After some testing, I am saying bye to the 100 and the 50/200 yard zeros

Thanks, CK, some good ballistic work. If you have a scope with a mil-dot reticle, it can be used for accurate hold over at longer ranges. I use this on my .270 out to 600 yards with a 100 yards zero. The first mil-dot is 300 yards, 2nd 400 yards, 3rd 500, and 4th is 600 yards. The 6.8mm doesn't have the performance to match the mil-dots in the manner the .270 does. However, the 6.8 works nicely out to 400 yards with a mil-dot reticle using a scope's magnification that provides true milli-radians, typically 10x. To accomplish using a mil-dot reticle with a 6.8mm, sight your 6.8mm initially at 50 yards then adjust elevation at 300 yards to be on using the first mil-dot and/or the 2[SUP]nd[/SUP] mil-dot at 400 yards (boxed outlined). The trajectory tables to accomplish this are shown below with associated 2[SUP]nd[/SUP] zero range. All the loads are pretty much on within a fraction of an inch at 50 yards.

Here are some hunting bullets. Note, that the 90 GD worked best using a 200-yard zero because of its lower ballistic coefficient [BC] which doesn't allow it to match the 300/400 mil-dots. This link goes into more detail on the process.

http://68forums.com/forums/showthre...et-Performance&p=549063&viewfull=1#post549063

Thanks for the idea of putting the data into a chart. I edited the above post to put the data into a chart, although not as nice as yours...so here is an image of the comparison. I don't know how to make it full size though, so you need to click on it to view it.

rifter said:

Actually, if you do it right, you can hold in the center of the zone, and your shot will be within the zone whether up or down. That's the whole point of point blank range.

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As I understood it, with that method your POA (point of AIM) is always the center, but the POI (point of IMPACT) moves up and down within the kill zone. When the POI is at the top...should you shoot just an inch or two high, then you could be out of the kill zone...and vise versa for when the POI is at the bottom. As a result, you are fine with POA and POI are close...but when the deviation between them approaches the edge of the kill zone you don't have any room for a less than perfect steady shot.

rifter said:

You can also figure in a fudge factor by making the zone a bit smaller. For example, if the zone is 12", use a 10" diameter when figuring your max point blank range....That won't affect the range that much, but it gives you some error room if you are off a bit.

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Understood...the method is simple...and effective when a person is an excellent shot and also makes their shots in ideal situations with steady rests and such, but I think it limits range too much when things are not perfect. Using your example, adjusting the POA to keeps the POI in the center gives one a range of 6" of error (12 / 2 = 6). Using the mrd/mpbr method, even with a fudge factor of 2" (which must be divided by 2 to split each side of the target)...you end up with only 1" margin of error. As a result, the shooter's range with the mrd/mpbr method is now restricted to being able to keep the shot within just 1 inch. Not 1 MOA...but literally 1" at all distances that are close to the edge of the zone. At 260-300 yards, I cannot guarantee my shot will be within 1" (less than 1/2 MOA), especially when in the field hunting. Too many factors are going on...and animals move. As a result, the shooter's range is limited a good bit in comparison to adjusting your POA to keep your POI in the center.

Am I missing something?

The 150 yard zero seems to offer the benefits of the mrd/mpbr method for ranges less than 175 or even 200 yards...should one not adjust the POA...and only requires adjustment of POA out past 200. With the mrd/mpbr method and no adjustment to POA, you better be able to shoot about 1/2 MOA on your long shots and do so in uncontrolled conditions on moving game. I cannot do that.

Waterloo Kid said:

Just curious, how many folk use a range finder when hunting?

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I always carry one with me and use it frequently. If I'm in a new location, I use it as soon as I set-up to determine distances to trees, rocks, etc. so I know what the engagement ranges are ahead of time. Even at my stand, the ranges go from 160 to 330 and even out to 500 yards in 180 degrees. You need to know range precisely if you are going to take long range shots even with a .270 or .300 Win Mag. When hunting out West for elk or pronghorn, I have found it impossible to reliable estimate range because of varying terrain and vegetation, e.g., a mix of trees or shrubs of different heights or no shrubs at all. The closest shot I have had was this year and was 200 yards on an elk, all others have been 300 to 400 yards. The pronghorn I harvested this year was my longest hunting shot at 450 yards. The range finder is around my neck before I start in the morning and is relied upon in these types of hunting conditions. I have a mountain sheep hunt next month and the range finder will be a must-have for long range and up-hlll/down-hill shots.

