September 23, 2010
Here's how to properly put an optic mount on the finest battle rifle ever produced.
Every great design has its weakness, and this rifle is no exception.
Though its widespread use as a service rifle was short, there is no doubt that the M14 is one of--if not the--finest battle rifles ever produced. It took the best features of the historically glorious M1 Garand and refined them. In its original form it is a true rifle--not a close-quarters assault weapon--and shoots a cartridge capable of long-range performance. It has none of the finicky manners of Stoner's design. Its accuracy is as good as the AK-47's is poor. Yet the M14/M1A has an achilles' heel. It is exposed when the need to mount an optic arises.
For most, a standard-configuration M1A mounts like a good shotgun, and the excellent iron sights line up comfortably and naturally. But mounting a scope poses several difficult problems: Cheekweld becomes nonexistent unless an adjustable or fixed cheekpiece is added, suitable mounts are expensive and somewhat involved to install, and, most importantly, suitable mounts must overcome a certain amount of action-flex and movement when fired and still maintain zero. Another obstacle to properly mounting optics is the tolerance variations in civilian-available receivers and different-era M14s.
Not to worry: It can be done, as is evidenced by the fact that the armed forces are, with increasing regularity, issuing optics-mounted M14s as DMRs (designated marksman rifle) to squad designated marksmen and to snipers that are deployed where increased volumes of highly accurate semiautomatic fire is needed.
The civilian-legal version--the M1A--is usually found on the firing line at Camp Perry or in the gun cabinet of shooters who believe it's a great rifle that can do it all--home defense, hunting, casual plinking, long-range shooting, and so on. Lots of shooters want a scope on their M1As, and while military armorers are well versed in properly mounting scopes on M14s, there is a lack of in-depth information on mount systems available to the average shooter and the process of properly installing them.
While Springfield offers a relatively inexpensive optic mount (and properly trained armorers can make it work), it's a two-point system, meaning it attaches to two contact points--the side of the action and the dovetail for the stripper clip guide. When developing criteria for quality mounts available to and mountable by the average shooter, I settled on those providing three contact points. Such mounts provide better stability under heavy use, abuse, and extensive shooting.
The first particularly successful M14 mount was a three-point design developed for the Special Forces in the '80s by Brookfield Precision Tool. I'll stick my neck out and say that almost all currently available three-point mounts, regardless of manufacturer, are some variation of the Brookfield design.
Key to the mount's ability to withstand the forces of high-volume heavy recoil without loosening or changing zero are those three contact points. One is the heavy screw in the side of the action, another is the stripper-clip dovetail, and the third is a pressure point on the top front of the receiver. That pressure point, which is absent in two-point mounts, makes all the difference. It minimizes the effect of action-flexion (yes, M14 actions actually flex slightly with each firing), supports the mount through recoil, and greatly broadens its base, adding stability that helps maintain zero.
The mounting process is very similar for the different mounts. Accompanying is a series of photos detailing the process, with additional photos showing any unique differences particular to mounts such as the A.R.M.S. #18 and Trijicon's ACOG-capable mount. Several of the mounts featured here, as well as the few tools necessary to properly attach them, are available through Brownells .
Once properly mounted, all the mounts tested and featured here will give good service. I mounted each one of them on a Springfield Standard M1A and tested for function issues or interference, running at least two full 10-round magazines of Black Hill's 155-grain match load or Hornady's 155-grain TAP ammo--two of my favorite, ultra-reliable, very versatile loads--through the rifle. I fired the first magazine slow fire, five or six of the second magazine with the rifle held off the shoulder with the ejection port facing up, and then dumped the remaining shots from the shoulder as fast as I could squeeze the trigger. I never had a malfunction or jam with that rifle with any of the mounts featured in this report.
1. It is necessary to remove the stripper clip guide from its dovetail at the top rear of the action before attaching any optics mount. It's fairly simple. Remove the trigger group and separate the barreled action from the stock, following the instructions in the manual.
