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Matching a scope to a centerfire rifle

6951 Views 33 Replies 11 Participants Last post by  J Miller
Someone requested the scope info be moved from Gunsmithing to the Scope topic so I did a copy-and-paste on part of my post and of course had to add some new stuff.

Here are some guidelines that might help when selecting a scope for a hi-power rifle. The basic rule is to match the scope to the type of shooting you plan to do and to the usable range of the gun.

Basically there are two types of shooting requirements for high power rifles; hunting and target/varmint. The needs are radically different.

Here are some things to consider for a hunting scope:

Eye relief: The range of distance your eye must be from the lens to get a full view. The more powerful the magnification, the more narrow the eye relief gets. This makes it very difficult to shoulder the gun and find a view in the scope. At 4X you'll have at least 1.5" of eye relief range. This means your eye can be anywhere from 3.5 to 5" from the lens and still get a full view. At 12X, that narrows the range to about a 1/4" sweet spot. Your going to spend valuable time just trying to get your eye to find a view.

Field of view: As magnification increases, your field of view decreases. Field of view is rated by how wide an area can be seen at 100 yards. With a powerful scope, you will have a hard time locating your target because you can't see a large enough area. At closer ranges, all you see is hair and you won't know if you are aiming at the head or ass.

Light transmission: The more powerful the magnification, the less light is transmitted through the scope. To compensate for this, manufacturers use a large objective lens. Though it fixes one problem, it generates several more. The scope will be longer, heavier, and will require higher rings to clear the barrel. Higher rings move the scope farther above bore line so the trajectory doesn't track as well. Additionally, higher rings make the scope more sensitive to recoil and position the scope above normal eye level.

Parallax: With scopes 9X or less, the factory presets the parallax to 100-150 yards. With scopes 10X and more, parallax won't track so an AO ring is required. Parallax amounts to having the cross hairs in the proper focal plane. The more parallax is off, the more cross hair drift you get. The higher the magnification, the more parallax is affected. Clamp your gun in a vise and position the cross hairs on a target. As you move your eye up/down, left/right, you can actually see the cross hairs move on the target when the gun is totally stationary. When parallax is adjusted properly, you won't see any cross hair drift. If you get cross hair drift because your eye wasn't positioned exactly centered, your groups will drift and give the false indication of poor accuracy. When hunting, you usually don't have time to play with the AO ring to correct parallax.

Wiggle factor: The higher the magnification, the more wiggle you see and the harder it is to hold on target. For me, 4X is about the most I can handle without a rest.

Despite what you may read, most non-magnum rifles have a max quick kill range of 200-225 yards. Any shot beyond that is iffy at best. No doubt, deer and elk have been killed at considerably longer distances but more times than not, you will wound the animal and it will run off, never to be seen again. Using the standard of 1X per 25 yards, and a range of 225 yards, a 3-9X scope is just about perfect. I always keep my scope on the lowest X setting. If game is spotted at a long distance, you will have plenty of time to adjust the zoom ring. If something jumps up close, you don't have time to find the target in the scope, adjust the AO ring, play with the zoom ring, and take the safety off. You need to be ready for action immediately.

The most common mistake hunters make is to "over scope" their guns. Your hunting success rate will greatly improve if you stay away from high magnification scopes. I like a 2-7X or a 3-9X scope the best (3-9 is the most popular scope on the market). The magnification tells you a story; if the target is too small at max X, it is probably out of range for a quick kill shot.

