I bought an AR 9mm with a 7.5" barrel. I was reading up on zeros and saw a video from Sean Ryan where he was talking about the 36-yard zero that he uses. I printed his target and went to the range and zeroed it. It works like he states, it’s just a bit awkward when shooting a target at 7 to 10 yards because you basically use the lower dash of the reticle to aim for where you want the bullet to go. Though I imagine that to be similar even with a 25-yard zero. Even at 25 yards you have to aim an inch or two high. Now it could simply be me needing to practice with it a lot more as I’m sure that is part of it. Is there a more “optimal” zero to use? The AR9 will be my primary home defense tool and the longest shot I would need to take is 8 yards but I want the flexibility to hit between 25 yards and 50 yards just in-case or even just to have some fun at the range. Any suggestions are welcome. Thanks - J
VE’s YT video is talking about 5.56 (let’s forget about barrel length and suppressor for now)… I’m assuming typical 5.56 ammo.
With a 7.5" 9mm AR, the trajectory is going to be completely different at the same zero. I don’t know if you have access to a range with 50-100yard targets, or if your range will allow pistol carbines on the rifle range, but I might suggest figuring out what ammo and zero keeps your shots within the lower and upper ring within your preferred distances.
Just my opinion… if I were to use random trajectory charts on google (found someone on AR15.com who posted his results with a 9mm PCC, I would probably sight in at 10 yards… maybe 10-15 yds depending on the sight height.
Just noting that I edited my post for clarity.
Thanks for the insight Scotty. I read a lot of the conversation in that link too and there are others that think 10 yards as well. If for some reason I need to hit something at 25 yards it seems quite capable of making that shot. But then others in the thread are saying to zero at 50, so I don’t know.
Again, just my opinion…
When you get into firearms that have fixed sights high above the barrel you have to factor in trajectory. This means the bullet starts off below your point of aim (POA), gets closer to your POA, hits your POA, goes above your POA, comes back to your POA, then drops below your POA at longer distances.
For simplicity (disregarding the inherent accuracy of the firearm or ammo), sighting in a zero such that one’s bullet will shoot within a, let’s say, 2-3" circle within one’s defined distances means that a center hold will most likely hit whatever object they are aiming at within that distance. For precision shots, e.g. shooting a penny at 25+ yards, one can then learn the exact hold over or under to hit that tiny object. It’s up to you (or your trainer) to determine how large a hold over or under at a given range is acceptable. This is the overall basic concept in the Shawn Ryan video you mentioned… I think he mentions a CD sized circle, but again, he’s talking about 5.56 ammo and it’s related trajectory and expected engagement distances.
From the link’s charts and using the 2" circle I mentioned in the previous paragraph, I would estimate the 10 yard zero for a 9mm PCC would make it pretty easy to hit a 2-3" target while just aiming with the center of your dot, out to 100 yards… although real world results may vary (e.g. elevation, taller sights/scopes, wind, ammunition, etc.), hence why it’s important to test it out at your local range with your setup and ammo.
Edit: Looking at the link, the velocity used for the trajectory seems pretty low. You might track down a trajectory chart that more closely matches your ammo in your barrel length.
The grain of the bullet effects the trajectory . 90 grain JHP +P has a 1624 fps of velocity. 115 grain Federal JHP has a 1234 fps of velocity. Federal 124 grain hydro shock has a 1040 fps of velocity. These will give you different zeros because the trajectory is different.
For 9mm I would set the sights to zero at the longest distance a shot could present itself in my house and know that I’m pretty good for anything closer. Then I’d go out and figure out the drop at 30 and 50 and just estimate from there. Unless you are looking to do only precise head shots you’ll be close enough for HD.
With a 9mm w/ a 7.5" tube you are in lightly charted waters as most reloading data and velocities are for a 4" tube so you might expect some increased velocity and less muzzle flash depending on your boolit weight. As @Scotty noted above the boolit leaves the barrel at a slight UP angle and performs a ballistic arc based on weight, velocity and Ballistic Coefficient (BC). The effect you are trying to achieve with a non standard zero is to MAXIMIZE the range at which you would need to hold high at. The ballistic arc for a particular round will remain the same no matter where you make it cross your line of sight. I would submit that with a pistol cartridge in a 7.5" tube you will probably reach your ACCURACY maximum before you reach your distance maximum, by that I mean at 45 yards you may only be able to achieve a 6" group or it may be 75 yards or 25.
So if you want to have a cone of fire that is no bigger than 6" (roughly the size of the a fore mentioned CD and 1/2" the width of a mans chest) that means at a certain distance the boolit will hit 3" ABOVE the POA and at some point further down range the boolit will fall 3" below the POA. The rub will come in when the accuracy at distance falls off. If you have a ratty hole at each distance out to say 25 yards and then it gets to the point where you are throwing a 6" group you have reached accuracy max which may or may not be your distance max.
This is not for precision work this is a “Hold center mass and send it” sight picture and therefore at any “regular” range you will be low or high, don’t worry about the X ring, worry about little bitty groups.
Others have done a fantastic job on explaining the “why”.
Hopefully the link below works… Adjust the grain weight, velocity, etc for your chosen ammo. An AR height over bore is around 2.5". You may have to do a little math to figure out velocity as a 7.5" barrel isn’t super common. Then you can adjust the zero distance to see how much rise or drop you’ll get at a given distance. I think 20 or 25yards works pretty well, but it depends on your ammo velocity.
Once you’ve chosen a zero, make sure to test it at the range and make sure real life matches up with the theory.
Thanks for all of the great feedback gentlemen.
RE Ammo: When I first got my pistol I watched ballistics data on 9mm ammo and decided on the 124 grain HST standard pressure. There was also data using 9mm carbines and it looks like standard pressure 124 grain HST is still solid in terms of penetration and expansion. Using 147 might be a little better perhaps but 124 grain seems good and I don’t have to buy a variety of ammo between my pistols and carbine. Unless somebody has compelling data to consider something else, I will probably stick with the 124 grain HST.
RE Zero: There’s a lot to consider here and ultimately I need to practice with my defense ammo. I will get back to the range tomorrow hopefully and will probably re-zero but not sure if I’ll go with 10-yard or 25-yard at this point, there seems to be a lot of info to support either / or.
If you have the ammo … sight in at 25 and get zero’d then bring it back in what ever increments your range allows and see if you are hitting high or low outside of your parameters. Then try the same thing with a 10 yard zero or 15 yard. I don’t run much 9mm but IIRC with a Beretta (5" tube) I was point and shoot at 3, 7, 10 and 25 at 15 I had to hold LOW to stay in the X/10 ring of a B-24 which is like a 6" tall and 4" wide oval.
General guidance is to zero for the longest distance you expect to shoot at. If you want to hit at 25-50 yards, one approach is to zero for 50 yards and then shoot at 25 yards to determine your hold over (this should be about an inch, but your particular combination of barrel length, bullet weight and sight will vary that a bit).
PCCs are a hoot - have fun!