I had a client in my store with an old 7mm Mauser with a Mauser action. The only marks on it were Fabrique d Armas he told me that 2 gunsmiths had refused to drill and tap for a scope mount because of possible occlusions in the receiver that could not be seen and the receiver would explode when shot. Is this something we should be concerned with? Also thanks to all of you at AGI for your videos and all of your help when I need it.
OK, I don’t know which Mauser model you have but it sounds like a small ring that cocks on closing. Many of these have a tendency to be a bit soft with their heat treat, so they develop headspace, especially with warm ammunition. First check all the safety concerns….. headspace, firing pin hole size, firing pin fit in the hole, firing pin protrusion, does the chamber look bad, does the bolt look OK, no cracks etc. Then if it appears safe I would fire the gun BEFORE you do any work. If everything works fine then go ahead and drill and tap it. Drilling and tapping won’t cause the gun to “blow up” but if done incorrectly can cause problems. If you drill into the barrel and go too deep you will be too close to the chamber and that is bad. Also you will want to be sure that the rear hole of the front scope base does NOT drill into the locking lug area. You will want it to be ahead of the locking lug of the receiver. You want to drill into the locking lug recess where the bolt lugs fit. If you drill into the locking lug support then it is weakened a bit and it can develop headspace faster but again the gun won’t “blow up” with standard ammo. If this is to be a complete rebuild / sporterize job just be sure to get the receiver and bolt reheat treated and you will be fine. Even if you decide not to reheat treat the bolt and receiver, be sure to test fire the gun after you have done all the work and keep that case for your records. Let us know what you find out and what you and your customer come up with. Ken
Reply:
Thanks for the information. Another question comes to mind. Are there any parameters for the minimum amount of threads that we should install for scope mounts that are tapped over the chamber? I do not remember this information being in any of the tapes. thanks again
Answer:
When I drill and tap a receiver over the chamber I simply go thru the receiver and that is all. That way I have not weakened the barrel at all. Then the rear screw will have as many threads as possible and still allow the bolt to close with clearance. A good rule for sights / scopes / etc. is that you must have 5 threads of the screw in metal to be as strong as the screw.
