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Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative
Discussions related to Guns and Firearms
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slimjim
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PostPosted: Tue Dec 01, 2009 6:27 am    Post subject: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

While reading the Winter 2010 issue of AR Rifleman (pg. 107), I picked up a tip from Gary Cook. “What he’s found is that matching a bullet with a .500 BC (ballistic coefficient) with the right velocity he’s able to match closely the mil dots to ranges between 300 and 700 yards.” Gary suggests loading low-drag bullets (boat-tails) for a velocity that achieves the following bullet drop. This trajectory corresponds to each Mil-Dot at various distances, e.g., 3.6 inches per Mil per 100 yards.

Range _ Bullet
/yards _ Drop
100 __ 0" ____ Crosshairs
300 __ -10.8" _ 1st Mil-Dot
400 __ -28.8" _ 2nd Mil-Dot
500 __ -54.0" _ 3rd Mil-Dot
600 __ -86.4" _ 4th Mil-Dot
700 __ -126" __ Top of Post

I took this information and set-up a spread sheet to help tune my scope and existing loads to the mil-dots. My 2.5-16x has its mil-dot reticle referenced at 10x (1 mil = 3.6 inchs at 100 yards). Increase magnification and this measurement decreases. Decreases magnification and the number of inches increases between the mil-dots. If your variable power scope keeps the size of the reticle that same as you adjust the magnification, typical of US scopes, you don’t have to change the velocity of your loads to match the reticle. You can change your magnification to match your load’s trajectory. As examples, a .30-06 with 150 gr Nosler Ballistic Tips closely matches this strategy with impacts within 3 inches out to 700 yards with true mil-dot spacing. For my .270 Win, velocities go from 2875 fps with Berger 150 gr VLDs (.531 BC) up to 3450 fps with Barnes 120 gr Banded Solids (.438 BC). I found via the spreadsheet that I could tune my magnification for each load and the respective trajectories matched within 2 inches. Below are the magnifications I calculated for each load and shows the flexibility of the Mil-Dot Reticle. I tried to optimize for ranges from 300 to 600 yards.

Magnification _ Bullet ___ Muzzle Velocity
11.2x _ 150gr Berger VLD ___ 2875 fps
13.0x _ 130gr Barnes TSX ___ 3150 fps
14.2x _ 110gr Barnes TTSX__ 3375 fps
16.0x _ 120gr Barnes BS ____ 3450 fps

I did get to the range this weekend and re-zero'd tmy 110gr hunting load to 100 yards and then shot at 325 yards. Bullet impacts at 325 were where I expected. Now I need to get out to the 500 yard range and check them all. If it works good I'll write up and article. Here is the spreadsheet if anyone wants to give it a try.



mil dot tuning r0.zip
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Dimitri
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PostPosted: Tue Dec 01, 2009 4:02 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Yup that is one thing that is not often considered.

However we must remember that is only valid at the magnification the mil-dots were meant to work at.

IE my Accupoint's mil-dots are only valid at 9x not the full range of 3-9x. Some Leupolds are FFP which allows them to range the same no matter what magnification setting you set it at.

Dimitri

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slimjim
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PostPosted: Tue Dec 01, 2009 5:09 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Dimitri wrote:
my Accupoint's mil-dots are only valid at 9x not the full range of 3-9x.

I was lucky that my scope had mil-dots referenced to 10x and I could adjust their spacing with magnification. Note that all my trajectories are calculated to shoot flatter than the nominal/valid mil-dot reference (increased magnification reduced the bullet drop compensation).
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gelandangan
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PostPosted: Tue Dec 01, 2009 8:47 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

I am using somewhat a similar system for my rainbow trajectory Whisper.
My main problem is to estimate the range correctly to use the mildot drop compo system reliably.

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slimjim
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PostPosted: Tue Dec 01, 2009 9:52 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

gelandangan wrote:
My main problem is to estimate the range correctly

I believe a laser range finder is an essential and critcial part of long range shooting. I can not estimate range outside of 300 yards accurately enough to provide shot placement for an ethical kill. At the longer ranges, shot windows can be as short as +-10 yards. To satisfy this requirement, I'm getting a Leopuld RX-1000.
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slimjim
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PostPosted: Thu Mar 04, 2010 7:37 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alterna Reply with quote

Well, got my laser range finder, loaded up some ammo, and joined the TacPro Shooting Center in Mingus TX. They have a range where you can shoot out to 1000 yards. Up until now I had done most of my longer range work out to 250 or 325 depending on the range I went to. I was very confident in what my rifle, scope, and ammo could do. I had four loads under 1 MOA, three of them 0.5 MOA.

