Curious because I'm mostly going to use M855 bulk but would prefer to zero my optic with 77gr because M855 groups worse than M193 - at least so far. I haven't tried the IMI M855 stuff yet.

I know further out it'll be significantly different but will my BDC (M855) be similar up to 350 yards?

You cannot reliably zero a gun for one ammo type with another.

Zero your gun with the ammo youre gonna shoot from it.  There is no other way.

I would say zero for the Mk262, and note where the M855 impacts.  I ran into this issue when zeroing for some Gold Dot 62gr soft point ammo.  With my carbines, its point of impact is about 2" higher than M193 at 100 yards.  With my 20" AR, it's 2" low and 2" left.   You just have to remember where your practice ammo will group.

This is poor advice.

You want good groups?  Shoot 77gr.

You want bulk training?  Shoot bulk stuff.

you want good groups and bulk training?  Have a gun for your 77s and a gun for your 55/62's

I don't disagree with you.

It's just easier to zero with 77 so I'm wondering if the POI is relatively close.



I think this is what will end up happening but was wondering if there's any data available to get an idea of what I can expect.

What he's telling you is that there is no way to know what the differences in the points of impacts will be from your barrel.

Many people seem to think that the difference in the points of impact between two different loads fired from a rifle with the same windage and elevation settings on the sight are due solely to the difference in the exterior ballistics (trajectory) of the two loads. This notion is false.  There isn’t a ballistic program on the planet that can predict these changes in the points of impact and trying to do so using the different muzzle velocities and different ballistic coefficients of the two different loads is a fool’s errand.  The only way to know what the difference in the point of impact between two different loads fired with the same sight settings, is to fire those loads from your rifle.

The difference in the points of impact between two different loads with the same sight settings on the rifle out to say 75-100 yards will be due in large part to matters of interior ballistics; barrel harmonics and recoil vectors for instance. These components may not be the same from rifle to rifle and are not predictable using ballistic software.

To illustrate the above points with a specific example, the exterior ballistic graph pictured below (calculated using Oehler’s Ballistic Explorer) shows that there should be nearly no discernable difference in the trajectories of the Sierra 55 grain BlitzKing and the Hornady 70 grain GMX out to 100 yards.




Here’s what happens in the real word when these two different loads are fired from the same rifle using the same sight settings.  When I fired the Hornady 70 grain GMX load from an AR-15 that had been zeroed for point of aim = point of impact at 100 yards with the 55 grain BlitzKings, the group of the 70 grain GMX impacted 2.9” LOW and 3.7” TO THE LEFT of the point of aim.

Just zero it with 77gr.
Then write down the adjustment to your M855 zero.
When you want to shoot your 77gr just dial it in.

Come on, we know that most people who ask this question probably never really shoot past 100 yards anyways....

Thanks for illustrating that. I think this will help people to clearly understand what you have stated numerous times.

Thank you Molon


Lmao

Mountains mullets and Merica actually had a very useful video for what I needed

Here is how you do it.

You take your gun and ammo to range.  You zero for a baseline ammo.  I use 55 ball at 200 yards and set that as my zero, personally.  You then mark a dot on your dial settings and housing with nail polish.  THAT is your guns zero.

Then you fire the other ammo at 50, 100, 200 yards, (or, just at 200 yards alone, if you are rushed) and note the impact offset.  Run a ballistic calculator and back out what the actual zero for that ammo is (that will give you that impact offset)  at the scope settings you left untouched.  

Once you get each rounds zero, run that through a ballistic calculator to get your drops and make your reference table.  Keep that with the gun.

Here is mine.  Note the blue row is the MY guns zero with MY ammo.   Yours may well be different, as your gun may flex different under recoil for a different point of impact.



In my case 55 ball zero at 200 is about a 100 yard zero with the heavies.  Yes, that took tikme to calculate and compile.  I'm an engineer, I like doing stuff like this.  I use Strelok, export to excel, and then us LOOKUP or INDEX function to pull the data over into a compiles tab (this one) for a summary table of my yards of interest.  Total computer and APP time is maybe 30 minutes or so (for the second gun, first one takes longer to figure all that out - once methodology is groved, can bang this out reasonably quick).

With this, you can show up at a gong range and be hitting steel at 600 yards with your first shot.

