The ornamental design for an endcapplugattachable to a firearmlowerreceiver, as shown and described.
FIG. 1 is a perspective view of an end cap plug attachable to a firearm lower receiver in a use configuration with environment;
FIG. 2 is a 180 degree rotated perspective view of the end cap plug attachable to a firearm lower receiver in a use configuration with environment;
FIG. 3 is a perspective view of the end cap plug attachable to a firearm lower receiver;
FIG. 4 is a 180 degree rotated perspective view of FIG. 3;
FIG. 5 is a front plan view of the design shown in FIG. 3;
FIG. 6 is a rear plan view of the design shown in FIG. 3;
FIG. 7 is a left side plan view of the design shown in FIG. 3;
FIG. 8 is a right side plan view of the design shown in FIG. 3;
FIG. 9 is a top view of the design shown in FIG. 3; and,
FIG. 10 is a bottom view of the design shown in FIG. 3.
The broken lines in FIGS. 1, 3, and 5 depict portions of the end cap plug attachable to a firearm lower receiver that form no part of the claimed design. The broken lines of FIGS. 1 and 2 depict environment of a firearm receiver that forms no part of the claimed design.