How to Stake a Castle Nut

Pre-Torquing/Staking Inspection

Before you torque and stake your castle nut, you should verify these 3 conditions to ALL be true:

Make sure the receiver extension does not protrude into your lower receiver far enough to interfere with closing the upper and lower together. Verify by installing the upper onto the lower receiver, closing the pivot pin, and pivoting the upper open and closed in the lower. If the upper receiver strikes the receiver extension or will not close, back the receiver extension out one full turn.
Make sure the receiver extension is screwed in far enough to retain the buffer retainer pin, but not far enough to bind the buffer retainer pin (i.e. the pin should be securely held in place and free to move up and down). If the buffer retainer is not securely held in place, insert the receiver extension one full turn farther into the receiver. If the receiver extension is pressing against the pin of the buffer retainer and preventing it from operating, back the receiver extension out one full turn.
Make sure the receiver extension is screwed in far enough to maintain sufficient gap between the back of the gas key and the lower receiver. To verify, install the buffer spring and buffer into the receiver extension. Using a bolt carrier assembly, push the buffer into the receiver extension until it bottoms out against the back of the receiver extension. The gap between the back of the gas key and the lower receiver should be at least 0.130″ (about the width of 1 quarter and 1 dime; we shoot for 2 quarters). If the gap is less, try to rotate the receiver extension into the receiver (clockwise) one full turn and recheck all 3 conditions. If doing so creates other issues (receiver extension protrudes into the lower receiver or binds buffer retainer pin), rotate the receiver extension back out (counterclockwise) a full turn; you will need to shim the inside of the receiver extension by dropping a shim, washer, or quarter into the tube before installing the buffer spring and buffer.

Once you confirm these conditions to be true, it’s time to tighten and torque the castle nut.

Tighten and Torque the Castle Nut

Tighten and torque the castle nut per our build instructions (Step L7).

Be sure to lubricate the threads and adjust your torque setting appropriately.

Staking Location

The stake should be about 1/3 of the thickness of the end plate away from the castle nut, at one of the locations of the staking notches. The diagram below illustrates the proper location (intersecting green lines).

Pre-Staking

We use a spring-loaded automatic center punch to create our initial staking impression in the end plate. Place the tip of the punch at the appropriate staking location.

Actuate the automatic center punch by pressing it against the end plate until it pops. This will create a small indentation in the end plate.

Your pre-stake should look something like this:

Final Staking

Once we have an indentation where we want to stake, we switch to the Spring Tools center punch. The simple mechanism of this tool imparts tremendous force on the tip of the punch, without any risk of deforming the receiver extension by wailing on it with a hammer. Note that you could continue to enlarge the pre-stake with an automated center punch or a manual punch and hammer, however, we get superior results with far less effort when we use the Spring Tools punch.

A note of caution, you must hold the Spring Tools punch VERY firmly against the end plate; failure to hold it securely may result in the tip jumping off of the intended staking location, potentially scratching or damaging the castle nut or lower receiver.

Place the tip of the Spring Tools punch in the indentation created with the automatic center punch. While firmly holding the tip of the punch against the end plate, actuate the Spring Tools punch by pulling the “hammer” end away from the tip and release. We find that 3-4 “strikes” with the Spring Tools punch creates the perfect castle nut stake.

If you find that material is not moving into the castle nut notch, your punch is probably too close to the center of the end plate. Try adjusting the punch angle toward the castle nut, slightly.

If the tip of the punch is breaking through the edge of the end plate, it is too close to the edge. Try adjusting the punch angle away from the castle nut, slightly. Depending on the severity, you may need a new end plate to achieve a proper stake.

Your castle nut stake should look something like this (note the rounded protrusion of end plate metal into the notch):

Stake a Second Location

Repeat the staking process at a second staking location (you will only be able to stake 2 out of the 3 locations on a standard castle nut).

Inspect Your Stakes

A good stake will push a bulge of metal from the end plate into the notch of the castle nut, without breaking through the edge of the end plate. This engagement between the end plate and castle nut provides additional resistance to rotation of the castle nut.

The holding effect of staking can be observed by measuring the reverse torque required to loosen a properly lubricated, torqued, and staked castle nut; the reverse torque measured is approximately 70% of the equivalent torque applied. For example, an unstaked but properly torqued (to 40 ft. lbs.) castle nut will take about 28 ft. lbs. to loosen. Each good stake adds the equivalent of approximately 10-15 ft. lbs. of security. So a properly torqued and staked castle nut will require approximately 40 ft. lbs. to loosen; a 50% increase. By our 70% observation, 40 ft. lbs. of reverse torque implies holding power equivalent to about 60 ft. lbs. of applied torque (which would likely strip the threads of the receiver extension, if attempted).

Two good stakes are better than one, but one good stake is better than none. One stake is probably sufficient, but two is the Mil-Spec.

If, for whatever reason, you aren’t satisfied with your staking job, you can always replace the end plate and try again. Remember: do NOT use a torque wrench to loosen a tightened or staked castle nut (this can damage the torque mechanism of most torque wrenches).