A target anomaly

A

Andy Cross

Guest
I was measuring some groups from my 243 win recently. Using the Neil Jones target measuring digital caliper I realized something was amiss. The group was measuring smaller than experience was telling me it looked like.

Although I should always measure a single bullet hole to find out what size hole that particular paper leaves behind I often dont. To my astonishment the single bullet hole measured .235" The etched circle on the pliexglass measures .243" I measured the bullets at .244 with a .0003 pressure ring at the bottom.

I have never found the difference between bullet diameter and the hole in the target to be as large as that before. The target paper was the standard type used at the range for registered matches. Is this error common ? and if so how do the target measuring people on the day accommoate it.
Andy
 
The second anomaly

Although there have been over 100 people visit this post and I have received this one response which didn't attempt to answer either query is yet another anomaly.
 
Andy its very normal for the hole to be smaller in the paper than the bullet.You have to judge the centre the reticule is a guide if the .224 gives you a better centre use it.
jim
 
Andy is there a black ring around the hole? Did you measure to the outside of the ring to see what that measurement was?
I have never used one of the gadgets as you describe so I cant offer any additional input.
 
I only officially score IBS Score targets, but the holes are always smaller than the bullet. 30BR holes clearly have a white ring around them when viewed through the scoring reticle; 6 PPC not quite as much, but still some. If you take a loaded round and push the bullet into one of the holes in the paper you will see it is a tight fit. The paper apparently closes back up a bit after the bullet goes through. The "new" paper IBS is using is the best we've had for years and resists tearing.
 
Vern said:
Andy is there a black ring around the hole? Did you measure to the outside of the ring to see what that measurement was?
I have never used one of the gadgets as you describe so I cant offer any additional input.
Click to expand...


From what I've been told the black ring is called the lead line even though it's actually caused by the jacket burning the paper these days. The lead line varies in width. However when measuring from the widest points the .244 projectile made a lead line measuring .235"
Never had one measure that small on that type of paper before. Which makes using the predetermined circles on the plexiglass tool useless unless you have a set of circles to use for each set of holes.

I know there are programs for scanning single bullet holes and groups and determining how many times one fits into the other. But it really makes me think just how accurate any group size is when measured with any sort of caliper, reticle, magnifer.
Andy.
 
???????, Does the barrel bore size have anything to do w/size hole bullets make in the paper? .236" & 237" bore dia.
 
Good question

The barrel on that rifle at the moment is a Shillen select match. I would think they make all the various calibre barrels to a tollerance so close from one batch to the next they would be scrapped if they didn't meet that. If the barrel is an influencing factor here then shooting some projectiles from the same box in a 6PPC with a madco on it should make a difference. I'll try some other BR targets left over from a few years ago to see if that has an effect also.
Andy.
 
The hole in the paper can vary in size and shape. We usually relate this to a function of the tune... a wobbling, unstable bullet will make a larger, non-round hole than a bullet that is perfectly "asleep".

The proper way to use the scoring caliper is to center the engraved ring around the bullet holes as you mark and move. Don't fudge it to the dark edges (lead lines). Remember, the device is directly measuring center-to-center, not edge-to-edge-minus-1-caliber. For well-tuned rifles that are making small holes, this results in groups with larger measurements than you would get if you use standard calipers and try to eyeball the edges.

This is one of the reasons why range-measured world records often don't hold up to the scoring committee. It is very difficult and somewhat subjective when trying to center the ring when measuring groups that are down in the zeros and low ones where all the bullets overlap. Often in those cases, you need to find a single reference bullet hole on the sighter and determine how how the hole should "center-up".

Rod
 
I really don't have a lot to add, except that for me, my 6mm bullet holes nearly always measure about .235 plus or minus a hair, so I have always considered the condition as normal and not an anomaly. I pulled out some targets from my last match and measured a couple of sighter holes at about .233. Measuring the actual groups at the widest point and subtracting the official measurement produced a variety of numbers from .207 up to about .240.
 
I can't remember what size holes my .22's and 6's produce, but I do know that no matter what paper, rifle, or bullet the hole in the target is always smaller than the bullet by a small amount which seems to vary some with the paper the target is printed on.
 
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