Thread: Zero to the Shooter??
7/30/2013 8:35am, #1
Zero to the Shooter??
I recently had an interesting discussion with some guys about weapon zero today and the issue of “individual zero” vs “weapon zero”. This pops up every now and then. "You have to zero the gun to the individual".
What I have learned/read over the years is that this is one of those "well it really depends" topics. When it come to zeros, scoped guns are different from iron sighted guns and both are different from red dot/holo sights.
On magnified optics (Sniper Rifles), scope parallax can cause differences in individual zeros depending on how the shooter mounts the gun…his distance of eye from scope..etc.
In a perfect world, where all of us use the exact same sight alignment/sight picture, all shooters would be “zeroed” with properly adjusted iron sights. Because there are differences in how we “hold” on target and how we center up irons there are going to be small differences in zero. But as long as they are “close” those differences are not drastic within realistic ranges.
The Army FM 23-9 states that:
“When standard zeroing procedures are followed, a rifle that is properly zeroed for one soldier is close to the zero for another soldier”....this allows soldiers to accurately shoot with another soldiers rifle if he needs to pick one up.
Zeroing is primarily about aligning the guns sights with the barrel..taking individual differences in sight picture into account to fine tune.
FM 23-9 also says:
“the similarity of individual zeros should be emphasized instead of the differences.”
“There is no relationship between the specific sight setting a soldier uses on one rifle (his zero) to the sight setting he needs on another rifle. For example, a soldier could be required to move the rear sight of his assigned rifle 10 clicks left of center for zero, and the next rifle he is assigned could be adjusted 10 clicks right of center for zero. This is due to the inherent variability from rifle to rifle”
Which is something many people don't realize. When I was a young private I thought for a long time that my "zero" was MY zero and that if I dialed it in on any M16 I was issued I'd be GTG. The fact of the matter is that zeroing is really about aligning the SIGHTS to the gun...not the shooter. If we all held a gun the same way and used exactly identical sight pictures/alignments a zero would be universal. Individual zeroing is really just a "fine tune" when proper marksmanship fundamentals are applied.
Red dot sights/holographic sights do not rely on sight picture or eye relief. If a RDS is properly adjusted so that the bullet impacts where the dot lays, that sight is zeroed for all shooters who use that weapon. Any variation with a RDS is based on the shooters breath/trigger control. Of course the dot only represents “zero” at 2 points of the bullets trajectory. With our 50 yard zero that should be at 50 and approx 200 yards. The round will strike below the dot when closer than 50 yards and approx an inch to 1.5 inches above the dot between 50 and 200 yards and then drop off past 200.
Of course time and a beating may loosen up the Aimpoint tubes causing a Zero shift.
7/30/2013 9:03am, #2
Everytime I bore sight a scope on a rifle, I then have to go to the range and sight the scope in to really dial it in. I just got done doing that with my .308. But I like doing it and getting on the range. But even after doing that, when someone else picks up my rifle, they will not be hitting the bull with my scope and rifle as well as I am. There is usually a little give. But other veriables can be at play too. Like trigger pull. I knew a guy who had a really shitty trigger pull. He ended up adjusting his sights to his trigger pull. So every time someone else shot it, it would shoot to the left. But when he shot it it would shoot dead on. Then when he jumped on someone else's rifle, he would shoot to the right. Drove me nuts.
7/30/2013 11:58am, #3
- Join Date
- Mar 2006
Zeroing is one of my favorite technical shooting topics - specifically as it relates to precision rifle building and long range shooting.
To clarify, zeroing is not about aligning the sight to the barrel. It's about aligning the sight to the bore, which is only possible if a rifle is built properly. I know that seems like splitting hairs but there's a difference, and it can be significant for a long range shooter.
Most people aren't aware that even the best rifle barrels are far from perfect. The bore is never completely concentric to the outer contour of the barrel. Usually, it's visibly off center. Also, even the best rifle barrels have bores that are crooked as a ************. Bore curvature can be measured by chucking the barrel in a lathe, finding dead center of the bore on the chamber end and measuring the runout on the muzzle end. .025” - .030” or more of runout is common on a really nice barrel. Curvature and lack of concentricity create some issues related to zeroing.
First, let's talk about the fact that bores aren't concentric to the outer contour of the barrel. This shouldn't be a problem because the scope holes should be drilled and tapped in precise alignment with the receiver threads. The barrel should then be threaded on the center line of the bore. So, in theory you'll have scope holes perfectly aligned with the chamber. But, the truth is the scope holes on factory rifles are often not where they're supposed to be. This is why custom builders will sometimes fill in the holes and start over with the drilling and tapping process when they're accurizing a rifle.
This issue is one of (but not the only reason) you'll often have to add clicks of windage to zero your scope at 100 yards. In a perfect world, this shouldn't be the case if you're using a quality optic. But when the holes are slightly crooked, your scope is not perfectly aligned – thus the need for a windage adjustment.
