Armory Sponsor
Posted: 3/31/2014 11:56:34 AM EDT
|
I gave my Grandson my Reemington Model 6 in .308.
It had a worn out 30 year old Tasco scope on it that I kept.He saved up over the winter and bought a Redfield Revenge 3x9. We couldn't get it sighted in. Had the elevation knob topped out(wouldn't turn anymore)and it was still hitting 16 or so inches low. I had the same scope on another rifle so I took that and used 1" High rings for another try. That helped but it's still 8" low and the elevation adjustment is topped out. I'm thinking of putting some shim stock under the front base. I hate to go extra high or see-thru rings. Question is,how much higher would the front base have to be raised to bring the point of impact up about a foot or 18"s ? Thanks! |
|
(You have to shim up the rear of the base, not the front to correct your problem.)
Here's the best way to do it for a medium-range hunting rifle.. Mount the scope in the rings that you most prefer. Run the scope's elevation all the way down until it stops, then all the way back up until it stops again, counting the number of turns of the turret it takes to go from one extreme to the other. Then turn it HALFWAY back down. For example if it takes five full revolutions from top to bottom, stop at 2-1/2 down. That will pretty much center the erector assembly within the tube, which will give you the best optical performance, the least potential parallax error, and the most range of adjustment later on. Then shoot a small group at 100 yards; (50 would be OK, too for what we're doing.) Measure from the aiming point to the center of the group and record that measurement. Let's say the group's center is 22 inches low. ... To be continued after supper! |
|
"(You have to shim up the rear of the base, not the front to correct your problem.)"
Wouldn't raising the rear of the scope lower the point of impact? "Run the scope's elevation all the way down until it stops, then all the way back up until it stops again, counting the number of turns of the turret it takes to go from one extreme to the other. Then turn it HALFWAY back down. For example if it takes five full revolutions from top to bottom, stop at 2-1/2 down." We did that with the original scope when we tried the taller rings. Just so we felt we were starting "fresh". Thanks for the help! |
|
Oops let me back up and answer your question; Edited:
Think of it this way. You need to keep the scope pointing where it was, and get the rear of the rifle lower in relation to the scope, which makes the muzzle end higher, which in turn makes the bullet strike higher on the target with the scope still pointing at the original aiming point. Push the rear of the rifle down, pivoting it on the front ring, by shimming the REAR ring! That make it easier to visualize? OK, where were we? Yeah, you're hitting the target 22 inches (example, of course), below the aiming point on the target, at 100 yards(again, example). NOW measure the distance between the rings on your base. It's best to use a dial caliper, but a ruler will get us close enough to fix the problem, easily. Let's say that the distance between the center of the front ring to the center of the rear ring is 5-1/4 inches. (Again, example). Now the conversions and the math: (We'll do everything in inches and decimal inches, so the 22 inches of group/aiming point disparity will need no conversions.) 22 inches. The 100 yards will have to be divided by 36 (inches in a yard) for a distance to target of 3,600 inches. The (Fractional) distance between bases of 5-1/4 inches will be simply be converted to a decimal value for 5.25 inches. To be continued once again after we settle things to this point. I promise! |
|
Quoted:
Wouldn't raising the rear of the scope lower the point of impact? To further make sure we're on the same page, this is your question I was referring to in my answer in red, in my two previous posts. And to put it another way, if you shimmed the FRONT ring -the one closest the muzzle- (as you originally wanted to do), you would be raising the front of your scope making it point or "aim" above the target. Then when you'd go to shoot, you'd have to lower the muzzle to get the scope aiming back on the target! This of course would cause the bullets to strike even lower than before, making your problem even worse. So no, raising the rear of the scope will NOT lower the point of impact in relation to the point of AIM. It will raise it! |
|
With apologies for the sidetrack.
To continue onward with my post 4004 a bit higher up... We've so far determined, in decimal inches, the following three factors in (an imaginary) scenario. ( We are going to use all three to then calculate the needed shim thickness to correct the problem of the rifle hitting too low.) 1. The current distance between Point of Aim and Point of Impact with the faulty setup, (but with the scope optically centered.) (22 inches). 2. The distance from the shooting bench to the target. (3,600 inches.) and 3. The distance between the scope rings on the base. (5.25 inches) So we will now divide 3,600 by 22 which equals 163.3. Now we take 5.25 and divide that by 163.3 which equals .032. So your shims under the rear scope ring need to be a total of .032" thick to correct a 22- inch error on a 100-yard target with a 5.25 inch ring spacing. Cool, huh? (Modify the math inputs for your actual situation accordingly, and the shim thickness will change accordingly.) Brownells sells shim stock, but you can make your own from an old tape measure, etc. in a pinch. |
|
Ouch, I pulled my brain muscle.
