I have a M1A Scout with a Vortex 2-7 scout scope on it. What is the most practical 100 yard zero for this set up? The scope is not a turret style, so it is set it and forget it.

I am familiar with the various preferred AR-15 zero settings, but don't have the same knowledge about .308.

Thanks.

Adjusting the scope to hit a little over a half inch low at 25 yards with will give you a 100 yard zero. After the 25 yard sight in, confirm the zero at 100.

By “practical zero,” I assume you’re not referring to zeroing it at 100 yards, but what the point of impact should be at 100 yards—?


Do you have a particular purpose in mind for the rifle? I.e., hunting big game out to some maximum distance, long range self-defense, some sort of competition, etc.? The specific type of ammunition you plan to shoot would also be a factor to consider.

I have a fondness for the 50 yard zero on most general purpose rifles. Try it at 100 and 200 yards. Generally everything lands within a 5 inch circle or better, depending on gun and ammunition choices.

I'm a zero at 100 yard guy. Everything is at or below the impact at zero for a 5.56 and 7.62x51.

Of course, it will depend on the load, height above bore, and what not. But it works for me.

As a rule of thumb I zero my POI for PPC's i.e. 22LR, 9mm. 5.7 (subsonic 300AAC) ect. at 50yds.

223 300AAC & 7.62x39; at 100yds

And anything with a larger case capacity than that, like the 22-250, 308, 6.5 Creedmoor, 8mm Mauser at 200 or about 1.25" high at 100.

Anymore its rare when I get the chance to shoot further than 100-200 ... but a friend has some farm land I can stretch out to 500, but thats shooting over a field and creek ... so conditions aren't always optimal.

1-1/2" high at 100yds. Should be zeroed at 200yds. If that is what you are asking.

quote:

Originally posted by old rugged cross:
1-1/2" high at 100yds. Should be zeroed at 200yds. If that is what you are asking.

This right here. All my .30 pills, save the AE, are zeroed like this.

quote:

1-1/2" high at 100yds

Yep. Mine too. You'll be on target from 0-200 yds.

Thanks everyone. I was insufficiently clear, but those who suggested 1.5 high grasped what I was looking for. The gun is used for range shooting, pig hunting, and worst case defense. I am trying to get the best MPBR with a cross hair hold.

Thanks for the help. This is my first .308, and I really don't have much experience with the round.

A

A point of impact of +1.5" at 100 yards with the 308 Winchester cartridge will be good for many applications, but if “MPBR” stands for “maximum” point blank range, the process of determining that becomes more complicated, and must take several factors into account.

For hunting, the first factor is the size of the zone that we want to be sure the bullet will hit. I don’t know anything about feral hogs, but based on a little Internet search, let’s say that the vital zone we want to hit is 8 inches in diameter. That means the bullet can hit 4 inches up or down when aiming at the center of the zone, so what would be the MPBR for such a scenario?

As mentioned, the specific load makes a big difference as well. But because my ballistics calculator has the Federal 308 Winchester 168 grain Gold Medal Match load at 2600 fps in its saved files, I’ll use that as an example even though it isn’t a hunting load. The sight height of my M1A rifle is 1.8 inches, and I’ll also assume that’s close to what yours is.

With that sight height and load ballistics data and using a point of impact (POI) at 100 yards of +1.5", the bullet will drop about 4 inches below the line of sight at 238 yards, and it will rise a maximum of a tiny fraction of an inch over 1.5" just beyond 100 yards.

On the other hand, let’s say that we adjust the POI to 3 inches above the point of aim at 100 yards. The maximum the bullet will rise above the POI will be about 3.3 inches at 130 yards, and it won’t drop to 4" below POA until just beyond 275 yards. The max PBR for an 8 inch target will therefore be extended by about 40 yards if the 100 yard POI is changed from +1.5 inches to +3 inches.

But another complication to all this is the precision of the rifle. If it’s capable of consistent 1 minute of angle precision, at 275 yards the bullet could deviate from the point of aim by about 1.4 inch for that reason alone. If the bullet hits 1.4" below the POI in addition to the 4 inches based on the size of the target, then we’ll have a miss. To take that into account we should reduce the calculated size of our target. And of course, MPBR is a calculated value that doesn’t take into effect any change in our point of aim based on the distance to the target.

Just picking an approximate value for your zero will probably work fine for you for most situations, as it evidently does for most people. For maximum accuracy, though, it’s best to analyze the specific trajectory of the load we’re using.

Thank you, sigfreund, that is exactly the kind of discussion I am looking for. I have done a fair bit of internet research, and have played with the Hornady ballistic calculator online. The answers I came up with varied as you note, between 1.5" and 3" high at 100. 3" seems to be a bit much for the work I will do with the rifle. If I have the opportunity to hunt over an open field, I will be using a different rifle. Given the comments in here, and my research, I will likely go with 1 3/4" or so at 100 zero.

The rifle is proving to be very consistent, and appears capable of tight groups. I am the limiting factor. I have been practicing with .22 LR, .223, .243 and .308 in an attempt to get better at natural point of aim, trigger control and recoil management. It is a long road, and my eyesight isn't helping.

I truly appreciate the thought and analysis put into the answers here.

A

quote:

Originally posted by sigfreund:
<snip>
But another complication to all this is the precision of the rifle. If it’s capable of consistent 1 minute of angle precision, at 275 yards the bullet could deviate from the point of aim by about 1.4 inch for that reason alone.
<snip>

I'm glad you brought this up as its a "complication" that people often forget.
A 1 moa gun is is 1moa at ~100 but as you stretch that out to 200, 300 and beyond, groups are going to get exponentially larger.

The other thing was to have reasonable expectations ...
Don't expect 1 moa groups from a 2moa gun shooting 2moa ammo, just because it got a 1moa group once.

Zero it at 200yds. Aim center of mass out to 200+ yds and at 300 you are still holding on hair, just aim for top of the shoulder. 3-4 MOA drop at 300 depending on your load.