I recently read a couple of articles in two of the major gun mags in which the authors spent quite a bit of time discussing the importance of “exit pupil” when evaluating scope performance. In case you didn’t know, exit pupil is a term used to “measure” the brightness of a spotting, rifle, or pistol scope. It’s expressed as a number in millimeters that’s supposed to represent the amount of light exiting a scope’s eyepiece.

     The concept is based on the fact that the pupil in the eye of a young, healthy individual will dilate to approximately a maximum of 7 mm’s. Of course when the eye is dilated to its largest diameter, the maximum amount of light is passed through the cornea to the retina. Ideally a scope should then have an exit pupil number of 7mm for the optimum amount of brightness.

     So how is exit pupil determined? Simple. Just divide the diameter of the scope’s objective lens by the magnification. So if you have a 44 mm objective lens on a 6 X 24 rifle scope, the exit pupil is just over 7mm at 6 power. At 24 power, the exit pupil is only 1.8mm. While 1.8mm is usable in bright sunshine, it’s not all that great on dark overcast days.

     It’s interesting to note that in spite of their significantly larger objective lenses, spotting scopes usually have exit pupil numbers much lower than rifle/pistol scopes. Why? Because spotting scopes usually come equipped with much higher magnifications. For instance, lets take a regular 60mm spotting scope with a run of the mill 20 X 60 variable eyepiece. At 20 power, the exit pupil number is 3 mm, which is ok but really not very bright at all compared to a good rifle scope. At 60 power, it’s only 1 mm, which is down right terrible. Even if we spend bigger bucks and get a jumbo 80mm spotter, the numbers change to only 4 and 1.3mm’s respectively. (4 mm’s is considered by many to be the minimum number useful in dark, overcast conditions or twilight.)

     High magnification powers not only makes the image unacceptably dark, but resolution (the ability to see small details distinctly) also drastically suffers. Of course, the ability to see small bullets holes at long distances is of particular importance to us as silhouette shooters. Additionally, color fidelity goes to the devil as well. Color fidelity isn’t a big deal to a target shooter, but it’s extremely important to a hunter trying to scope a buck in the timber or brush, or a birder trying to spot that yellow belly sap sucker in the maple tree.

     Considering that brightness is one of the prime considerations that shooters use in selecting a spotting scope, you can’t help but wonder why the manufacturers insist on furnishing them with super high power eyepieces that drastically reduce their brightness and therefore their usefulness. I recently put that question to a very good friend who works for one of the major scope outfits, and he replied “because the public believes that when it comes to power, more is better”. He added “The public doesn’t understand that brightness and clarity are far more important than magnification in seeing the target well.”

     Although I own two different spotting scope with eyepieces that will go up to 45 and 60 power respectively, they’re always set on their lowest power setting for maximum brightness (15 & 20X), and they work great that way. This is especially important for myself because, although I hate to admit it, I’m past my prime years physically and so my eyes probably aren't dilating to 7 mm any longer. I’m probably in the 5 or 6 mm range now so I need all the brightness I can get and it’s only going to get worse.

     In an ideal world, I’d like to see someone make a 60mm spotting scope with a power range of 8.5 X 15, and an 80mm scope with a power range of 12 X 20 power. At these power levels, brightness would just about be ideal for the scope user.

     While exit pupil numbers might have some theoretical value, they’re really a very poor way to evaluate a scope’s optical brightness. Say we have two 60mm spotting scopes and both are equipped with a 15 X 45 power eyepiece. One scope is an $69.95 discount store special made by a no name company in Lower Elbania. The other is a premium quality major brand scope selling for $500. Both scopes have identically sized objective lenses and equal magnification powers. Therefore, they will also have identical exit pupil numbers. Does that really mean that both scopes have equally bright images? Absolutely not! I’m sure the manufacturer of the inexpensive scope will brag about its exit pupil numbers in its literature, but the relationship of those numbers to a decent optical image is pretty tenuous at best.

     So what makes the difference between the brightness of the images produced by the two scopes? Only little things like the quality of the optical glass, or perhaps the fact that some of the lenses on the cheap scope may not even be glass at all, but rather plastic. The design, type, and grade of the lenses used, and the quality or the ability of the internals to hold everything in precise alignment are also prime issues.

     Are the lenses coated? Are they multi coated? Are some of the lenses coated or multi coated and some are not? Are all of the lenses multi coated on both sides or on just one side. How many coatings of what materials do they have?

     I’m making a major issue of the coatings because they are actually an extremely important factor in determining the level of performance that a scope will deliver. Why? Because they will actually increase light transmission above the theoretical exit pupil number. Additionally, they’ll also increase contrast and reduce reflections, glare, optical flare, and a number of other components affecting the quality of the image.

