Revolver locking notches

**Aguila Blanca** · September 7, 2017, 06:43 AM

I have a replacement cylinder for an Italian SAA clone that was begun for me by an older machine shop owner who was a Vietnam veteran. Unfortunately, he became ill and had to close down his shop before the cylinder was completed. What's left to do is deepening the notches for the bolt to lock into.

I can't find any information on the correct dimensions for these notches (radius of cutter, and depth and width of cut). Even if I had the information, I doubt it's anything I could accomplish at home. But with the information I might be able to find a local shop that could handle it. Does anyone have this information?

Second question: can anyone recommend a revolver gunsmith who is qualified to do this?

Tidewater_Kid · September 7, 2017, 09:35 PM

It would seem to me that you could measure the width and length of your bolt, add a few thousandths and that will work for the slot. You could measure bolt protrusion from the frame to get a approximate depth. To me laying them out would be the most difficult task.

I found this drawing on the web that gives frame dimensions for various manufacturers. You don't say who made yours. I am assuming it is an older piece made by a company that is no longer in business?

**Aguila Blanca** · September 8, 2017, 10:55 PM

Quote:

Originally Posted by Tidewater Kid

It would seem to me that you could measure the width and length of your bolt, add a few thousandths and that will work for the slot. You could measure bolt protrusion from the frame to get a approximate depth. To me laying them out would be the most difficult task.

I have laid them out. I measured a completed cylinder from a different SAA optically, using an optical comparator, and came out with a notch length of .375" and a width of .155" + ,005 (or so). Depth seems to measure approximately .040".

After entering all that into AutoCAD, what I come up with is that I need a Woodruff Key cutter with a diameter of 7/8" and a face width of 5/32". Does that sound about right?

If so, I'll buy the cutter, and then I'll have to figure out how to make the cuts -- reliably located. They're started, but they need to be cut a bit more than twice as deep as they are now.

**4V50 Gary** · September 9, 2017, 08:30 PM

I'd use a key cutter too and a milling machine with a rotary index head.

If you can't do it, my friend has the machinery and he was a machinist for 17 years before attending TSJC. http://thronearms.com/

Tidewater_Kid · September 9, 2017, 09:08 PM

I agree on the key cutter as the way to go. I don't have a milling machine so I would outsource it.

Shimpy · September 11, 2017, 03:27 PM

"I'd use a key cutter too and a milling machine with a rotary index head. "

Use a key cutter as mentioned or grind an oversize one to your exact dimension. I'd rather build a fixture with a pin to locate on each cylinder bore so if there is any variance hole to hole the cut will be in the right place in relationship to the bore.

**4V50 Gary** · September 12, 2017, 09:50 PM

That would work too but are the notches center of the cylinder hole? Even if not, the jig could be made such that the key cutter would be in the right spot.

A jig would be good for production but I don't see any advantage over an index head. Once that is set up, you leave it alone. Make the cut, back off. Rotate the head whatever # of times to the next position and then move it back to the cutter.

Can you post a sketch of the jig you have in mind?

**Unclenick** · September 13, 2017, 02:28 PM

I would guess he's got bolt/latch offset from the cylinder pin holes that he can measure in the frame. An important point is that a six shooter has one chamber at 6:00 when another is at 12:00, and that offset often doesn't move the notch very far from the 6:00 chamber wall. It's a weak point on all six guns (the reason a lot of the heavy caliber modern revolvers are five-shot rather than six). On the other hand, the pressure of the 45 Colt is pretty low. Bottom line, though, is that I would try to err on the side of shallow and err on the side of as much offset as you think will still function.

**Aguila Blanca** · September 13, 2017, 06:11 PM

The notches are already there (and they are offset), but they're not deep enough. Locating them isn't the problem -- cutting them is the problem.

**Aguila Blanca** · September 15, 2017, 08:37 PM

Bought the Woodruff Key cutter with a diameter of 7/8" and a face width of 5/32" from MSC Supply. Worked very well. Cost me a grand total of $22.58, and I have a cutter that may have other applications down the road.

