Determining cross hair height above bore

[johanvb]

[killzone]

Very informative. It is basically what Marc explained. Thanks Guys and apologies for the Hi Jack @Maroelas

[Dick]

Measure bolt and ÷ 2, measure scope main tube and ÷2. Measure gap between bottom of scope tube and top of bolt, add results of above and you have height above bore.

Yes, exactly. Couldn't be simpler. But, as Adoons says, it makes no meaningful difference in terms of practical shooting. Where it DOES matter, as I found in fitting a lot of scopes, is in choosing rings of sufficient height that the objective bell clears the barrel. I fitted a lot of new scopes to replace old scopes. The old scopes were typically 4 x 32 which cleared the barrel comfortably with low rings. Many of the new scopes, particularly those with 50mm objectives, wouldn't clear the barrel and new (higher) rings had to be purchased in many cases. I have also seen a lot of guys buying rings that were too low. The correct height of rings can be determined in advance by measuring rifle and scope. One thing I noticed was that some modern objectives can be so big as to position the scopes so far above the rifle that a proper cheek weld is impossible. The only solution is to modify the stock. Finally, Marc05, you forgot one thing - it isn't easy to take those measurements without a caliper of some sort. In practical terms that means a vernier caliper. No handloader should be without one of those plus a 25mm micrometer. Vernier calipers, although not quite as precise as micrometers, are amazingly useful tools and not expensive.

[moose]

The best way to measure is to take the bolt out and feed a ram rod into the barrel , then measure from the top of the ramrod to the bottom of the back bell of the scope , next measure the bell of the scope.

to the first measurement add 1/2 of the measurement of the bell of the scope and you are to withing 1/2 calibre measurement to the correct bore to scope measurement.

eg if you measure 25 mm form the top of the ramrod to the bottom of the bell of the scope and the scope bell is 34 mm, then your correct height is 25 + 17 = 42mm

[Dick]

The best way to measure is to take the bolt out and feed a ram rod into the barrel , then measure from the top of the ramrod to the bottom of the back bell of the scope , next measure the bell of the scope.

to the first measurement add 1/2 of the measurement of the bell of the scope and you are to withing 1/2 calibre measurement to the correct bore to scope measurement.

eg if you measure 25 mm form the top of the ramrod to the bottom of the bell of the scope and the scope bell is 34 mm, then your correct height is 25 + 17 = 42mm

No, "within half calibre" is way too sloppy. Also, a cleaning rod poking out the back of the action is so flexible as to be wildly imprecise. Marc05's method is neater and more accurate.

[DLRX]

Yes, exactly. Couldn't be simpler. But, as Adoons says, it makes no meaningful difference in terms of practical shooting. Where it DOES matter, as I found in fitting a lot of scopes, is in choosing rings of sufficient height that the objective bell clears the barrel. I fitted a lot of new scopes to replace old scopes. The old scopes were typically 4 x 32 which cleared the barrel comfortably with low rings. Many of the new scopes, particularly those with 50mm objectives, wouldn't clear the barrel and new (higher) rings had to be purchased in many cases. I have also seen a lot of guys buying rings that were too low. The correct height of rings can be determined in advance by measuring rifle and scope. One thing I noticed was that some modern objectives can be so big as to position the scopes so far above the rifle that a proper cheek weld is impossible. The only solution is to modify the stock. Finally, Marc05, you forgot one thing - it isn't easy to take those measurements without a caliper of some sort. In practical terms that means a vernier caliper. No handloader should be without one of those plus a 25mm micrometer. Vernier calipers, although not quite as precise as micrometers, are amazingly useful tools and not expensive.

Not exactly true.
Virniers has a 1/20mm 0.05mm or 1/50 mm 0.02mm measurement accuracy.
A digital vernier has a 1/100mm accuracy.
Mics has a 1/100mm accuracy.
For all practical purposes a vernier is more that accurate enough and much more user friendly and easier to Zero than Mics

[Maroelas]

For the record I used Marc05's method and it worked very well. My guesstimate wasn't that far off.