Because the latch rod on HW guns depends on the angle and depth of the "catch" to hold it in the cocked position.
Unless the rod was much larger in diameter you're not gonna have enough meat for it to "catch" on.
It would also depend on the latch rod to guide fit.
If the rear guide is made to close enough tolerance then it will add some structural stability to the latch rod. Might work if you make it a close fit.
The rear cap may also prevent it from jumping the "catch" if you machine a split sleeve to insert into the cap to tighten up the tolerance.
Flying chuck keys will make you st,st,st,st,studder!!