**Unclenick** · September 16, 2017, 06:00 PM

May I suggest you measure the offset of the edge of the notch closest to a chamber wall and then figure out how thin it will make the metal between itself and the chamber. A hoop stress analyses will then show how much pressure the resulting chamber can take. Jack Belk pointed out a Chiappa Rhino 44 Mag that had .045" between the chamber and the bottom of the locking bolt slot that blew out and cut off a trigger finger. So, even though you will be at much lower pressures, it's not a consideration to simply ignore without checking. That's why you were wise to ask for a drawing to see what the original value was. I'm just sorry nobody had one of the cylinder to offer.

**Aguila Blanca** · September 16, 2017, 08:18 PM

Quote:

Originally Posted by Unclenick

May I suggest you measure the offset of the edge of the notch closest to a chamber wall and then figure out how thin it will make the metal between itself and the chamber. A hoop stress analyses will then show how much pressure the resulting chamber can take. Jack Belk pointed out a Chiappa Rhino 44 Mag that had .045" between the chamber and the bottom of the locking bolt slot that blew out and cut off a trigger finger. So, even though you will be at much lower pressures, it's not a consideration to simply ignore without checking. That's why you were wise to ask for a drawing to see what the original value was. I'm just sorry nobody had one of the cylinder to offer.

That's a sobering consideration. Using the dimensions I have for the cylinder and standard SAAMI dimensions for the chamber diameter, I modeled it in AutoCAD and I come up with a wall thickness of .0345" between the deepest part of the notch and the chamber wall. That's using a .44 Magnum chamber, which is what this cylinder began life as. But it was cut down to the diameter of a .45 SAA cylinder. Notches in a SAA cylinder measure .040" deep and I cut mine only .030", so a .45 cylinder would leave much less wall -- about .0205". I'm loading very light, just for plinking, so I think I'll be okay.

That said, perhaps I'll use a wire pull rod to activate the trigger for my first dozen or so rounds.

Thanks for helping me not be overly close-focused.

[Edit to add] I ran my bullet through the Hodgdon reloading web site. I use Winchester 231/HP-38, so that gets me right on the mark. The test load I first ran through the modified cylinder (before recutting the notches) was the starting load of 4.5 grains. There was essentially NO felt recoil (about like shooting a .22), and the brass was black -- clearly not obturating. So I'll bump it to 4.7 grains, which is still well below the max load of 5.3 grains. The max load is shown as producing 9,400 CUP, and the starting load just 7,000 CUP. At 4.7 grains, I'll be maybe at 7,500.

.44 Magnum loads for the same powder run in the 38,000 CUP range, or five times what I'll be shooting. I think I will use a pull rod for the first few shots, but I don't think I'm into dangerous territory.

**Unclenick** · September 18, 2017, 08:02 AM

Sounds like a plan! I also read about a gun that, rather than blowing apart, merely pushed the floor of the notch to bulge outward over time. Can't recall the gun or the chambering, but I'm thinking you could take a light and a probe like a dental pick with you and make sure you don't see or feel any depression forming inside the chamber nearest to the notch. Check it from time to time for cumulative effect. At the pressures you are are running, the brass will spring back to shape pretty completely, so I don't know if you can count on it to mirror such an indentation, but monitor it over time anyway.

45 Dragoon · October 9, 2017, 07:04 AM

Hmmmm, if I were having a dedicated cylinder made for a S.A. of any caliber, I would have a Ruger type notch (thin, which extends the offset) and fit the bolt head for the new locking notch. That way, you build in strength/safety. (It's always best to fit the bolt to the notch, not the notch to the bolt.)

As far as the Rhino, I knew there was a reason I didn't like the "firing" chamber being that close to my hand!!

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

September 7, 2017, 06:43 AM	#1
Aguila Blanca Staff Join Date: September 25, 2008 Location: CONUS Posts: 18,459	Revolver locking notches I have a replacement cylinder for an Italian SAA clone that was begun for me by an older machine shop owner who was a Vietnam veteran. Unfortunately, he became ill and had to close down his shop before the cylinder was completed. What's left to do is deepening the notches for the bolt to lock into. I can't find any information on the correct dimensions for these notches (radius of cutter, and depth and width of cut). Even if I had the information, I doubt it's anything I could accomplish at home. But with the information I might be able to find a local shop that could handle it. Does anyone have this information? Second question: can anyone recommend a revolver gunsmith who is qualified to do this?

