PMA Tool now offers a unique “adjustable” Stock Weight System with variable weighting from 2 to 8 ounces (including internal sleeve). This $65.95 system allows the shooter to add or remove weight (in the buttstock) to balance the gun, or adjust the weight to meet class weight limits. Say, for example you were running at max weight but then changed your scope for a new optic that weighed 4 ounces less. With this system, you can easily get back up to the “legal limit”. You can also use the weight to adjust balance when running barrels of different lengths or contours.

The PMA Stock Weight system is made up of a sleeve, a nut and three interchangeable weights. The sleeve and nut weigh 2 ounces (combined) and weight inserts of 2, 4 and 6 ounces are included in the system. The sleeve is machined from aluminum, while the nut and weights are machined from stainless steel. All weights are roll-stamped with their weights and “coin-slotted” so they can be easily installed using a screwdriver or coin. The nut utilizes a 1/4″ hex wrench for removal from the sleeve and installation of weights.

While installation of these Stock Weight Systems is fairly simple, PMA states that: “The sleeve should be installed into the buttstock by someone with some mechanical aptitude and an understanding of stock construction, preferably a trained gunsmith or stock-fitter.”

Can you guess what your next barrel will weigh? In many competition disciplines, “making weight” is a serious concern when putting together a new match rifle. A Light Varmint short-range Benchrest rifle cannot exceed 10.5 pounds including scope. An F-TR rifle is limited to 18 pounds, 2 oz. (8.25 kg) with bipod.

One of the heaviest items on most rifles is the barrel. If your barrel comes in much heavier than expected, it can boost the overall weight of the gun significantly. Then you may have to resort to cutting the barrel, or worse yet, re-barreling, to make weight for your class. In some cases, you can remove material from the stock to save weight, but if that’s not practical, the barrel will need to go on a diet. (As a last resort, you can try fitting a lighter scope.)

Is there a reliable way to predict, in advance, how much a finished barrel will weigh? The answer is “yes”. PAC-NOR Barreling of Brookings, Oregon has created a handy, web-based Barrel Weight Calculator. Just log on to Pac-Nor’s website and the calculator is free to use. Pac-Nor’s Barrel Weight Calculator is pretty sophisticated, with separate data fields for Shank Diameter, Barrel Length, Bore Diameter — even length and number of flutes. Punch in your numbers, and the Barrel Weight Calculator then automatically generates the weight for 16 different “standard” contours.

Calculator Handles Custom Contours
What about custom contours? Well the Pac-Nor Barrel Weight Calculator can handle those as well. The program allows input of eight different dimensional measurements taken along the barrel’s finished length, from breech to muzzle. You can use this “custom contour” feature when calculating the weight of another manufacturer’s barrel that doesn’t match any of Pac-Nor’s “standard” contours.

Smart Advice — Give Yourself Some Leeway
While Pac-Nor’s Barrel Weight Calculator is very precise (because barrel steel is quite uniform by volume), you will see some small variances in finished weight based on the final chambering process. The length of the threaded section (tenon) will vary from one action type to another. In addition, the size and shape of the chamber can make a difference in barrel weight, even with two barrels of the same nominal caliber. Even the type of crown can make a slight difference in overall weight. This means that the barrel your smith puts on your gun may end up slightly heavier or lighter than the Pac-Nor calculation. That’s not a fault of the program — it’s simply because the program isn’t set up to account for chamber volume or tenon length.

What does this mean? In practical terms — you should give yourself some “wiggle room” in your planned rifle build. Unless you’re able to shave weight from your stock, do NOT spec your gun at one or two ounces under max based on the Pac-Nor calculator output. That said, the Pac-Nor Barrel Weight Calculator is still a very helpful, important tool. When laying out the specs for a rifle in any weight-restricted class, you should always “run the numbers” through a weight calculator such as the one provided by Pac-Nor. This can avoid costly and frustrating problems down the road.

Caution: Same-Name Contours from Different Makers May Not be Exactly the Same
One final thing to remember when using the Barrel Weight Calculator is that not all “standard” contours are exactly the same, as produced by different barrel-makers. A Medium Palma contour from Pac-Nor may be slightly different dimensionally from a Krieger Medium Palma barrel. When using the Pac-Nor Barrel Weight Calculator to “spec out” the weight of a barrel from a different manufacturer, we recommend you get the exact dimensions from your barrel-maker. If these are different that Pac-Nor’s default dimensions, use the “custom contour” calculator fields to enter the true specs for your brand of barrel.

