Distance Between Scope and Barrel
When you are sighting in a scope, how does the distance between the center of the scope and the center of the rifle barrel effect accuracy/setup? Due to the fact that the scope, the barrel, and the point where you are aiming form a triangle, it seems you would be about 2 inches low at a short distance. At some point you would be right on. Then you would be high. (assuming no bullet drop due to distance).
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[8D]triangle??? look again! Whats the question?[?][?][?]
On your mark-get set- go away!!0 -
If you have a 2" center-to-center and had both items at center, then you would have a 2" distance at the muzzle. As the bullet departs the muzzle it begins to fall. As the distance increases, the departure between the two grows greater.
Now - what we want to do is make that triangle of yours match up so we can have both scope and bore aligned at some point to impact at the same spot (Point Of Impact). Let's say you have a .308 Win and shooting the standard 150 gr factory ammunition. We carefully secure the rifle where we can bore sight through the breech at a target some 25 yds away. After aligning the bore, and without disturbing the rifle, we then adjust the scope to dead center on the target. Verifying all this is done and the rifle remained stationary, we fire three rounds to see where they group. We adjust the scope until the group impacts at center of the target and the scope is centered, also. What we've done is to cause the muzzle to be elevated slightly. The bullet will now cross line of sight at this distance and again at a further range, usually between 100 and 200 yds, because of the force of gravity.
Keep off the Ridgeline0 -
jlight, You are correct about the problem of scope mounting. In general, it is better to mount the scope as low as possible over the line of the bore. The bullet will cross the line of sight relative close to the rifle (say 30 yards or so) then cross the line of sight again at the range for which you have it sighted in (say 200 yards). I have never heard it described as a triangle before but I understand what you mean. If you project a line from the center of the bore and a line to where the scope is aimed they will converg. Welcome to the forum. You can learn a lot here but unfortuately some misinformation gets posted from time to time as some of us don't read the question carefully. Other times some of us just don't know what we are talking about. [:)] 0 -
To amplify a little more, you are two inches low at the muzzle. Then you are dead on at thirty yards. Then at 100 yards you are an inch and a half high. At two hundred yards you are dead on again. 0 -
Hello you have the right Idea just remember the flight of the bullet is an arc. Now for the part that I have a differt opinion on is what is the best height of scope above bore line. I think for a hunting rifle it should be 3 inches let me explain .If you want the max range where the bullet will be 3 inches or less from point of inpact and the flight of bullet is an arc then if you start out -3 the bullet will cross the line of sight further away from the fireing point then cross for the second time much further and finely drop to -3 inches much greater distance from the gun . The only negative is you should not cant the rifle. 0 -
P.Shooter
That's either going to be 1 ugly rifle stock (barrel below the wood?) or else your head is going to be way above the butt stock.
The additional amount of "point blank" range is miniscule from raising it this high (std is 1.5-1.75 above bore) Using somthing fairly fast (300Wby 150gr) 1.5 above bore yeilds a 325yd PBR raising it to 3" increases the PBR to 344yd (19yd increase). Same thing but with a "slow" cartridge (170gr 30-30)1.5 above the bore yeilds a PBR of 199yd increasing it to 3" gives a PBR of 210yd (11yd increase). In either case the major decrease in shootability outweighs minor increase in PBR.
Some guys like a mag full of lead, I still prefer one round to the head.0 -
HELLO TAILGUNNER. At least I got a rise out of you I have 2 firearms that I think I can prove my point with. One is a STYER AUG and the other is a VALMET 412S combo gun shotgun on top and rifle on the bottom. If we took those 2 guns and shot them side by side with 2 standard rifles at 100 200 300 & 400 yards with the same ammo the firearms with 3inch differance between bore line and sight line will shoot closer to the + OR - 3inches then the rifles with 1+1/2 inch differance. Neither of my guns are a thing of beauty but like I stated it is just IMHO.Cheers Karl 0 -
I understand Karl's statement. The higher placement of the sight does create a point blank range. How much...I do not know. The thing is that the scope should also be placed so that you can obtain a comfortable and consistent cheek weld to the stock when your eye is properly aligned behind the scope. In some cases, a high mount may make a good cheek weld harder to achieve.
A higher scope placement will also exaggerate the effect of any cant, as Karl pointed out...the same way it will extend the point blank range.
When you cant sights (sight line not directly above bore, in a vertical line) your sight-line follows a left or right 'track' that angles away from the bore.
However,...the projectile will follow the natural laws of gravity upon exiting the bore or channel. The projectile will immediately become subject to the effects of gravity and will begin to drop in a straight line relative to the bore or channel...but the bore will be angling left or right of the sight line. This is because the bore (when held perfectly vertical to the line of sight) is angled upward for a 200 yard zero...that is what causes what is referred to as the 'rise' in a projectile.
In a perfect world, with the line of sight and the bore in perfect vertical alignment, the shooter's only compensation would be for drop (we'll say in zero wind conditions). When sights are canted the line of sight and the projectile path are divergent in both vertical AND horizontal profiles. This makes a huge difference at distance... particularly in long-range rifle.
"They're in front of us, they're behind us, they're to our left and to our right...they can't get away now."
Chesty Puller, Chosin Reservoir, Korea
SEMPER FI0 -
The accepted wisdom is to mount the scope as low as possible. However if you are contemplating shooting at relatively large game (deer or larger) there is an advantage to a fairly high mount. If you mount scope 2" above boreline and sight in so that at the longest possible range you will shoot you are 2" low, then you will havbe a relatively (+/-) long interval of being on target within 2".
Morty0 -
King999
I used +/- 3" (your using 2") and a change in sight height of 1 1/2" I showed a increase in "range" of between 11&19yards (depending on MV and BC) With your +/-2" window and a increase in sight height of only 1/2", the increase in range will be much smaller than that.
Easygo6
The numbers I used in my answer are streight off one of the better balistics programs, and deminstrate that a 1 1/2" rise in sight height will yeild less than a 20yd increase in PBR with even one of the hotter magnums.
PS
No doubt the bullet (from the higher scope) will be slightly closer to the aiming point, but will it be enough closer to make any difference? I'm still having visions of the old "Iron sighter" see-through mounts on a M-94Win, not a rifle like yours that's designed that way from the get go.
Some guys like a mag full of lead, I still prefer one round to the head.0
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