Rear Bag
Also: Rear Support Bag
A small filled bag placed under the buttstock that the shooter squeezes to make fine elevation adjustments on a supported precision shot.
A rear bag is a small filled support bag placed under the toe of the buttstock to hold the back of the rifle steady on a supported shot. By squeezing or releasing the bag, the shooter raises or lowers the muzzle in tiny increments, giving fine elevation control that the hands alone cannot match. This pairing of a front support with a rear bag turns the rifle into a stable platform that holds its aim with minimal muscle input.
The rear bag works in concert with the bipod up front and with loading-the-bipod to keep the whole system locked together during recoil. A consistent squeeze and a repeatable bag position help the rifle settle into the same natural-point-of-aim each time. The shape and firmness of the bag are often matched to the contour of the stock so the buttstock rides smoothly without rocking.