The ornamental design for a bolt handle extension, as shown and described.
FIG. 1 is a perspective view of a bolt handle extension showing the extension attached to a rifle;
FIG. 2 is a front elevation view of the bolt handle extension of FIG. 1;
FIG. 3 is a left elevation view of the bolt handle extension of FIG. 1;
FIG. 4 is a right elevation view of the bolt handle extension of FIG. 1;
FIG. 5 is a rear elevation view of the bolt handle extension of FIG. 1;
FIG. 6 is a plan view of the bolt handle extension of FIG. 1; and,
FIG. 7 is a bottom view of the bolt handle extension of FIG. 1.
The broken line showings of a rifle and of portions of the bolt handle extension are for the purposes of illustrating environmental structure and form no part of the claimed design.