How to check dimensions on a Picatinny rail

How to check dimensions on a Picatinny rail

Before you finally order your Picatinny rail, you should check that it fits your rifle. The A/B/C dimensions show the distance between the screw holes in the rail and are used to compare the rail with the holes in the receiver of your rifle.

The measurements are taken from the center to center of the holes. If the A/B/C dimensions of the rail match the holes in the receiver, the rail fits the rifle.

Short Action and Long Action

Some rifles are available in several receiver lengths, typically Short Action and Long Action. This means that the same model name may require different Picatinny rails.

The caliber can often help you in the right direction, but it should not be used as the sole check. Manufacturers do not always use Short Action and Long Action in exactly the same way, and some models have their own solutions.

Therefore, use the action type as a guide, but let the A/B/C dimensions determine the fit.

Drawing showing A, B and C dimensions on a Picatinny rail

What do A, B and C mean?

A, B and C are the distances between the screw holes in the rail. They are always measured from the center of one hole to the center of the next hole.

  • A-dimension: The distance between the two front screw holes.
  • B-dimension: The distance between the front and rear hole pairs.
  • C-dimension: The distance between the two rear screw holes.

On the product pages, you will find the A/B/C dimensions under the specifications. Compare them with the dimensions of your rifle before ordering.

How to measure correctly

  1. Find the screw holes in the receiver of your rifle.
  2. Measure from center to center of the holes.
  3. Compare the measurements with the A/B/C dimensions on the product page.
  4. Also check the length of the rail if you are unsure about space or overhang.

Feel free to use a caliper if you have access to one. It provides a more precise check than a regular tape measure.

If the rifle has previously had a mount installed

If the rifle has previously had bases, rings or other mounts installed, you should still check the holes in the receiver. Do not measure according to the old mount unless you are absolutely sure that it fits the rifle correctly.

Remove any bases and check the holes directly in the receiver. This provides the most precise basis for comparison.

Brief summary

  • Measure from center to center of the holes.
  • Compare your measurements with the A/B/C dimensions on the product page.
  • Use Short Action, Long Action, and caliber as guidance – not as the definitive answer.
  • Always check the dimensions before ordering if you are in doubt.