2. Cradling the barreled action upside down in a gun vise or cleaning cradle, and with the bolt forward, which exposes the stripper clip guide attachment pin from below, carefully tap said pin out with a 3/32 or slightly smaller diameter punch. Don't drive it out from the top of the action because that can create a burr inside that will interfere with the function of the bolt. Then, while supporting the left side of the action below the stripper clip guide on a block of wood, gently tap the guide out from right to left. It should come easily and may even slide out under firm thumb pressure.
3. Before attaching the mount, degrease the tapped hole in the left side of the receiver. The basic process begins with making sure the mount lies perfectly flat against the left side of the receiver. Sadlak Industries recommends checking the surface-to-surface contact with Prussian Blue Paste. Eyeballing the contact from all angles will give you a pretty good read on the fit (no light should be visible between the mount and the receiver), but a thin application of Prussian Blue will allow you to clearly see the contact surfaces. Make sure the rail on the mount fits into the horizontal groove in the left side of the receiver. Although it's b
est, it does not necessarily need to fit tight. There's a fair bit of variation in the tolerances of different makes and eras of receivers.
4. If the mount has a cam washer, install it with the tab at 9 o'clock and hand start the side screw into the receiver. I like to finger-tighten it to make sure it threads in cleanly before applying Loctite (use the red stuff). After applying Loctite, finger-tighten with the mount held snugly against the side of the receiver and then snug it a fraction of a turn past finger tight. We're talking 1/8 turn or less.
5. With a plastic mallet, tap the tab on the cam washer (if present) clockwise, seating the rail in the side surface of the mount against the top of the horizontal groove in the side of the receiver and drawing the mount backward until the angled face of the mount contacts the face of the stripper clip dovetail. The mounting screw will want to turn with the cam washer, so it will be necessary to keep it from doing so with your wrench or Allen key, otherwise the screw will tighten and prevent the cam washer from doing its job. The face of the stripper clip guide is one of the less-consistent tolerances on most M1A receivers. Ideally, the tab should snug up between 10 o'clock and 2 o'clock.
6. If the mount — like the Trijicon TA-70 and A.R.M.S. mounts shown here — doesn't use a cam washer, barely finger-tighten the side screw and manually seat the angled rear face of the mount against the stripper clip dovetail. You want firm contact, but don't overdo it and torque the side rail out of the groove in the receiver.
7. Install the degreased dovetail key into the stripper clip dovetail. It should provide a slip fit; if it doesn't, you may need to hand file it to fit. You don't want it too tight to move with finger pressure.
8. Align the screw hole, apply red Loctite, and install the screw to just past finger tight.
9. Trijicon's TA-70 mount has two screws, one on each side, providing a clean mounting surface for an ACOG optic to be mounted with bottom-entry screws. The ACOG must be attached before mounting the TA-70 to the receiver. Using a torque wrench, tighten the side bolt and then the dovetail key screw to the manufacturer's specifications (found in each mount's instructions).
10. Sadlak Industries uses a set of unique dovetail-key locking screws on its mounts, one on each side, to provide added stability and insurance against the mount working loose under hard use. Install these before torquing the main side mount screw to full specs and tighten them 3/4 turn past finger tight. Then after torquing the side screw, torque the setscrews to 20 inch-pounds, finishing with the dovetail-key screw.
11. At the front of the mount, loosen the small locking Allen-head setscrew, if present, and screw down the front contact screw until very light contact is made. Unless instructions say otherwise, turn no more than 1/8 turn past contact point. Apply red Loctite to Allen-head setscrew and tighten.
12. Some rifles may throw empties at a steep enough upward angle that a shell can bounce off the bottom of a mount and back into the action, where it will ricochet around and can cause malfunctions. For Springfield customers, such rifles can be shipped back to the factory with the mount, where the shop will tune the ejector for perfect function free of charge. Photo is of an actual jam with a rifle other than the Springfield M1A Standard I used for this article's tests.