Reading Choke:
     The BoreMaster 
                                                                                                                                                                                     Shotgun Multi-Bore Gauge
Watch Instructional Video!

Measures all the inside dimensions of your shotgun:
1.    BORE -- .410 through 4 gauge and rifle barrels .405 and larger accurately in thousands
2.    CHOKE -- fixed or screw-in. Measures screw-in chokes in or out of the gun
3.    CHAMBER -- Chamber dimensions -- Chamber length -- Forcing cone dimensions and RIFLE CHAMBERS 
                               with diameter dimensions of .400" and up.          
OPTIONAL:
4.    BARREL WALL THICKNESS -- down to 6" from the muzzle and 6" from the breech

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)?

Specifications
 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.  Accuracy:  +/-0.001"
  4.  ID Measurement:  Range-0.375" to 1.200".  Depth to 6".
  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

 

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 on the left 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.

Watch Instructional Video!

BoreMaster Instructions

ENTERING BORE:   Depress spring-loaded 

           probes  together to enter barrel 
                       
   READING BORE DIAMETER: Release
       probes to read bore diameter 
            (shown 0.729"-- 12 GA)

h "zero"

Reading Choke:

                                Touch "zero" when the probes are in the bore. Depress
                                    probes and move to the muzzle area of the choke. 
                                           Read choke constriction (shown 0.021")

when the probes are in the bore. Depress probes a

 
Measuring Barrel Wall Thickness  (Optional Kit Required)
You will need the optional BARREL WALL THICKNESS KIT which includes an "O" Ring and the black Barrel 
Wall Thickness (BWT) plastic fitting

1.   Fit "O" ring over both probes before pushing on the BWT fitting.
      The "O" ring will keep the probes tightly closed. 
           
2.   Fit the BWT fitting over the right probe – push on. Make sure that the BWT offset flat aligns with the bead of the left probe. 
3.   Push "zero" on BoreMaster control face. Pull back the right probe several times so that it sets into the BWT device and 
      establishes a zero point. The zero point may vary by a couple of thousandths. For the purpose of these measurements, 
      these variances will not matter.
4.   Insert the probes over the barrel wall as shown.  Allow the BoreMaster to settle in. Read the result.
      Please note: Accuracy is +/- 0.002", however, what you are trying to establish is the presence of very thin barrel wall 
      thickness, which this gauge will do.
      Please note: If you are reading the choke dimension, remember that you are reading half of the constriction.

5.  Use the supplied 0.025" calibration strip to confirm the BoreMaster's BWT accuracy.
6.  After use, remove the "O" ring from the probes to prevent it from stretching. The "O" ring will need replacing if it no 
      longer compresses the probes tightly. The "O" ring size is ½" I.D., 11/16" O.D., and 3/32" thickness.       


     

n

STANDARD BORE, CHAMBER & CHOKE DIMENSIONS 
GAUGE
BORE
CHAMBER
CHOKE
FULL
IMP MOD
MOD
IMP CYL
CYL
A
B
C
D
E
F
G
J
K
J
K
J
K
J
K
J
K
10
.775
.841
.933
.8854
2.875
.074
.026
.739
2-1/2
.748
1-7/8
.757
1-1/4
.766
5/8
.775
0
10 MAG
.8379
3.500
12
.729
.798
.886
.8118
2.750
.072
.026
.693
.701
.711
.720
.729
12 MAG
.7968
3.000
16
.662
.732
.820
.7458
2.750
.065
.026
.636
.6425
.649
.6555
.662
20
.615
.685
.766
.6988
2.750
.060
.024
.589
.5955
.602
.6085
.615
28
.550
.614
.688
.6284
2.875
.060
.022
.530
.535
.540
.545
.550
410
.410
.463
.537
.478
3.000
.060
.020
.390
.395
.400
.405
.410

This drawing and the specification information was released by Ithaca prior to advent of plastic shot protector.

d move to the muzzle are the choke. Read choke constriction (shown 0.021")

                                    VARIOUS BORE DIMENSIONS (INCHES) 
        BORE SIZE (GAUGE)
4
5
6
7
8
9
10
11
12
13
14
15
16
20
21
22
23
24
25
26
27
28
32
 BORE DIAMETER (INCHES)
1.052
.976
.919
.873
.835
.803
.775
.751
.729
.710
.693
.677
.662
.615
.605
.596
.587
.579
.571
.563
.556
.550
.526
Useful Information

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 given in the enclosed literature.

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.

Enjoy your guns and remember to take a kid out shooting. Our sport needs new blood!

You can always call us with your questions. Each BoreMaster is tested for operation and accuracy before it leaves the factory. Your BoreMaster should read perfectly right out of the box.


PRICING: 
BoreMaster complete with BWT Kit and 4 Calibration Rings.......$398.00 
BoreMaster with BWT Kit and 12 Gauge Calibration Ring............$314.00
BoreMaster only (with 12 Gauge Calibration Ring)...................$279.00                                   
Barrel Wall Thickness Kit ..........................$35.00
Additional Calibration Rings Available:  $28.00 each  
   - 20 Gauge, 0.625"  
   - 28 Gauge
   - .410 Bore, 0.413"                 
       (For the small bore specialist, "zeroing" the BoreMaster                
      with the .410 calibration ring guarantees accurate and repeatable                
      readings for the .410 bore barrel.)
Home
Robert Louis Company
31 Shepard Hill Road
Newtown, CT  06470  
Phone:  (800) 979-9156
             (203) 270-1400
Fax: (203) 270-3881
Email:  sales@shotguncombogauge.com


 

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