Sunday, March 3, 2019

More often than not

Recently I prepped a Winchester Model 70, Pre-64 receiver for a set of rings for a Schmidt and Bender 1" Summit. Due to the geometry and position of the original Winchester bolt handle and its relation to the bolt body you can always count on having to use Medium height or equivalent rings and bases to allow enough bolt handle clearance on any standard size ocular bell. The larger the ocular bell the higher you have to go in ring height for proper clearance.

I have a box of old factory rings and couple sets of mine that I have scrapped for what ever reason that I use to get the preliminary height established for the front ring. When the front ring is at a stage that it can be screwed to the barreled receiver I place the scope in a selected front ring, tighten down the top half and visually see how much room I have to work with in regard to the objective bell and barrel ahead of the receiver. At the same time you also check the bolt handles clearance with the ocular bell. At that point you can determine if you want to lower the front scope ring anymore, test again then carry on and start fitting the rear ring. All simple procedure. 

However some Pre-64 bolts have had a more than generous amount of material removed from the underside of the bolt guide pad. The pad was designed to help prevent the bolt from binding up during rapid manipulation of the bolt. This system worked out pretty well over the long haul but every now and then you run into a bolt that has a slightly under-size recoil lug in regard to thickness or height on the left side of the bolt and a slightly over-sized lug raceway, again on the left side of the action. This is a case of stacking tolerances working against you. So the bolt is clearing the lug race-way as you open the action but due to the "stacking slop" it over-rotating ever so slightly as you retract the bolt.

Echols where is all this going ?

I determined the ring height I wanted to use with this Summit and the bolt would clear everything but that damn rubber bumper at the extreme end of the rapid focus ring. Can anyone tell me why we need to have a rubber eye piece ? if the manufacture made scope with a minimum of 3-3/4" of eye relief we wouldn't require such nonsense anyway.

Now pay attention as there will be a quiz

To correct this situation you could make or install a higher set of rings. In this case at least .180 higher to allow that cheese ball rubber ring to properly clear the bolt handle. This might mean raising you head higher off the comb to get full field of view. Some would have cut the rubber ring off and some would have just allowed the bolt handle to be forced over the rubber duck.

Having seen this before, I determine the left race-way height with Gage blocks, yep .002 oversized towards the rear of the raceway. Then I measured the thickness of the left recoil lug, pretty close to nominal but tapered so its narrower at the outside edge of the lug, the very contact area that rides on left the rail. Call it this .0015 under nominal from the right side lug. With the bolt body placed in the mill vise between V-blocks I then indicated the underside of the left recoil lug so it was parallel with the mill table then ran the indicator back to the anti-bind pad and found that the pad has been grossly milled off in the bowels of New Haven during birth.

By inserting increasing larger Gage pins under the anti-bind pad and the top side of the left rail I determined that a .015 Gage pin would just allow the bolt to barely move under tension. By having the Gage pin, the bolt body and the scope in place at the same time I could see the bolt handle now clears the eye piece rubber ring with more than adequate space.

By adding height/material to the underside of the anti bind pad, which is closer to the center-line of the bolt body we decrease the amount of rotational arch on the bolt handle side at the contact postilion of the bolt handle and rubber ring. Simple geometry at its best. Now how to best to correct this ?

The first time I tried to correct this I had the AB-pad Tig welded, adding the required material and surface grinding it down to fit, this worked OK but took quite a bit of time and added expense. Depending on the guy doing the welding you could very likely warp the bolt in the middle then you'd have real problems. Today Laser welding it might be the way to go but you still have the down time and shipping expense.

Curt Crum once told me that he had used Nylon pins to correct this issue. The Nylon pins stand proud of the pad checking that added rotational arch. I tried and used that method a few times, substituting Nylon with Delrin and to my knowledge the "fix" on those bolts are still operational and working fine. Making of the pins took quite a bit of extra time as they need to be lathe turned to fit the drilled holes.

Finally I settled on 1/16" annealed O-1 round stock, drilled 3 holes on a .500 span allowing the holes to crowd the inside edge of the AB-pad flat with a Carbide two flute Micro drill bit. DO NOT try to use High Speed or Cobalt as you will work harden the surface and break the bit. Then you have more problems.

These 1/16th holes are cut .150 deep. My O-1 round stock that runs approx. .0625 is then slightly tapered with a diamond hone as its being spun in my lathe so the bottom .050 of the pin is .0615 or there abouts. The pins are left .250 in length a first. The tapered section of the pin should just enter the drilled hole. A very small drop of Loctite 380 Black Max is swabbed around the inside of the degreased 1/16" holes, then each pin is driven/slammed in place with a 8oz hammer and punch. These pins are now permanent.

Wait 24 hours for the 380 Black Max to completely set then return the bolt body to the mill vise between a set of V blocks, rotated the bolt until the lugs are level with the world and snug up the vise.
Then using a 3/16" carbide end mill lower the quill until you can just slip a .0015 feeler Gage between the bottom side flutes of the end mill and the original anti bind pad surface CLOSET TO THE BOLT BODY. Remember that factory induced slant on the pad.

Since a .015 Gage pin sipped under the pad would just allow the bolt to move from experience I know that I'll need to remove very close to half the thickness of the pin before its all said and done. But If you've never done this, easy does it Sherlock. Remove .003 of pin material, remove the bolt from the vise and slide it into the raceway. To tight ? it should be, remove .003 more and check it again. Run bolt in and out of the race way as one spot is bound to allow some restriction. Now also note the position of the bolt handle and knob, this why we're doing this exercise anyway. You should now have ample clearance between the top side of the bolt handle stem and your Ocular Rubber Nose Ring. The amount of gained clearance will surprise you.

Return the bolt body to the mill vise, set up one last time and remove another .001 to .002 of material from the top of the O1 pins, we're now at .007 to .008 of pin height. Remove the bolt again, knock off any burrs with a hard rock stick and some 320 grit W-D paper apply some light oil to the bolt and raceway and return the bolt to the receiver then manipulate the bolt as if you were in the field. The bolt should run smoothly.

Lastly and this is important, return the bolt to the mill vise, level the bolt, drop the end mill to the original surface of the ANTI-BIND PADS and carefully remove approx. .015 to .020 from the OUTSIDE EDGE of all three pins. The will insure the bolt stop will not come in contact with the pins when the action is completely reassembled and the bolt manipulated.

Now if we all lobbied Scope Manufactures to quit adding on all this extra crap they feel we must have on a scope we could mount a scope closer to the center-line of the bore and the comb like it use to be.

Rubber Ducks indeed.