Nikon M-308 Riflescope Review
With each new rifle I review, I always like to pair the rifle up with a new riflescope. Recently I received a new Ruger SR-762 rifle for review and I was immediately on the hunt for a riflescope. The SR-762 is a piston driven AR styled rifle chambered in 7.62 NATO (.308 Win) and clearly has the capability to deliver energy down range, so I wanted a good riflescope for this AR platform that wouldn't break the bank, yet one that still provides good zooming capability and quality. Today it seems that there are more quality riflescopes on the market than ever before and manufacturers are adding scopes to their product lines that are directed specifically towards the AR styled Modern Sporting Rifles (MSR). A few years ago, Nikon was one of those manufacturers with the release of their P Series and M Series optics. The P and M designations relate back to Nikon's Prostaff and Monarch lines that were the foundation for their new P and M Series riflescopes. These two series of scopes got their optical performance and basic features from the Prostaff and Monarch scopes, and then Nikon added to their features target style turrets, side focus (parallax) adjustments and reticle options directed towards AR style rifles in calibers such as .22LR, .223 REM, .308 WIN and .300 BLK.
Over the years, I have become a fan of clean uncluttered reticles, target style turret caps and a side focus (parallax adjustment) knob. These features are why I was continually drawn back to the Nikon M-308 4-16x42 Riflescope as I was doing my search for a new scope. Another feature that helped me decide on the M-308 was that the scope comes with a 20 MOA mount which represents a cost savings. Last, I have reviewed some other Nikon rifle scopes such as their P-300BLK and Coyote Special and have found them to be good quality scopes and reviewing the M-308 gives me the opportunity to take a detailed look at their Monarch optics.
Since the Nikon M-308 comes in two different reticles, I was faced with a decision on which to get. Nikon offers the M-308 in either a Nikoplex or BDC 800 reticle.
Figure 1 - Nikoplex
Figure 2 - BDC 800
The reticles are not the only difference between these two scopes. The elevation turret cap markings are also considerably different. The Nikoplex version comes with an elevation cap that is marked in yards and calibrated for a 168gr HPBT bullet with a ballistic coefficient of .458 to .478 and a velocity of 2680 feet/second. The BDC 800 version is a traditional style turret cap marked in 1/4" MOA adjustments. I feel it would have been a nice touch if Nikon would have provided both turret caps with the Nikoplex version scope. Doing so would have allowed the shooter to have a calibrated turret cap for use with a specific match round and a standard MOA style cap to allow the ability to dial in an elevation correction for a greater range of bullet types and velocities. I discuss the use of the Nikoplex cap in detail further in this review.
If you choose the BDC 800 version of the scope, then none of this is an issue. You can use the elevation turret just like you would with any target style turret, or you can use the BDC 800 subtension features that are calibrated to the 168gr HPBT at 2680 feet/second. Also, Nikon provides their "Spot On" Ballistics Match Technology program to help you determine the subtension values on the BDC 800 reticle for nearly any bullet and velocity combination.
When you consider the features of the BDC 800 version scope, it probably makes you wonder why I chose the Nikoplex version for this review. To be honest, I struggled with the decision, but in the end I prefer an uncluttered reticle along with the fine cross hairs in the middle of the reticle. I also feel that the yardage adjustments will be close enough for my shooting situations and most likely the elevation turret will be set on 200 yards for the majority of my target engagements which is how I zero my traditionally scoped (no target turrets) hunting rifles.
Since price is a consideration for most of us, it seems that Nikon wanted to keep the cost of this scope relatively competitive with the market. I would consider the Nikon M-308 riflescope to be a mid-range priced scope with their MSRP of $530 for the Nikoplex version and $550 for the BDC 800 version. At the time of this review, Nikon was having "save $100 instantly" sale and you could order the scopes direct from Nikon for $430 or $450, respectively.
During my reviews I like to compare my results to the manufacturer's claims where possible so the following text in colored italics was taken directly from the Nikon website on 2/14/14 and gives the Key Features and Specifications for the M-308 4-16x42 Nikoplex Riflescope. The , and are my way to keep up with details that I have covered in this review with either photos, commentary or both.
The Nikon M-308 riflescope came boxed as shown below.
I included these next several photos so you can see the advertising information provided on the outside of the box.
The end of the box had a label with the critical information for the scope, such as:
What's In The Box
When I removed the box top, the contents were packed as shown below.
Inside the box were the following items:
The Nikon M-308 Riflescope
The Nikon M-308 Riflescope comes in a black matte finish and measures 13.5" in length with the eyepiece fast focus set and a mid range position. The scope comes with the "M-308" sticker on the eyepiece, but this sticker is easily removed.
