The rifle in question is a otherwise unmodified Pre War Winchester 70 with very good blue left on the receiver. The bore is dark and pitted and was a coppermine to boot. I got this gun cheap because it was 'junk and don't shoot good'- two 6-48 holes were drilled off the centerline on the rear bridge and a chewed aluminum Weaver mount was crush fit- propped up on the edge of the clip slot groove. That's the background on this project. I have procured a nice '41 .30GOVT06 barrel now I need to take care of the holes...
How can I ensure the 8-40 drill bit won't wonder and just follow the off center holes left by the 6-48 tap?
How would you set up for this job? I'd rather not bugger it further. Your opinion is appreciated...
Posts: 360 | Location: PA | Registered: 29 September 2001
You will not be able to drill them. You will have to use a small endmill to correct the offset.
You will have to set it up in a milling machine.
Due to the hardness of the prewar action it will have to be colbalt or an carbide end mill of 9/64" dia , .140".
Then tapping the hole is yet to be done, buy the premium 2 flute taps from Brownells and use good tapping fluid. Aslo use a tapping guide and take it slow.
Those rear bridges are TOUGH, I normally will dull a tap when doing the two holes in the rear bridge.
Jim Wisner
Posts: 1473 | Location: Chehalis, Washington | Registered: 02 April 2003
Would it be possible to plug the mount and rebore or mill the holes offset to match the receiver?? At the worst you would be out a rear mount and not have a buggered reciever.I realise it would be better to center the holes on the action , but............
Posts: 48 | Location: Northern NY | Registered: 03 November 2003
If the holes in the rcvr are offset enough, I will plug the holes in the mount and then drill them to match the rcvr. Only do this if the client does not want the holes plugged in the action, usually for asthetics.
Posts: 5521 | Location: Minnesota | Registered: 10 July 2002
The proper way to do this, if there is such a beast, is to plug the holes and redrill/re-tap, preferably in a mill.
An improper, half-assed, but very workable way would be to purchase a scope base blank from Brownells and drill it to match the off center holes, if they are not too bad.
My first intention was to have the holes in the rear bridge welded up then recut properly.
Metalsmith Ross Billingsley recommended not welding the bridge because it would 'air harden' and be very tough to get good tapped holes. Since I know only the basics of welding and nothing of the Pre War Winchester metallurgy, I was swayed by his suggestion to mill for 8-40s.
I would still consider having the bridge welded if I thought this would work as well or better...
Posts: 360 | Location: PA | Registered: 29 September 2001
Jeff (Celt) Hicks at HD Rifles offers "8-40 Scope Base Conversion with base holes aligned to barrel centerline and scope mounted" for $65. Celt precision aligns to bore centerline six inches past the receiver. His work is the best I've seen for the conversion to 8-40 and it's the standard in the tactical rifle community.
I had a similar problem on a Pre-War M70. Someone had drilled the bridge off-center. I sent the gun to Mark Stratton to have him make custom bases for it using the existing holes. They are truly exquisite and not "half-assed" at all.
I'd like to know how Jeff Hicks determines bore centerline at 6 inches past the receiver? The bore rarely runs true the whole length of the barrel. The best he could do is match it to the centerline of the barrel.
quote:Originally posted by DeBee: Seems simple doesn't it?
The rifle in question is a otherwise unmodified Pre War Winchester 70 with very good blue left on the receiver. The bore is dark and pitted and was a coppermine to boot. I got this gun cheap because it was 'junk and don't shoot good'- two 6-48 holes were drilled off the centerline on the rear bridge and a chewed aluminum Weaver mount was crush fit- propped up on the edge of the clip slot groove. That's the background on this project. I have procured a nice '41 .30GOVT06 barrel now I need to take care of the holes...
How can I ensure the 8-40 drill bit won't wonder and just follow the off center holes left by the 6-48 tap?
How would you set up for this job? I'd rather not bugger it further. Your opinion is appreciated...
It's a nasty project alright. I'd locate a local EDM shop and have them burn the 6-48 holes out to the proper diameter for tapping 8-40 screw. At least this way you won't have to worry about the drill or mill toll drifting and EDM doen't care how hard the steel is.
Then again, one could purchase a new Weaver bridge base and re-cut the mounting holes on the base to match those on the receiver.
Posts: 938 | Location: Oregon | Registered: 23 November 2002
DeeBee , I'd agree w/ Mr. Billingsley . I have seen MIG welds crystallize hard steel and "pop" off , taking a small crater of the surronding area w/ them , and it is an awfully small weld to do with a MIG and get a neat job. Probably someone with a TIG system could do it , but still there is the hardening/crystallizing thing to consider.I think I'd stick w/ milling the receiver or making offset holes in the rear mount.
Posts: 48 | Location: Northern NY | Registered: 03 November 2003
Rear bridge only? depending on how far out of alignment they were, I would not necessarily rule out TIG welding the holes followed by a slow normalizing of the welded area.
The rear bridge area where the holes are to be placed, does not have to be of a particular hardness to perform that function. It is plenty easy to set up and protect the rest of the bridge and receiver from any possible heat damage that the TIG welding and normalizing might otherwise create.
quote:Originally posted by Zach: I'd like to know how Jeff Hicks determines bore centerline at 6 inches past the receiver? The bore rarely runs true the whole length of the barrel. The best he could do is match it to the centerline of the barrel.
You got a phone? Call him and ask. That's why I provided a link. How lazy are you anyway? Celt prefers to do the job after the face of the action has been trued.
Posts: 257 | Location: Radio Free Texas | Registered: 20 September 2001
Tig heats the entire bridge but would still work. I mig welded an eddystone P17. I think the welding was milder than the action itself.The sight birdbath had already been welded. If u use an offcenter base it'll bug you everytime you look at it.Mark
Posts: 109 | Location: Sask.Ca | Registered: 27 February 2001
Mount the new base if it is two piece .25 back or fwd and forget the old holes underneath. Far as making the custom base, why not should not be that hard just drill the new base with the front holes with a screw size drill and then line up your drill with the old holes in the back, mount the new base and drill it with a center drill for location, and then drill it with the proper clearance drill redrill the front holes in the base with the same.
Posts: 56 | Location: Howard City, Michigan | Registered: 04 November 2003
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