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Scope base on 1903 barrel
riley p
Member Posts: 217 ✭✭
I'll be putting a scope base on a 1903 barrel to mount a Unertl type scope next week. Screws are 6-48 (I assume) I can figure out the drill size easy enough but am not sure how deep I should go. The barrel measures about 0.795" at the location for the base which gives me around 0.240" worth of "meat" to drill into before I strike aww-shucks.
Is there "convention" here? About 0.140" depth would give me about 5 threads and 0.100" to the rifling. Is that OK? What's right here?
Thanks,
Scott
Is there "convention" here? About 0.140" depth would give me about 5 threads and 0.100" to the rifling. Is that OK? What's right here?
Thanks,
Scott
Comments
The general rule is diameter at the point of the attachment minus the groove diameter then divide by 2. This yields 1/2 the wall thickness at that diameter.
I have used a taper tap then a bottom tap to make sure I get the greatest number of threads in a shallow hole. I always use a mill, finding top dead center first. I can't stress the importance of straight, true and top dead center.
Brownells has information such as this on their website along with many other formulas and helpful guidance.
Best.
Additional: The 7.2" spacing of the blocks makes for 1/4 minute adjustment per click. Putting the blocks closer together (this might be necessary due to scope tube length) will result in greater than 1/4" minute change of bullet impact per click.
Some old rifles with external adjustment target scopes will be found with the bolt handle ground for scope clearance. If the bolt does not clear the scope on your rifle I suggest you just buy a replacement bolt and grind or bend it. They are readily available and cheap.