Analyzing effectiveness of bracketing

In a recent FT match I've bracketed almost every brick, which was used to hold the targets down. It was big concrete block 8x16 inches.

I wrote down target number and amount of MOA I observed in the scope during the match for later analysis and accuracy review.

After the match I've obtained actual distance data from match director and compiled results spread sheet, which I'm happily sharing with you guys.

I've used Aztek Emerald scope set at 18x. It is calibrated to be true MOA at this marking. 

I'm pretty happy with the results and believe that this is pretty viable method for ranging.

Make sure you measure the brick. The brick size is just like lumber and is smaller than stated.

I did measure the brick, it was 1/8 of an inch short of 8 inches. I re-run the numbers with this actual brick size and error from this was negligible.

Couple things, as I've been using bracketing for years.

Verify that your scope, at 18x, is actually 18x. It's also quite simple to calculate the bracketing at other distances by multiplying by a factor of actual-mag / true-mil-dot-mag

I primarily use bracketing, but now with the 16x limitation in hunter I use the side-wheel as a 2nd opinion.

Not sure what happened on the 10 & 8 yard difference... possible that the brick on those lanes was different size? In my experience I find that bracketing is very accurate, typically within 2 yards, which was usually more accurate than my scope wheel. And it will be more accurate the larger the target.

Thank you for suggestions.

Scope has two calibration lines, like in the picture below, at 9x it is 2 MOA and at 18x it is 1 MOA. I did verify this, so no problems here.

This is the reticle of the scope I used.

Reasons for errors might be that I bracketed it on the wrong zoom, as I also was using side wheel to range and I might have forgotten to move it back to 18x from 25x, which was max zoom I used for ranging.

Other possible reason is that some block were tilted and I bracketed from far corner to lower.

I found side wheel does very good job and is quicker at closer distances.

Posted by: RochesterFieldTarget

Couple things, as I've been using bracketing for years.

Verify that your scope, at 18x, is actually 18x. It's also quite simple to calculate the bracketing at other distances by multiplying by a factor of actual-mag / true-mil-dot-mag

I primarily use bracketing, but now with the 16x limitation in hunter I use the side-wheel as a 2nd opinion.

...

Agree with you there.

Though these are the concrete block dimensions that I have always used:

Things to be aware of:

Standard blocks have a tolerance. Maybe +/- 1/8". That can cause a 3% variation in the reading. And you need to know what you are looking at, because there are blocks others than "standard" blocks. That will mess up any reading.

If the blocks are not square to the line of sight, it will also cause an over-distance reading.

There are plenty of pitfalls, but bracketing is still a viable method in many instances. Though with the new 16x rule, less so. Once I get over 24x scope magnification, I find that focus range finding is good enough to negate much of the benefits of bracketing. Though I will still use bracketing as a verification when I have high confidence in the objects dimensions.

I shot the Sonoran Grand Prix FT match this last weekend. I used a 24x scope that I had set up to rely mostly on focus range finding. I was pretty good out to almost 50 yards. I think you need maybe 32x for adequate ranging out to 55 yards. Though I prefer 24x as the max mag to actually shoot with.

This last weekend most blocks were partially hidden but I did use bracketing as verification in a few instances. The focus and bracket readings usually agreed within about 5%.  I mostly deferred to the focus range reading for this match.

Excellent info Gentlemen. Bracketing will work only as strong as you can hold steady on the reference point you are bracketing.  I have also used it off and on for a few years now.  Many obstacles of bracketing have been identified and I find that coordinating bracketing with your scope wheel  parallax while on a time clock can be a little nerve racking ?   Not to mention the time it takes to develop the correct mildots at each distance and chart them and count them correctly. I usually make things harder than they really are but its a pisser to work this hard to get a distance number you have confidence in and get off a good shot only to watch a stiff breeze turn all this perfection into a Zero! I'm leaning towards a nickle on metal. Might encourage new shooters to stay in the game longer and as far as I can see  wouldn't change the overall outcome of the winners circle.  

I think you hit the nail right on its head Bill, it takes time to bracket and it would be nerve wrecking on timer.

What I got out of this, is that I will do it for longer range shots, 45 to 55 yards. I can memorize 5 reference points and will save time by not looking up distance.

For shorter shots I will use paralax side wheel to range.

I recently got a 3D printer. It's very handy for making all types of little parts. I printed an extra wide sidewheel so that I could incorporate more data (target_distance/holdover_clicks/bracket_info). And then made an eyepiece attachment that holds lenses so that I don't need to use my reading glasses to read the wheel. The bracketing data is minimal but specific to a couple of dimensions that are very common at FT matches (signs/targets/cinder_blocks). My new strategy for this year is to use focus ranging as the primary, and verify it with stadia subtensions when convenient/possible. Avoiding the need to refer to a dope sheet in most instances. I used that strategy at the Sonoran Desert GP match. It worked well in most (not all) instances.

When we were shooting Hunter at 12x, bracketing provided more of an advantage. As magnifications increase, I use it less.

Very nicely done Scott, I really like your setup! How did you design and attached that nice wide tape? Does that piece with red line move up and down to adjust for temperature shifts?

I recessed the 3/4" wide tape area  .02" deep around the perimeter of the wheel to help center a 3/4" wide strip. I laid out the 3/4" wide tape in AutoCAD and laminated the print out using some packing tape. Then I taped it in place.

This gun does not have any significant POI temperature shift. The red line is a sharpie mark and does not move, though I could make it adjustable. If there were temp shifts related to focus range finding, I thought about having different colored lines to indicate different temperatures. But I'm not sure if temperature induced ranging shifts are occurring in this scope yet as I have not used it at enough matches to date. There does seem to be some ranging differences depending on brightness/sun location. I'm thinking that an eyecup or some kind of head shroud might help that.

A good thing about bracketing for range estimates, it is not affected by temperature.

Excellent setup Scott.  I think I have the brother to your cat.  I've always been a dog man but since I lost my german  shepard  last April My cat Benny is a lot of fun. He has a obsession with any kind of plastic. Best cat I have ever owned and never thought I would think so much of a feline.   Must be getting soft in my senior years.