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Master
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.50 BMG custom made to specific actions. |
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The AR Master Caliber Gauge is designed especially for the AR family of rifles. The Service Rifle teams gauge their rifles often because they want to know exactly where they are as far as barrel life is concerned. They know at what point their rifles are about to lose top accuracy and when to replace their barrels. Military depots use erosion gauges to determine if the rifle needs to be rebarreled or just refinished. The top long range and course shooters also keep close watch on their barrels using erosion gauges. Shooters, who load their own ammunition, with the proper use of this gauge, can get more barrel life out of their ARs by knowing exactly where their throat is located. Shooting the AR without an erosion gauge is like having a car without a working mileage meter and guessing when you should change your oil. The military M16 gauge has only one reading: REJECT. Other than that, it is anyone's guess as to exactly where you are in the life of your barrel. What is not widely known is that the REJECT point on the military gauge is the point where the M16 shoots 7.2" groups or larger at 100 YARDS! Obviously, this is not acceptable to the match shooter. In addition, the M16 gauge is designed to gauge chrome lined bore ONLY. Ideally, the AR Master Gauge is first used on a new barrel and the reading recorded in your Round Life Data Book. Top shooters keep meticulous records on exactly the number of rounds they have fired through their barrels. If you are not keeping these records, REMEMBER THERE IS NO REJECTION RING ON THIS GAUGE. The AR Master Gauge has been calibrated against a new Colt AR-15 Heavy barrel and cross referenced with a after market chrome lined barrel as well. A new barrel should gauge at or about the fourth ring on the gauge (See reading the Gauge below). However, since there is a wide variation of barrel manufacturers out there you may see different readings on a new barrel. For this reason additional Witness Rings have been added in case you have a shorter than normal throat. One new barrel checked read only two rings at -0- rounds and may read as low as the first ring. You do not know until you check. The AR Master Gauge has several unique design characteristics. First off, there are enough rings to gauge the useful life of any barrel, and you can trace the throat wear up until the point it fails. There is a support shoulder on the gauge. As the gauge is placed in the chamber, the support shoulder will rest on the rear of the chamber and keep the gauge at or near the middle of the upper receiver group. This assures you do not get a false reading by having it canted excessively. You will note the gauge is tapered. This allows it to find the location of the front of the throat so you will know how much more the bullet has to jump before it takes the rifling. The AR Master Gauge is precision made of stainless steel. With proper care, you will be able to pass this gauge on to your children for their rifles. Always replace the protector cap when not in use to protect the point of the gauge. Gauges are no better than their care. |
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| The Master Caliber Throat Erosion Gauge can be one of the
Competition Shooters most valuable tools. First off, most shooters have
seen the military erosion gauges for the M14 rifles or perhaps the gauge
for the M16 family. These gauges are mostly useless for the civilian
family of firearms because these gauges are calibrated to determine the
wear/rejection point of chrome lined bores. For instance, the Rejection
Point rejection point on a M14 gage is 8.8 inches, a M1 Garand is 8.0
inches, and on a M16 is 7.2 inches at 100 yards with ball ammunition,
which is about 10,000 rounds.
Obviously to the competitive shooter, the rifle barrel should have been
replaced well before that point. Military ammunition is also loaded
under very controlled conditions: the same bullet weight, ogive,
diameter, and to the same length. Another point to remember is military
propellant has been thoroughly tested to insure it does not exhibit
excessive erosive qualities while civilian propellant generally have no
such controls. The military gauge is not applicable to civilian competition shooters for several other reasons. 1. A wide variety of commercial barrel designs exists that varies in diameter from a minimum diameter of .298 to .3015 in the 30-caliber family alone. Chrome moly, stainless, and the other barrel materials will affect the erosion progression as well. The variation in diameter on two barrels cut with the same reamer and zero rounds will give as much as three rings variation. 2. The civilian chamber can also have a large variety of throat variation. Some reamers are custom made for as little as .025" freebore all the way to .150" freebore. This variation will give 1 to 2 rings variation. 3. Civilian barrels can be two groove to six groove which will give different readings as well. Civilian barrels have no performance requirement insofar as barrel life is concerned. Recently observed was a somewhat new commercial barrel that "went out" at 700 rounds requiring setback and rechambered with a short throat reamer. Close examination and erosion gauge readings taken. On the second run the barrel went for 1100 rounds and went out again at which time it was sectioned and found to have the rifling burned away for approximately ¾" in front of the chamber. This barrel was never exposed to a rapid-fire string and was always fired slow-fire strings with 150 to 168 grain Sierra bullets. 