need opinions on mounting a rifle scope.

[too_pointer]

Heres whats up. I went to sight in my new .35 Rem Marlin 336,

with a new Bushnell Trophy XLT 3-9x 40. I started out about 40 yards, and I found out it was hitting very low, and missing the cardboard. I moved closer, around 25 yards. I was able to at least hit the bottom of cardboard now. I made a small adjustment to the right, and cranked the scope to hit higher. I basically walked my holes right up the target till I touched bullet holes in the bulls.

I shot the whole box at this point and need to get more shells to move a greater distance. Here's my problem, I used all the adjustment to go higher, bottomed out. I have never ran across

this before. I have decent base and rings. I used my removable Loctite for all the screws, which I always do. Has anyone in here ever shimmed your scope, and if you did, did you shim the base or rings ? Did you buy the shim kit, or was able to make your own shims ? Since I'm here, anybody lap your scope rings ? I hope this all makes senses. :camera:

thanks ahead of time.

too_

[Shoobee]

I always start by zero-ing the travel of the scope within the scope, before I mount it.

Don't know if you did this or not.

The L/R adjustment (windage) should be centered, as should the U/D adjustment (elevation) before you mount it.

The next step is to mount it with the shortest posts that give you enough barrel and receiver clearance. The closer you can get your scope to your barrel, the better your accuracy will be.

Don't know if you did this as well.

Next, I will mount the scope using a laser boresighter, from the table to the wall, and make sure the + of the scope is exactly the amount of inches above the center of the bore as shown by the laser as the scope is mounted above the barrel.

This way the scope is now centered and the rifle is shooting flat. That should have solved your original problem. This will tell you if the elevation adjustments by centering are off to begin with, due to faulty manufacturing.

Not sure if you did this either.

Once I get this all set up, I will slowly remove the scope mounting screws, on one side at a time, and replace them with locktight or with clear fingernail polish, samee same G/I.

Don't know if you did this also.

If you did all this, then now you are ready to go to the range.

Our range at the 100 yard section also has a few 50 yard and 25 yard benches as well. And on some ranges you can move the targets up to 25 or 50 or 75 yards from 100 yards as well.

You should start on the 25 yard range first. Your bullet impact should be the same distance below your + aiming point as your scope is mounted above the bore line.

Next at 50 yds, it should be slightly lower, if at all. There is not much drop on a rifle bullet at 25 or 50 yards.

You can adjust your scope to zero at any range you want, but the closer you do it, the more parallax you may be introducing, depending on how high your scope is mounted above the bore line due to the height of the posts.

At some given distance, due to the laws of physics and gravity, you can zero-in your impact point at either the earliest or latest point of the arc of the bullet from the muzzle to the target.

Near maximum range, you have only one choice, at the far end of the arc, after the bullet has first travelled above the gun-target line.

But while the bullet is still travelling below the height of the posts supporting the scope, there is another such point as well.

Typically, whatever range you sight your scope or set your scope for, halfway to that point will be the highest point of travel of your bullet.

That's why a military sniper with a scoped rifle set for 700 yards will shoot for the chest at 700 yards, belt buckle at 600 yards, knees at 500 yards, feet at 400 yards, knees at 300 yards, belt buckle at 200 yards, and chest at 100 yards. Because the midpoint of the bullet flight is going to be around 350 yards on a 700 yard shot. This sniping example shows the dynamics of the bullet travel. Same is true for hunting big game as far as the bullet dynamics goes.

Not sure why you had so much difficulty, unless you skipped one of those critical steps.

Good luck next time around.

Edited September 19, 2012 by Shoobee

[too_pointer]

Shoobee, Thanks for spending the time in your answer, I appreciate it. I still need to know about shimming the scope, as I don't have any adjustments left to raise my point of

impact. Your explanation was great. I would prefer to make my own shims if I can.

From what I know, I would need to shim up the back of scope base to raise my

point of aim. Also, I have never lapped any scope rings, and wonder if that is popular ?

Thank you all. :clap:

too_

[Strut10]

You might want to try a shim cut out of the side of a pop can. Usually runs in the .0040"-.0050" neighborhood.

[dbHunterNY]

lapping the rings might work, but i'd do what shoobee said first. Don's idea sounds good with the pop can. also not sure if the type you've got would allow it, but you could try switching the rings (move front ones to the back and back ones to the front). to add to what's been said i always turn screws to contact rings. then i turn each screw a 1/4 turn at a time, alternating to opposite screws (example: front ring left screw to back ring right screw). that way it doesn't migrate in the rings or turn as you're tightening the screws.

[too_pointer]

O.K., that all makes sense. I think if I need to shim, I will shim the rear end of the back

base.

thanks all.

too_

[pruts]

you could try switching the rings (move front ones to the back and back ones to the front).

I work with a guy that had the same problem as you and he switched the bases front for rear and his problem was solved. Apparently the set he had, had a front and a rear. I don't know if this is common or not

[LETMGROW]

I work with a guy that had the same problem as you and he switched the bases front for rear and his problem was solved. Apparently the set he had, had a front and a rear. I don't know if this is common or not

I would check the rings or get different ones first. While you could shim the scope I wouldn't recommend doing this unless it was a last resort. I still wouldn't do it.

Something is not properly aligned to start with. Find the problem and correct it. Shimming a scope will put undue stress on the scope whem it is tightened down. Eventually this will lead to trouble. The scope should lay comfortably and squarely in the bottom 1/2 of the rings and paralell to the barrel without the aid of anything else. If it doesn't, try setting another scope in the rings. Does it sit ok now? If not the rings are bad or installed incorrectly. If the scope sits ok now the new scope may not be straight to begin with.