Thank you brotha

I don't think Strelok is available anymore on the apple store.

Yea, though you can get the APK if you look.  Though backdoor forcing a Russian App from an underground source onto your phone may or may not be a great idea.  Fortunately there are other apps that I'm sure export to Excel as well.

Also, to Molon's point when 62 M855 first came out. Thr point of impact shift to the AR15 of the time was PROFOUND.  Both in windage and elevation.

For whatever reason, it seems much less so today.  I suspect its a combination of short 16" BBLs of better metallurgical QC (more uniform steel = more uniform grain structure = more uniform "flexing" etc.) And typically are free floated now.  Haven't really studied it. But in general my POI horizontal shift in an AR15 from 55 to M855 is nothing like what it used to be.  Might just be me, I haven't really paid enough attention to make a real claim - just casual anecdotal really.  

OP:
Maybe I should re-watch that video but to be honest............ I found alot of flaws in it.

Be that as it may.....................
What others have said:

It's been my experience in shooting different ammunition against one another or trying to find a common zero that usually it doesn't work.
They all shoot slightly different, which of course, is magnified the further out you go, especially to 350yds.

50-75-maybe 100 yds on, say an IPSC target no............. send it.
But 200yds +................  there will be a difference.  How much?  Can't tell you......... you need to shoot it and see in your rifle, with your ammo.

As others have said........... shoot it and write the 2 zeros down.   Done.
Of course if you have 2 uppers you could zero one for each.  

Me personally.......... I have access to long ranges............ so I shoot and zero out to the distance I want.
In other words............ if you want to shoot out to 350............ then shoot out to 350 and get a confirmed zero.  

Seemed like up to 200 yards, he was getting very similar POI. It was at 300 where the big differences happened.

FPNI

my 55gr hornady SP handloads and 77gr SIERRA have different WINDAGE at 100yrds

there is no substitute for range time

I'm not going to go back/forth and critique his video................
Instead I'll say this, his video has nothing to do with what YOU might experience out of YOUR rifle and ammunition.  
I, nor he, can tell you that.  
You need to shoot your "stuff" to see what happens.  

Yes.........it's been my experience, and others, that the closer in, whatever differences there or (or not) the less of an issue it is.
The reverse of course is true.  

Here's an example of one test I did about this very question:

https://www.ar15.com/forums/AR-15/200yd-Groups-Velocities-of-Winchester-62OT-mk318-64-GD-and-others-/16-744061/?page=1&anc=bottom#bottom  

Look at the comparison of differing Point of Impacts between the Mk318 and the 62OTM.  
And BTW, the test was at 200yds.  

TLDR:
".....The mk318/ WIN 62 OT group:  Shot with the HBAR, It shows the typical groups I was getting with those two.  I shot that to see about comments that those two may have the same trajectory.  For me they don't.  Those two groups are about 4'" from each other

and total spread is about 10.7."  With those results, if you use 12" as a target, past 200, you'd really be struggling.  Now, 200 and in:  accept the different POI and you could!  (PS....The 2 groups were shot one after the other, same sight settings and sight picture)....."

blah.

Yes, it does.  
Nothing beats range time.......... and any excuse to shoot more is GREAT!  :)

I hear you.

The drop will be what I consider "close enough" out to 350 but their will be a POI shift at your zero distance and that difference will stack as distance increases.

So, for example, I have all three of my working set ups zeroed with AAC 77 gr. OTM. My 11.5 and 14.5 are zeroed at 50 yards, and my 16" is zeroed at 100 yards. After zeroing the 11.5 and 14.5, I sent a group with PMC Bronze 55 gr. FMJBT223A to note any shift. Both were a couple minutes low at 50 yards, with windage being within the adjustment increments of the optics. This is pretty typical, but sometimes you might also note a significant windage shift. It really just depends on how different the bullets are and how precise you are measuring. The 11.5 and 14.5 will both be shot mostly with the 55 gr. PMC, but thats because most of the targets will be either USPSA or PCSL targets at less than 50 yards. Anything significantly smaller or further than that on a stage and I'm loading up 77gr. AACs.

M855 is dumb. It has slightly better performance against barriers and significantly worse terminal and external performance compared to M193.

He mentions he re-zeroed for each load as well.  He is demonstrating the difference based on a 36 yard zero for each load.

Same sort of process as this image: