Easy way to zero your rifle

[pilotguyo540]

There is plenty of front sight adjustment on a carbine length fsb to get a gnats ass zero @ 100 yards. The problem is that the front post looks bloody huge. Mid length and rifle length may be different as it takes more adjustment to get the same shift.

[ucrt]

Think again.

http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143

Quote:
Originally Posted by ucrt
===========================


Molon,
Thanks for the link.

It is hard to tell with the resolution in the 100-yard Zero Bullet Path Chart at the "IBZ Link" but does the bullet cross the los slightly and then come back down to 100-yard zero or is the bullet's maximum rise at 100-yards?

Kind of looks like it is at the los around 95-yards and just "hovers" there until about 115-yards.

Do you consider the "zero" to be the point at which the rifle crosses the los the second time? I guess with the above reference, you could say that "zero" is the last point the bullet crosses the los, this way you've got the second time and the only times covered??

Thanks.
Thanks

[Molon]

Quote:
Originally Posted by ucrt
===========================


Molon,
Thanks for the link.

It is hard to tell with the resolution in the 100-yard Zero Bullet Path Chart at the "IBZ Link" but does the bullet cross the los slightly and then come back down to 100-yard zero or is the bullet's maximum rise at 100-yards?

Kind of looks like it is at the los around 95-yards and just "hovers" there until about 115-yards.

Do you consider the "zero" to be the point at which the rifle crosses the los the second time? I guess with the above reference, you could say that "zero" is the last point the bullet crosses the los, this way you've got the second time and the only times covered??

Thanks.
Thanks

The 100 yard zero with a .223/5.56mm AR-15 carbine is a unique trajectory in that the bullet just “kisses” the line of sight at 100 yards and rides along it for approximately 10 yards before dropping back down below the line of sight. (Technically, the bullet does travel above the line of sight, but by only 0.010”; a fraction of the diameter of the bullet itself.)







For all other zeroing schemes, there are going to be two points were the bullet crosses the line of sight; the near-zero and the far-zero. For the near-zero, the bullet will cross the line of sight while traveling upwards towards the apogee or “maximum ordinate,” its highest point of travel. For the far-zero, the bullet will cross the line of sight while traveling downward from the maximum ordinate.

Now, when assigning a name to a particular zeroing scheme, it would be helpful if that name gave descriptive information about that particular zero; that is, the name should give us information about the trajectory and how it is unique and differs from other trajectories.

As a point of reference, the Santose Improved Battlesight Zero is often referred to as a 50/200 yard zero, however this is incorrect. It is actually a 50 yard/200 meter zeroing scheme; and this is only with a very few particular combinations of bullet weight, barrel length/muzzle velocity and height of sights above the bore. As an example, a 20” barreled AR-15 A2 firing 62 grain M855 will not match the 50 yard/200 meter IBZ. Neither will a 16" barreled RECCE firing 77 grain MK262, nor a 14.5” barreled M4 carbine firing the 70 grain 5.56mm Optimized "Brown Tip" load. The same concept applies when people refer to a 50/225 yard zero. Only a very few specific combinations of bullet weight, barrel length/muzzle velocity and height of sights above the bore will match that description.

What this is all leading up to is this; except for a very few specific combinations of bullet weight, barrel length/muzzle velocity and height of sights above the bore, a 50 yard zero is a different zero than a 200 yard zero. For a 200 yard zero, we know that this trajectory will produce a far-zero in which the bullet will cross the line of sight at 200 yards in its downward travel from the maximum ordinate. (It is physically impossible to produce a 200 yard near-zero with any of the commonly available loads and barrels lengths used in .223/5.56mm AR-15s.) Other than for a very few specific combinations of bullet weight, barrel length/muzzle velocity and height of sights above the bore, the near-zero of the 200 yard zero will not be at 50 yards.

Conversely, a 50 yard zero tells us that this trajectory will have a near-zero in which the bullet crosses the line of sight at a distance of 50 yards in its upward travel to the maximum ordinate. For those who think that a zeroing scheme must be named after its far-zero, it is physically impossible to produce a far-zero of 50 yards with any of the commonly used loads and barrel lengths in .223/5.56mm AR-15s. The 50 yard zero can only be the near-zero.

Other than for a very few specific combinations of bullet weight, barrel length/muzzle velocity and height of sights above the bore, the far-zero of the 50 yard zero will not be at 200 yards; and for all practical purposes it matters not one bit. Whether the bullet crosses the line of sight for the second time (far-zero) at 189 yards, 200 yards or 215 yards will not make the slightest bit of difference in the practical application of the AR-15 as a defensive weapon. In each case we will be holding the same POA (beyond CQB distances) and know that we will be hitting within approximately 2 inches above or below that POA out to 200 yards (or more depending upon barrel length and load.) You should have an idea what your actual far-zero is when using a 50 yard zero and confirm such at distance when possible, but again it’s most likely not going to be a 200 yard far-zero and again it does not need to be.