Another problem you have related to concentricity is with receivers that were tapped for scope mounts by a gunsmith after leaving the factory. Most of them use a shitty fixture that rests the barrel in v-blocks and aligns the holes with the outer contour of the barrel. They completely ignore the fact that the outer contour isn’t in line with the chamber. Why? Because they’re knuckleheads and they think that since this fixture has been in use for ages it must be good. Wrong. To properly tap a receiver after the fact, you need to remove the barrel and use a mandrel to align the holes dead center on the receiver.
This brings us to the next issue – bore curvature. Accept it. Your $5,000 custom rifle has a bore shaped like a banana. Okay, that’s exaggerating a bit but it is definitely curved. They all are. The question is how does that curvature effect your rifle and what do you do with it?
Timing of bore curvature is a major point of contention among precision rifle builders. Assuming you’ve cut a square and true chamber and understanding that your bore is curved you can arrive at the conclusion that the end of your muzzle is pointing in a slightly different direction than your chamber, which your scope holes are aligned to.
There are some who argue that the curvature should be timed to 12 o’clock so the curvature is pointing upward and you don’t introduce any mechanical windage issues. I’m with that group. Others say “fuck curvature, it doesn’t matter.” In my opinion that second group is full of **** – sort of. I’ll explain in a minute.
Say you don’t time your curvature to 12 o’clock. You just spin the barrel on and the curvature happens to be timed to the left or right as you’re sighting the rifle. That runout that I mentioned above is going to come into play now. Your scope is going to be pointed directly at the target. Your muzzle is going to be pointed slightly to the left or right. You have to make a small windage adjustment to zero the rifle.
Some argue it’s all good once you zero it at 100. Oh no. What you have is two lines that intersect at 100 but continue to move further apart again after they intersect. If you’re shooting at say, 1,000 yards this difference will add up. The more runout in your bore, the more windage you’ll have to use to bring your rounds on target at long distance. This can contribute to your scope running out of windage adjustment at long range.
The reason I say the bore timing naysayers are only partly full of **** is because in a practical sense it doesn’t matter much. Any serious shooter is going to work his rifle in at multiple distances. If he always needs X amount of windage adjustment at a given distance, he’ll know it and adjust for it.
But most shooters don’t know what’s really happening and I don’t like ignorance. Often, they’ll assume the need for an adjustment is due to spin drift or some other factor, when part of the adjustment is really to correct for their untimed bore curvature. In addition to that, timing the curvature to 12 o’clock is just a neater, cleaner way to deal with the fact that the bore is curved, instead of just ignoring it and saying it doesn’t matter. It amazes me how some of the most anal rifle builders you’ll ever meet will argue that bore curvature should just be ignored. Bullshit. They’re avoiding it because they don’t understand it.
I know this is long winded and nobody probably gives a ****. I also realize it’s probably a moot point because most people don’t own custom rifles anyway so they have to live with what they have. And I know most people don’t shoot stuff at 1,000 yards. But, like I said, this is one of my areas of interest so if you’re bored – tough ****.
Last edited by Devil; 7/30/2013 12:03pm at .
7/30/2013 12:14pm, #4
Good **** Devil.....thanks.
7/30/2013 12:30pm, #5
I don't know if it's still the same in the Army but, when I was in it was common practice to return M16 sights to mechanical zero when being reissued. Hell I remember having to mechanical and rezero my issue weapon on occasion (wtf).
Knowing what I know now, I would think that leaving a zeroed weapons sights alone and just shooting to confirm zero would make more sense.
7/30/2013 12:44pm, #6
- Join Date
- Mar 2006
I agree. Better to leave it, I think.
We did the same thing in The Corps. I didn't really think about it then. Looking back, the only decent reasons I can think of are (1) to learn how to do it from scratch and (2) to count your clicks from mechanical zero so you know for damn sure what your dope is if you lose track of your clicks and have to get back by counting from zero.
7/30/2013 12:47pm, #7
That's good stuff, Devil. So it would seem, then that you should time the curvature to 12, 6, 3, or 9 o'clock. That way you can adjust with windage or height. But if you are anywhere in between you are going to be adjusting with both. So it would be cleaner to adjust with height on the 12 or 6 that because you are going to have to adjust for it anyway depending on distance. But you would only need to adjust windage if there is wind and may not have to mess with it otherwise.
7/30/2013 1:18pm, #8
- Join Date
- Mar 2006
12 o'clock is the way to go. You definitely don't want to be at 3 or 9. You're better off working with the elevation than the windage. Timing to 12 o'clock can actually give you more elevation adjustment at long range. The flip side of that coin is that you could potentially run into a situation where you've got too much elevation to get down to zero at 100 yards and there's the potential for having to zero at a further distance. That's not common though if you're working with a high quality barrel with minimal curvature.
The only reason to time the curvature to 6 o'clock would be if you want to spend a lot of time shooting at very short distances, less than 100 yards for some reason.