Zeroing a 9mm PCC, Strange Ballistics.

[Chomps]

Not sure this is the right sub forum,.. but it does involve marksmanship and gun handling so,… 🤷 😁

PCC ZERO ISSUE

So I’ve gone and zeroed my PCC Using my carry ammo of Federal HST 147 grain hollow points with my Holosun AEMS red dot at 15 yards.

With my 10” FM9 zero’d @ 15 yards, Im putting bullets thru the same holes. 😎. I’m literally using 1 inch pasters to cover up 3, 4 & 5 bullet holes at a pop!

As I understand the charts,.. I should be shooting low inside of 15 yards. Which appears to be the case. At 10, 7, and 5 yards I’m shooting anywhere from 1” to 2.5”-3” inches low. Accurate, but low. And That’s roughly where the online calculators I used say I should be hitting with the 9 mm, 147 grain HST load.

The issue I’m having is according to the ballistic calculators & charts, (… Which admittedly I am still trying to understand & figure out.) I should be shooting a little high at 25 and 50 yards,… And then it should come back down to zero out again right around 85 yards.

That’s not what’s happening! At 50 yards I’m shooting inches high and POI is moving to the R. At 85 yards. I am shooting even higher and still shifting right. At 100 yards,.. Its still going even Higher & further Right by several more inches. Plus,.. the groups are opening up significantly.

Even if I’ve read the charts wrong,… At 100 yards with a 9 mm load it should be dropping, no? Not continuing to track up.

While I am using a red dot without magnification and with my astigmatism, it blooms badly from time to time. I am wearing my distance rx. And Once I get out past 25 yards I turn the brightness way down to eliminate the worst of any blooming. Even so, shooting at 75, 85, or 100 yards,.. the dot does cover a pretty Significant portion of an 8 inch target. So it’s possible my aim is off. Still,.. I would expect most, if not all of my hits to be dropping not consistently going high & right.

I am at a loss to understand why my hits continue to move up and to the right the further from my zero distance I aim. 🤷*♂️.

Any one have any insights as to what might be causing this?? BTW,.. This issue seems to be present and consistent with my various 124gr. FMJ practice ammo as well.

Here are the images from the range Session:

[BN]

First, you aren't really zeroed at 15 yards. You're already high and right. To be centered at 15 you would need to shoot out the red mark.

I think I zeroed my Ruger 9mm carbine at 50 yards. edit: I found my data. Yes I'm zeroed at 50 yards. 25 yards will be almost the same impact point as 50 yards. The bullet will come slightly above the line of sight from 25 to 50 yards and then begin falling below. You can see how my hits began falling below the line of sight. Sighted at 50 yards, You will need to hold over at distances closer than 25 yards. Go back and zero at 50 yards and see what happens. Good luck.


I shot my Ruger PCC at 25, 50, 100 and 140 yards.

The chicken is at 50 yards, the small popper is 100 and the full size popper is 140 yards. I was holding center of the round part of the poppers.

[WobblyPossum]

First, you aren't really zeroed at 15 yards. You're already high and right. To be centered at 15 you would need to shoot out the red mark.

This is my guess as well. If your POA is the red dot in the center of the target at 15y, your POI looks about an inch to the right and half an inch or so high. Small inaccuracies with your zero at close ranges magnify proportionally as you increase the distance to the target. Make sure you get a solid zero at your chosen distance (15y in your case) before you start checking POI at farther ranges.

[BN]

I put data in my calculator as if you were sighted in at 15 yards and yep, you would be hitting way high as you went out in distance.

[Chomps]

I put data in my calculator as if you were sighted in at 15 yards and yep, you would be hitting way high as you went out in distance.

Yeah,.. and as I mentioned, the charts I saw said the same and I expected to see that @ 25 and 50 yds. What doesn’t make any sense to me is that the rounds keep hitting higher and higher @ 85 & 100 yds. At 100 I should be holding High to compensate for bullet drop. Not shooting low to hit 6”-8” or more high. Right? But that’s not what Im seeing & I find that confusing. Im already more than a little lost in this regard. But this seems counter to what would be expected.

I absolutely accept that the problem could be me start to finish,… But I’m still at a loss to explain why it’s happening this way. Why my rounds are landing where they land when I’m aiming where I am based on what you would expect from a ballistic trajectory.