From these photos you see that the scope has target style turret caps and a side focus (parallax adjustment) knob. The mounting length (total length of the 1" tube) measures about 6.8" with the 1" tube on the objective lens side measuring 2.32" in length and eyepiece side measuring 2.15" in length. Overall, this is a generous amount of mounting length for the scope.
After studying the one-piece tube construction and overall finish, it appears that Nikon has done a good job manufacturing this scope. On the bottom of the turret housing is the port used to nitrogen purge the scope.
The side focus knob has the "Nikon" name located on the knob so that when the side focus is set to 100 yards, the lettering is inline with the body of the scope. Unless I'm specifically shooting at close or long ranges, I keep my scopes set to be parallax free at 100 yards which is generally the standard for centerfire scopes without a side focus (parallax adjustment) knob.
The scope weighed in at 20.2 ounces which was a little over the 19 ounces stated in the specifications.
The photos below show the weights of the M-308 mount (5.1 ounces), lens caps (1.2 ounces) and ARD (0.5 ounces). If you add in the weight of the M-308 mount and lens caps, the total weight of this optical system weighs in at 26.5 ounces. If you consider this includes the mount weight, cap weight and the features you are getting (4-16x42 scope with side focus and target turrets), this weight isn't too bad.
The outside diameter measured 49.34mm and has an internal objective lens of 42mm. The 42mm lens and 4-16x power range of the scope gives you exit pupil diameters of 10.5 (42/4) to 2.6 (42/16). For maximum brightness in low light conditions, you are going to need to stick with a power range of 4 to about 8 power so the exit pupil diameter will be closer to your eye's pupil diameter. On each side of the objective end is the "M-308" in gold raised lettering.
The turret caps have a distinctive look with their large gear-style sculpted features. This design allows for a good gripping surface when making adjustments.
The elevation turret cap on the Nikoplex version scope is marked with the key information needed when making adjustments and identifying the type of ammunition to use which matches the yardage markings on the cap. For this scope, one click equals 1/4" at 100 yards. Also, the yardage markings are intended for shooting a 168gr HPBT bullet (BC of .453 to .478) at a velocity of 2680 feet per second (fps). Depending on the length of the barrel of your AR style rifle, 2680 fps may not be possible.
With the turret cap marked in yards, zero is intended to be with the 100 yard mark lined up with the mark on the turret housing. On this particular scope, the marks didn't line up perfectly. One click difference seemed to shift the mark just to the left or right of the reference line.
Between the two photos above and three photos below, you can see all the markings on the elevation turret cap. Yardage is marked at 100, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 and 800 yards.
The windage turret cap is marked in 1/4" MOA increments with whole MOA adjustments labeled at each even number (2, 4, 6, etc.). Both the elevation and windage turret caps have a total of 20 MOA of adjustment per revolution. For this cap, my zero adjustment aligned perfectly with the index mark on the turret housing. For resetting zero on both the elevation and windage caps, you pull the caps out until you hear a click, rotate them to their zero position and then press the caps in until you hear a click again. Also, for both the elevation and windage adjustments, the click adjustments are very distinctive and audible.
I decided to pull one of the turret caps off and see what may be underneath. The photo below shows the actual turret portion of the scope. I was a little surprised to see that there were no visible O-rings sealing the cap. Nikon states the scope is both waterproof and fog proof so I'm sure there are seals somewhere within this arrangement. The Instruction Manual states the riflescope is waterproof and will suffer no damage to the optical system if submerged or dropped in water to a maximum depth of 2 meters for up to 10 minutes.
This next photo gives you a look at the inside of the aluminum turret cap and the the shape of the steel cap screw.
Side Focus (Parallax Adjustment) Knob
Nikon decided to go with slightly less aggressive sculpting on the ridges of their side focus (parallax adjustment) knob.
One feature that seems different on the side focus knob versus some other scopes I have used is that the knob has a locking feature. With the knob pressed in, the knob is in it's locked position and will not rotate. You must pull the knob out to unlock the knob for making adjustments. I will admit, this took some getting used to, but after a while I got the hang of it. The knob rotates smoothly throughout it's range of adjustment. Also in the photo below, notice that the elevation turret housing has marks to indicate where you are in the range of adjustment.
The side focus knob is marked with increments of 50, 60, 75, 100, 150, 200, 300, 500, 1000 and ∞.
The eyepiece end measured 44.0mm in diameter and is about 2.5" in length not including the power adjustment ring. The end of the fast focus rings has a layer of rubber to help in the event of an eye socket strike.