Since I joined, I’ve been out to TacPro twice and have enough I can report some of what I have experienced. Shooting out to 500 yards has brought a few surprises. But this the real thing and why you practice. My initial plan was to set-up a target at 500 yards with enough vertical height to shoot with my 100 yard zero and group points of impact (POI) up to 54 inches below the point of aim. All my work up to 325 yards and ballistic calculations showed I had paper to spare. First surprise - the 150 gr Berger VLDs with their slick 0.531 ballistic coeffiecnt (BC) fell significantly short of the paper. Och! Second surprise - the 120 gr Barnes Solid which was shooting consistent 0.5 MOA, fell apart with groups greater than 3.5 MOA. Wow, there went both my loads that I was expecting to shoot out to 1000 yards with. Here is what my set-up looked like today, the second time I went out. I shot this after I reverified I had the correct 100-yard zeros. I used 8-foot furring strips to make sure my target was elevated high enough above my 4-foot section of cardboard. You can also see my groups and how there was a significant separation in the POI.




Below are the actual groupings with their bullet drop in inches listed on the masking tape. Temp was 65F and wind was variable 6 to 10 mph coming from behind, sometimes off either shoulder. I didn't show the 110gr Barnes TTSX because I messed up the scope zero adjustment, twice, and didn't get a vaild grouping. With this many loads and all with a different zero, I was bound to mess one of them up. Loads left to right, top to bottom are:

130gr Barnes TSX BC .431, 56gr IMR4350, CCI Primer, Remington Brass, COAL 3.300"
130gr Hornady GMX BC .460, 55.5gr IMR4350, CCI Primers, Remington Brass, COAL 3.325
150gr Winchester XP3 BC .503 (commercial purchase)
150gr Berger VLD BC .531, 51gr IMR4350, FED Primers, Remington Brass, COAL 3.345



Vertical group size ranged from 0.7 MOA down to 0.25 MOA. Good loads to work this distance with. The 130gr Barnes TSX has turned out to be the most reliable performer in that it is consistently grouping under 1 MOA and was spot on compared to predicted performance with an estimated/derived muzzle velocity of 3150 fps. The 130gr Hornady GMX is a new bullet I got last weekend that interested me. It has shot very well though I was surprised how much slower the velocity was compared to the Barnes. It’s estimated/derived from its drop to be 2875 fps, almost 300 fps less and there is only a 0.5 grain of powder different. The 150gr Win XP3 is ammo I picked up when I bought this rifle a year ago. I shot my first group from the rifle at 150 yards and it was 1.5 inches. Because the ammo is so darn expensive, I have not used it since and was saving it for the day I go on a dream elk hunt. I’m impressed with its performance. Wish I could buy just the bullets over the counter but can’t find them. The 150 Berger VLDs dropped 60 inches. Did I say 60 inches, 50% more than the Barnes? My estimated muzzle velocity of 2800 fps is either way off or Berger’s claimed BC is overly optimistic. Probably a combo of both.

With the horizontal tape, I was able to adjust the scope’s magnification to have the 3rd mil-dot align with the appropriate tape mark. I then made an initial mark on the side of my scope for a reference. The setting to match the 3rd mil-dot to POI at 500 yards is Barnes, 12.5x; Hornady, 11x; Winchester, 9.5x; and Berger 9x. The true mil-dot reference is 10x. Until I learn more, I’m just using the small pen marks.



I always like to practice shooting at a near life-size deer target because I just don’t seem to group my bullets as well compared to shooting at a lined paper target. Both these deer are only 12" high at the chest. The first target is from my initial trip and was shot at 500 yards using the magnification-adjusted Mil-Dot reticle on the 3rd dot. The green dots are the 110gr Barnes TTSX and the magenta dot is the 130gr Barnes TSX. The green dot off to the right is my first shot where I read the wind incorrectly (my wind doping has got to improve if I’m going to shoot beyond 300 yards).


Tikka T3 Lite with Bushnell 6500 2.5-16x

This second target is from today. I found these at Cabela's Archery shop last weekend for $3 ea. I only had 150gr Berger VLDs left so shot one each from 300 yards, 400, and 500 yards with the scope adjusted to 9x. Want to guess, which one hit its mark? The shots at 300 and 400 yards are low and to the right. Why? Possible answers, I didn’t have as good a rest as on the other shots at 500 yards where I had my sand bags set-up. I had hiked 1500 yards up and down the range so my heart beat was noticeable. The wind was shifting. I also have to admit, I haven’t shot enough at the different ranges to figure out why the Berger’s aren’t performing as I expected.



Well, more work to do, more shooting, and practice, practice, practice. I can’t say this alternative use of a Mil-Dot reticle is working just yet. I’m going to concentrate on shooting just the Berger bullets for a while till I have them totally understood. I’m also going to check out the scope to ensure the accuracy of the mil-dots. It better be on in its spacing for the price I paid for it but I can’t leave anything assumed. Most important, this weekend I'm getting a chronograph! I’m going to need that to figure out what is really going on. I’ve been avoiding it mainly because my garage is full and I’m not sure where I would store it. However, after seeing pictures of Vince’s garage, I’m sure I will find a niche somewhere.
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Vince
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PostPosted: Thu Mar 04, 2010 8:11 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Slim wrote:
I’ve been avoid it mainly because my garage is full and I’m not sure where I would store it. However, after seeing pictures of Vince’s garage, I’m sure I will find a niche somewhere.

