308 scope question

I don't recall having a problem in seeing at the end of legal shooting light with a 40mm objective, although I grant that a 50 might be a smidgen better.

4-12 or 4-16

My 308 wears an older Nikon Prostaff 3-9x40 with their BDC. It has been a great scope and I have no issues recommending them to others. The 50mm will gather more light and help during dusk/dawn. Through trial and error, I figured out that my 308 loads correspond exactly to the BDC when at 8x magnification. My range is only 350 yards though, so that is as far as I have been able to stretch it out. I think you may be able to find better prices online, but you may like the idea of being able to put your hands on the item before you plunk down 200 clams. Buy the scope either way; I'm sure you won't regret it!

The older I get the more I depend on extra power. When I was in my 20's and 30's I could shoot 1 inch groups at 100 yards with a 4 power scope. Now I hunt with a variable set on 6 power and if I have the time before a long shot I turn the power up to 10. I've never found the need for an objective lense larger than 40MM even in low light, and you can't go wrong with a Leupold variable in dual dovetail bases. The best thing that ever happened to a rifle scope is a 30MM tube but they are expensive.

The lense diameter has nothing to do with the brightness of the light coming through a scope. That is deteremined by the scopes light transmission rating. A larger objective will under certain circumstances let in more light volume, but the brightness is determined by the lense quality, not size. A 40mm scope rated at 92% light transmission will be brighter than a 50mm lense rated at 88%.

You will get a better quality lense at the same price with a 40mm lense. A 40mm lense set on 8x will let in exactly the same volume of light as a 50mm lense will at 10X, as well as a 20mm lense set on 4X. Assuming equal quality glass a 50mm lense will offer a slight advantage only when set on about 7X-9X. At any magnification greater than 9X or less than about 7X there is simply no difference. Bigger lenses only allow you to use higher magnification in low light.

Nikon makes a good scope, but the same scope with a 40mm lense will save you money, be easier to mount and use, and still give you more light than you can use until long after legal shooting hours are over as long as you never go over 8X magnification.

The bigger the objective lens, the more light hits it. For 2 equal scopes, say, 2 Nikon Prostaffs, more light into the scope = more light into the eye.
Take the light from 1000 square mm, or 2000 square mm, and focus it down to 20 or 40 square mm, that spot of light is brighter. This is easily demonstrated.
If you want better low light performance, get a bigger objective, and learn where to set the magnification to work best for your eye.

I take the most game at last light, so I like a lot of glass. 4 of my rifles wear 3x9x40's, two are leupolds, two nikons. My 336 wears a leupold 2.5x7x33, and a 10/22 high-end build wears a leupold VX IV 4.5x14x40 AO.

When I know I am going to be sitting until dark in my farthest blind to feeder, I use a savage weather warrior .308 wearing a bushnell elite 5x15x50 AO. The optics are extremely bright, easily as good or better than my leupolds. It is bulky and heavy, though. I would not choose it for hiking or woods hunting, and even though the elite series are well made and not cheap, it is probably not as robust for hard hunting. It really is best suited for stationary hunting. It is awesome for grading deer. It is not uncommon to have 6-8 feeding together. A lot of glass makes choosing the best shooter much easier. The dark woods (heavy canopy) behind that feeder offer an occasional 230 Yard shot, and with the tack driving rifle and the clarity and light gathering of that scope, I have tremendous confidence to take a long shot.

2 equal scopes, both set so the exit pupil is the same size as (or just a little bigger than) the entrance pupil of the shooter's dark-adapted eye, the bigger objective is brighter.

FWIW, I have 2.5-8x36 scopes on my Ruger 77 RSIs (.308 & .270) and on my No. 1A in 6.5x55. If you're shooting at 300 yards or less, this is plenty, both as to magnification, light transmission and, importantly, weight.

YMMV.

FH

I have a Nikon Buckmaster 4.5-14 x 40 on my 308. I've been very happy with it.

I have a half dozen rifles in .308, all have Leupold VX3's or Mark 4's in 4.5-14 to 8.5-25. Probably my favorite is the 6.5-20x50mm Mark 4.

