Scope base on 1903 barrel
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
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I think after two full thread its bonus. I'd be a lot happier with a low temp silver soldered base. I saw a 45-70 contender barrel with more meat than .1 in the chamber stretch into the holes. 0 -
riley p,
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.0 -
Thanks guys. I'll try going 0.100" and see if that gets it done. That should give me 3 threads plus. I do use a mill on these projects and a center drill to do the starts. I'm not certain my front base will give me the height to center the cross hairs (within their range) on the scope so am reluctant to do the silver solder route. I can always add a shim or mill the base if the height is not correct. Even though it's my own gun I just hate doing this kind of work. High stress; worse still when it's someone else's gun I'm responsible for. 0 -
This is basic but will pass it on in case you don't already know. Springfield Armory put the rear scope block on the receiver ring and the other 7.2", center to center, forward of that on the barrel. From an old Lyman application chart I have found the following. Top of receiver to top of block is .225". From top of barrel to top of front block is .475. The chart shows the front block height as fitting both the 1903 and 1922M1 Springfields. The front block would not be a perfect fit on both as the 1922M1 has a slightly thicker barrel. I suppose the slight difference could be taken up by the elevation adjustment on the scope. FWIW
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.0 -
Herschel: THANK YOU!! That was my next quest (to figure out how far the "barrel base" was from the front of the receiver). Didn't know that or where to look to find out. It's my own gun and with that darn rear sight being waaaay out there in front of the receiver the thing is near useless to me as a competition gun of any sort. So, with the Leatherwood folks making those USMC 8x Unertl replica sniper scopes I thought I could press this back into service as a CMP vintage sniper match gun. Getting it "correct" is the task I'm working on. 0
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