How to Measure Shotgun Chamber Length?
Measuring the chamber length of a shotgun is a crucial step in gunsmithing, repairing, and customizing firearms. Accurate measurement is necessary to ensure proper function, reliability, and safety when loading and firing the weapon. In this article, we will guide you on how to measure the shotgun chamber length, the importance of accurate measurement, and provide tips and precautions for the measurement process.
Contents
Why is it Important to Measure Chamber Length?
Measurements of the shotgun chamber length are essential for the following reasons:
• Safety: A proper measurement ensures that the shell head can safely ride the rim or breech face of the action, preventing accidental discharges or malfunctions.
• Reliability: The chamber length affects the pressure and velocity of the gas generated during firing. Measuring the chamber length enables you to optimize the ammunition selection and ensure consistent functioning.
• Function: Accurate measurement is vital for the proper function of the action, extracting shell casings, and allowing for smooth cycling of the pump or slide.
Tools and Materials Needed for Measurement
To measure the shotgun chamber length, you will need:
• Calipers or a precision measuring instrument
• A bore micrometer or a Chamber-Go gauge
• A reference point, such as a chamber datum reference point (CDRP)
Calipers:
- Digital calipers provide accurate measurements up to 0.0005 inches.
- Analog calipers can be less precise, but still accurate.
Bore Micrometer or Chamber-Go Gauge:
- These devices measure the internal dimensions of the chamber, including irregularities and deviations from roundness.
- The Bore-Go gauge checks for the minimum internal clearance, while the Chamber-Go gauge measures the inside diameter of the chamber at various points.
Chamber Datum Reference Point (CDRP):
- This point is the top surface of the breech face, which is referenced for measuring the chamber length.
- The CDRP ensures accurate measurement of the chamber length from a fixed point.
Step-by-Step Measurement Process
Follow these steps for accurate measurement:
1. Clean and inspect the shotgun chamber:
- Remove any debris, old wads, or burnt powder from the chamber to ensure a clear path for measurement.
- Visually inspect the chamber for scratches, rust, or dents that may affect the measurement.
2. Align the calipers or measurement instrument:
- Carefully position the calipers or measurement instrument over the chamber datum reference point (CDRP).
- Adjust the instrument to align it with the CDRP, ensuring the zero reading is accurate.
3. Measure the chamber depth:
- Extend the measuring instrument or calipers through the chamber, stopping when the measuring tip contacts the shell head or rim of the action.
- Note the measurement reading (dimension A) in the corresponding unit (e.g., inches, millimeters).
- Repeat the measurement a few times to ensure consistency and accuracy.
4. Measure the chamber radius (optional):
- If using a bore micrometer or Chamber-Go gauge, measure the inner radius of the chamber, which will provide information about the chamber’s geometry.
5. Record the measurements:
- Take note of the dimension A (chamber depth) and any additional measurements for the chamber radius (optional).
- Record the findings for future reference.
6. Verify and recalibrate (if necessary):
- Double-check your measurements using a second calibration method or consult a knowledgeable gunsmith if necessary.
Interpretation and Application of Chamber Length Measurements
When interpreting chamber length measurements, consider the following:
- Average value: Record the average dimension A from multiple measurements. This will provide a better representation of the chamber depth.
- Dimension variability: Take note of the chamber length’s deviation from its average value. A slight variation might be acceptable for most shotguns.
- Comparison to manufacturer’s specs: Check your measurement against the manufacturer’s specifications or standards for the shotgun’s intended use (e.g., hunting, competition).
- Customization or adjustments: If the chamber length measurement is outside the expected range, consult a qualified gunsmith for necessary modifications or adjustments.
Examples of Chamber Length Measurements (in inches):
| Shotgun Model | Average Chamber Length (in.) |
|---|---|
| Remington 1100 | 1.95 – 2.05 |
| Browning BPS | 1.95 – 2.10 |
| Remington 870 | 2.00 – 2.15 |
| Winchester 1300 | 1.90 – 2.00 |
Tips and Precautions for Measurement:
- Handle the chamber with care: Avoid applying excessive force or bending that could damage the action, breech face, or chamber walls.
- Keep the chamber clean and dry: Debris and moisture can affect accuracy and contaminate measurements.
- Verify calibration: Double-check your measurement instruments or calipers for accuracy to ensure reliable results.
- Consult a gunsmith: If you are uncertain about measuring the chamber length or interpreting the results, consult a qualified gunsmith for guidance.
Conclusion
Accurate measurement of the shotgun chamber length is crucial for ensuring safety, reliability, and function. By following the step-by-step measurement process and recording the results, you will be able to diagnose any issues, optimize your firearm’s performance, and enjoy a safer and more successful shooting experience.
