If the screw holes are correctly located the base should be in firm contact with the receiver to prevent the base from shifting forward and shearing off the screws.


    Quote Originally Posted by Float Pilot View Post
    The screw holes and threads are buggered now.. So bigger screws are in the near future. I inherited a few odd things when I obtained the action.
    Living the urban lifestyle so I can pay my way and for my family's needs, and support my country. And you?
    ".. ask not what your country can do for you, ask what you can do for your country" JFK

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    Quote Originally Posted by tvfinak View Post
    The important factor that many miss - esp. in D&Ted military guns - is having the bottom of the base tight against the top rear of the receiver ring. The rear of the cut-out on the base for the receiver ring will then take the recoil instead of the screws. It is worthwhile to add a bit of steel filled epoxy at that point to ensure positive contact and then your screws should never shear off regardless of size.
    Yup that is one of the ways to key it. Hard to tell whatís what in pictures to see exactly what it needs but there is always a way to spared the force out so they stay.
     
    But fixing eyes so they donít come apart isnít so easy. A good brake does help that a lot, amazing how well they tame recoil. Lots of guys hate them but a good one can take a 50bmg recoil from I ainít ever doing that again to about like a 30-06.
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    Here I flipped over the mount that was on there and photographed it next to the buggered up holes... No wonder I got such a good deal on the action.
    But I can see why they pushed the mount back further so the single back screw hole would not be close to the edge. This thing needs a little longer mount or a two piece.

    Yeap,,, two or three years back I shook my eyeballs blurry when working up 416 Taylor loads. Between 200 rounds of those and a bunch of hot 45-70 loads I managed to have a cheek that stayed bruised looking for a month...
    Reminds me of the time I dislocated some ribs while competing with a 50cal. M2HB machine gun. I did not feel it until a couple days later.
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    Another mount will still sit way back too unless you TIG up those holes, drill new ones and refinish it. I would build from what you have. Fix the holes then mill a key to fill in the bottom of that mount so it indexes to the back of the front ring and TIG it in place. You could do the same with a grinder and file using JB Weld fix it in place. Then bed the mount to the receiver top so it sits dead flat (I can see by the marks its not sitting well at all) and it will stay.
     
    I donít see anyplace for another screw but if itís sitting well 3 that mach the centers of the holes in the base should be fine. Which brings up another point, just running a drill bit down the boogered holes may mess up the spacing. Twist drills flow the hole down the middle, thatís great if the middle is where you want it but it may not be in a badly boogered hole.
     
    I plunge in with an end mill (they donít follow) in my milling machine where I can see the spacing on my readout to be sure the hole is well placed then drill for size and tap. If you want to do it you can do a good job with twist drills by super gluing and clamping the mount on overnight. Then drill through the mount holes (with your tap size drill) using them as a guide. Your spacing may not be exact but will be very close and well matched to both parts. Once they are all matched heat with a plumbers torch will pop the glue loose so you can tap the receiver.
     
    Drill the mount so the screws pass and countersink them. To get a flat bottom countersink drill with a pointed bit, stop when the small hole is to depth. Then make a bottoming bit by grinding the point flat, this will follow the sides you just drilled and flatten the bottom. Itís a lot of fiddly work without a mill but it can be done, drill press or making a tap jig are almost mandatory to start the tap straight though.
     
     
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    Ya know--IMHO if our poster was smart, he would take the whole gun and the mount et-al and mail it priority mail to Andy with instructions to "fix this mess" and be sure that it is properly bedded. That way it gets fixed properly and all the grief is gone. I assume that Andy has a TIG. If not, he can send the receiver to my buddy Dan Armstrong in Fairbanks (http://www.accu-tig.com/) He does fast work and he is considered one of the best in the world. I'm going to send the 30S to Dan to fix the 7 errant holes in it. I also need him to fix the bolt face as someone cut it out larger than standard, but smaller than a magnum, and this gun will now become a standard .270 win.
    Andy--When working on these type actions, have you ever considered milling off the recoil lug and installing an oversized Remington style lug. My thought that when doing a heavy recoiling conversion; you would not need to put an extra lug on the barrel.
    Just some thoughts---Craig

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    Speaking of the super small recoil lug on the bottom of a 1917 action....

    I initially tried a few loads in the Boyds laminated stock and the recoil was denting the laminated wood. So while bedding the barrel and action, I also installed a steel recoil lug for an old Vz24 stock that i had laying around. I filled in a huge channel under the barrel channel area with Micro-Spheres and then put regular Accu-glass bedding compound over the top of that.. So it helped cut the weight. This rifle weights 7.9 pounds without a scope.
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