Installing scope blocks

[TexasMac]

I recently finished drilling & tapping new block holes in a Browning BPCR & thought I'd share the following with you "shade tree" gunsmiths that don't have a lot of experience installing scope blocks, which includes myself.

Wayne

[TexasMac]

BTW, when tapping take it slow & easy with plenty of cutting oil. The last thing you want is to break off a tap in the hole. I was tapping the 2nd 6-48 hole when the tip of the tap broke off. Fortunately only about 2 threads broke off near the top & it came out relatively easy with some light taps from a sharp punch. Since it broke off so easily I figure it was already cracked from previous use.

Wayne

[TexasMac]

The previous illustration is accurate but this one may be a little clearer when following the drilling instructions.

Wayne

[Aviator]

Wayne, you have at least 2 typo errors.
The OD of a # 6 screw is .136, not 1.36
.860 divided by 2 is .43, not .48

[patchbox]

Hi Wayne,
Had a question concerning scope mounting blocks - I have a Meacham Highwall that I bought used - it came with scope blocks; however the center to center spacing is not quite 7.200”. How critical is this distance? I believe the center to center distance is roughly 7.150”. The only thing I can see that it would do is just create a slightly larger delta or angle change to the scope centerline compared to the bore centerline for a given elevation or windage adjustment.

I was thinking of getting some type of MVA scope to put on this thing. I have no experience with shooting scope on holy black rifles.

Thanks,
Eric

[patchbox]

When I trig out the difference at 100 yards it doesn’t seem to change all that much.

If rear scope block center point is 2.001” from bore centerline and front scope block center point is 2.000” from bore centerline and scope mount centers are at 7.200” the distance of the 2 points projected by centerline of the scope and centerline of bore is 1.501” at 100 yards. Changing scope centers to 7.150” changes this distance to 1.49750350” so a total delta difference of .0034965” at 100 yards. At 1000 yards the delta difference of the projected points is .034965”.

Does this look correct? If so it seems like center to center distance between scope blocks is not all the critical.

[patchbox]

So it looks like the 7.200” center distance was incorporated to give a approximate 1/2 minute angle change for every .001” of change on the rear scope block position.

[TexasMac]

Wayne, you have at least 2 typo errors.
The OD of a # 6 screw is .136, not 1.36
.860 divided by 2 is .43, not .48

Thanks Aviator.

I must have proof read it at least a dozen times & somehow missed those. Following is the corrected illustration.

Wayne

[patchbox]

Wayne,
I just read your article on considerations & math for external adjustable rifles scopes. That answers my previous question. Thanks for that article.

[TexasMac]

Found another significant typo. Here's the corrected illustration.