Yeah yeah...pick on Vince Laughing

There is always room for shooting / hunting bits and pieces mate...even if it means throwin' out the missus's good silver cutlery set. Hiding

I like what you are doing with your research mate...you have certainly put in the "hard yards"...no pun intended. I am pretty lucky in that none of my shots are ever likely to be more than 250m - 300m, and the zero on my rifle will keep me well within the kill zone on fallow deer. Be interesting to see what my loads shoot like out to 500m though...might just have to check it out one day.

Cheers, Vince

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44marty
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PostPosted: Thu Mar 04, 2010 8:25 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Definitely the chrono will help. I finally got one - and I found out this week that my 3000 fps loads (by the book) were actually going 2777 - and feel much better about my about using my mil-dot scope. Bullet drop is actually making some sense now.
That wind is a bitch, though. I mainly target shoot at home where I have a lane cut through the woods, and on a hillside very sheltered from the wind. That helps a lot in evaluating loads, but doesn't give me "real world" practice.

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Dawgdad
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PostPosted: Fri Mar 05, 2010 6:08 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Preaching to the choir - You have to shoot at distance to know how a specific load will behave in TRW...

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slimjim
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PostPosted: Sat Mar 06, 2010 4:35 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Got the chronograph today, now to find a good tripod. Then out for some more real world experience!!

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PostPosted: Sat Mar 06, 2010 6:30 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alterna Reply with quote

Jaw Drop

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slimjim
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PostPosted: Wed Mar 17, 2010 7:57 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Got back to the range today but was limited to 250 yards. I at least got to run the loads through the new chronograph and expand my understanding of what is happening with my trajectories. The Digital ProChrono from Competition Electronics worked beautifully with no confusion about what buttons to push to find the data I wanted. I shoot 100+ round through it with not an error.

Here were the average velocity for my loads.
_______________ Chrono __ Derived from bullet drop
Barnes 110 TTSX _ 3313 fps _ 3375 fps
Barnes 130 TSX __ 2994 fps _ 3150 fps
Hornady 130 GMX 2999 fps _ 2875 fps
Berger 150 VLD __ 2650 fps _ 2800 fps

My first conclusion is that trying to derive bullet velocity by sighting your rifle in at 100 yards and using bullet drop at a longer distance comes in a poor second to having an accurate chronograph. Deriving bullet velocity via bullet drop just isn't precise enough to predict how your loads will shoot at the longer ranges.

I also have pondered more why the 300 and 400 yards shots using the Berger 150 VLDs were so low. I did remembered that the rounds prior to these two were Winchester XP3s which have a dry lubricant. This could have resulted in a loss in velocity for those two shots. Also, with the new velocity numbers and resultant ballistic drop, the mil-dot settings could have been 1 to 3 inches low for 300 and 400 yards. So, I cleaned the barrel to ensure the dry lube was gone and, as stated before, I'm going to go reshoot at 100, 300, 400, and 500 plus check the accuracy of the Mil-Dot reticle. Give me another 30 days to report back on that.
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slimjim
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PostPosted: Wed Mar 17, 2010 8:19 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alternative Reply with quote

Using the new velocities from the chronograph, I've also concluded that the deviation from predicted POI may be caused by a 100 yard zero being off. Example, Barnes 130 TSX had 10 inches less drop at 500 yards than the Hornady GMX when they both have the same launch velocity and GMX has a higher BC. The Barnes may be sighted a tad high and the Hornady a tad low. One more aspect to double check.

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slimjim
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PostPosted: Fri Jun 11, 2010 3:25 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alterna Reply with quote

Well, I started this project in December and that last time I was at the range was the beginning of March. I'm not setting any records. True to form, last week when I couldn't go the wind was dead calm. Today blowing from 10 to 20 mph coming over the left shoulder but variable. Didn't matter, I needed to go to clear my head. I'm progressing but not total confident in my shooting beyond 300 yards. Last time I got some low impacts to my intended point of aim. It happened some more this time and I'm really no closer to understanding what is occurring.

I did check my zeros and made some adjustment. I only did 2 loads this time to reduce the number of scope adjustmest that could go wrong. Green dots are 110gr Barnes TTSX (3300 fps) and black dots are 150gr Berger VLDs (2650 fps). I did shoot and measure bullet drop at 300 (305), 400 (408), and 500 (507) yards (see image below). That helped build confidence and also highlighted a problem area to spend more time on.

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slimjim
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PostPosted: Fri Jun 11, 2010 3:35 pm    Post subject: Re: Bullet Drop Compensation w/ Mil-Dot Reticles: an Alterna Reply with quote

(I'm posting in sections instead of one complete post)

I adjusted the magnification, 15.5x for the 110gr and 9.2x for the 150gr and then went up and down the range and checked that the 1st mil-dot was on at 300, 2nd dot at 400, and 3rd dot at 500. I was very pleased how closely they matched so I started firing at the deer target.



The red dashes are 6-inches apart and the middle one was my intented point of impact while offsetting for the wind. I'd try to shoot during lulls but as you can see this did not work out.
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