Shotgun Multi-bore Gauge measures all of your shotgun’s inside dimensions.

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The BoreMaster measures all the inside dimensions of your shotgun:

  • BORE — .410 through 4 gauge and rifle barrels .405 and larger accurately in thousands
  • CHOKE — fixed or screw-in. Measures screw-in chokes in or out of the gun
  • CHAMBER — Chamber dimensions — Chamber length — Forcing cone dimensions and rifle chambers with diameter dimensions of .400″ and up.
  • BARREL WALL THICKNESS — down to 6″ from the muzzle and 6″ from the breech (Barrel Wall Thickness Kit optional)

With the BoreMaster Shotgun Multi-Bore Gauge, you can answer these questions:

  • Have the chokes on a gun been altered from the barrel markings?
  • Are the barrels overbored? Original or aftermarket?
  • Are the chambers 2″ or 2-1/2 “? Have they been altered to 2-3/4″ or 3”? Reproofed?
  • Is the barrel wall thickness safe (6″ from the muzzle or breech)?


  1. Spring-loaded probes always exert equal pressure on the bore, making readings accurate and repeatable
  2. LCD resolution: 0.001″/0.1″mm switchable inches/metric
  3. ID Measurement: Range-0.375″ to 1.200″.  Depth to 6″.
  4. Accuracy: +/-0.001″
  5. Hardened steel construction
  6. Brass probe beads: 0.040″ projection
  7. 6″ probes graduated in inches and metric
  8. Measure barrel wall thickness (BWT) with BWT device. Accuracy: +/0.002″
  9. ABS scales always read true position
  10. Floating zero, relative measurements and absolute measurements
  11. Automatic shut-off
  12. Operates on a single type 357/SR-44 battery, 2 year life
  13. Includes 0.725″ calibration ring and calibration strip 0.025″ for BWT measurement
  14. Includes instructional DVD


  1. Barrel Wall Thickness Kit
  2. Four Calibration Rings are available in the following gauge sizes: 12, 20, 28 Gauge and 410 Bore.  The 12 Gauge Calibration Ring is included with every BoreMaster.  The 20, 28, and 410 rings can be purchased individually.

A Good Reason to Own A BoreMaster: A Personal Experience Worth Sharing
by Bob Foege, BoreMaster Inventor

At a recent pheasant hunt, one shooter was using a magnificent Parker 12 gauge Frame 4. I routinely use the BoreMaster to measure older guns – for safety reasons as well as my own curiosity – and I discovered that this Parker had been drastically cleaned up inside; bore diameter after the chamber was 0.753″ and bore diameter 5″ in from the muzzle was 0.744″. Nominal 12 gauge bore size is 0.729″. The barrel wall thickness 5″ from the muzzle was 0.023″!

Although the owner was shooting target loads successfully, I warned him against using heavy pheasant loads and suggested that he have the barrel wall thickness measured mid-barrel.

The photo illustrates what a 1-1/4 oz. pheasant load did to the left barrel of this compromised gun.

Luckily no person was injured. Although the owner ignored my advice, the BoreMaster did its job by indicating a potentially dangerous condition. If the owner had used the BoreMaster when buying the gun he probably would have wisely declined the purchase.

The BoreMaster is an easy-to-use and serious tool for the gun owner and gun trader, providing critical information for all gauges, not generally available without this tool.

Video on How to Use the BoreMaster 

BoreMaster Instructions:

=>> Download complete BoreMaster Instructions as a PDF document

=>> Download “Useful Information” as a PDF document





Additional information

Weight 10 lbs