[JCN]

Yeah,.. and as I mentioned, the charts I saw said the same and I expected to see that @ 25 and 50 yds. What doesn’t make any sense to me is that the rounds keep hitting higher and higher @ 85 & 100 yds. At 100 I should be holding High to compensate for bullet drop. Not shooting low to hit 6”-8” or more high. Right? But that’s not what Im seeing & I find that confusing. Im already more than a little lost in this regard. But this seems counter to what would be expected.

I absolutely accept that the problem could be me start to finish,… But I’m still at a loss to explain why it’s happening this way. Why my rounds are landing where they land when I’m aiming where I am based on what you would expect from a ballistic trajectory.

Does your ballistics calculator have a place to input height over bore? If it’s a pistol calculator then it might have a default 1.5” set.

For a long gun or similar cheek weld thing, height over bore can be 2-3” which changes the intersection quite a bit at distance.

Looks like in your second picture you have a 3” offset and a 25 yard zero. Why not do that?

15 yard zeros on long guns always wind up crazy high.

I like a 25 yard zero for PCC minimum. Like others said you were way off at 15 yards anyway, you just didn’t notice.

[JCN]

This is like a 10 yard zero. And it’s way right.

That’s why I don’t like close zeros. If you’re not careful you can miss that you’re way off the actual red mark where you should be centered or under.

Generally people tug down which means if you get any rounds higher that’s probably where the gun wants to shoot….

[TGS]

Yeah,.. and as I mentioned, the charts I saw said the same and I expected to see that @ 25 and 50 yds. What doesn’t make any sense to me is that the rounds keep hitting higher and higher @ 85 & 100 yds. At 100 I should be holding High to compensate for bullet drop. Not shooting low to hit 6”-8” or more high. Right? But that’s not what Im seeing & I find that confusing. Im already more than a little lost in this regard. But this seems counter to what would be expected.

I absolutely accept that the problem could be me start to finish,… But I’m still at a loss to explain why it’s happening this way. Why my rounds are landing where they land when I’m aiming where I am based on what you would expect from a ballistic trajectory.

I would expect what you're describing based on your picture of your 15 yard zero. You say you're zeroed at 15, but as others have pointed out...you're not. You're hitting several inches high, which is going to throw things off in a pretty dramatic fashion considering you're trying to zero at such an extremely close range.

You have a pretty extreme delta between the bore and point of aim. You're basically launching your rounds into the air like an artillery piece. A 15 yard zero is extremely close to begin with; a 25 yard zero will be more reasonable, and make sure you're actually zeroed instead of several inches high and right.

[LittleLebowski]

Go for a 25 or 50 yard zero and learn your holdovers (in close and further away - example: 15, 50, and 100 yards). I would lean towards a 25 yard zero with a PCC, but I need to test that with my MP5s, maybe I can pull off a 50 yard zero.

[Chomps]

Thanks for the feedback. It seems Imma haffta repeat the whole process again and pay a little closer attention to accuracy and precision. Damned good thing I scored a great deal on 147 HST’s. Still, this is getting to be expensive. 🤦*♂️

For the record,.. technically, this is a pistol. Not a “long rifle.” It’s a Foxtrot Mike, 9mm AR. PCC with a 1:10 Twist, 10” barrel.

However, I was not using a pistol calculator for my bullet drop calculations. (…it was some online ballistic calc I found.) It did have a section for height over bore for the sights & IIR,.. I used 2.5” or 3” since the AEMS Holosun sight sits very high.

I figured since it is technically a pistol, and intended as a PDW, that a closer zero would be somewhat preferable. My thoughts were,.. “Zero it @ the desired up close distance,.. then document where my POI landed at various other distances,.. and adjust my hold over accordingly.”

Full disclosure,.. I’ve changed zero a couple times. Initially, I tried different zero distances. One of which was 25 yds. IIR, My first zero was @ 10 yds I believe. And my precision and accuracy was much better. (…pretty much punched out the bullseye). Im not sure why I decided to change it. But I decided to try a 25 yd zero. Unfortunately, Between my astigmatism and poor distance vision,.. Even with my glasses, I just wasn’t happy with the results. I can’t recall my exact objection, But POI and grouping @ different distances wasn’t what I hoped. So I went back to using a closer zero and settled on 15 yds.

Those initial close zero’s were dead on accurate. As shown here…





Shooting high as expected @ 25 yds…


And low in close…


I intend to triple check all this this weekend, paying closer attention to the precision of my zero. Then I’ll check to see where my POI and holds are @ longer distances. Then I’ll make a final decision on whether to use a close 15 or 25 yd zero.