I have been to one Appleseed, where I shot 176. Yesterday I zeroed two rifles off the bench, then used them to practice the AQT. I found that I am shooting 4 moa low (both guns). One is a 513T surplus four position rifle - no way am I bending the stock or the barrel! I had the same problem with my 10/22, so that's three guns with the same problem. I have come to the conclusion that it must be me.
This happens in all positions. My groups are not that bad (I compensated by holding over and shot a 198).
Any ideas?
The sling doesn't bend the barrel per se but it does affect the harmonics of the barrels vibrations which occur during "launch". Thus the exit trajectory of the bullet is affected. It doesn't matter if you have a fully floated barrel and the sling doesn't interfere directly with the barrel. The bracing, stiffness, sturdiness of support between the bench rest set up and the "you and the sling" setup affects, via the receiver, the harmonics of the barrel.
If you are getting a consistent group it is a commendation of the repeatability of your steady hold factors and sling usage in the position. You merely need to adjust your sights to account for this new setup.
If you zeroed the sights from the bench the zero can be different than when shooting prone or sitting using the sling. I think that V is correct. If you have tight groups that are low when you use the sling, you probably just need to adjust your sights.
When your slung up and shooting versus bench shooting there are going to be variations in the group. Remember, the sights are designed to be zeroed to you!
You may be closer to the sights, different angle, if it's a peep sight the diffraction of light can make a difference through the rear aperture based on your distance from it, low cheek weld etc.
Bottom line, if your grouping well then just adjust the sights so the POI is right for your prone position and you'll be golden! O0
Devnull and jmdavis are right. Where your eye is in relation to the rear sight will determine your point of impact. When you change position radically i.e. sight in at a bench and then shoot from a sling supported prone position your point of impact will change.
Adjust your sights to move your point of impact to the center and I bet you will shoot a Rifleman score.
VAshooter
Good information in all of the responses you have received Ben.
Now comes the bad part.
SamD(Jaffe) alias Dr. ZORBADAGREEK wants to know just what do you think you are doing at A BENCH! &)
Them things are bad juju. Ruin ya they will. Dr Zorbadagreek knows.
Keep doing stuff like that and Jane Hancock will never awaken from her 13 year coma. ;D
I had a similar problem back in April. I mounted my scope and sighted it in off the bench. However, when I tried positional shooting at the event, my eye relief was all wrong. I've readjusted it since then, and I think it will help me when I go again later this month.
Wish I could test it out before then, but the local range is indoors with windows 4 feet off the floor so it is impossible to shoot from the sitting or prone positions.
I've seen this myself, and solved it by not using the bench anymore. ;D
I can see the sling affecting the barrel harmonics and the zero. Hence also the need for consistency in sling tension.
/dev/null - I don't understand the shooting position affecting the zero:
If the sight alignment is correct - the front sight in the center of the apperature - I have established a line. Add to the line my eye on one end of it and the bull on the other. There are now 4 points on the same line.
To zero, I adjust that line until it meets the bullet impact at a specified range.
If I move my head back and forth on the stock (position changes) my eye still has to be on that line for the front sight to be in the middle of the apperature - or I don't have correct Sight Alignment. (i.e. if I move one of the points, the other three can't line up.)
If my cheek weld changes some, I either have my head tilted to compensate, or I can not align the sight. (Of course, the proper way is to bring the rifle to me
Am I missing something?
Quote from: gunville on June 11, 2009, 12:07:48 AM
If the sight alignment is correct - the front sight in the center of the apperature - I have established a line. Add to the line my eye on one end of it and the bull on the other. There are now 4 points on the same line.
Thats the big "if". If you are closer to the rear sight you see more of the front sight in the aperture, more of the wings, etc. Further away you may only be able to see the post without the wings, etc. The point is that an aperture sight depends on the minds natural ability to "see" symmetry and "centeredness" If the picture is different, think optical illusions, then your mind may have a different idea about where the "center" is. This doesn't matter if you are always using the same "picture", your mind assumes the same center so no foul and once the sights are adjusted for POA/POI all is well. But now you move the head back or forward and change the picture and your mind switches to a different idea of "centered" and now POA/POI is off again.
Then you throw in all the lighting, etc, etc.
Yet another problem solved by owning an AR!
If you put your nose on the charging handle, whether shooting from a bench (EEEeeeew!) or while laying in the mud, your zero will remain in the same place. Why?
Consistent cheek weld.
As covered above, when you sight in from a bench and then move to the sling, your sling "tightens you up" and usually moves your face a little closer to your sights. It really pulls you in and thats why your groups go down. (You can test this right now by making a little circle with one hand and a little front sight post with your other. Place the front sight post in the middle of your circle and then back your head up. See what happens? You have to move up, right? Now, move your head forward. Moving POI down, right?)
