Leupold BDC's and M3 scopes
( Kindly Consolidated for Sniper Country off the Duty Roster by "FatBoy" - Dec 31, 2002)
I'd like to start by saying that I'm no expert on Leupold products, ballistics or the manufacturing of BDC turret systems. The information that follows was gathered from over 980 posts in the past 43 months and about 20 months of shooting and competing using a M3LR/308win combo. All of the posts that I used to glean this wealth of information are available at any time in the Archives of the Duty Roster and some of the wording here is directly plagiarized from these posts. This was put together to consolidate some of the information, and to make it easier to access for someone just getting started with their M3 series of scope. Nothing that follows is written in stone or guaranteed to work exactly for you, there are too many variables to encompass every scenario. As all things worthwhile, it takes good information and some work to meet your objective, but a little range time and some practice is all you should need to benefit from the potential the M3's offer you as a tactical shooter.
What's a Leupold M3 BDC? The concept is simple, but the terminology is flawed. Leupold has taken it's Mk IV 10X scope and it's 30mm bodied, side parallax focusing, Vari-X III scopes and changed the turret internals to move the reticle 1 MOA elevation per click and 1/2 MOA windage adjustment per click. That's the meat and potatoes of these scopes. Leupold went a step further and added a hash mark above the standard 1 MOA markings to dictate where you're scope's elevation should be set to attain a hit in 100 yards/meter increments from 100 thru 1000 yards/meters with a given "spec'd" load. This system is often referred to as a BDC "Cam", but no camming actually ever happens. The scope tube isn't moved at all with this system. The erector cell is all that's moved, functioning exactly like a standard scopes erector/turret combination but with a courser adjustment. The M3's BDC turret caps are normal caps that have "hash marked" guidelines etched into them. They don't do anything special and really aren't more than a standard 1MOA cap re-marked to make elevation adjustments quicker. Also, there is also no "drop compensation" either. The scope isn't compensating for anything and in no way change the internal or external ballistics of the round. You could argue that it's moving the reticle to allow the shooter to alter the angle of the rifle to compensate for gravity and wind effect, but that's what all adjustable sights do.
So what's the problem? Well, there has been much discussion over Leupold's tactical line of M3 scopes not tracking as the manual says they should. Most of the problem stems from the literature that Leupold provides with the scopes and to several websites (Premier Reticle, SWFA to name a couple) who then re-post Leupold's data charts and tables. Some of the come-ups for these charts were derived from old ballistic information used for ammunition that is no longer made. Other turrets were set up for the military, to their specifications. The Military being as they are, didn't inform Leupold that the particular round they're testing has changed, nor did they mention when they went from meters to yards. So, is it Leupold fault these turrets don't track the external ballistics they advertise? Yes and no. Remember that these scopes were initially developed for the military, and the military said they are spot on so Leupold ran with them as is.
Why'd they run with an unproved product? From what I've gathered from the Archives, Leupold never wanted the M3 series of scope to get into civilian hands. It seems that one of Leupold's own, Mr. Carl Fetty, was fired over the whole ordeal so we are actually lucky to have the scope to be bitching over in the first place. What Leupold didn't know was that the Army had gotten a new round, now called the M118LR, to replace the older M118NM and M852NM. The Army said the scope BDC turrets tracked beautifully, so Leupold had no reason think any differently. They simply made the scope to the Army's spec, and when they had an overrun, they started selling to the public using the old ballistics tables from the previous generation of cartridges.
What follows is a brief summary of what these BDC turrets were actually designed to track. Conditions during testing are 59 Deg F. 29.53 in hg, 0' ASL and 70 deg ammo temp. Conditions most of us will never see.
308M Designed for the M118LR round or a 175SMK @ 2685fps. It tracks in meters.
30-06 Designed for a load that is no longer available (180SMK). It is an almost perfect match for the M118-LR load or a 175SMK @ 2685fps. It tracks in yards.
300WM Designed for the Navy's A-191 load. It also tracks Federals 300WM GMM load which is a 190SMK @ 2950fps. It tracks in yards.
.223 This turret will match most 55gr pointed boat tails at 3200fps. No more verified info available at this time.
NOTE: There is also a special order turret cap for the target load of 168SMK @ 2600fps (Fed GM, and Black Hills 168 load). It tracks in yards.
Recently, with the help of one of SC esteemed Patrons, Leupold has announced that there will be 6 new turret caps available to replace the old caps listed above. The new set for the M3LR will be marked differently, so they won't be confused with the old ones. The old style caps were marked "308" the new ones are marked "7.62"
"7.62 175gr" both meters and yards, @ 2685 fps
"7.62 168gr" both meters and yards, @ 2600 fps
"300WM 190gr" both meters and yards @ 2950 fps
These are the standard military (and civilian equivalent) loads. The caliber and bullet weight will be marked on the top of the turret cap as well as meters or yards, marked after the "x100"
The .223, and the 30-06 will be dropped from the lineup.
308M Designed for the target load of a 168SMK @ 2600fps (Fed GMM and Black Hills 168 Match) It tracks in yards.
M118 NATO looks cool (has a CDI factor of 8) but has the same markings/come-ups as the standard 308M turret cap. It tracks in yards.
30-06 Designed to shoot the M118-LR round or a 175SMK @ 2685fps. It tracks in yards.
300WM Designed for the Navy's A-191 load. It also tracks Federals 300WM GMM load which is a 190SMK @ 2950fps. It tracks in yards.
.223 This turret will match most 55gr pointed boat tails at 3200fps. No more verified info available at this time
NOTE: The top two turret cap (308M and 118 NATO) turrets track the 168SMK @ 2600fps in yards. The NATO turret cap says meters, but it isn't.
NOTE: There is NO turret cap for the Mk IV M3 that will track the 175SMK in meters correctly, YET.
