REXUS UltraShims Muzzle Device Shim Washer Set

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Orient, or "time," your 5/8-24 muzzle device with our REXUS UltraShims extra-thin shim washer set, which includes 2 each of 5 thicknesses of stainless-steel shim washers for 10 total. Shims have a .742 outside diameter that mates perfectly with our line of UltraSlim muzzle devices to allow a .750 gas block to slide on and off. The thinnest, .002, accounts for roughly 17° of muzzle device rotation, the .003 for 26° rotation, the .004 for 34.5°, .008 (69°), and .016 (138°).

By mixing and matching, one can fine-tune timing in .001 increments. REXUSUltraShims provide device timing while allowing maximum thread engagement, unlike thicker methods like lock nuts. Further, UltraShims are infinitely reusable, for those who want to uninstall their muzzle device for cleaning. Finally, unlike crush washers, UltraShims do not introduce misalignment which could damage muzzle devices or expensive suppressors.


1. Screw on your muzzle device until it bottoms out hand-tight at the muzzle threads shoulder.

2. Unscrew muzzle device until it is oriented, or "timed," where you want it. Either measure the gap between the muzzle device and muzzle thread shoulder with calipers or eyeball it — bearing in mind that final tightening with a tool will reduce the gap very slightly by roughly 1/8" rotation.

3. Either measure or eyeball a shim or stack of UltraShims extra-thin shim washers corresponding to the gap — bearing in mind that final tightening will reduce the gap very slightly by roughly 1/8" rotation.

4. Remove muzzle device and lube the rim of its rear face that will press against the shims, and, standing up the barrel so gravity will work for you, slip the necessary shim or stack of shims over the muzzle threads. (At this point, we recommend lubing the muzzle threads, to make future removal easier, with the same moly-lithium grease you use on barrel extension threads.)

5. Screw on muzzle device until it bottoms out hand-tight against the UltraShims, pressing on all sides of the shims to keep them centered and from sticking out too far on one side or another. (Test whether a .750 gas block can slide over them.) Finally, snug up muzzle device with a tool (wrap the tool jaws with tape if necessary to prevent scratching muzzle device) the final roughly 1/8" rotation to tighten it to the desired timing.