To solve this problem, you need an indicator to let you know where your cheek is planted when you zero so you can return to that same exact spot every single time. The AR has a built-in indicator, the charging handle. You can use your thumb or hand or even a groove on your stock, anything - but you have to have something so your eyes are looking through that sight the exact same way every single time. I've been recommending a band-aid as it holds pretty well and is kind of coarse so it's easy to feel. Duct tape always works, and if you're a real John Wayne type, stick a little strip of sandpaper on there!
just my opinion;
recoil begins before the bullet leaves the barrel:
off the bench, the barrel rises during the shot
when in a sling, snug, the upward rise is inhibited and thus you POI will be lower.
I see this with almost all of my rifles when I am working up a hand load for accuracy and velocity. When I switch to field positions the POI shifts. you really see a change when you try "free recoil" off the bench, like a benchrest shooter, and then go to a sling and field positions!
good shooting
TAZ
Reading some of the comments it just occurred to me...do the front sights have wings? I mean I know they do, but I can't tell you what they look like as part of the sight picture. I can tell you what the front sight posts look like, but not the wings. If I make an effort to look at the protective wings/ears while just holding the rifle in my hands I could tell you what they look like (wide, short, long, curved, shiny spot, etc. but I can't recall actually taking note of them while firing a rifle.
You either put more or less stress on the front sling swivel as your position changes and your sling gets tighter or looser, or your eye changes its position behind the rear sight (up, down, left, right, forward, backward) as your position changes. I've seen lots of statements from experienced high power shooters who say they have to make elevation and windage corrections as they go from one position to another.
The charging handle suggestion above is something I regularly point out to folks at Appleseeds. Even with all these collapsable stocks on the carbine versions of the AR15 people seem to think the stock has to be fully extended when they are shooting. NO!! It doesn't have to be fully extended. Set it where it allows you to put your nose on that charging handle. Take a nail, or screwdriver, and put marks on the stock to show you where to set the stock. I'm shoot M1As and M1 Garands, I'm 6'3" tall and I partially collapse my carbine AR stocks so I can get my nose on the charging handle every time. I spent some additional money and time finding a scope mount for my vARmint rifle to make sure I could get my nose on the charging handle without the scope jamming into my eye (scope had to be up and forward to fit me right).
It's your rifle. Do what you have to make it fit you. Anyone here shoot trap/skeet? I've heard those guys spend money to get their shotguns to fit them just right so when they put it on their shoulder everying lines up just right. A shotgun. If it's important to have consistion cheekweld, angle, fit, etc. with a shotgun it sure as heck is important with a rifle. Shoot it enough to find out what works for you. Its your rifle.
Seems I saw another good statement here awhile back - Its not the rifle that makes the rifleman, its the rifleman that makes the rifle.
Yeah, same thing goes for scopes - if your eye is not in the same spot every time, the bullets won't be in the same spot on the target. Scopes don't magically correct poor technique, they just help compensate for less than perfect eyesight and if used correctly can help you see targets that may be small or partially obscured and therefor difficult to see.
Have a good one.
Where on the road to Rifleman do we talk about barrel harmonics? Four safety rules, yes. Six steps, yes. How to adjust a sling, yes. How to get a solid position, yes. Cheek weld, yes. Steady hold factors, yes. Natural point of aim, double yes.
If you want to shoot 1000 yard or even 100 yard bench rest matches you can worry about barrel harmonics but shooting a 10/22 at 25 meters prone with a sling, barrel harmonics do not move you out of the four minute square.
VAshooter
This is a great question and I perceive to be a common problem. Not only with my Savage .17 bolt gun
but also when I made transition to my AR-10. I payed close attention to getting close to the charging handle
with a scope I risked getting a third eye. Well the bruse wasn't too bad.
What I learned from my Shoot Boss "Eel" and fellow instructor "Oddball" was that while standing
your natural point of aim is established, your elevation aim is adjusted by merely moving your rear foot
inward or outward. This placed the reticle for a more repetitive shot group for me. However, another instructor "EME"
brought to our attention that placing the horizontal plane of the reticle at the head instead of the base of the target
would counter the effect of otherwise shooting low, when using a sling. Yes, this did solve my problem.
For prone position I have mounted a hard rubber ring to my forehand stock to assure my elbow plant will be anchored the same each and every time without searching for it. This works for me just like having a kisser button on my bow string which anchors to my
incisor tooth. The anchor point remains constant every time. This carries over to rifle shooting as well I have discovered.
Hope this helps.
Best regards,
Castle Mountian
CM,
I also use an AR 10. LaRue Tactical makes an extended scope mount specifically for the AR 10 (the SPR-S). The height off the rifle's bore and extension forward are corrrect. My ocular lense is between the first and second slot in the flattop rail but you'll have to fine tune that depending on your scope's eye relief. The standing position forces my cheek weld just a touch back so I have that set for the longest eye relief and set for 3X,from prone if you dial up power on the scope shortens the eye relief just right. Proper turkey neck is the solution to scope eye but you need a mount that will allow it. The mount is alittle spendy ($210) but I've had mine for a few years now and it's the way to go. Even the quick release throw lever tension is adjustable for proper lockdown/repeatable zero.
Feel free to PM if you need help in this reguard.
Reguards,
JoeZ
Also,
I agree with Tazdevil. That's the reason heavy bullets zero higher at 100yds. More time in the bore = higher initial zero.