ONE: Thou shalt choose the best resting spot. The performance of your balance depends greatly on the surrounding environment. Choose a location away from the main traffic flow of the room, especially doors. Also be aware of heating and cooling vents as these produce air movement. You can adjust the environmental settings on your balance to provide the best performance in the chosen location. Balances must be placed away from magnets as they affect the weigh cell performance.

TWO: Thou shalt avoid vibrations. Vibrations can come from large machinery in production environments and from fume hoods in laboratories. An alternative to fume hoods are Power Safety Workstations which are designed specifically for use with a balance.

THREE: Thou shalt watch temperature changes. On an analytical balance a one degree temperature change can cause a 1 digit (0.0001g) drift. Although Denver balances have temperature correction built-in, it is still important to calibrate your balance when the temperature changes significantly. Choosing to place your balance in a temperature controlled room, away from sunlight, and calibrating often helps minimize the effects of temperature.

FOUR: Thou shalt calibrate often. Upon installation and each time the balance is moved you should calibrate your balance. For example moving an analytical balance to a location that is only 13 feet higher changes the weight reading from 200.0000 g to 199.9997 g; which means the result is 0.0003 g lighter than the actual mass.

FIVE: Remember to check the level. The instrument should be leveled upon installation with all feet (two front feet for round pan units, four feet for square pan units) touching the countertop. If the level changes, the balance should be re-leveled and recalibrated. As an example, a 200g sample would weigh 0.0025 g less when tilted at an angle of 0.3°.

SIX: Honor thy weights. Keep in mind that weights are only as reliable as their quality and certification. Remember, a 1 g does not weigh precisely 1.00000 grams. Weights should be recertified annually. Denver Instrument offers recertification services on all weights 1 mg to 5 kg. Check to make sure you have selected the proper weight class for your balance. The weight tolerance should be better than balance readability. Always use tweezers or gloves when handling weights as smudges and indentations change the value of the weight. Keep weights in cases so they don’t get scratched or dusty.

SEVEN: Thou shalt always use a small container and weigh in the center of the pan. Especially when using an analytical balance, the effects of air buoyancy increase as the sample container size increases. Using a small sample container will minimize the effects. Items placed on the pan provide a downward force. Placing them directly in the center of the pan keeps corner loading errors at a minimum.

EIGHT: Thou shalt not unplug. To perform within published speci-fications, balances must have power applied for 30 minutes to 48 hours depending on the resolution of the balance. Denver balances have a standby mode which turn the display to standby but keep power cycling through the electronics.

NINE: Thou shalt not ignore static. Static is one of the most common weighing “noises”. It can cause reading to appear too high, too low or just be unstable. Denver balances include grounding methods to reduce the effects of static. However sometimes extra supplies are needed. Consider anti-static weigh dishes, anti-static brushes or low tech ways to increase the humidity of the chamber like placing damp cotton balls or glass wool in a small vial in the corner of the analytical draft shield.

TEN: Thou shalt clean often. Dirty weigh pans and powder in weighing chamber can contribute to static issues and lead to a wide variety of problems. Denver weigh pans are made from stainless steel and can be cleaned using a variety of household and laboratory chemicals. A small paint brush can be used to get power away from the edges of the draft shield for easy clean up.

For general info on barrel weight calculation for straight and straight tapers, read this article on Lilja’s website. Click HERE for another article explaining weight calculation with barrels that have a radiused (curved) contour section.

Here are the free software programs offered by Dan Lilja. Right click and “Save As”:

Straight Contour (.exe file) | Straight Contour (Excel file) | Contoured Barrels with Radius (Excel file)

It is well-established that mid-barrel tuners can work on rimfire rifles, and we also know that certain types of materials (such as rubber, cork, and Delrin) can have beneficial damping effects on both rimfire and centerfire barrels. Given these facts, we were quite interested in the new Flexi-Weight System introduced by AirForce Airguns at the 2010 SHOT Show.

The Flexi-Weight system consists of a cluster of 3 to 6 metal weights, held in place by a rubber O-ring. Multiple Flexi-Weight clusters can be installed on a single gun and the fore-to-aft position is easily adjusted. The shooter can simply slide a Flexi-Weight cluster back and forth along the barrel until he finds the optimal position.

We have no idea whether Flexi-Weights can improve accuracy on a centerfire rifle, but it’s worth a try. Flexi-weights are affordable ($29.95 for a set of five, 48 gram weights) and you can slip them on your barrel without cutting threads or making any other permanent modifications. The weights are designed to fit a 1.25″ diameter tube. For more info, visit Airforceairguns.com or call (877) 247-4867. Airforce Airguns is a U.S. company based in Fort Worth, Texas.