Concentricity gauge - Sinclair
A case can be perfectly sized and still have a neck that doesn't sit straight around the body axis. A bullet can be seated squarely and still pick up a slight offset from neck tension. Neither is visible to the eye. The Sinclair Concentricity Gauge turns that deviation into a number.
How it works
Place the case or loaded round in the two roller blocks, slide them until the measurement point is under the indicator, and spin the case while pressing gently down and to the side. For neck concentricity the indicator goes over the neck. For bullet runout, move it to the bullet axis, at the ogive or toward the tip. What the dial reads is the TIR, the total indicator runout.
Consistent datum references matter. Measuring at 5mm from the case mouth on one round and 15mm on the next makes the numbers meaningless. Pick a fixed location relative to the case mouth and stick to it for every round you measure. That is the only way to compare results between loads, dies, or presses.
Construction
The two roller blocks travel in a milled slot in the base plate, not on top of it. That keeps them in alignment regardless of how many times the clamps are tightened and released. Large thumb levers make adjustments fast. The indicator tower adjusts both vertically and laterally so you can position the indicator correctly for any case length or cartridge. The mount takes standard 3/8" stem dial indicators. If you have a spare indicator on the bench, it drops straight in.
What you measure and what you do with it
Neck concentricity shows how well the case neck aligns with the body. Bullet runout tells you how much the bullet's axis deviates from the case axis. Together they give you a clear picture of what your reloading process is producing. High runout typically points to a die problem, uneven neck wall thickness, or inconsistent seating.
The practical use is sorting. Rounds above your runout threshold go into the training ammo box. Rounds below it go into the match box. Where you draw the line is up to you, but you can only draw it once you have actual numbers. That is what this tool is for.
Comparing the Sinclair with other options? The Lock-N-Load Concentricity Tool - Hornady measures bullet runout only but adds a correction function for minor deviations. The Up-Right comparator dial stand - Derraco offers an alternative measurement setup for those already running a comparator system. For neck thickness and tension measurements alongside your Sinclair results, the Case neck gage pin sets - K&M Precision is the logical companion tool.
Specifications
• Brand: Sinclair International
• Model: Concentricity Gauge (with dial indicator)
• Application: case neck concentricity, bullet runout on loaded rounds
• Capacity: cases up to .50 BMG
• Roller blocks: two, adjustable in milled base slot
• Indicator tower: adjustable vertically and laterally
• Dial indicator mount: 3/8" (0.375") standard stem
• Construction: anodised aluminium
• Origin: made in the USA
Who is the Sinclair Concentricity Gauge for?
Reloaders who want to understand their process, not just execute it. If you shoot regularly at 300 meters or beyond and want to know whether your die is working correctly, whether your bullet seating is consistent, or whether sorting your rounds by runout actually makes a difference, this tool gives you the data to answer those questions. It is precise, well-built, and covers ground that no other measurement in your reloading routine does.
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