     All these factors and more have a tremendous impact on the brightness of the image delivered to the eye of the observer, yet the value of all of these features aren't addressed, and can’t be addressed by over-simplified and over-used exit pupil numbers that seem to be the darling of some. So really, what good are these numbers? Answer - not much. The only and best way to judge the brightness of a scope is to look through it and see for yourself what the image looks like. If your local retailer won’t let you compare the image in a variety of scopes that they have for sale, shop elsewhere. Check out the scopes your friends are using and get a feel for what looks good and above all, don’t get wrapped up in exit pupil numbers.

How Important Are Spotting Scopes Anyway?
     When ever you see a photo of a silhouette match in progress, what do you notice first? Usually, the photo depicts a sea of spotting scopes with the spotters intently peering through the various eye pieces. Oh yes, then down on the ground you finally notice the shooters.

     Spotting scopes are obviously an important or even a critical piece of equipment in our sport. I've always felt that a good spotter with a good scope can be worth 2 points to even a well skilled and experienced silhouette competitor. For the less experienced and skillful, the value of the spotter actually increases, but only if they are equipped with a good scope which allows them to clearly see what's going on. A good spotter not only observes the placement of the shot but also can act as a coach, teacher, advisor, or even father confessor.

     So why is it then, that so many shooters skimp when it comes to their spotting scopes and hobble the effectiveness of their spotters to do their job of helping the competitor score points? It doesn't make sense. It's not unusual to see spotters using scopes 30+ years old whose lenses have become dim and yellow with age and whose internals are far out of alignment from years of being dragged and bumped around.

     Then there are the discount store specials. Wanting to be open minded about such things, I recently decided to do a review of just such a scope from a well known company. The low priced 60mm scope was visually attractive, waterproof, and rubber coated (even the lens caps).

     NRMA also has a deal where you can get a bundle of materials called the Catalog of Catalogs. It contains five reloading guides, two mail order catalogs from reloading suppliers, seven component and equipment catalogs, and a safety guide for only $10. This bale of catalogs weighs in at over three pounds and has just about all the info anyone would need to get started in reloading whether about powder, bullets, equipment, or whatever. To get the package, just send a check or money order to NRMA, 1 Centerpointe Dr, Suite 300, Lake Oswego, OR, 97035 and ask for the Catalog of Catalogs. Going through all this stuff will keep you busy for a long time.

Proper Mold Temperature
     Determining proper mold temperature is something of an art. As most bullet casters are aware, mold temperature is critical to the casting of bullets that are properly filled out and without imperfections. Just like the porridge in the story of Goldilocks and The Three Bears, the temperature of the mold has to be “just right” - neither too hot or too cool.

     Of the two conditions, being too cool is probably the most vexing. If the mold is too cool, the bullets will come out wrinkled, indented, and looking generally strange. Even when the bullet seems to be normal, the surface can have an uneven appearance in color. This is an indication that the internal density of the bullet is probably not uniform.

     The most subtle problem occurs when the mold reaches a temperature that is close to the correct temperature but still not quite there. Under a casual examination, the bullets will appear to be ok. However a close, critical examination will reveal faint, but very real flaws. At this point the casual caster might be fooled into thinking that the proper temperature has been reached and will accept bullets that are actually substandard.

     Since we don’t have an easy means of directly measuring the temperature of the mold itself, how do we determine when it becomes hot enough to produce quality bullets. Actually there is a very simple, but indirect way to determine when the correct temperature has been reached. Examine the underside of the sprue. For the uninitiated, the sprue is the puddle of molten lead that accumulates on the top of the mold when it’s poured down into to the cavities. Once it solidifies, the caster hits the sprue plate with a wood mallet or whatever, and the now solid lead puddle is sheared off.

     If the mold has not reached the proper temperature, the bottom side of the sprue will be wrinkled with lines or mini crevices meandering across its surface. However, when the mold has reached the appropriate temperature, the bottom of the sprue will be perfectly smooth without any lines what so ever. Flawless bullets will now be dropping out of the mold.

     We now have to worry about the mold getting too hot from continuous use. Gun writers with lots of money recommend using two of the same mold or perhaps two different molds, alternating between one and the other so neither gets overheated. I don’t like this method as it takes longer to get the two molds up to the correct temperature. This can be shortened somewhat by pre-heating the molds on the side of the electric pot while it’s coming up to temperature and melting down your lead. Drape a piece of aluminum foil over the top of the pot to trap the heat when doing so. This method works well with a single mold also. Never the less, getting two molds up to the right temperature is a pain.

     Rather than using the dual mold method, I prefer to use a small fan on the loading bench to prevent my molds from overheating. When I notice that the bullets are looking a little frosty, or perhaps developing “whiskers” on the side, or the sprue mark on the bottom of the bullets doesn’t have a smooth shear across, I’ll just hold the mold in front of the fan for about 5 seconds. That takes care of the situation with no problems. The fan, which I bought for $1 at a flea market, also helps to keep me cool, increases air circulation and disperses lead fumes.

     Follow these simple procedures, and you’ll be as content as Goldilocks eating porridge that’s juuuust right.