Power Adjustment Ring
The power adjustment ring has what I would consider to be a very slight texturing and had firm resistance when making adjustments. If there were one single feature I would change on the M-308 scope, I would have made the texturing more aggressive to allow for a better slip free grip of the ring when making adjustments. The ring is marked with 4, 5, 6, 7, 8, 9, 10, 12, 14 and 16 powers, all of which are in white lettering.
Fast Focus Adjustment Ring
The fast focus adjustment knob has a smooth feel with a total travel of just under one turn from fully in to fully out. The center photo below shows an index location on the knob that lines up with the dot on the eyepiece when there is no optical correction. The rubber texture of the ring makes for a slip-free grip when adjusting.
Nikon states the eye relief to be 4" of constant eye relief and then in the specifications they state 3.7"-4". Using these next two photos and scaling based on an eyepiece diameter of 44mm, I was able to measure an eye relief of 3.86" at 4x and 3.50" at 16x. Overall I feel the scope has a good eye relief, but it is not a constant 4". Also, my measurements are probably a little more crude than Nikon's, so I'm going to say their specification values are correct.
The M-308 Mount
The Nikon M-308 Riflescope comes with their M-308 Mount. This mount is an all aluminum mount that include 20 MOA of angle to allow for maximizing your elevation adjustments for long range shooting.
The mount measures about 5" in length and has two cap screws per cap. My personal preference would have been four screws per cap, but I can say that throughout my range testing (~200 shots) the scope has never shown any indication that it has shifted. During installation, I torqued the four cap screws to 20 in-lbs and the three cross bolts to 50 in-lbs.
The forward portion of the mount is offset to allow the front ring to extend past the upper receiver on an AR style rifle. For my scope installation, this offset was needed.
The mount is attached to the rail with three cross bolts.
The mount has three steel inserts so that the cross bolts are threaded into a higher strength steel instead of the aluminum.
The rail attachment is actually made with two clamp bars. Each of the cross bolts comes with some type of thread locking compound already installed on the bolt threads.
This mount is like a self-centering mount where as you tighten the bolts, it pulls the mount tight into the rail and aligns the mount on the rail.
The bottom of the mount has three slots that work in conjunction with the bolts to form a recoil lug so that the mount will not shift forward under the recoil of the rifle.
The M-308 riflescope comes with a set of Nikon lens caps. The caps fit great over the scope and I had no issues with them working loose when range testing.
Both caps are spring loaded to pop up when deployed.
The Anti-Reflective Device
The scope also comes with an Anti-Reflective Device (ARD) which is basically a polymer part that has a honeycomb grid that prevents light from hitting the objective lens surface from off angles. Since the ARD is made of a polymer material, the threads on the ARD are also polymer which means you need to be careful when screwing the ARD on the scope to prevent cross threading the ARD.
Although the lens cap does work with the ARD, the fit of the cap to ARD is not as snug as I would have liked. Most likely the cap would come off the ARD after a few shots.
Each time I review a scope, I always struggle trying to take photos that give the reader the same level of optical clarity I see when looking through the scope with my eyes. Regardless of how hard I try, I'm never able to truly capture the same eye relief, focus, color and brightness I see through the scope, so don't take these next photos alone as the gospel on the M-308's optical performance. Make sure you read my comments.
To start off, this first photo should give you a good idea on how crisp the Nikoplex reticle can look along with overall brightness of the scope compared to a background image when at 4x power. Nikon puts fully multicoated optics in this scope for up to 95% light transmission. I have no way of measuring this, but looking through the scope in various lighting conditions, I feel the scope was still bright in low light. As you increase the power of the scope (or any scope), doing so will decrease the amount of light (exit pupil diameter) getting to your eye, so in low light conditions and at higher powers the image does start to darken.
This next photo should give you a good idea on how the image stays in focus through the entire field of view. Looking through the scope is even better than the photo. The details all the way to the edges are still in crisp focus and overall the image has good contrast.
These next three photos shift from 4x to 16x looking at the same objects. I struggled with camera focus issues while trying to get these photos, but they give you a good example of what to expect.
Overall I believe most people would be pleased with the optical performance of the Nikon M-308 Riflescope. It seems sharp, clear and bright and throughout my several sessions of range testing I never got the feeling of eye fatigue.
For range testing, I installed the Nikon M-308 Riflescope on my Ruger SR-762 Rifle which I was also reviewing. You can see the configuration below.
While at the range during my range tests of the rifle, I shot several different types of ammunition and got some chronograph data as shown below. Since the barrel length on this rifle was 16.12", the velocity for the Hornady 168gr BTHP ammunition averaged about 2504 ft/sec instead of the 2680 ft/sec used to define the elevation turret cap yardage marks. I knew this difference would exist when shooting a shorter barrel than the standard barrel length of 22" used for generating most ballistic data for the .308 WIN caliber.