A lot of people will say this is BS. The manual clearly states that the M3LR with the 308M turret tracks the 168 @ 2600fps and the M3LR and the Mk IV M3 show the bullet for the 300WM is the 220SMK @ 2650. The manual is wrong! There has been a lot of time and effort put into finding out exactly what these turrets markings track and why. One patron in particular has spent about two+ years on the phone with Leupold drilling them with the correct information, and two years after that getting them to product updated and corrected turret caps to end the confusion. He and others have spent countless hours on the range trying different rounds at different velocities to prove the information above. Follow Leupold's information if it makes you feel better, but you will NEVER get your turret markings to track correctly if you believe the M3 tables from Leupold. If you develop a load that matches the above stated specs, your turrets will get you there. Maybe not perfectly, but close enough that you can either compensate with hold over/under or change your come-up to match the rounds from YOUR rifle. That brings me to my next point.
Load development is key. You may be able to track with these BDC's with a factory round but YOU are going to have to go to the range and check the muzzle velocity of said round in YOUR rifle. There is no free lunch here. You may have the exact same rifle as your buddy, but get the two side by side at the range and his may shoot an identical load 150fps faster than yours. You don't know how a round will perform in your rifle until you actually check it. To further complicate things, if you use up your current supply of said rounds and have to buy a different lot, you get to start over again. That is where making your own rounds becomes a great advantage. You determined when YOUR lot is about to expire, not the local gun store or ammo supply outlet.
Using MOA instead of a marked come-up is probably the easiest and most effective way to work around the turret's BDC markings. You want to use Black Hills 175's or FedGMM2? Go to the range, shoot at hundred meter or yard increments and record your MOA setting when your POA and POI are where you feel comfortable. Then keep it in a log or on a chart on your stock or in your scope cap. Doesn't matter where you keep it. In you head would be best, but it really doesn't matter where so long as you know how your rifle shoots in the climate/condition you're in that given day with that given ammo. No BDC will ever give you that. Remember, these turrets were marked for conditions of 59 Deg F. 29.53 in hg, 0' ASL and 70 deg ammo temp. If you're in North Dakota shooting at Prairie Dogs or Florida trying to hit a paper plate, you're probably not going to see the conditions you zeroed the rifle in if you're from south Texas, so why lock yourself into one set of numbers for every situation. It's best to now how your rifle shoots in the situation your in RIGHT NOW. The only way of attaining that is knowing your MOA come up in relation to your POA/POI with the ammo you've tested and keeping good records to look back upon. LOG IT, LOG IT, LOG IT!!!!!!!
Another option to customize the turret is custom etched or remarked turrets. You can re-mark a turret you have by painting it, taping over it or re-etching it. You can buy turret tape like "Turret Tagz" or you can use a piece of masking tape. It's up to you. You can also buy custom-made turrets. Armament Technologies and Kenton Industries will make a turret to your exact ballistic profile, but again that is YOUR profile, which YOU will have to determine. If you change something in your load after you get your new turret, you're starting all over again. The weather changes 40 degrees? You guessed it, back to the range for new come ups.
Zeroing is another point where people get P.O.'d about the M3. Some cannot accept that their 100 yards zero is off by 1/2". That is the nature of the beast when it comes to 1MOA adjustment scopes. This 1/2" can be corrected by lapping .005" off the either the front or rear ring. (Front to move POI up, rear to move POI down) You can also use nail polish and create a "chemical shim" on the ring that will bring you POI to the desired height. It can be made to zero perfectly at a given day with given ammo. Change the temperature 20 degrees or change any variable with your ammo, you could be right back where you started. You could zero perfectly and the turret markings won't track out past 300 yards. That brings you right back to load development, re-marking or making a custom turret. So what's the point of having a M3 if you've have to do all this to make it work?
SPEED!!! Remember, these scopes were designed to hit a man at distance without the operator having to dial in 257 clicks to get the range dialed up. They were made to get him there quick 'cause you don't have time to be BS'n with your scope when you're target decides to appear and you've only got a moment to dope the conditions, ready the rifle/scope and make the shot. Do you want a good clean shot at 700 meters, of course. Will you take a meat hit 5" from your POA? That's up to you. It all comes down to the mission. If you want to shoot a golf ball at 700 meters and you have all day to adjust your scope, these scopes are probably not for you. I'm not saying the M3's aren't capable of precision shooting, but that was not the scopes intended purpose. If you try to make them into be something they're not you're going to come away from the range frustrated and thinking you've got a POS. Remember, mission dictates equipment, so get what YOU need to accomplish the mission.
I'd like to re-iterate, all the information above has been taken from posts, which are available in the Archives of the Duty Roster. I'd also like to recognize some of the shooters, which I have collected this information from. It is not an all-inclusive list, and I apologize for anyone that I have left out.
Mr. Bain, BrandX, Dan, Dennis (USMC Spud), Steve"NATO", TR, Kevin Mussack (Andy's Dad), Allen, Kevin of the GWN
And I'd like to extend a special thanks to the Masters and Patron's who have worked so hard at perfecting imperfect equipment.
Mike "UnDude" Miller, Scott "X-Ring" Powers, Sinister Dave (Master at large), Master Gooch, Master Rick and last but not least,,,,,,,
The Patron Saint of M3 BDC's… Patron 'Lito. Without the diligence and persistence of Patron 'Lito, most of the improved M3LR products, and subsequently this article, would not have been possible. Thank You.
Leupold Product Specialist
Ask for Mr. Garth Kendig
They offer white of florescent tape covers for the turrets
Premier Reticles, Ltd.
175 Commonwealth Ct.
Winchester, VA 22602
Phone: (540) 868-2044
Monday-Friday 10am-5pm (Eastern Time)
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