Do You Have a Screw Loose?

How you treat people affects how they’ll treat you. So it is with screws.

Do You Have a Screw Loose?

When a shot is in the offing, there’s no time to check ring screws. A loose mount can scuttle a hunt.

Once you put something together, you expect it to stay that way at your peril. Periodic checks are cheap insurance that your marriage won’t suddenly unravel or your scope come loose. In either case, the cost of sudden failure can be stunning. As when, for example, screws holding a scope on my dangerous game rifle had had enough. Like me, they’d endured jarring recoil for most of an hour. But once a whisker of slack developed, the upshot was certain. Each blast that slammed the screws’ tiny, inclined planes nudged them incrementally outward.           

They lost all grip in spectacular fashion. I thought for an instant a bird of prey had mistaken me for a rodent and descended in a record-smashing stoop. The blow dented my brow. The scope ricocheted off into the bushes. Less violent results can cost you even more dearly.           

Namibia’s night was drawing the shades as an eland bull ghosted through a glade a stone’s toss away. Easing from a crouch into prone, I snugged the sling. A surer shot was hard to imagine. But to my surprise, the bullet struck with a sodden “whunk.” It had strayed. After the crashing faded, I hurried along the track. Small, dark blood stains showed no froth, no spray. To push this bull would have been foolish. A tracker joined me next morning and followed the deep prints at a trot. Charitably, the eland jumped in low bush that gave me a clear shot to its neck. The 1-ton beast piled up.           

Assuming I’d muffed both the shot and the call the evening before, I continued hunting without a zero check. When another animal ran off injured, I consulted the sandbags.             

My first shot drilled target’s center. What? Pondering, I picked the case from the ejector. That’s when I noticed the right-hand windage screw on the Redfield mount no longer held the base of the rear ring. A nudge pivoted the scope nearly a quarter-inch at the rear. Recoil was bouncing the scope from one windage screw to the other! The resulting error increased as the right-hand screw slowly exited. With the ring against that screw, impact moved more than 3 feet at 100 yards. Recoil threw the scope back to the stationary left screw, so the next bullet flew true. That shot in turn sent the scope again to the loose screw.           

I should have trusted my calls instead of shrugging off every other poke. Such insidious screw failure can happen on light-recoiling predator rifles, too, no matter the base and ring design. A little shudder over time can wear or unseat almost anything.

A goon with a cheap screwdriver marred this screw and tang, bleeding value from an old Winchester.
A goon with a cheap screwdriver marred this screw and tang, bleeding value from an old Winchester.

Hard vs. Soft Screws

There are hard screws and soft screws. Hard screws snugged aggressively into soft metal can strip hole threads. A hard receiver or scope mount is a blessing when you must drill out the remains of a soft screw, a curse when you must open, then re-thread a hole ruined by the drill or hard screw. Snugging any screw that must be tight, you’re smart to use a torque wrench. There’s no describing the feel that tells you when to stop turning.           

Gunsmithing houses such as Brownells list affordable torque wrenches just for firearms. They read in inch/pounds and can be set to “break” at any level you wish. The proper setting depends on the screw and what is absorbing the pressure — but also on whom you ask! The industry doesn’t speak with one voice on proper torque.            

Joining a scope mount base to the rifle, I snug 6-48 screws to 25 inch/pounds, a little tighter than advised by Badger and Leupold but in line with advice from Nightforce and Warne. Leupold suggests 28 inch/pounds for the larger, increasingly popular 8-40 screws (20 percent more torque than for 6-48s).           

Because ring-to-base attachments vary, recommended torque securing rings ranges from 14 to 65 inch/pounds. Weaver specifies 30 inch/pounds for crossbolts under 1-inch rings, but a supplier of similar mounts hikes that number for 30mm rings, and again for 34mm. Talley advises 30 inch/pounds for the bottom screw gripping the base of its vertically split steel rings, 20 for the top screw. For 10-32 screws in its QD mounts, the numbers are 35 for the bottom, 20 for the top. Take care applying a wrench to the nuts on crossbolts cinching rings to Picatinny rails — even if they’re said to brook 65 inch/pounds.           