Due to these difference in velocity, I knew I needed to spend some time with a ballistics calculator to understand these differences and potentially build my own lookup table to use with this elevation turret cap. The starting point for this effort was to determine how many clicks (1/4" adjustments at 100 yards) were made when dialing to each yardage mark on the cap. Column B below shows the clicks represented by each yardage mark. Keep in mind that the Nikon turret cap has identified average marks for bullets having a ballistic coefficient (BC) between .453 and .478.
Next I wanted to compare this data against Nikon's Spot On ballistics calculator using their 2680 ft/sec and a common BC in the range specified. I used the Sierra MatchKing 168gr BTHP BC of 0.462. In the calculator I used standard atmospheric conditions (59° F, 78% humidity, Barometric Pressure 29.92"), a standard sight height of 1.5", velocity of 2680 ft/sec, BC of 0.462 and a bullet weight of 168 gr. The click value results are shown in column C below. The click values for columns B & C were close, but there is an issue with the column C values because the data used to calculate these values doesn't match my rifle setup. The sight height for the M-308 riflescope on my SR-762 AR style rifle measured closer to 2.55" than 1.50". I re-ran the Spot On calculator with this new sight height and put the values in column D. When you compare columns B & D, you can see the number of clicks for each yardage distance deviates based on the correct sight height.
Everything so far has been good information, but I still needed to determine what will happen with the ammunition in my rifle having a shorter barrel, so I updated the ballistic calculator data to model a Hornady 168gr BTHP match load with a BC of .506 and a velocity of 2504 ft/sec. Column E shows the clicks for each yardage mark. In my mind there is a good theoretical match between the Hornady 168gr BTHP match ammo, SR-762 rifle and Nikon M-308 scope and for the distances which I typically shoot (out to about 450 yards) and I shouldn't have to make any extra corrections and can follow the turret cap yardage marks. Column E shows the clicks for each yardage mark.
I also wanted to verify the ballistics of another load before I headed to the range so I re-ran the Spot On Calculator again for the Hornady Steel Match 155gr BTPH ammunition. In this case extra corrections would be needed and in column F below, I identified a "+" amount of clicks required correct using the yardage marks on the turret cap.
Before heading to the range I simplified this table above and took the following information.
At the range I first confirmed that with my elevation turret cap set to 100 yards and windage at 0, my scope was zeroed for the 168gr bullets. After a couple of minor tweaks, I confirmed zero and then shot the 155gr bullets to determine the difference in impact. I found that the 155gr bullets were hitting 1.5" high at 100 yards and recorded this offset for my future tests.
I setup a steel gong and torso at both 300 and 400 yards, respectively, and using the yardage marks on the turret caps I was able to hit the targets and be lethal without issue. Since it was a windy day, I didn't collect any group data, but I was convinced I can use the turret cap yardage marks with the Hornady 168gr BTHP Match ammunition.
Next I switched to the 155gr bullets. Since my zero was 1.5" high at 100 yards (6 clicks), I needed to make a -6 correction to any adjustment. From the table above, I knew that at 400 yards I needed to add 7 clicks, but since I also needed to reduce 6 clicks due to the zero shift, I added only one click. When I pulled the trigger, I was near dead center on the 400 yard torso with some drift due to the wind. I made several shots to prove that it wasn't just luck and I was pleased. I made similar corrections for the 300 yard gong and had similar results. I know this probably sounds complicated and may be some effort, but if you are really going to try to engage targets at longer distance, you have to do your homework.
If you purchase the Nikoplex version of this scope and intend to use the scope for long range shooting, you need to take the time to get some velocity data on the ammunition you plan to shoot and spend some time with a ballistics calculator at the range to make sure you understand what is happening when you adjust your turret caps based on the yardage marks and differences in zeros and bullet drop with different types of ammunition.
The Nikon M-308 Riflescope is a quality product and I have enjoyed using it over the past 5 months with various trips to the range and using it while reviewing several other products. The optics seem clear and bright and the time spent at the bench was enjoyable. I initially struggled with which version to get (Nikoplex or BDC 800) but settled on the Nikoplex and have no regrets. I was actually surprised at how well the yardage marks on the Nikoplex version elevation turret caps matched the ballistics of me shooting 16.12" barrel, taller scope height and different bullet weights. A buddy of mine had the same SR-762 rifle with the Nikon BDC-800 scope and we were able to confirm the subtensions in his scope were on target at the 300 and 400 yard ranges. If I could change one feature, I would increase the texturing on the power adjustment ring so it doesn't seem as slick. Other than that, I'm pleased with the Nikon M-308 Riflescope and think most people would be also.