22 WMR to 22 K-Hornet

[oldred]

On my scratch built scaled down High Wall single shot I chose to chamber it in 22 WMR and while it shoots really well I have been having second thoughts and thinking I would really rather have the 22 K-Hornet I originally had in mind when I built this rifle. I already have a center fire breech block about 90% completed from when I first started the project so basically a new firing pin, extractor and some finial fitting is all that would be needed for the centerfire conversion, I'm a bit puzzled about reaming the new chamber however. Since I already have a 22 WMR chamber and setting back the barrel would be impractical how would the new reamer be guided correctly since the pilot would be an extremely loose fit at the start?


BTW, the entire rifle is built from 4140 and the receiver/barrel is actually over-built for 22 WMR.

[rking22]

I would consider setting it up by the 22WMR chamber body (running true) and roughing in the body of the K hornet With a small boring bar so that the reamer pilot could reach the bore . That would then allow the reamer to cleanup the chamber to final dim.
Never did this exactly but I have stayed in a holiday express recently. Nother words , just a thought to consider.

[M-Tecs]

Boring is a normally a good option but in this case you only have .050" total (.025" per side) to work with.

If your 22WMR chamber is running true the K hornet reamer will follow the 22WMR chamber. This would be basically be the same as step drilling for roughing. I am not a fan of step drilling for roughing chambers since drills tend to wander some.

If you are concerned about the reamer not following the current 22WMR turn a sleeve to slip onto your pilot. Of course you cannot go deeper than the 22WRM chamber but this will get you to the rifling so the K-Hornet pilot will enter the bore.

Are you using a solid pilot or a bushing reamer?

[oldred]

I have not ordered the reamer yet and the only two chambers I have done have been with solid pilot types but that bushing idea sounds good, maybe a bushing reamer would be a much better bet in this case?

[M-Tecs]

I use Pacific Tool & Gage carbide reamers with USR oil groove bushings exclusively. I have bushings in .0002” increments. I don’t have K-Hornet but I am debating getting one.

The USR oil groove bushing are standard on carbide reamers. They are longer than standard and grooved for through the bore oil flushing.

http://www.pacifictoolandgauge.com/bushings.htm last pic on the right

I am not sure how beneficial the solid reamer pilots are as the pilots are normally .001” to 002” undersize. If my chambers run out is more than .0003”TIR they will normally get recut.

Unless you have bushing within .0002” of your bore you K-Hornet will follow the run out in the 22WMR chamber.

[W.R.Buchanan]

I am not a real live gunsmith per se ,,, However, I am a pretty skilled machinist.

How about "Step Reaming?"

As long as the hole is bigger than the lead on the reamer, and the starting surface is square to the hole,,, the reamer will follow it perfectly. As you know a normal reamer only cuts on the angled portion of the face. The flutes are all about guiding the reamer down the hole and the deeper it gets the closer if follows the hole.

I have a friend who owns Thompson Gun Drilling in North Hollywood CA. I have seen holes that were drilled and reamed thru 57" of 17-4 stainless and were within .002 in any direction in relation to the theoretical centerline. They were 1/8" in Dia! That was a pretty good trick!

Reaming any more than about .010-.015 at a pass can introduce eccentricity because when you introduce the reamer into the hole, the edge of the hole is on the face of the reamer and not on the angled portion which centers the cutter in the hole. Strait Reamers only cut on the angled portion on the front end of the reamer, usually a 45 degree angle.

You have, according to above posts, about .050 to remove out of the chamber before the K Hornet is done.

Trying to take it all with the chamber reamer may introduce some eccentricity, however if you went in with say a .235ish and then .250 reamer just short of the depth of the shoulder, then your chamber reamer would effectively be doing just a skim pass to take the chamber to final size, and the pilot would probably be in the rifling soon after being introduced into the hole.

Obviously a chambering reamer does cut on the length of the flutes so the less you have to remove the better the finish is going to be.

Highly recommend using vast quantities of magic spuge cutting oil IE: Tap Magic, Moly Dee, etc. in the process as well as finish is going to be an issue with 4140, which even on a good day machines like ship.

Hope this helps you figure this process out. And please tell us how you accomplished the task.

Randy