Range Buddy Accuracy

[geezerhood]

I have read or watched every tutorial I can find on the Android Range Buddy app. I cannot get accurate measurements no matter what I do. Sometimes they are very close but often they are significantly over 1/10 of an inch too big or too small. Not a problem for a gun that shoots larger groups, but for me the difference between .3 and .4 is significant. Should I give up and stick with a dial caliper for accurate group measurements?

Here is how I measure a group.


Set the bullet diameter in settings
Before taking a photo of the group, align a 1" square grid on the target with the green grid on the screen
Set the spacing of the grid marks on the target using the "crossed pencils" button
Take the photo
Carefully center the cross hair on each bullet hole
Hit the yellow menu on the left bottom list to show the results.

Is there something I am missing or is +/- 0.10 the best I can hope for?

[Stumpkiller]

You're doing better than me. I couldn't even get the initial group calibrated.

5710

[J.Baker]

+/- 0.10" is probably about as good as it's going to get. Apps like this were never meant for measuring benchrest worthy groups and are better suited for the average Joe's loosy-goosy hunting rifle sized groups. Distance of the phone to the target will cause a variance in the calculated size, as will the phone being at any slight angle to the target when you snap the photo.

Stick with the calipers if you want dead nuts accuracy.

[CFJunkie]

I swear by the On Target Precision Calculator and have used it for 8 years.
I don't know if it has a mobile device app but it works on a lap top or desktop.
It is $11.99 but they used to have a more basic free version to try out.
https://ontargetshooting.com/ontarget-pc/

[CFJunkie]

Geezerhood,

Thinking about your problem, there is one thing that I found using group measurement tools.
The bullet size on the target often isn't the size of the caliber.
I find that for some lighter target papers, for non-wad cutter bullets, and for bullet speeds that are well below Pmax, the paper stretches around the bullet body and the resultant hole is smaller than the caliber diameter.
I print my own targets because I like to shoot at a white background with a small sighting point cross hair (keeps me from canting my scope) with a diamond on top of it where the rounds will hit so my aim point will not be destroyed. I use a high powered scope (30X t0 36X) when shooting targets to test loads and measure groups. The weight of paper makes a big difference in the final hole size. 20 lb. paper stretches a lot, but I have found that 80 lb. paper is much better.

For example, my .308 tipped or HPBT bullet holes measure closer to 0.277 than to 0.308, the 6.5mm bullet holes are closer to .243 than .264 and the .223 bullet holes are closer to .204 than .224.


Interestingly enough, the .22-250 bullet holes are just about at .224, probably because they are moving faster than the .223s.

My .22LRs are closer to .177 than .224, but they are moving half the speed of the .223s.

Center to center measurements shouldn't be impacted by caliber but you might try understating the caliber to see if that helps.

[geezerhood]

Thanks for the comments and suggestions. I was hoping it would be a bit more accurate than that. It certainly seems like it could be if the calibration of the size of the target was accurate, as well as the calculation of the spacing between centers. I measured the same group several times with a new photo and new calibration of the image, and got a variation of over 1/10 in both directions.

As for bullet hole vs bullet diameter, this app has you center a cross hair on the bullet hole, which if zoomed in can appear to be be very accurate, probably less than 0.05" error from the actual center. It doesn't seem to matter what bullet diameter you choose as long as the cross hair is centered on the hole. Of course a 50 cal bullet diameter cross hair is going to be more difficult to center on a .224 diameter hole, but if you get it right, the group size will be the same. The most critical step seems to be calibrating the image using a known distance before marking the holes. If that is off then the measurements will be also.

Stumpkiller - I am just guessing here, but possibly the problem with your testing of the app was that sherds of glass may have fallen off, enlarging the bullet hole diameter on the display. :o