I think I follow on the front/rear thing. I was thinking by raising the front base point of impact would rise and I could always lower the scope cross hairs.(Redfield claims their scopes have 24" of travel in all directions) But anyway,rings are 3.625" apart measured from the cross pins. Do you think the rings should be lapped after shimming? Or would that counteract what we just accomplished with the shim? Going to have to pick this up tomorrow. My turn for supper.And AR15 on dial up acts funky. (Not sure where this going to end up in the thread) Thanks again! |
|
You could mount 12" rings on that rifle and it still won't solve your problem. The issue is not with the height of the rings.
You could shim it but then you'd also better plan on lapping the rings to avoid potential damage to the scope tube. With a shim you'll be creating a slight angle between the scope tube and the top and bottom flat surfaces of the rings. If you do not lap then you'll have two relatively sharp corners per ring digging into your scope. No thanks. In extreme cases of scope misalignment I use the Burris Signature Posi-Align rings (See Here). The offset rings allow you to position the scope as you need it without shimming and lapping. They're quick and easy to install and hold very well. |
|
Quoted:
You could mount 12" rings on that rifle and it still won't solve your problem. The issue is not with the height of the rings. You could shim it but then you'd also better plan on lapping the rings to avoid potential damage to the scope tube. With a shim you'll be creating a slight angle between the scope tube and the top and bottom flat surfaces of the rings. If you do not lap then you'll have two relatively sharp corners per ring digging into your scope. No thanks. In extreme cases of scope misalignment I use the Burris Signature Posi-Align rings (See Here). The offset rings allow you to position the scope as you need it without shimming and lapping. They're quick and easy to install and hold very well. The only rings I use on my bolt guns. Have only needed the offset inserts once, they did the job. The polymer inserts grip well, don't torque the tube (no lapping), and protect the finish on your scope from ring damage. 
If you decide to go with the signature rings, I might have an extra set of offset inserts. They have been mounted, but should be still good. I'll see if I can find them tomorrow. If I can, and you can use them, I'll send them your way. |
|
Quoted:
You could mount 12" rings on that rifle and it still won't solve your problem. The issue is not with the height of the rings. You could shim it but then you'd also better plan on lapping the rings to avoid potential damage to the scope tube. With a shim you'll be creating a slight angle between the scope tube and the top and bottom flat surfaces of the rings. If you do not lap then you'll have two relatively sharp corners per ring digging into your scope. No thanks. In extreme cases of scope misalignment I use the Burris Signature Posi-Align rings (See Here). The offset rings allow you to position the scope as you need it without shimming and lapping. They're quick and easy to install and hold very well. True, which is why I told him to mount the scope in the rings he prefers before doing anything else. Possibly, but it may be that there's already such a misalignment that shimming would correct. Either way, it isn't a bad idea to lap the rings to prevent such damage. If it is still out of whack, a careful look at everything should reveal potential problems before he goes caveman on the ring saddle screws. The Burris Signature System is great, and I use it often, but it isn't always necessary to buy new rings. Careful shimming and a bit of caution will probably correct the OP's problem without having to spend another fifty bucks and having to wait a week for shipping. BTW, the Dual Dovetail models linked to won't work with the OP's bases unless he already has Dual Dovetail bases. If you aren't familiar with the system, it's easy to order the wrong rings, (and the offset insert packs are sold separately for another 15 bucks. New rings are shipped with only a set of concentric inserts.) |
|
A couple additional notes;
When you go to adjust almost any modern riflescope for elevation, you are not "raising" or lowering the crosshairs per se, (nor are you moving them left or right with a windage adjustment.) What you are actually doing by turning on the turrets, is moving a complex assembly of lenses and prisms within the scope tube. You're in effect moving the entire image-(everything in the field of view.) That's why the crosshairs still appear to be centered in the tube even after extreme adjustments. (This wasn't always true. some old scopes actually did move the only crosshairs, often with them ending up grossly off-center in the field/tube.) |
|
BTW, the Dual Dovetail models linked to won't work with the OP's bases unless he already has Dual Dovetail bases. Unless I missed it we do not know what he actually has for a base. I simply linked to the double dovetail to give him an idea what is available. I figure he's smart enough to search around for the correct Burris rings for his base. Another thing that he might try (depending on his base) is to swap the front and rear rings. That little trick has worked for me several times. |
|
Quoted:
Unless I missed it we do not know what he actually has for a base. I simply linked to the double dovetail to give him an idea what is available. I figure he's smart enough to search around for the correct Burris rings for his base. Another thing that he might try (depending on his base) is to swap the front and rear rings. That little trick has worked for me several times. Quoted:
BTW, the Dual Dovetail models linked to won't work with the OP's bases unless he already has Dual Dovetail bases. Unless I missed it we do not know what he actually has for a base. I simply linked to the double dovetail to give him an idea what is available. I figure he's smart enough to search around for the correct Burris rings for his base. Another thing that he might try (depending on his base) is to swap the front and rear rings. That little trick has worked for me several times. You're correct; we don't know what base or rings he has. I just wanted to point out that those particular rings probably weren't what he needs, before he went ahead and ordered them. I should have asked him at the start what rings and base he actually has. |
|
Lots of good info here,I appreciate it.