Under 300 yards, a 3X-9X will be more than adequate. A quality fixed 4X or 6X would allow you to buy better glass for the same money as a variable magnification with inferior glass.

A larger objective does transmit more light, but the upper end seems to be about 50mm. Anything larger and the eye does not take in more light, even though the scope technically transmits more.

The bigger the objective lens, the more light hits it. For 2 equal scopes, say, 2 Nikon Prostaffs, more light into the scope = more light into the eye.
Take the light from 1000 square mm, or 2000 square mm, and focus it down to 20 or 40 square mm, that spot of light is brighter. This is easily demonstrated.
If you want better low light performance, get a bigger objective, and learn where to set the magnification to work best for your eye

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This is correct, though, as jmr said, all else isn't always equal. Sometimes you see lower quality glass on the larger objective to save costs, though this is an issue more with lower end scopes. This shouldn't be a problem with Nikon, but I'm not that familiar with their Prostaff line.

Another thing to consider with a larger objective is that you may need to mount it higher.

vortex 2.5-10, i personally keep eyeing one... I'll probably have one before next hunting season.

I have two Nikons, one on each of my 308s, both with BDC. I have a 3-9 on my BLR and a 2.5-10 on my GSR. No problems into sunset on either. However, i am shooting 100 yards at the range and under 50 yards in my hunting spot.

Scopes

I have a Leupold Vari XIII 3-9 on my 30-06, A Redfield Widefield 2-7 on my Ruger model 77 lightweight .308 The 2-7 is just right on the Ruger. I have yet to kill a deer with a scope turned up higher than 5. I doubt I'll buy another 3-9 scope, much less a bigger scope.

This one. (Nikon)



and this one. (Leupold)

I'll throw in a wildcard here. I have a 4x12x42 Redfield on my .308. I shot my first deer ever with it last month. 200 yard shot about five minutes after legal shooting light (1/2 hour before dawn here in OR). I thought the scope performed very well in an extremely low light situation. They wont cost an arm and a leg and have a lifetime guarantee. Just my 2 cents.

The lense diameter has nothing to do with the brightness of the light coming through a scope. That is deteremined by the scopes light transmission rating. A larger objective will under certain circumstances let in more light volume, but the brightness is determined by the lense quality, not size. A 40mm scope rated at 92% light transmission will be brighter than a 50mm lense rated at 88%.

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Ummmmm..... not exactly.

The amount of light that an objective lens will collect is directly proportional to its surface area. A 50mm lens vs. a 40 mm lens works out to a 1.56X advantage.

The transmission efficiency of a scope does affect your ability to see shadow detail in the presence of off-axis light. The reason is that light that does not get transmitted gets scattered inside the scope, and washes out shadow detail. So transmission percentage is important because with better transmission, you get better contrast. In any decent system, the contribution of transmission percentage to perceived brightness is minimal.

Exit diameter is front objective diameter divided by magnification. If the exit diameter is greater than the size of your eye pupil, the extra light is just wasted. 2mm is pretty slim pickings, and 7mm is as much as you can use. A 3-9x40 scope set to 4x has more light than you can use, but at 9X it's 4.5 mm, which is enough.

Personally, I don't care much for magnification beyond 9X in a hunting scope. Even with my 70 year old eyes, that's plenty for big game at 3-400 yards. More is mostly a waste.

If you do opt for more magnification, then a larger objective lens would be important.

................. HK GUNS: You have a 308 cartridge loaded backwards in your magazine. (Look at your pic of the MR 762 A1 you posted. The mag all in poser position has a rd loaded backwards......)

Nice rifles, but good grief young man......

You could put your eye out.....

i love the backwards loaded round always get a kick out of it.

fragout said:

................. HK GUNS: You have a 308 cartridge loaded backwards in your magazine. (Look at your pic of the MR 762 A1 you posted. The mag all in poser position has a rd loaded backwards......)

Nice rifles, but good grief young man......

You could put your eye out.....

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Intentional, not young and thanks.