Some reference material. Except where noted, all barrel lengths are 20 inches



Courtesy of zrxc77





M855 25 yard zero





M855 25 meter zero





M855 36 yard vs 100 yard zero






M855 and M193 25 meter zero






M855 and M193 50 yard zero from 16” barrel





M193 25 meter, 50 yard and 100 yard zeros from 16" barrel






100 yard zero






25 meter vs 50 yard zero, M855 from 16” barrel






M855 300 meter zero






M855 200 meter vs 300 meter zeros





M855 36 yard vs 50 yard zeros

[nickdrak]

Well, Im pretty sure what Molon posted above is pretty much exactly what I was talking about earlier in the thread, just in more detail.

Thanks again Molon, for the excellent visual references!

[ucrt]

Molon...golly!...thanks!

Your reply (understatement calling it a "reply") was awesome. Thanks for taking the time to explain it so well and so thoroughly. I've been shooting hunting guns for 40+ years and have been trying to get a grasp on the various “AR theories” the past year. Your "dissertation" cleared up a lot. Thanks.

Now…for my assumptions. For a HD/SD AR, reading your reply, seeing the bullet paths, reading Pat Rogers AAR’s, replies, etc., it seems that a “near zero” of 50-yards is most practical. Most practical for several reasons: practical self defense range(as you state), ease of finding a 50-yard range to practice, ease for old eyes like mine in getting decent sight pictures & groups(confidence), good “point blank” range out to 200 yards or so, etc.

After a 50-yard “near zero”, one should verify bullet path at different yardages to “get to know” your rifle/ammo capabilities. I think for the average shooter, far zeroing at 200 yards introduces other variables that could “mess up” instead of tighten up the near zero, especially if adjustments are hastily made with low round count groups. These variables are wind, proper sight picture, old eyes, skill, triggers, etc.

Am I far off on my “assumptions”?

Thanks again.

.

[nickdrak]

I'm not an expert on this, but those that I think are would disagree with you. Your statement to me reads like "I don't agree with the idea that earth only has one moon".

Second crossing point is the zero, as it has been explained to me.

If all the shooter does is dial it in @ 50 yards and doesn't spend the time to go out to 200 yards to dial it in there, then the "Zero" is 50 yards. The "second crossing point" is just theory unless the shooter actually confirms & corrects @ 200 yards.

I also think you misunderstand Pat's methods and reasons. I've trained with him 4 times (I think, it might be 5) and have been through his "zero" process every time. Calling it a zero process is gracious as I think Pat would agree. He's getting people that show up to class all ****ed up to a point that they can be workable for the next three days and move on to other things.

The bolded part had me at a loss for the better part of the day trying to decipher what it was you were saying.

Unless you posted the above prior to my "clarification" edit on my earlier post, then it looks like we are on the same page in-regards to why Pat does what he does Re: "zeroing" during his classes.

[rob_s]

After a few classes with Pat I've learned to read between the lines with some things.

Walking the shooters through the "zero" process at 25 and then 50 yards tells an instructor a lot about the group of students he has in front of him. I wish I had the time to do it every time we had a drills night. The side effect is that you get people on paper as needed for the rest of his course. If a guy can't get a good near-zero (since that's the term we're going to work with) at 50 it tends to be the least of his problems over the remaining 2.5 days. "That Guy" shows up pretty early.

Randy's take of working shooters out to 200 and back over and over is more in line with a "rifleman" approach. This is also a large part of the reason Randy's class may be as little as half the overall round count as Pat's. FWIW Randy's class is the perfect pre-requisite for Pat's. Randy will really work your fundamentals ad over the course of the three days will overcome all those excuses of wind, sun in my eyes, my eyes suck, etc. to get you a good, hard, confirmed zero at 200. This way you can stand back and snicker at the ****ups before lunch on TD1 at Pat's class.

[Molon]

Am I far off on my “assumptions”?

It sounds like you’re getting it. Keep in mind too, that when using a 50-yard zero with the .223/5.56mm Ar-15 platform, regardless of the commonly used barrel length or load/ bullet-weight being used, they will all have nearly identical trajectories to 50 yards

[Molon]

Thanks again Molon, for the excellent visual references!

Da nada.

[uwe1]

It sounds like you’re getting it. Keep in mind too, that when using a 50-yard zero with the .223/5.56mm Ar-15 platform, regardless of the commonly used barrel length or load/ bullet-weight being used, they will all have nearly identical trajectories to 50 yards

Molon, do you happen to have the graphical data on where the second intersection takes place for the more popular .223/5.56 loads i.e. Hornady .223 TAP, 5.56 TAP, various Federal LE loads...etc...? Thanks.