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Fitting a .22LR Cylinder into a .22 Mag Frame

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Z

Zero Knives

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Jul 20, 2007
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I picked up a Hi-Standard Sentinel MKIV (or something like it) in .22 Mag at a local pawn shop that's in great shape. It's strange since the barrel is only marked ".22 Caliber" but after some consulting I'm sure it's a magnum. To be sure, I dropped a .22LR in the cylinder and it fell right past the ejector.

I was hoping to find a .22LR cylinder made for it, but so far they've proven to be hen's teeth. In its stead, I found a .22LR cylinder made for a similar gun, a Sentinel R-101. They look almost identical and the outside dimensions are almost identical. All I need to is shorten the ejector rod and I should be able to test the timing, fit etc.

My main concern is safety. I have safely tested pistols and rifles before (mainly with a wheel, a vise, a rope and a prayer), but I don't know what to look for when I'm fitting. How much of a gap between the cylinder and barrel is acceptable for a .22?

Thanks in advance,
Ram
 
A .22RF GO headspace guage is .043".

The rim thickness of most .22 RF ammo is between .037" to .042".

It is desirable to have the headspace set between .043" to no more then .046" to provide free rotation in a revolver cylinder and still allow reliable ignition.

BTW: You sure know how to pick'm for a first gunsmith project! The Hi-Standard DA's are a real can of worms to put back together! You will want to make some slave pins I betcha!

rc
 
Thanks, rc. Pardon my ignorance, but just to get it straight:

The gap between the cylinder and the barrel should preferably be .043" (just a hair over mm) and no wider than .046". I'm assuming any wider and I'll have some nice marks on my fingers after each shot.

Haha, yeah. I'm not real bright. Hopefully all the work I'm doing on this will all be on the outside, God willing the timing is identical on both cylinders. Worst case, I've got all kinds of round stock on hand...:D
 
We're talking about two different things here: Barrel/cylinder gap and head space.

Barrel/cylinder gap is the space between the rear of the barrel and the front of the cylinder.
The ideal gap is 0.005". A gap under 0.003" may cause binding problems, and over 0.009" or so may be inaccurate and spit lead.

The head space is the distance between the cartridge case head and the breech face.
Rcmodel gave you the specs for that on a .22.

The problem is in setting those standards.
The head space is usually set by trimming the rear of a NEW cylinder and ejector assembly to give the correct space. If the cylinder is used and already fitted to a different gun, it may be too short to be fitted to your frame at all.
This leaves you with gun butcher fixes like silver brazing a shim to the back of the ejector.
The ejector is trimmed by using a precision hand filing fixture or better, a precision surface grinder.
You don't just file it by free-handing it.

Barrel/cylinder gap is also a problem.
If you're lucky, the gap will be too small, which is corrected by trimming the rear of the barrel and probably re-cutting the forcing cone.

If you're unlucky and the gap is too wide, the only repair is to set the barrel back one thread, set the gap, then re-cut the forcing cone.
Re-cutting the forcing cone requires an expensive cutter and lapping tool that works down the bore, and a special plug gage to gage the cone.
The cone is not just a funnel, its a precision gaged area that can't be eyeballed.

As you're finding out, revolver cylinder work is one of the pistolsmiths most complicated and difficult jobs. Cylinders don't drop in.
After fitting the cylinder for head space and barrel/cylinder gap, then you need to adjust it for timing and alignment, which is a whole new can of worms.

The good news is, Gun Parts Corp lists .22LR cylinders and ejectors for the HS Sentinel Mark IV for $94.00. You NEED a cylinder and ejector assembly, since they have to be fitted together as an assembly, THEN fitted to the gun:

http://www.e-gunparts.com/products_new.asp?CatID=8468
 
Wow, thanks for the information, dfariswheel! That's exactly what I'm looking for. I get tripped up on terminology as much as anything and that was fairly easy to understand.

My saving grace so far is that the cylinders themselves are almost dimensionally identical. The cylinder is the same diameter and almost the same length. The notches on the cylinder are timed the same (though I don't know what'll happen once it's installed!). The holes are are surprisingly identical distances from center to center comparatively.