Most target and varmint shooting is done from a rest where time is not critical. That means you have plenty time to get a good sight picture, adjust your zoom and AO ring, then get very stable on a sand bag. Here's where high magnification is more desirable. Yes, you still have the same issues as above but from a bench rest, they are much easier to deal with. Target rifles are more accurate than hunting rifles and are capable of small groups out to 300 yards or more. The general rule for magnification is 1X per 20 yards. Therefore, a 4.5-14X is one of the best power ranges for prairie dogs or punching paper up to 300 yards. Long range target shooters often go up to 8-24X or more.
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Iowegan, what would be the best for 444 marlin at shorter range and in the bush? 2-7x or is there one better?
quote:Originally posted by white dog

Iowegan, what would be the best for 444 marlin at shorter range and in the bush? 2-7x or is there one better?
My choice would be a 1-4X or 1.5-5X. You have plenty of magnification for a long shot and just crosshairs for close shots.
very handy information thankyou very much for reposting in its own topic.
white dog, The 444 retains plenty of energy down range to kill a deer but it has a trajectory like a rainbow. If you zero the scope at 140 yards (correlates with 1.5" high at 100 yards), it will give you a 4" channel. That means the bullet will hit not more than 2" above or below the cross hairs from the muzzle out to 170 yards. After 170 yards, the bullet drops pretty fast. Low power (2X) and the good light transmission that goes with it is valuable when brush hunting. Using 1X per 25 yards as a reference, that would make 7X the highest magnification. Yes, a 2-7X would be optimum if you want to take full advantage of the gun's range.

If you know you will never have a shot longer than 100 yards, then follow 2400's advice.
Thanks 2400 for the help and thank you Iowegan for the advice and informational post.
Another thing to keep in mind when buying a scope is that the higher the magnification the harder it is to "hold it steady". I've got either 4X or 2-7X on all my big game rifles and I've never felt left out by not having more magnification power. In fact I rarely turn the scope up past 5X unless I'm sighting in or working up new loads.
If you have a 3-9X or 4-12X next time you're hunting or just shooting when you're done look and see where you have it set. I may start on 6-7X but always seem to wind up between 3-5X at the end of the day.

On my varmit guns I have high magnification scopes (6-18X) but the targets are a lot smaller and the average shooting distance is farther.
As you said... I hunt with the lower end... Then raise the power for shot placement to around 7-8X... Benched for sighting around max...

I am considering new lower scope mounts, but it may be to attach it to a new Ruger M77 MKII...:D
quote:Originally posted by RNettles

As you said... I hunt with the lower end... Then raise the power for shot placement to around 7-8X... Benched for sighting around max...

I am considering new lower scope mounts, but it may be to attach it to a new Ruger M77 MKII...:D

Well, did you get a new gun? :D
My favorite scope for my hunting rifles is either a 3.5X10X50 VXIII or a 4.5X14X50 VXIII Depending on the caliber
quote:Originally posted by 2400

quote:Originally posted by RNettles

As you said... I hunt with the lower end... Then raise the power for shot placement to around 7-8X... Benched for sighting around max...

I am considering new lower scope mounts, but it may be to attach it to a new Ruger M77 MKII...:D

Well, did you get a new gun? :D
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RNettles, that all ya' gonna say about that beaut is Yeppers....shess...ya' could at least give us a range report or sumpin" Yeppers....?
I think if you check the forum, I already have...:D
thanks,Iowegan for the lesson on how to pick a scope. I learn so much from your postings, thanks again.
Excellent info by Iowegan but I'd like to make a small addition. My serious hunters have fixed power scopes, 4X or 6X. If I have trouble seeing the target at 300Yrds, I don't take the shot. Fixed power scopes are lighter and brighter, usually with better field of view at a given magnification than variables. They have fewer optical elements, thus better light transmission under unfavorable conditions and you don't have to fiddle with the variable feature wasting time. Yes, I do use variables for varmints and target shooting.;)
Ahab, I did not address antelope hunting but there really isn't much difference in scope requirements than other types of hunting except the shots are often taken from longer distances. I still believe 1X per 25 yds is the best magnification.

Not many years ago, there was a 3:1 zoom ratio limit in scopes (ie: 3X9). Now that has been extended to a 4:1 ratio (ie: 3X12). Lens elements are now ground via computer control and the man-made glass is far superior to the best flint glass used a few years ago.... better light transmission. In the past, any scope with more than 9X had an AO for parallax correction. Now that threshold is well above 10X. Field of view has been improved as has eye relief. What all this means is scopes have really improved in the past few years. Now to get these improvements, you will have to go with a top shelf brand (ie Burris, Leupold, Nikon, etc). I doubt a Tacso will be much different than before. Of course higher magnification still has its draw backs as I stated before.

