Comparator Headspace Gauge .450" - .338 Lapua Magnum - Derraco
The Derraco Comparator Headspace Gauge with .450" diameter is specifically designed for accurate headspace measurements on .338 Lapua Magnum cases. This insert is part of the modular Derraco measuring tool system and provides a level of precision essential for long-range precision shooting.
Optimal Measurement Position for .338 Lapua Magnum
For the .338 Lapua Magnum, many precision reloading specialists choose the .450" gauge diameter instead of the standard .420" bushing. This is because the .450" size measures more accurately on the shoulder line of the .338 LM case. When calculating the correct gauge diameter, you add the neck diameter and shoulder diameter together and divide by two. For the .338 Lapua Magnum, this works out to approximately .450", allowing this gauge to represent the actual headspace more accurately.
Precision CNC Manufacturing
The Derraco headspace gauge is manufactured from 6061 aircraft-grade aluminum with Type II hard anodizing. This ceramic-like coating provides excellent wear resistance, even with intensive use. Each gauge is individually checked using a pin-check system, with deviation kept within 12 microns (half thousandth of an inch). This accuracy guarantees consistent measurements between different sets, enabling shooters to share and compare measurement data.
Applications in Long-Range Reloading
In long-range precision shooting with the .338 Lapua Magnum, maintaining consistent shoulder setback is crucial. The headspace gauge measures the distance from the case base to the shoulder datum point. By monitoring this measurement, you can determine how much the shoulder moves back during resizing. For optimal performance, a setback of 0.002" to 0.003" is typically maintained. This ensures easy chambering while the case still fits properly in the chamber.
Compatibility with Measuring Equipment
This .450" gauge fits into the Derraco comparator body that attaches to your caliper. The screw-on design ensures better concentricity and consistency than push-fit bushing systems. The gauge has no chamfer on the inside, providing a sharp, clear measuring edge along the case shoulder. This delivers more accurate measurements than sandblasted or chamfered bushings.
Already using the Derraco Ugly Headspace and Bullet Comparator Set? Then this .450" gauge is a valuable addition specifically for the .338 Lapua Magnum.
