U.S. Optics SR-8c: Test 4 Results

This is an interesting test. This was another drill suggested by SLG (as was the previous one). The goal is to obtain 3 precise groups individual while keeping track of time. When you keep track of something, it generally takes on significance whether you mean for it to or not. I really didn’t intend to do anything with the elapsed times for this drill other than to look at and compare them, but after doing a few of these I think they say something.

What the drill comes down to is how easy is it to get a decent position behind the scope relative to its eyebox, and how easy is it to acquire and maintain a decent sight picture long enough to break the shot? Unlike the previous drill, which seems to be more of a test of me than of the scope, this test vividly illustrates the things I’m trying to get at with the test, many of which are common to the previous test, but under different circumstances.

Starting in a standing position with the scope on the desired setting (8x in this case), bipod deployed, round chambered, safety on, at the buzzer signal I dropped into bipod prone and fired 10 shots. Following the string of fire I recorded my times, reset the targets, and repeated the sequence for a total of three runs.

I fired one shot into ten bulls on some On Target TDS targets:

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IMG_5601
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Then I compiled each shot into a single 10 shot group using On Target TDS:

TgtGfx

I repeated the process two more times (I’ll skip the photos of the actual targets and just get to the compiled groups:

TgtGfx2
TgtGfx3

Then I could put all the groups together into one 30 round group:

TgtGfx2108

Here are the results in an easier to read format
Group      Extreme Spread (MOA),    Mean Radius (MOA)
1.                          2.6                                   0.915
2.                          2.5                                   0.715
3.                          2.8                                   0.92

Avg.                      2.63                                 0.851
Total                     3.1                                   0.914

One thing you should be paying attention to that probably doesn’t mean anything at all to you right now is the mean radius.  Notice in the total where the extreme spread is larger because of the outliers.  The extreme spread is more constant.  You actually don’t expect it to change much over the course of a large sample size.  The larger sample only increases the confidence in the number.  This number is the thing that will keep you from going nuts when you get a flier, which is guaranteed once in a while.  Dispersion happens.  Just accept it like I did.  Using mean radius will help.  Thanks to ballisipedia.com for the explanations, which start out as something I can comprehend and quickly go into the heavy math jungle where I’m not equipped to follow.

It’s a shame I couldn’t come up with anything better than XM193 to use for this test, as the results are less than impressive, even though I am using the fabled lot, #v 55 Z531, which I obtained from a Red Cell Navy Seal Operator at a gun show once (this stuff should shoot sub minute all day long [that’s my tribute to a post about dispersion that I read on AR15.com]).  Rest assured that I’ll be using the same lot, #v 55 Z531 for all the scopes.  Note that the rifle will actually shoot this ammo better when I’m not going for speed.

The convenient thing about this test is that the relatively large sample size of the group gives me high confidence to know where the rifle’s mean point of impact is to adjust for the next test. We’ll get to said test in the next exciting installment. Same bat time, same bat channel.

One thought on “U.S. Optics SR-8c: Test 4 Results

  1. Glad to see you’re doing all the heavy lifting (and not me!).
    Splendid job. I was actually going to shoot some rifle and handgun today (finally…) and got thunderstormed out. Well maybe next week…

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