Robert Louis Company, Inc., 31 Shepard Hill Rd, Newtown, CT 06470, USA

(203) 270-1400

Products designed to make you a better shooter, instructor, gunfitter!


The Shotgun Combo Gauge is an accurate and convenient device that measures all of the outside dimensions of your shotgun, which you need to know if you want your gun to fit properly:

  • Length of Pull
  • Drop at Comb and Heel
  • Angle of Pitch
  • Cast

The Shotgun Combo Gauge is a 24″ vernier caliper slotted at one end to hold a sliding Drop Meter.  It can be used alone or with our 23″ EXTENSION which bolts on to the Combo Gauge to make the overall drop/pitch length 48″.  The Extension also has a neodymium magnet installed which essentially “glues” the whole Combo Gauge to the gun’s rib for hands-free operation, further enhancing its convenience and usability. 

99% of our customers purchase the Shotgun Combo Gauge with the Extension.

One DROP METER is standard on the Shotgun Combo Gauge, but a second Drop Meter can be added as an option, which gives greater versatility in measuring drop (you can measure at any two points along the comb simultaneously), or drop and pitch, or drop and cast simultaneously.

Our Shotgun Combo Gauge is patented - U.S. Patent # 7,287,338.


  • Reads both Metric and Inches for use worldwide
  • Has easy-to-read bold numbers
  • Lightweight — Made of aircraft aluminum
  • Portable — Easy to travel with
  • Optional Extension with Magnet. The magnet “glues” Shotgun Combo Gauge to gun rib for hands-free operation
  • Optional Dual Drop Meters


  • Length for drop measurement: 28″
  • Length of pull: 24″
  • Overall length: 29.5″


  • Length for drop measurement: 48″
  • Overall length: 49.5″

Shotgun Combo Gauge in use.

The Shotgun Combo Gauge is used by Gunsmiths, Firearms retailers, Manufacturers and Gun hobbyists from around the world.  

Some of our customers include:  Holland & Holland, Beretta, Boss, Chris Batha, Jerry Parks Young (CPSA Senior Coach MICSI), Dickson & MacNaughton, Browning/Winchester, Ruger, Griffin & Howe, British Sporting Arms, Safari Outfitters, Brownells, Cabelas, Orvis, Kittery Trading Post, Kevin’s Catalog, Bass Pro Fine Gun Room, Dakota Arms, Jeff’s Outfitters, L.L. Bean, and many more.

Click here to watch gunfitter Ian Coley of the  Ian Coley Shooting School and Gunshop use the Shotgun Combo Gauge.


For ease of measuring, it is best to place your gun on a GUN REST.   If you don’t already have one, we offer three options:

Plastic Gun Rest

Gun Fitter's Case

Gun Fitter's Case


Plastic Gun Rest with storage compartments for cleaning supplies or space to hold our LaserShooter and LaserPro OR BoreMaster 

Gun Fitter's Case

Gun Fitter's Case

Gun Fitter's Case


Canvas and leather Gun Fitter's Case has gun cradles that serve as a gun rest.  Holds Shotgun Combo Gauge with Extension,  BoreMaster, LaserShooter and LaserPro.

Read Reviews & Testimonials

The BoreMaster Multi-Bore Gauge 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)

The BoreMaster is patented - U.S. Patent # 9,305,941.


With the BoreMaster, 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)?


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


  • Barrel Wall Thickness Kit
  • 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.


Useful Information for Using the BoreMaster

We have measured hundreds of shotgun barrels and have now developed anecdotal results that we want to share with you.

Remember, when measuring with the BoreMaster, you CANNOT push into a measurement – you must insert the probes beyond the measuring point, then WITHDRAW the BoreMaster, allowing the spring pressure to do the measuring without interference from your hand.

1. Shotgun bore diameters are all over the place, varying as much as 2% of nominal diameter. An example of this is an underbored Perazzi 28 gauge measuring .537/.538 (nominal is .550), a Browning Double Auto made around 1957 at .720 and a 1964 Browning Superposed 20 gauge at 0.625 (overbored). The question is how does one confirm that the BoreMaster is reading accurately? The method we use to verify the bore measurement is by measuring the CHAMBER dimensions. The chambers are typically held to a very tight spec which we measure to the thousands. Chamber dimensions are provided with the BoreMaster Instructions.

2. BARREL WALL THICKNESS can be accurately measured 6″ into the bore. (OPTIONAL KIT REQUIRED)

3. RIFLE BARREL CHAMBERS can be accurately measured. Calibers with case diameters over .400″ – that includes the 30/30 and 30-06 variations — and metrics like the 8 mm and 7 mm Mauser and larger can be measured. Obviously the barrels have to be removed from bolt or lever guns, but single shots and any break guns are readily measurable. This is an extremely fast and accurate method of verifying a gun’s chamber – especially unusual metric, Continental, British or obsolete American barrels. It also verifies if a chamber has been altered to a wildcat configuration.

4. MEASURING TECHNIQUES. We have found that measuring a handheld or vertical gun is difficult, resulting in errors. Place the gun (barrels) horizontal on a table or countertop at rest and insert the BoreMaster probes keeping them parallel to the barrels. That technique will always result in accurate and repeatable readings.

5. MEASURING CHOKES — The BoreMaster as the “De-Liar.” The results obtained by measuring your fixed or screw-in chokes will surprise you. What one manufacturer calls Mod is another’s I.C. Buy screw-in chokes (12 ga) designated for steel shot and I.C. may be 0.003″ Modified around 0.010″ and Full AT 0.018″. These are readings from a Perazzi Mirage with Briley thin wall chokes for steel shot. Those of you with Polychokes can now accurately find the TRUE choke constriction for each designation on the Polychoke. These numbers will both surprise and enlighten you and add to the usefulness of this great product.

6. MEASURING CHAMBER LENGTHS. When buying or evaluating British and Continental guns, chamber length is a critical factor in the gun’s value. An expensive side-by-side marked 2-1/2″ chamber length on the barrel flats may be worth its full value until you measure the chamber length with the BoreMaster and discover that during the gun’s life, someone lengthened the chambers without reproofing the gun. Now what is it worth? Have the forcing cones been altered?

These aforementioned measuring jobs are accomplished accurately in a minute, not an hour. Foremost, the BoreMaster brings accuracy, convenience, portability, ease of use and the capability to measure all gauges at an affordable price.

Instructional BoreMaster Video

Read BoreMaster Reviews & Testimonials

BoreMaster Downloads

BoreMaster Instructions (pdf)


Gun Scale

Gun Scale Case

Gun Scale Case


Our Gun Scale is the gun enthusiast’s perfect product for the instant and accurate weighing of your guns.  Accurate to 1/10th of an ounce in a clear digital readout with a maximum capacity of 13 lbs. (6 kilos).  Reads selectively in pounds/ounces or kilos.  

Gun Scale Case

Gun Scale Case

Gun Scale Case

Keep your Gun Scale out of harm’s way when traveling with the optional Gun Scale Case.

Keep your Gun Scale out of harm's way by storing in our optional Gun Scale Case.