All the OP has done is a mpbr chart, but backwards by putting the constraint on the zero distance rather than the rise/fall distance over line of sight. Mpbr picks a rise/fall constraint based on velocity and BC, then let's that determine the zero. OP has chosen a middle ground zero that give him an acceptable rise/fall over line of sight for his specific situation with multiple rifles.

Myself, I use 200M zeros (218 yards) but most here know that I don't shoot a typical 6.8 in typical scenarios. I also maintain logs for each rifle with different zeros for different loads, temperatures, altitudes, shooting positions (i.e. standing vs prone), along with the various associated drops for each variable or combination. If I decide to shoot my 6.8 in a standing match at 4500' ASL on a cold rainy day, but my previous zero is set for 600' ASL on a warm dry day in bright sun while shooting prone, I can dial in a cold bore shot 95% of the time. (Wind is the culprit the other 5%, lol)

Knowing and maintaining data for your rifle is very important if repeatability is something you value. I've shot high-master scores with no sighters because I trust my data. I verified my data. I've continuously logged my data. My D.O.P.E book is about the only thing as valuable as each rifle to me.


-Alexander

ATexan, I agree...and I understand the 200 yard zero, and I liked it better overall than the 100 zero for the reasons you mention. Since I don't get many really far shots (over 300) with the 6.8 or the .223/5.56 when hunting...and my kids definitely do not...I pulled the "zero" in a bit to work a little better than the 200 for these calibers and my usages.

Fast14riot, I also agree that what I did is very similar with the maximum point blank range concept with the "maximum" range pulled in and replaced with "average," which creates a similar effect but now improves accuracy for most shots yet requiring adjustments for the maximum range...basically modifying mpbr the concept four ways..

1) I no longer get to just "shoot" at further distances without compensation, which means I do need to remember to compensate when shooting 200-300 yards,
2) I don't mind that since the numbers I have to remember are very easy to remember,
3) kill two birds (calibers) with one stone (set of data), and
4) and I have now allowed for a larger margin of error in my shots (allowing for mistakes in shooting technique when firing, shooting without an ideal rest/brace, game moves, wind is present, etc) since these changes put POA and POI closer together throughout 25-400 yards as long as one uses the hold over amounts provided from 200-400.

Chimera Kennels said:

As I understood it, with that method your POA (point of AIM) is always the center, but the POI (point of IMPACT) moves up and down within the kill zone. When the POI is at the top...should you shoot just an inch or two high, then you could be out of the kill zone...and vise versa for when the POI is at the bottom. As a result, you are fine with POA and POI are close...but when the deviation between them approaches the edge of the kill zone you don't have any room for a less than perfect steady shot.

Understood...the method is simple...and effective when a person is an excellent shot and also makes their shots in ideal situations with steady rests and such, but I think it limits range too much when things are not perfect. Using your example, adjusting the POA to keeps the POI in the center gives one a range of 6" of error (12 / 2 = 6). Using the mrd/mpbr method, even with a fudge factor of 2" (which must be divided by 2 to split each side of the target)...you end up with only 1" margin of error. As a result, the shooter's range with the mrd/mpbr method is now restricted to being able to keep the shot within just 1 inch. Not 1 MOA...but literally 1" at all distances that are close to the edge of the zone. At 260-300 yards, I cannot guarantee my shot will be within 1" (less than 1/2 MOA), especially when in the field hunting. Too many factors are going on...and animals move. As a result, the shooter's range is limited a good bit in comparison to adjusting your POA to keep your POI in the center.

Am I missing something?

The 150 yard zero seems to offer the benefits of the mrd/mpbr method for ranges less than 175 or even 200 yards...should one not adjust the POA...and only requires adjustment of POA out past 200. With the mrd/mpbr method and no adjustment to POA, you better be able to shoot about 1/2 MOA on your long shots and do so in uncontrolled conditions on moving game. I cannot do that.

Click to expand...

MPBR is a method that is designed to use the ballistics of the cartridge to determine max range. One, muzzle velocity and bullet weight establish the base line. Two, ballistic coefficient determines the trajectory. Three, those combine to determine how much energy is available at every step along the flight path of the bullet. If it takes 800 ft-lb to kill a deer then the point you fall below that amount is max range part. The second part is what the trajectory determines. If the kill zone is 12", then the bullet has to travel no more than 6" above or below the line of sight. That may shorten the max range figure depending on the caliber, or it may extend the range beyond the energy point. If the rise and fall gives you a max range of 500 yds, for example, but the energy requirement stops at 350 yds, then your max point blank range is 350 yds. That's the theory.