4. The military style gauge is designed for one rifle and one caliber and cannot be used for other calibers, i.e. 7.62 Gauge cannot be used in 30.06 or other calibers such as magnums. How is this gauge used? Ideally, your Master Caliber Throat Gauge is GENTLY INSERTED into the bore. Care should be taken to keep the gauge centered to give repeatable readings. It is precision polished to match the throat so it will not scratch or scar the barrel. Looking down from directly above the action watch as the gauge is inserted. Count the rings as they disappear under the receiver bridge. To make things easier every fifth ring is extra wide. Therefore, if you pass the first heavy ring and then proceed two more you are at 7 rings or part thereof, i.e. 7 1/3 rings, 7 ½ rings etc. If you have a new-barreled action, take time to record this reading in your notebook as -0- rounds. Then every 500 or 1000 rounds take additional readings and record how much further the gauge follows the throat erosion down bore. On 30-caliber government barrels with government ammunition, the erosion progresses at approximately 0.100" per 1000 rounds. The rings are evenly spaced each .100" apart regardless of caliber. If you are using this gauge on a used barrel for the first time record the reading at the number of rounds you have fired. For instance, your reading is 8 rings at 835. At 1835 rounds, you take the reading again and determine how far the gauge now goes into the barrel. If it has increased one ring in one thousand rounds, you pretty well know what it is going to read at 3835 rounds. To make it simpler, take an additional reading at an even point such as 500, 1000 rounds and you can pretty well guess what your barrel was when it was new. If you are using propellant that is hotter than the propellant loaded by the government or you are using heavier bullets etc., in all probability, your readings will vary. Many people rebarrel at a certain number of rounds but the barrel may not be eroded to the point you need a new barrel. For instance if you have selected the bullet, primer, propellant combination that gives less than average erosion you can get much more life out of your barrel. If you observe the ring readings increasing, you should know to seat your bullets further forward to be up close to the rifling. Many people use a loaded round seating it out further until it touches. This is a dangerous practice and is to be avoided. The erosion gauge is fast, easy and accurate. No guesswork, if the ring reading has increased one ring, you seat depth is going to follow appropriately. Each bolt gun action is different from the throat to the front bridge opening as well. Therefore, this gauge is useable in Remington, Winchester, Springfield, Enfield, and other actions in those calibers for which the gauge is designed. You need only one gauge per caliber. For instance the 30 cal. Gauge can be used with the bolt rifle in calibers from 303 British, 308 Winchester, 30.06 all the way to the 300 Win. Mag. cartridge. Wildcat cartridges are also measurable, thus the multiple rings. Remember in the longer calibers 30.06, 300 Win. Magnum you will count more rings before the gauge finds the throat and comes to a stop. Thus, the heavy ring every fifth segment to make it easier to read. The 6MM Gauge will record readings from the 6 BR to the 6/284 cartridge. The 6.5MM gauge will fit 260 Remington to 6.5/284. The 7MM gauge will fit 7BR to 280 Remington. There are two types of 22 center fire gauges. The first will fit bolt rifles in calibers 222 Remington to 220 Swift. The other one is for the AR-15 service rifle. The basic difference here is where the gauge is read. Bolt guns will be read as above. The AR family of rifles is read from the rear of the upper receiver. While the rifle is broken down for cleaning, gently insert the AR gauge while looking across the rear of the upper receiver group. As the rings disappear into the upper group, count the rings. Keep a log of what you detect. Make sure to keep the gauge centered in the upper bolt way. These gauges are precision made instruments and should last a lifetime if properly cared for. You can pass this gauge on to your children. The great advantage of this gauge is they are stainless steel so they are less likely to rust giving false readings. A very durable carry case can be fabricated by the owner for pennies. A half inch piece of PVC water pipe with one cap glued in place and the other slipped on will protect your gauge for years. The design of the gauge takes into consideration it will be accidentally dropped or dinged on the point. If this happens just take a fine whetstone and dress up the point as little as possible. The critical contact point is approximately 1/8"from the actual point. The point is .002 to .003" smaller than the smallest bore to add this protection. |
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Good luck and good shooting. |
| AR Master Caliber Gauge $85.00 | Bolt Rifle Master Caliber Gauge $100.00 | .50 BMG Bolt Rifle Master Caliber Gauge $150.00 |
| Postage is a flat $5.00 | ||
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Page last updated 24 August 2007.
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