My fear at this point is exactly what you said, establishing the gaps. Since the length of the assemblies are a few hairs apart, I was hoping to establish the spacing by fitting the crane width backward or forward, depending on the initial fit. It's a little thicker, thankfully, so I'm hoping I can trim the thickness flat enough for a repeatable fit. Believe it or not, I have access to a surface grinder, but at that point I'm abandoning the project.

Thanks for the tip, but that cylinder/ejector assembly from Numrich was at my house last week. :D I returned it with a note informing them it was in fact for a Sentinel but for the R-101 series, not the MkI/IVs. I ended up swapping it for some Rem 700 parts and bought an R-101 cylinder off GB for half the price! I'll send them an e-mail to hopefully catalog it correctly.

I'm going to trim the ejector rod tomorrow night so I should find out pretty quick if any of this will even matter. Worst case, I bought another ejector rod to swap, resell the cylinder and enjoy my .22 Mag. Either way, I truly appreciate the lesson. ;)
 
22 Mag at a local pawn shop that's in great shape. It's strange since the barrel is only marked ".22 Caliber"
Click to expand...
You might should measure the bore by slugging it.
Drive a .22 bullet through it with a brass rod and measure the resulting slug with a mike.

.22 RF generally uses a .222" bore with lead bullets and .22 WMR uses a .224" bore with jacketed bullets. Convertable guns might use a compromise .223" bore.

rc
 
When I owned a Ruger Single Six convertible it was extremely accurate with the .22 WMR in place and so so with the .22 LR. I was told the bore was the reason.
 
IIRC, the ".22 Caliber" barrels were made for the convertible model, so I think that is OK.

But if I understand correctly, Zero Knives wants to keep the .22 WMR cylinder and install a new .22 LR cylinder. So if the b/c gap is too small, he can't trim the barrel to fit the .22 LR cylinder, that would make the b/c gap too large with the old .22 WMR cylinder. He has to trim down the new cylinder. Doing that at the back is not easy due to the way that H-S ratchet is made flat with the rear of the cylinder, so the job might require a lathe and turning down the front of the .22 LR cylinder. Maybe there is adjustment in the crane or maybe he will be lucky and things will fit all right, but the job could turn into a nightmare.

Jim
 
Jim, that's correct about the model. On this one, fitting the LR cylinder is so I can shoot the hell out of while plinking, not so much for accuracy.

I figure this'll turn into nightmare on a dime, at that point I'll cut my losses. Without the crane in it's slot, I can fit the cylinder and the fit looks good. It looks tight up front and there's enough clearance on the back, probably due to being almost the exact same size as the WMR cylinder. My concern at this is point is if the crane has enough meat on it to be fitted to the correct spacing. The only cutting I'm gonna do on this sucker is trimming the rod and the crane. Once it fits, if the timing is wrong or the gaps are off, I'm done!
 
So the cylinder is fitted; all it took was chopping the ejector rod and taking some meat off around the pivot hole of the crane. In the picture below, you can see the original .22 Mag cylinder on the left, an original R-101 cylinder on the bottom right and the modified cylinder on the top right.

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It fit right in and locked into place once it swung into the frame. The timing seems 99.9% percent. The cylinder rotates and locks into place, but the action is a little crunchy and not quite as smooth as the original cylinder. I think the cylinder is just a hair too close to the hand. My concern now is that it's going to wear out the hand.

The barrel/cylinder gap is now at about .0047 whereas with the .22 Mag cylinder it was almost imperceptible. This should be within tolerance, but I'm nervous about testing. Looking down the barrel, it lines up with the new cylinder just as well as the old one, but I've never done this before! What's the safest way to test?

attachment.php


Thanks again for everyone's help! This was fun...
 

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Well, it's not going to BLOW UP blow up.

At worst, you will get case rim splitting and gas escape between the rear of the cylinder and the recoil shield.

I'd probably put on a leather work glove and just shoot it.
But that's not to say you should too.

You could tie it to a tree in the woods and jerk the trigger with a cord.

rc
 
I'll put on a welding glove and put a few cylinders through it, if it lets me. I'll check for accuracy and examine the cases as well. I've done the tree thing before with a bunch of T-53s; that was an adventure...
 
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