In practice, if you know your rifle and load, you can adjust on the fly to some extent. MOA is a function of the mechanical ability of the rifle to group well. It has little effect on hunting because you're not shooting groups. Every shot you take is an independent event, and as long as the rifle is reasonably accurate (doesn't string shots vertically or horizontally, or generate random fliers) your skill is the determining factor. MPBR allows you to just aim and shoot. You still have to be able to figure range reasonably accurately, and you still have to have proper trigger discipline. Regardless of what sighting method you use, your skill is the determining factor.

I'm old fashioned enough that I don't believe in extreme long range hunting, as seems to be the trend today. Thus, I'm not a big fan of the magnum rifles that have enough energy to drop an elk at 1000 yds, etc. Max point blank range 99.9% of the time gives you more than enough range capacity and quite often provides more range capacity than many people should be shooting at. I shot metallic silhouette for many years, and shooting offhand at 500 meters is a lot tougher than people think it is. Even though I got pretty good at it, I would never try to shoot at live game at those distances when you add in adrenaline rush, huffing and puffing after running to get into position, wind factors, etc.

Bottom line is, MPBR allows you to take maximum advantage of what the cartridge you are using is capable of for the game being hunted.

rifter said:

...If the kill zone is 12", then the bullet has to travel no more than 6" above or below the line of sight...

...your skill is the determining factor. MPBR allows you to just aim and shoot...

...I'm old fashioned enough that I don't believe in extreme long range hunting, as seems to be the trend today.

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I broke your quote into three parts.

1) I agree with that. My problem is I know that when I am at that upper or lower limit that puts my bullet on the edge...even with a "fudge factor" built in...is that I cannot guarantee pin point accuracy. That is why I like to adjust to have my POI closer to the center of the kill zone...so when I screw up in the woods where things are not static...I still have a comfortable margin of error. With the 150 zero, all the way out to 175 yards, I am within an 1" of the center of the kill zone without any adjustment, which leaves me a considerably large margin of error within those ranges...and remembersing 2" for 200, 1/2 foot for 250, 1 foot for 300, 21" for 350, and 31" for 400...leave me only having to remember five easy to remember numbers to keep me in the center of the kill zone all the way out to 400.

2) I agree that we should limit our range to our skill too. I get more range by adjusting to keep my POI in the center than I would with the mpbr method.

3) I agree with that as well...I don't know where all those long range snipers exist. I have a shooting range in my own front yard that stretches out to near 200 yards, and I have yet to see any hunter put their bullets in a group that is as tight as they say they do. It seems as if they remember their best groups, but forget their average shooting skills...and then in the woods...where we have unknown factors...wind, distance, movement, etc...things get worse. Generally, I don't shoot over 300, but if things are perfect I could reach out to 400. I however would let most shots over 300 walk by...unless I have a great rest, have a good estimate of distance from previous knowledge, and the wind is calm.

steeltiger said:

Can one of you smart folks recommend a zero distance for me? Longest shot on my place is 230 yards and I'm trying to find the best zero for 0-230 where I don't have to do anything other than put the crosshairs on the chest and pull the trigger. I did the 50/200 with 120 SST and am just wondering if that is still the best method.

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The 200 yard zero works pretty well for that. Depending on your scope height and actual velocity from your barrel (length), you will probably be around 2.2-2.4" high from 100-140...and about 2.2-2.4 low at 230 yards. If you are okay with being 2.2-2.4" off in what may be your most common range, then that is fine. If you are shooting at deer and point at the heart, you will always get the heart or lungs with the 200 zero when you take shots that are below 200 yards...and then aim at the lungs when you are at 230, which you said was your max range...and all is good.

Here is the ballistic chart for the Hornady SST, which has a factory fps reported at 2450 and a BC of 0.400. I assumed your scope was at 2.55" over your bore axis...which is standard sight/scope height for an AR...but if you are running a different mount then these may not be the right values. Even if everything is right...double check it on the range to see if it works for you.

200 yard zero...

The 50 yard zero doesn't match the 200 zero for the 6.8 with that set up though.
Here is the 50 yard zero...

Again though, I like the 150 yard zero as it is less than an 1" off all the way from 30 yards to 170 yards...and then just requires you to remember 3" at 200 and 6" at 240...which will keep you in the center of the kill zone.

150 yard zero...