I have a 10.5" .300 AAC Blackout upper/pistol/SBR. As of now it just has iron sights on it, but I picked up a SIG Sauer Romeo 7S for a good price and I'm going to mount on this upper.

I mostly use Burns 120gr. OTM load @ 2200fps. The iron sights were zeroed at 100 yards, but I'm looking for a good home defense/self defense, general purpose zero on the red dot.

So what says you?


ARman

I would co-witness it with the irons if possible. If good at 100 yds. It will be fine at 3 to 10 yds as well. At home defense ranges should be gtg I would imagine.

Your red dot should be zeroed at the same distance as you irons.

Your zero distance depends on your comfort level with hold overs/unders for distances other than your zero. With supersonic ammo, a 100 yard zero almost always means there are no hold unders -- only hold overs. For defensing purposes you should be comfy with your sights offset at closer distances.

This is a good time to bring up the value of becoming proficient using ballistic calculators.*

If you know or can determine the inputs, ballistics solvers’ calculation results can make it possible to pretty closely answer the question of where do we want our bullets to be with respect to the line of sight at different distances, and without guessing or depending upon others’ ideas and preferences. For example, and as fritz pointed out, with most loads a 100 yard zero means that the bullet will be below the line of sight at all distances (except 100 yards, obviously). On the other hand, many shooters of ARs who anticipate using them only at shorter distances zero at 50 yards because even though the bullet rises above the line of sight for some distances, the trajectory is still generally flatter at closer ranges.

Determining the actual trajectory of a load becomes even more important when it’s something unusual like yours. If we were referring to almost any load for a 16" AR chambered for 223/5.56, general guidance would be pretty close and good enough for most shooters. For you, though, do you want “good enough” or do you want more precise information at least to start without having to rely on extensive experimentation at the range?

A good online ballistics calculator is JBM.

https://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

* Although my advice is usually ignored, it can be valuable enough for those who don’t for me to keep making the effort.

One thing I’ll ask, though, is what ammunition are you really using? Is it Barnes, not “Burns”? If so, I’m curious about the velocity you cite. I was able to find only one reference to the 120 grain Barnes JHP load, and that said its velocity was 2100 fps. The barrel length wasn’t given, but I would bet a nickel that it was longer than your 10.5 inches. If so, determining your actual velocity would be important for any ballistics calculations. Having a chronograph, even an inexpensive one, is something else that is important for any serious shooter.

quote:

Originally posted by sigfreund:
This is a good time to bring up the value of becoming proficient using ballistic calculators.*

I didn't answer because I'm a complete novice but I'm in this camp.

Figure out the maximum point blank range for the ammo you're using. Figure out the yardage where your point of aim calculated from your bore equals point of impact and zero to that range.

I plan to use Shooterscalculator.com.

I have a question for you, sigfreund: How or where do you get the ballistic coefficient for the ammo you're using? I've looked at the packaging of some of my ammo and I searched the internet and came up with zero. Is there like a table for 9mm JHP, RN, 556, etc.?

quote:

Originally posted by Rey HRH:
I have a question for you, sigfreund: How or where do you get the ballistic coefficient for the ammo you're using? I've looked at the packaging of some of my ammo and I searched the internet and came up with zero. Is there like a table for 9mm JHP, RN, 556, etc.?

JBM ballistics is a web program which has drop down tables for bullet types. The program fills in the bullet BC for you. IMO JBM is a more complete program than Shooterscalculator.

Some of the companies that offer ballistic calculators have libraries of ballistic coefficients. If you go to the JBM link above and click on “library,” many different bullets are listed.
Applied Ballistics even has “custom” drag curves for countless bullets based on their own testing and which are claimed to be more accurate that the G1 or G7 values that are usually available.
If you can’t find a BC in a library, the manufacturer will usually have it listed.

For example, Barnes lists the BC of its .308 caliber 120 grain JHP bullet at 0.297 which is probably the G1 value. Some authorities and shooters will point out that very often manufacturers’ claims are exaggerated, and that’s why I like the Applied Ballistics custom values, but for short ranges some claimed BC inaccuracy isn’t too important.

I’m in the camp of, if you have irons on it the red dot should co-witness.

