Tune Rimfire Rifles With A Torque Wrench

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An additional option for shooters looking for maximum accuracy

Hunters who like tinkering with guns in order to wring maximum performance from their firearms often miss an important option. Rimfire shooters chasing maximum accuracy will already be testing various kinds of factory ammunition in their rifles and finding that one brand shoots the best, then stocking up on that product. That’s a great first step, but for the true experimenter, there’s another angle left to explore – tuning the rifle with a torque wrench. It’s an overlooked step that can make a huge difference in how well a rifle shoots. And with spring here, and since spring is rimfire season in western Canada, it’s appropriate to examine that method of tuning rimfire rifles for increased accuracy.

The vast majority of rimfire rifles in use today use screws to hold the stock and barrelled action together. Better quality rifles will usually use two screws, while less expensive guns will only use one. Whatever system is employed, the screws are typically found on the bottom of the stock, in the vicinity of the trigger guard. The advantage to a pair of screws is that it allows the barrel to float free of what can be accuracy-damaging contact with the rifle stock’s forend. But whether the rifle has two screws or one, the degree to which those screws are tightened will be a factor in how well the rifle shoots.

The tightness of a screw is measured using torque, which is simply a measure of the turning force applied to it. In the firearms industry this is usually expressed using the Imperial unit inch-pounds. The greater the turning force applied, the higher the number; therefore, 20 inch-pounds of force is greater than 10 inch-pounds.

In an ideal world, all rimfire rifles would shoot their best with the action screws tightened to one specific, known torque setting. Of course, that’s too easy to be true, so a shooter interested in squeezing maximum accuracy from a rifle has to spend some time at a shooting bench experimenting. But then, spending an hour or two shooting is never a bad thing, and if it means more accuracy in the field I think it’s well worth it.

The first step is to source a torque wrench capable of inch-pound increments and which will take screwdriver bits compatible with the screw heads on your rifle. This pretty much means a gun-specific wrench. While I’m aware of several choices on the market, the most commonly available is the FAT Wrench, marketed by Wheeler Engineering. I’ve seen these at all the big box outdoor stores in western Canada, as well as the smaller gun shops. I have one myself and it’s worked great. The only caution that’s necessary is that like all torque wrenches based on a calibrated spring system, the wrench absolutely must be reset to zero, when not in use. Failure to do this can result in incorrect and erratic readings.

With a torque wrench in hand, a rifle, targets and a good supply of ammunition, it’s time to go shooting. As with any testing procedure, we’re trying to eliminate human error, so a solid rest is important. Because rimfires are sensitive to being pushed around by the wind, it’s also important to shoot on a day with minimal wind and mirage. Put targets at a distance that reflects how far the rifle is normally used; 50 to 75 metres is common for 22 Long Rifle firearms, while 100 metres is a good distance to work with the rimfire magnums.

When testing rimfires, a good place to start is a torque setting of 20 inch-pounds. Adjust all screws to that setting and then, using your best shooting technique, fire a 10-shot group at one target. When you’re done, add five inch-lbs and shoot another 10-round group on a different target. Keep adding torque in five unit increments and shooting 10-shot groups until 40 or 45 inch-pounds is reached. That’s usually the upper limit I go to with rimfires. But please note that these numbers do not apply to centrefire rifles. When dealing with the big guns, completely different torque values are called for.

Why 10-shot groups? Because we’re trying to develop a solid statistical base for forming an opinion, and three or even five-shot groups aren’t going to cut it. Once you’ve generated half-a-dozen targets with 10-shot groups and laid them out on a table, you’ll likely see a pattern emerging. Typically, there will be a steady progression in group size toward and away from one particular torque value. That’s the sweet spot for this rifle and ammunition combination.

If no torque setting looks any better than the rest, you can likely assume that your rifle has some other problems. Perhaps the scope has gone bad or is loose, the bore needs cleaning, the crown is damaged or some other issue is causing a problem. Rimfires being what they are, it’s also not uncommon to see a single wild shot in a 10-round group. Is that wild shot a result of shooter error, a gust of wind or maybe even an out-of-spec cartridge? Evaluate your results carefully, and if any one group is called into question, back off the screws to where they are loose and then reset them to the torque value at which that questionable group was shot. It’s a simple matter to re-shoot a group and confirm your results are valid. It’s actually something you should do as a matter of course, once you’ve formed an opinion as to which torque value gives the best accuracy.

The table shows the results achievable using this method. Note the best and worst groups for each rifle. It’s a huge difference. Setting the torque values of the action screws to the same optimal setting every time can yield a large increase in accuracy.

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