beans
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Posts: 248
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Post by beans on Feb 23, 2016 20:50:11 GMT -5
This is just a topic for those in center fire and SML long range guys: We all talk about MOA vs 1" groups and how major this is at long range....and mathmatically it is, just like Keith explained in another post a while ago. But how much can you fine tune adjust if A) your scope is mounted a few degrees from being plumb to the gun? And even if perfectly mounted and plumb, if you tilt/cant the rifle a few degrees, what does that do to POI 1000 yds away?
I am sure there are answers to this but all the time spent on turrets, MOA calcs and the best wind reading must all go in the garbage if the gun/scope isn't perfectly aligned and leveled/plumb OR the shooter tilts/cants the gun 1 or 2 degrees. I am sure there are calcs for those errors as well. Richard? Keith? (I know one/both you will have an eloquent answer)
My assumption is that if we were to be off a few degrees in mounting a scope perfectly....or holding a perfectly set up gun slightly tilted/canted, all the best assumptions on windage and elevation adjustments will cause major misses at 1000+ yds....maybe closer.
I know that there are ways and devices to assure the gun is set up properly. I have my way. What methods are used to assure the gun is held perfectly level/plumb when shooting? Is it the natural ability to visualize a plumb vertical line? A perfectly horizontal line? How do guys shooting in combat, either at humans or deer, at 1000 yds assure the perfect vert/horiz sight picture?
I can't wait to hear the answers from guys that know this stuff like the back of their hand.
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Post by keith on Feb 23, 2016 21:11:29 GMT -5
Cant will causes misses. I see it a lot. Any time I see a guy who misses low and to the side when otherwise shooting well I immediately cut my eyes to his turrets because you can see it quickly. Your eyes can resolve better than 5° just like they can resolve about 1MoA. It has to be part of your process just like position, breathing, sight picture, trigger control, etc. My gun gets its initial look for level as soon as I get in position and gets a final look once I'm on target.
I use the Accuracy 1st levels. Is the only good one I've used. Most setups are a $6 level in a $50 wrapper.
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Deleted
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Post by Deleted on Feb 23, 2016 23:52:51 GMT -5
Although it doesn't Have to be, I set my scope directly over the bore with a vee block level tool that I have. At the same time, I align the vertical with a string and plumb bob at 100 yards and install a level on the scope tube. From that point forward, I perform the following procedure from a well respected long range competitor...................................
The following assumes that your rifle is now WELL zeroed at 100yds - the group is centered on the POA - and you have a bubble level that will attach to the scope tube.)
Once the scope is in the rings (and you are presumably at the range), set up a plumb line on a target that has a large vertical size – equal to the full amount of your total available UP elevation, plus 20 inches. If you scope has 50 Moa of “up” elevation available from the 100yd zero, use a 70” tall piece of paper.
Drop the line and mark a ½” aiming point, 10” from the bottom, on the line.
Then count the total MOA you can get and multiply that number by 1.047 and make another dot that much higher from the aiming point.
Now remove the plumb line (so you don’t shoot it!)
Aim at the lower dot, with the vertical part of the crosshairs intersecting the upper dot, and shoot a group.
Now crank in the MOA that you used to calculate the dot spacing, and AIMING AT THE LOWER TARGET – the same on you used before, fire another group.
In a perfect world, the second group will be smack in the middle of the higher dot.
But – two things – if the click spacing on your scope is not accurate you will see it now - the group will be higher or lower than the second dot. You can use this difference and calculate what the real value of the scope clicks are - ?
If the second group is off to one side of the second dot, we need to correct for crabbing, because your crosshairs drifted off to one side as you cranked in elevation.
To do this, make another dot an equal amount on the other side – if your second group is 2 inches to the left of the top dot, make another dot two inches to the right of the second dot.
Now go back to the bench and set the rifle so the crosshairs are intersection the bottom aiming point, and THE NEW DOT at the top – the one you just drew.
Now with trial and error, set the bubble level so that the bubble is centered when the crosshairs are intersecting the lower aiming point and the new, second dot you drew that is an equal amount on the other side of the top dot.
What we have done is canceled the crosshair offset by making the bubble centered when the spindle is vertical because we have set it up to cancel the error.
Do the above shooting test again, and for the second group, keep the bubble centers and the second group will be in plumb with the first – now the scope can make longrange elevation adjustments without cranking in windage.
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Post by keith on Feb 24, 2016 7:05:38 GMT -5
I set my gun up similarly to scat. I use a level get my gun level in the vise. You need a good one because cheaper ones will read differently if you reverse them (like the Wheeler set that comes with Army sniper rifles). A cross test level works but lately I am using an Xtreme Hardcore Gear "Tank" level.
I then set my turrets square just to get in the ballpark but I use the water tower behind my house or a plumbline in my yard if the sky is overcast and I can't see the tower's hard edge to level the reticle.
If the reticle and turret aren't square to one another the scope goes back (took Leupold 4 tries to get one right). If you only dial It's more important that your bubble level is square to your adjustments. If you shoot a Horus or similar reticle is more important that your reticle is married up to your level.
I see no reason to compromise given what good optics cost. Besides, while I shoot using my reticle for 95% of my shooting there are times I will dial because holding everything can be hard: doing a partner shoot from the back seat of an SUV at a Texas Star that's 386m away or shooting a .308" bullseye nearly straight down from a tower where it appears to be further due to look angle but is 7yds on the plane that matters.
Once you are all square (even if you set your gun up for cant) then I do a Tall Target Test like what scat talks about. I've posted them here before if you need a reference. Until you do one you have no idea what you are actually dialing and even good scopes will shock you. I had one at work that was 2MoA off by the time I dialed on data for 700m. It goes back to being informed which is why I harp on IPHY vs MoA.
As to how you do it in the field, it depends. Shooting prone you do it like you do on the range. That doesn't happen a lot tho. Shooting alts I worry a lot more about building a position and then give my level a quick glance before I crack on.
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Post by Richard on Apr 29, 2016 20:13:59 GMT -5
Beans.........sorry for not replying sooner?.....As I had not seen the thread. In our long range benchrest game we have the advantage of shooting sighters at that distance. A few ranges will have "pits" like at Quantico and you just shoot at the adjacent target. At most of the ranges I shoot there are no pits but embankments with clay birds and you adjust your scope to hit the birds......there are very close to your actual target. But like Keith, I set my gun up in a vise and level it, then level the scope. When I shoot at my range, we had permanent channel iron holders that we set our own personal targets in. All my target frames have levels set in them. My bench rest also has a level in it. Our forends are flat and square to the receiver. When I set up, I adjust my rest to be level. Invariably when I look at my target, the crosshairs are level.
So, in our game, we do not have to shoot at various distances during a match so most of this stuff does not come into play.
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