The rings I have right now are Weaver High and the base I think is Weaver(put it on like 30 years ago,can't remember) one piece. After looking around yesterday I might get a set of Warne two piece bases. Start with new everything. Yeah,something is FUBB'd. If it was still my rifle I'd try a different brand of scope. Or put that $40 Tasco back on. But it's a 13 year old kid's first deer rifle,and he shoveled alot of snow to buy that scope.Which I recommended. Thanks for the offer e-AR,let me see what I can come up with before I get the Burris set up. |
Not a gunsmith. More like "Joe Bob The Gun Plumber".
I decided to take a page out of the 1903 A4 sniper system book and use beer can as shim stock. After EXTENSIVE research I found that each layer of Bud Light can provides approximately 7 MOA of elevation (rear scope mount). I have used this as a band aide for mine and a few of my buddies rifles when we were trying to get out to a 1000 yards. It worked so well we just left it and kept shooting. |
|
Quoted:
If you have to "shim" (a scope base) or a ring, something is FUBB Well, yes. Jokey established that much in the third sentence in his Original Post. ( His rifle is still shooting 16 inches low at 100 yards and he cant turn the elevation dial in the UP direction anymore because the erector assembly within the tube has run to its mechanical limit.) I'd call that FUBB, too. Now-here's the REASON: The condition is that the axis of the barrel is not parallel to the top surface of the receiver. This is actually a pretty common situation with Remington pump and semi-auto centerfire rifles, notably the following Models- 4, 6, 74, 76, 740, 742, 760 7400 and 7600. I've seen several of them in which the barrel pitches downward noticeably, causing the exact situation discussed here. I suspect there is a bad jig somewhere in the Remington factory that has produced many of these ugly children over the years. Who knows? (And I'll bet there are thousands of them out there working just fine with a few beer can shims under the rear of the base. It's not witchcraft. It's geometry, with perhaps a bit of trig tossed in if we want to get precise about fixing it.) So either shim the rear of the base, or buy new Burris Signature Rings WITH THE OFFSET INSERTS and install them exactly per the instructions. Everything else you throw at it will be a waste of time and money, including new Warne Rings. As good as they are, THEY won't fix this issue. The only other possibility would be to buy a new scope with a LOT more elevation range than the one you have, but that would be a very expensive Band-Aide. |
|
Quick update; put a .010 shim under the rear of the base.
Recentered the recticle and it was 2.5 inches high at 62 yards. Had to turn it up 24 clicks to get there. Going to turn it back over to the #1 son and Grandson. They can sight it in the rest of way off a bench. Best I can do in the back yard is kneel behind the bird house for a rest. Thanks for the help! |
|
Quoted:
Quick update; put a .010 shim under the rear of the base. Recentered the recticle and it was 2.5 inches high at 62 yards. Had to turn it up 24 clicks to get there. Going to turn it back over to the #1 son and Grandson. They can sight it in the rest of way off a bench. Best I can do in the back yard is kneel behind the bird house for a rest. Thanks for the help! Hopefully with the low rings, so they can get a solid cheekweld on the rifle when firing it? Sounds like you're getting closer to ideal... one or two more shims should do it up right if I understand the current status correctly. |
Armory Sponsor