No sights just a red dot……100 yds

But know that if you pop one off at ten yards it’s going to be about an 1 1/2” lower than the dot.

I used to train people and I took several targets and shot the AR15 at 10, 20, 30, 40, 50, 60, 70, 80, 90 & 100 yds. I had a helper go down range and mark each round after it was fired. Then we all looked at how far off the round was from the point of aim. This was so that if an officer had to shoot closer than the 100 yds the carbine was sighted in he would know how far below the point of aim the round actually impacted.

You should do that too!

quote:

Originally posted by ARman:
I have a 10.5" .300 AAC Blackout upper/pistol/SBR. As of now it just has iron sights on it, but I picked up a SIG Sauer Romeo 7S for a good price and I'm going to mount on this upper.

I mostly use Burns 120gr. OTM load @ 2200fps. The iron sights were zeroed at 100 yards, but I'm looking for a good home defense/self defense, general purpose zero on the red dot.

So what says you?


ARman

If this is going to be a HD type rifle setup with red dot, you can’t go wrong with a 50 yard zero.

Make sure you know your hold overs/unders and you’ll be good to go.

https://youtu.be/jttB1kUXfJE


This is what I went with for the 2 AR rifles and the AR pistol.
The logic is sound to me and since I mainly use an EoTech, it made sense.

“What range would you zero at?”

The range I anticipate shooting things at the most.


(Not trying to be a jerk but isn’t that the right answer?)

quote:

Originally posted by cas:
“What range would you zero at?”

The range I anticipate shooting things at the most.

A better answer is to zero at the distance where the shooter can most effectively deal with the differences between POA and POI, for the expected range of distances to target.

I prefer a 50yrd zero on personal defense ARs with red dots.
100yrd zeros for the ones with scopes.
Of course you do have to shoot to prove the zeros vs just assuming your results will match an image. But mine have resulted in very nearly the same deviation.

Great graphic.

I too use the 50 yard zero. Recently, I shot 350 and held about a foot over the target (pepper popper). I scored 10/10 hits at that distance with that holdover.

Here is a good video explaining a 36 yard zero and a link below the video description to a printable target you can use at 25 yards.

https://www.vigilanceelite.com...e-blogs/36-yard-zero

OP is asking about 300 BLK, so those holds would be different, of course.

quote:

Originally posted by Oat_Action_Man:
OP is asking about 300 BLK, so those holds would be different, of course.

Winner, winner, chicken dinner. At least one understands 300blk isn't 223 Remy.

Assumptions used in the following estimates:
2200 fps MV, as stated by the OP. Seems a little fast to me, and 2100 fps is more likely, given the barrel length. This lower MV increases the drop at 300 yards by around 3 inches.
2,000 feet Density Altitude. I don't know where the OP lives.

POI for 50 yard zero
-1.0" at 25 yards
zero at 50 yards
+.5" at 75 yards
+.5" at 100 yards
-1.4" at 150 yards
-6.0" at 200 yards
-25.1" at 300 yards

POI for 100 yard zero
-1.1" at 25 yards
-.2" at 50 yards
+.2" at 75 yards
zero at 100 yards
-2.1" at 150 yards
-6.9" at 200 yards
-26.5" at 300 yards

As MikeinNC states, the POI/POA differences inside 100 yards are likely more important for a HD rifle.

quote:

Originally posted by Oat_Action_Man:
OP is asking about 300 BLK, so those holds would be different, of course.

Depending on the bullet weight they’re close to 7.62x39 but I’ve not looked to see if the company has something for 300blk.
Not really a vast difference with a 50yrd zero out to 150.
*chicken dinner*

quote:

Originally posted by cas:
The range I anticipate shooting things at the most. (Not trying to be a jerk but isn’t that the right answer?)

A lot of people anticipate shooting at HD distances; sometimes so much so that they say any further engagement would be irresposible and reckless. If you zero an AR at seven yards, you'll contend with quite high POI at intermediate ranges, obviously. So I would say, in that case, it is the wrong answer. But, if you believe in your close range only mindset, I guess it wouldn't matter. *I don't mean you specifically. I think the point blank range zero is logical, just so long as you know your close range holds. There are plenty of situations that may call for a precision shot inside 10y, and that couple inches will matter in a big way.