Fellas, I could use some help from those of you experienced with drilling and tapping receivers for scope mounts. This is a long one, so if you'll bear with me I'd appreciate it. I'm a student and I've been instructed on how to use a Forster Universal Sight Mounting Fixture. However, I've given a lot of thought to this methodology and I'm not confident I understand the best way to accomplish this. I'll admit up front I'm particular as hell. I'm not knocking what I've been taught but I also won't be satisfied until I'm sure I'm going about this the best way. I've also already used this fixture to install a one piece base on a Mauser that ended up cocked to one side. No biggie. That's part of the learning process I suppose, but I plan to get this figured out before I do another one.
Here's my first question. I've read through the instructions for the fixture carefully and here's one of the statements that jump out at me: "The V-blocks align the gun by the barrel. Even if the action is not exactly in line with the barrel, the fixture automatically corrects this error and drills the holes true with the barrel." This bothers me. It seems to me that this is not a correction at all, but is instead reinforcing a problem.
I've chambered a couple Mausers and I know the bores in those barrels were nowhere near concentric to the outer contour of the barrels. They were visibly off center and I understand this is fairly typical. So if I align the barrel in the V-blocks and the bore is off to the left or right, and my barrel shank is threaded concentric to the bore, then my receiver is going to be out of line with the barrel and my holes are going to be off center on the receiver. I'm pretty sure this is what caused the problem with the receiver I screwed up.
It seems to me this fixture has inherent design flaws based on the false premise that receiver holes should be lined up with the outer barrel contour. Am I off base here? I know everybody and their brother uses this fixture, but it's got to make sense to me before I'll go along with it.
So on to the next piece of the instructions that grabbed my attention: "If the desired holes are not on the center line of the barrel, the fixture still can be used to hold the gun squarely and steadily in the drill press. In this case, the over-arm is not used." This seems like it would be a better way to use the fixture - as a work holding fixture only, not for aligning your holes. At this point I feel like I'd be better off if I took the arm off and slung it out in the weeds.
The front receiver ring was ground with a surface grinder. I was thinking I should use an edge finder on the outside of the receiver to locate my first hole. Then maybe a center finder in the screw hole in the tang to make sure everything is lined up before drilling the rest of my holes. What do you guys think about that method? BUT........if I don't use the arm that leaves me with the problem of drilling my holes with no support bushing. I don't see why I can't do that. It seems like if I start my holes gently with a center drill I shouldn't have any problem with a drill walking or anything like that. But I know that's frowned upon. I'm wondering about your experiences with that too.
Then I realized I have another potential problem. If I align the holes on the receiver but the receiver threads happen to be out of square I'll end up with a receiver pointing one way, a barrel pointing the other way and potential zeroing issues. This could probably be eliminated by drilling the holes in line with the receiver threads before barreling, then timing the bore runout to 12 o'clock. Problem is I have to deal with actions that are already barreled.
Last but not least, I know I want everything to be as true as possible, but ultimately it has to look right too. Regardless of the methodology I use, if I end up with screw holes that appear off center or a base that is cocked to the side when positioned on the round receiver - I can't have that either.
So this is my long winded way of asking you guys how the hell you do it. How do you drill receivers? Have you run into these types of problems? What do you do about it?
Thanks in advance for your help.
Here's my first question. I've read through the instructions for the fixture carefully and here's one of the statements that jump out at me: "The V-blocks align the gun by the barrel. Even if the action is not exactly in line with the barrel, the fixture automatically corrects this error and drills the holes true with the barrel." This bothers me. It seems to me that this is not a correction at all, but is instead reinforcing a problem.
I've chambered a couple Mausers and I know the bores in those barrels were nowhere near concentric to the outer contour of the barrels. They were visibly off center and I understand this is fairly typical. So if I align the barrel in the V-blocks and the bore is off to the left or right, and my barrel shank is threaded concentric to the bore, then my receiver is going to be out of line with the barrel and my holes are going to be off center on the receiver. I'm pretty sure this is what caused the problem with the receiver I screwed up.
It seems to me this fixture has inherent design flaws based on the false premise that receiver holes should be lined up with the outer barrel contour. Am I off base here? I know everybody and their brother uses this fixture, but it's got to make sense to me before I'll go along with it.
So on to the next piece of the instructions that grabbed my attention: "If the desired holes are not on the center line of the barrel, the fixture still can be used to hold the gun squarely and steadily in the drill press. In this case, the over-arm is not used." This seems like it would be a better way to use the fixture - as a work holding fixture only, not for aligning your holes. At this point I feel like I'd be better off if I took the arm off and slung it out in the weeds.
The front receiver ring was ground with a surface grinder. I was thinking I should use an edge finder on the outside of the receiver to locate my first hole. Then maybe a center finder in the screw hole in the tang to make sure everything is lined up before drilling the rest of my holes. What do you guys think about that method? BUT........if I don't use the arm that leaves me with the problem of drilling my holes with no support bushing. I don't see why I can't do that. It seems like if I start my holes gently with a center drill I shouldn't have any problem with a drill walking or anything like that. But I know that's frowned upon. I'm wondering about your experiences with that too.
Then I realized I have another potential problem. If I align the holes on the receiver but the receiver threads happen to be out of square I'll end up with a receiver pointing one way, a barrel pointing the other way and potential zeroing issues. This could probably be eliminated by drilling the holes in line with the receiver threads before barreling, then timing the bore runout to 12 o'clock. Problem is I have to deal with actions that are already barreled.
Last but not least, I know I want everything to be as true as possible, but ultimately it has to look right too. Regardless of the methodology I use, if I end up with screw holes that appear off center or a base that is cocked to the side when positioned on the round receiver - I can't have that either.
So this is my long winded way of asking you guys how the hell you do it. How do you drill receivers? Have you run into these types of problems? What do you do about it?
Thanks in advance for your help.
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