Caps of horizontally split scope rings needn’t be tighter than 20 inch/pounds. In a note to shooters buying competition scopes, Vortex pegs the limit at 18. Leupold and Badger concur: 15 to 18. Snug ring screws alternately, as you would lug nuts: diagonally (four-screw) or directly across (two-screw).


Anaerobic Adhesive

During the Pleistocene Epoch, predator hunters were using iodine to rust scope mount screws in place. A more civilized option is Loctite Threadlocker. Made by Henkel Corporation, this anaerobic adhesive now comes in several guises. All Threadlocker bottles are red, a signature color that dates back decades, when the only Threadlocker adhesive was a red liquid. That’s still the most powerful. Once in place, it releases its grip only when heated with a torch. Medium-strength Blue doesn’t require such persuasion. Loctite’s Green, medium-high on the strength spectrum, is most used on electrical components. Purple, or Loctite 222, has become popular with shooters, who evidently view it as a happy marriage of Red and Blue. It shouldn’t require heating to disengage. Loctite insists all these products cure within 24 hours, and keep screws stationary in temperatures from -65 to +300 F. 

As I often switch scopes on rifles for photography, I don’t use Threadlocker on scope mounts. (In fact, much-turned screws get periodic oiling to minimize wear on them and hole threads). Warne does not recommend adhesive on screws for its mounts, reminding shooters that fresh, uncured Loctite of any hue lubricates threads like oil. Dabbing Threadlocker before cinching a screw makes it eager to spin; and you might then unwittingly apply more pressure than your torque wrench suggests.

RealAvid markets this affordable, spill-proof field kit of drivers and hard, high-quality magnetic bits.
RealAvid markets this affordable, spill-proof field kit of drivers and hard, high-quality magnetic bits.

Those Other Screws

How you snug other screws on a rifle can affect its function and accuracy. Most hunters after big game or predators favor bolt rifles, which commonly have two guard screws. Some have a center action screw. The forend screw found notably on early Winchester 70s is pretty much gone. 

Here’s a good way to marry stock and bottom metal to a barreled bolt action. Place the rifle topside down in a cradle. Inexpensive polymer gun cradles by MTM  and RealAvid serve nicely. Insert front and rear screws; spin them in with your fingers. Turn the rifle vertical and bounce the butt on the floor lightly to seat the recoil lug. Snug the front screw, then the rear screw with a light touch on the screwdriver. If there’s a center screw, insert it now, finger tight. 

Tighten the front screw to 45 inch/pounds (per advice from Remington and H-S Precision). Give the rear screw 30 inch/pounds. It must merely keep bottom metal and tang snug in the stock. Center guard screws are happiest when treated gently. Limit torque to 15 inch/pounds, lest you bind the bolt, or even spring the receiver. (A rifle glass- or pillar-bedded, or with an alloy bedding block, can be cinched tighter, front and rear — to 65 pounds, say some sources.) After assembly, check cycling. A bolt that won’t rotate into battery might mean the front screw is contacting the lower locking lug. If so, remove the screw and carefully file it as short as you must. Do the same if the rear screw peeks into the bolt race.           

Engaging slotted screws, use a hard, hollow-ground bit that fits. Cheap one-piece screwdrivers have soft, wedge-shaped tips that bear only on the base and top edges of the slot. Ragged lip edges result. Such a tip also tends to slip under pressure and can cause irreparable damage to what’s around the screw. Engraved, contoured or obsolete screws might be nigh impossible to replace. In a trice, cheap screwdrivers have drained many rubles from the worth of collectible firearms and left unsightly scratches and dings on predator rifles that, if not elegant, would look better unmarred. 

One of the best investments you’ll make, shy of flowers on your anniversary, is a set of gunsmith screwdrivers from Brownells or Midway USA . My Brownells block includes more than 100 hard, magnetic, precisely shaped bits. RealAvid also peddles excellent driver sets, including a cleverly contained field kit. 

Any help you can get securing screws will seem cheap if instead you neglect that job and lose an animal to a poor shot or get thumped in the noggin by an airborne scope.                                                     

For want of a nail, the shoe was lost. Check those screws before you forfeit a match or a hunt!


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