H
Harry Fuller
Guest
On the USARBR website, in your "A barrel indexing test" article (very good) you indicate the barrel muzzle ID (presumably the bore/ lands) as 0.2157".
When measuring your groups you subtract 0.168" from the group OD diameter (outside edge to edge).
Am I correct in assuming 0.168" is the measurement you have found to be the average for the OD of individual clean holes that your .22 cal pellets (Exact RS?) made in the target paper which you used?
If I am correct IMO the inferred measuring method is an excellent one when ctc measurement is made in the field. It does require that a clean specific pellet's hole be measured in the particular card stock used. One bench rest rimfire club I occasionally attend uses the method and requires a sighter or clean hole for reference measure with a digital caliper which can then be zeroed to that hole's measurement. The OD of the group is then measured for score. I have found groups measured there to have results that correlate extremely well with later "On Target" measures I have made to check.
To contribute something here as an example: I find my .25 cal pellets make holes from 0.20" for Polymags down to 0.125" for JSB Kings depending upon the pellet used and target card stock. Yet with the same card stock some .177 pellets 8.4 gr Exacts may make 0.150" holes.
Further I have official SSAA card stock in which .22 cal Exacts make holes of just 0.10" and even less. ... This highlights the considerable error in ctc measurement that many shooters are making in measuring worst edge holes and then subtracting the nominal pellet calibre, say 0.22" or even 0.224". In my last example a 100 yards target shot with the .22 on that particular card stock may measure say worst edge to edge as 1.20". If .22" is subtracted it becomes a sub moa ctc group of 0.980". Correctly processed it would actually be 1.10".
I enjoyed both your barrel indexing articles and can personally relate to your results. ........... Best regards from Harry in OZ.
...
When measuring your groups you subtract 0.168" from the group OD diameter (outside edge to edge).
Am I correct in assuming 0.168" is the measurement you have found to be the average for the OD of individual clean holes that your .22 cal pellets (Exact RS?) made in the target paper which you used?
If I am correct IMO the inferred measuring method is an excellent one when ctc measurement is made in the field. It does require that a clean specific pellet's hole be measured in the particular card stock used. One bench rest rimfire club I occasionally attend uses the method and requires a sighter or clean hole for reference measure with a digital caliper which can then be zeroed to that hole's measurement. The OD of the group is then measured for score. I have found groups measured there to have results that correlate extremely well with later "On Target" measures I have made to check.
To contribute something here as an example: I find my .25 cal pellets make holes from 0.20" for Polymags down to 0.125" for JSB Kings depending upon the pellet used and target card stock. Yet with the same card stock some .177 pellets 8.4 gr Exacts may make 0.150" holes.
Further I have official SSAA card stock in which .22 cal Exacts make holes of just 0.10" and even less. ... This highlights the considerable error in ctc measurement that many shooters are making in measuring worst edge holes and then subtracting the nominal pellet calibre, say 0.22" or even 0.224". In my last example a 100 yards target shot with the .22 on that particular card stock may measure say worst edge to edge as 1.20". If .22" is subtracted it becomes a sub moa ctc group of 0.980". Correctly processed it would actually be 1.10".
I enjoyed both your barrel indexing articles and can personally relate to your results. ........... Best regards from Harry in OZ.
...
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