PDA

View Full Version : T&E Bobro 30mm Single Lever mount, RTZ testing



JGifford
29 March 2016, 18:20
https://scontent-dfw1-1.xx.fbcdn.net/hphotos-xfp1/t31.0-8/1269423_801129220061_8937045206002388379_o.jpg
The test ammunition is the 77gr 5.56 Black Hills TMK.

The test optic is a Kahles K16i. It weighs 17oz, per product literature.

The mount, and subject of this test is a custom mount that Andrew Bobro made for me. It is a 30mm with 0MOA bias, and the lever on the RIGHT side. The clamping springs used are the heaviest Bobro stocks. It weighs 7.5oz, and is the single-lever version.

The rifle is a Daniel Defense with a 16.1" Chrome Lined, Hammer forged, .gov profile barrel. It is freefloated. The suppressor is a Surefire 556-212, mounted on a 212a mount. The trigger is a Geissele Super-V. The rifle will be fired with the front of the rail braced over a sand-bag.

The protocol for this test will be tailored to display RTZ (or lack) of the Bobro mount. It is as follows:

- After zeroing, two targets with 1" grid will be placed at 100 yards from me, the shooter. I will fire a 10-shot group without removing the optic into the target on the left. I will "come off of the gun" after each shot. This is because it is necessary to do so to remove the mount efficiently in the second string of fire, and will prevent the disruption of cheek weld being a potential discriminatory factor in over-all group size, or POI shift.

I will then fire 10 shots into the target on the right, removing the mount from the rifle between each shot. The first shot will be fired after removal and replacing of the mount.

The two groups will then be measured for over-all size, and any POI shift of the group centers will be noted.

This will be a video review, and as such, you will be forced to watch the painfully slow process of this, or more likely, FFWD to the last few minutes of video.

*Video coming Tuesday*

Video won't happen. There were too many people at the range. Also, instead of using the 77gr TMK, I used 75gr Gold Dot. The TMK was grouping terribly (>2MOA).

The rest of the protocol was as described. Also, of note, I could see bullet holes clearly at 100 yards using the K16i. This agitated my spirit.

The largest single shift I could measure from the Bobro mount was 0.733 MOA. This was "high". It also negates to take into account that this is about a 1.5 MOA rifle/ammo combo, and I am typically a 0.5-0.75 MOA shooter on any given day, if using a bolt gun with quality ammo and optic off the bench. Statistically, I did not discern any POI shift that would concern me. Even if using our "largest extreme single measurement", we are off by roughly only 50% of the intrinsic accuracy of the platform. Put another way, at 1000 yards, you will "miss" by 7.33", at the absolute very worst, assuming perfect intrinsic accuracy of the system.

I do not think there is a 0.733 MOA shift in this system, if one were to use statistically significant data, which mine is not, because who's to say that 1 shot wasn't pulled 1/4-1/2"? I know when I really throw one (1 MOA+), but I can't call 1/4-1/2 MOA pulls. Also consider, the variance of total group size from the group without detachment vs. detachment each shot (including before the first was fired) varied by only 0.482 MOA.

Anyway, here is the raw data for your consideration. maybe someone with some software can upload the groups and give a "center" POI shift that appropriately weights the distribution of the 10 shots in each group:

http://i63.tinypic.com/351uwxf.jpg

*I would also note that I have been using my 1-4 NF in a Mil-Spec Unimount, torqued to 65 in-lb. I removed it for this test, and re-attached it afterward using a tq wrench. The RTZ confirmation showed no discernible shift. It still punched a tiny 3-shot group dead-on the bulls-eye. I did not care to perform a statistical analysis of it. It's "on", and that's fine.

cjd3
29 March 2016, 20:05
938
10 removals and reinstallations, very nice. One of the main reasons I bought my Brobro and dumped my QD Burris mount that shall not be named.

JGifford
29 March 2016, 20:38
938
10 removals and reinstallations, very nice. One of the main reasons I bought my Brobro and dumped my QD Burris mount that shall not be named.

Thanks! Looks like I am showing a 0.385 MOA shift, if I read right?

cjd3
29 March 2016, 20:47
Thanks! Looks like I am showing a 0.385 MOA shift, if I read right?
Right, but with 10 different external adjustments. I believe if you shot three 3-shot groups between removals, that number would be even lower.

JGifford
29 March 2016, 20:59
Right, but with 10 different external adjustments. I believe if you shot three 3-shot groups between removals, that number would be even lower.

I wanted an "abusive" test.

Jerry R
10 April 2016, 17:11
Nice write up, thanks.

SwissyJim
12 April 2016, 11:26
results look great, much like I found in some tests I did too. If I use a QD mount, it's a BoBro for me. I tested the Burris, and the results were the direct opposite - HORRIBLE.

cjd3
12 April 2016, 17:37
results look great, much like I found in some tests I did too. If I use a QD mount, it's a BoBro for me. I tested the Burris, and the results were the direct opposite - HORRIBLE.
It peppered the target, didn't it

BoilerUp
12 April 2016, 19:23
It peppered the target, didn't it

https://media.giphy.com/media/imJROsRKwBdeg/giphy.gif

SwissyJim
12 April 2016, 20:56
It peppered the target, didn't it


https://media.giphy.com/media/imJROsRKwBdeg/giphy.gif

I see what you did there... LOL