Revolver rimfire keyholing

I have a Model 63 no-dash S&W revolver (J-frame 4-inch .22x6) that I've been shooting bullseye with, it's a blast. It's functioning perfectly, the timing is spot-on for all six chambers after finding a loose yoke screw.

The issue is that a third to half the shots are keyholing more or less randomly. The bore, crown, cone and chambers are great. But I see this with several standard velocity cartridges (CCI, SK, etc). I want to stick with 40 grain LRN.

Should I expect a difference from a higher velocity like Federal Automatch or CCI Blazer? The barrel does appear to have a pretty quick twist. Not looking for perfection, just round holes at this point. Those tiny kit gun sights are enough of a challenge!

None of the ammunition should be key holing.
It is an indication that something is not correct, the most likely of those are leading, the crown, cylinder faces, cylinder alignment/timing, or on the forcing cone. Things like the crown are not always obvious.

I've looked at most of those but -cylinder faces, hmm, they do get a bit black. What do you suggest I look for there? The gap is .006, my understanding is that's in spec but perhaps on the high end. There's no visible contact with the barrel.

The problem is more than likely bullet failure.  Could be lubricant failure.  Even with poor lockup or bad jump bullets don’t usually keyhole.  Since it’s 3 out of 6 it has to be ammunition failure.  Have you really cleaned it?  Even get it professionally cleaned.?   It’s a fallacy that “you don’t need to clean 22s”.  So, I’d start with a thorough cleaning and look for leading.  Then try different ammo to see what shoots best.

Grip can do it too. Your grip, not the grips on the revolver.

I'm going to try some dry ammo (Federal Auto Match) and see if things change without any other fiddling. If not, I will give the forcing cone a good cleaning. The borescope does show a slight amount at the rifling entry. Very slight.

And yes, it could easily be me I guess. I'm a bit of a rookie with a revolver, and the J-frame is hard to hold properly with my large-ish mitt especially in DA. I do have a rather nice Nill on it right now though, which helps a lot.

Leading is often well polished and hard to see. Clean it good with, Kroil, kerosene and or firebrush it.

You'll be amazed

I wouldn't think the ratio of thread diameter to bore size on a 22 would lead to this, but over torqued barrels on revolvers create a constriction that sizes the bullet down. AFAIK, its only an accuracy issue. Seems unlikely it'd be so bad as to cause keyholing.

Combined with leading, ?????

I'd give it a serious scrubbing and see what you get. Another quick check would be to see how a loaded rd fits being inserted from the front of the cylinder.

I've got a few that have stupid large throats, and some that are smaller than the groove dia of the barrel. Those are fixable ... unless they're 'collectable'.

Wes is onto a couple of other key items. The cylinder size compared to bore size. And! I have seen a number of revolvers that have been torqued to the point that there is a reduction in bore dimensions at the frame. Slugging and measuring will tell you. For the bore, you will be able to feel the difference as you push the slug along the bore. 

Fyi. I'm not sure about their .22lr's but in the larger calibers S&W uses 5 grooves, so a standard micrometer will not work to give diameter. You will need a special v-mic or an optical comparator if it is 5 groove, but feeling the slug pushed through by a cleaning rod will indicate a restriction/ change.

This is a very low-mileage pistol, and it's the early pinned barrel. I truly doubt it's ever been apart actually. There's no visible barrel restriction or blip examining through the scope so I'm not thinking I need to slug it. The same scope tells me the cylinder throats, gap space and timing are all consistent and good. But I am seeing a bit more lead than last time, so I'm thinking more and more that the slower waxier ammo has been building up deposits.

I'll be trying Mini-Mags in it tonight to see what changes with no wax and higher velocity. Then scrub-a-dub and I'm hopeful that's going to be it.

Thanks for these ideas, I'm learning! Revolvers are mysterious beasts.

@LenV did you post a question about my Nills? I'll PM you the details, they're really nice.

How is the Crown?

I did post a question about the grips. But then I did my research.

I did post a question about the grips. But then I did my research. Nills does not make J frame square butt grips. I guess they are not very common. This is definitely square butt.

LenV wrote:I did post a question about the grips. But then I did my research. Nills does not make J frame square butt grips.

They do, but they make them really hard to find. My 63 is square butt, I got the ones in the pic above just a few months ago. I sent you some info via PM, will post it here if it's of general interest.

Constriction of the bore won't be visible. Needs to be slugged to find it. Revolvers are a pain, have to be done from the muzzle, unless you get creative and have plenty of time to waste.

Assembled at the factory, the barrel is machined to seat up with a bit of rotation left. If the amount is too much, more torque is required to bring the sight to vertical. The angle on the threads squishes the bore down where it's seated in the frame. And it's really surprising how much it will shrink, bigger bores being much easier to constrict.

I completely overhauled an old Super Blackhawk some years back. Had to square up everything on it, and set the barrel back a turn. First try was too much, second pass I took off about .001 more than I'd planned. It almost torques up by hand now, but doesn't seem to have moved with the little I've shot it.

Re r_zerr's comment about groove count, I checked my 17-2 and M-41 and they're both 6 groove. And I think the 41 slugged at .224 ...

6 grooves on the Model 63 rimfire barrel.

I'll consider slugging.

My S&W 15 (.38 Spec) had considerable thread choke. Using gauge pins, I chose one that just slid in the muzzle end and then tried it in the breech end. No go, a good .001" of choke. Re-fit the barrel to where it just snugged up by hand with the sights aligned and a little red Locktite on the threads. Also had to re-size the cylinder throats, as they were under size .That all solved the problem.

Good results last night at 25yd with just the ammo change. I tried CCI MiniMags and Federal Auto Match, both in the 1200fps range and dry, the keyholing vanished. The shots felt great, nice and firm, landing on call. I did have a few FTF's which I attribute to me not properly seating all the rounds in those recessed chambers (there is some sticky wax in them still).

The crown/muzzle looks pretty good, there might be a slightly faint sector at 7:00 but the snapshot lighting is part of that, it's only minorly different.

I'm going to clean the forcing cone and chambers to get any residual lead and wax out, then shoot it this way for a while. I don't think it's the barrel itself, at this point.

Thanks for all this!