If a hunter can place a shot for a successful kill at a distant antelope, it's hard to argue that a 4X or 6X is a bad choice. I would say that most hunters use their equipment for many years without upgrades and may not even know a better mousetrap is available. Kind of a "don't fix what ain't broke" concept vs a "bury your head in the sand" concept.

Fixed power scopes are almost a thing of the past. Not many companies even offer them now. I firmly believe if you compare a good 6X fixed with a newer good quality 3-9X with the dial set to 6X, you won't be able to tell the difference.
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I'm not a scope user normally. I prefer aperture sights. However for my birthday last August I received a Marlin MR-7 bolt action rifle in 30-06. It has an older Simmons 3-9 X 40 8 Point scope mounted in Weaver rings on Weaver bases.

Well it turns out that the variable power setting is jammed, frozen, or what ever. I've been told that happened when somebody overtightened the scope rings.

So, I'm going to test fire this rifle hopefully soon before the weather here in IL turns sour and see how it works. The scope although jammed is on 3X, so I should be able to shoot it that way.

My worries are that there may be insufficient room between the rear of the scope and my eye brow. I shouldered the rifle normally and had my wife measure that distance.
Shouldered normally there's 3.5" clearance. However at that position there is a dark shadow around the outer perimeter of what I see when I look into the scope. If I pull in so I get a complete clear view the distance between my head and the scope reduces to about 2" to 2.5".
The scope has a rubber ring around the eye end, but I still don't feel comfortable with it.
Also the scope is as far back on the rings as it will go so I have no leeway to reposition it.

Is this normal? Remember I know zip about scopes. I think you'll remember I usually call them carrying handles when I tease the guys on TRF.

My plans are to test fire the rifle, then pull the scope and send it back to Simmons. Hopefully since this one is discontinued they'll replace it with something "better" maybe.

As for my intended use, well until I get out of IL it will be a range rifle occasionally. Once out of here I plan on trying some hunting.
I kind of like the idea of the 3-9 X, although since I've never used a scope I have nothing to compare it with.

Any comments, suggestions, or instructions would be appreciated.

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J Miller, Please don't be offended but Simmons scopes are not worth the postage to send them in. What you are experiencing is very common for cheap scopes. I know I'll be blasted by those Simmons owners that swear by them but believe me, they are at the bottom of the barrel. New retail cost for a 3X9 8 Point is under $50.

Ideally, when you shoulder your rifle and your head is positioned like it would be for iron sights, the scope should be mounted in a position where eye relief aligns and you get a "full picture" view on the highest zoom setting (natural eye relief). You'll find eye relief has at least an inch of tolerance at the lowest zoom setting but as you turn the zoom ring up to the highest magnification, eye relief becomes a narrow "sweet spot". The actual distance from the eye should be about 3". Not to worry ... your head follows your body during recoil so you shouldn't get a black eye.

Based on your post, it sounds like your scope is mounted way too far forward and that could be why the zoom ring locked up. I would loosen the ring screws and reposition the scope back until you get "natural" eye relief. Maybe the zoom ring will start working too.
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I can't reposition the scope any further back. The front ring is already butted up against the bell of the front end. And the rings are as far back on the bases as they can go. Here's a pic of me holding it:

However I have been tempted to loosen the ring clamps and see what happens.

You mentioned the steel Leupold mounts in a post above, can you give me the model or part numbers so I can make note of them? I do prefer steel to aluminum, and eventually I will replace this with a much better scope. I'm just not sure what scope yet.

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If you go with a one piece base, you should be able to put your scope where ever you need. Any good gun store should be able to help you out with mount.

By the way, nice rifle, whats the model and caliber?
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