September 9, 2017, 08:30 PM	#4
4V50 Gary Staff Join Date: November 2, 1998 Location: Colorado Posts: 21,832	I'd use a key cutter too and a milling machine with a rotary index head. If you can't do it, my friend has the machinery and he was a machinist for 17 years before attending TSJC. http://thronearms.com/ __________________ Vigilantibus et non dormientibus jura subveniunt. *Molon Labe!*

September 11, 2017, 03:27 PM	#6
Shimpy Senior Member Join Date: August 27, 2015 Posts: 153	"I'd use a key cutter too and a milling machine with a rotary index head. " Use a key cutter as mentioned or grind an oversize one to your exact dimension. I'd rather build a fixture with a pin to locate on each cylinder bore so if there is any variance hole to hole the cut will be in the right place in relationship to the bore. __________________ The Villages, Florida.

September 12, 2017, 09:50 PM	#7
4V50 Gary Staff Join Date: November 2, 1998 Location: Colorado Posts: 21,832	That would work too but are the notches center of the cylinder hole? Even if not, the jig could be made such that the key cutter would be in the right spot. A jig would be good for production but I don't see any advantage over an index head. Once that is set up, you leave it alone. Make the cut, back off. Rotate the head whatever # of times to the next position and then move it back to the cutter. Can you post a sketch of the jig you have in mind? __________________ Vigilantibus et non dormientibus jura subveniunt. *Molon Labe!*

September 13, 2017, 02:28 PM	#8
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	I would guess he's got bolt/latch offset from the cylinder pin holes that he can measure in the frame. An important point is that a six shooter has one chamber at 6:00 when another is at 12:00, and that offset often doesn't move the notch very far from the 6:00 chamber wall. It's a weak point on all six guns (the reason a lot of the heavy caliber modern revolvers are five-shot rather than six). On the other hand, the pressure of the 45 Colt is pretty low. Bottom line, though, is that I would try to err on the side of shallow and err on the side of as much offset as you think will still function. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

September 7, 2017, 09:35 PM	#2
Tidewater_Kid Senior Member Join Date: July 3, 2005 Location: Alabama Posts: 925	It would seem to me that you could measure the width and length of your bolt, add a few thousandths and that will work for the slot. You could measure bolt protrusion from the frame to get a approximate depth. To me laying them out would be the most difficult task. I found this drawing on the web that gives frame dimensions for various manufacturers. You don't say who made yours. I am assuming it is an older piece made by a company that is no longer in business?

September 9, 2017, 09:08 PM	#5
Tidewater_Kid Senior Member Join Date: July 3, 2005 Location: Alabama Posts: 925	I agree on the key cutter as the way to go. I don't have a milling machine so I would outsource it.

September 13, 2017, 06:11 PM	#9
Aguila Blanca Staff Join Date: September 25, 2008 Location: CONUS Posts: 18,459	The notches are already there (and they are offset), but they're not deep enough. Locating them isn't the problem -- cutting them is the problem.

September 15, 2017, 08:37 PM	#10
Aguila Blanca Staff Join Date: September 25, 2008 Location: CONUS Posts: 18,459	Bought the Woodruff Key cutter with a diameter of 7/8" and a face width of 5/32" from MSC Supply. Worked very well. Cost me a grand total of $22.58, and I have a cutter that may have other applications down the road.

September 16, 2017, 06:00 PM	#11
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	May I suggest you measure the offset of the edge of the notch closest to a chamber wall and then figure out how thin it will make the metal between itself and the chamber. A hoop stress analyses will then show how much pressure the resulting chamber can take. Jack Belk pointed out a Chiappa Rhino 44 Mag that had .045" between the chamber and the bottom of the locking bolt slot that blew out and cut off a trigger finger. So, even though you will be at much lower pressures, it's not a consideration to simply ignore without checking. That's why you were wise to ask for a drawing to see what the original value was. I'm just sorry nobody had one of the cylinder to offer. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

September 18, 2017, 08:02 AM	#13
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,061	Sounds like a plan! I also read about a gun that, rather than blowing apart, merely pushed the floor of the notch to bulge outward over time. Can't recall the gun or the chambering, but I'm thinking you could take a light and a probe like a dental pick with you and make sure you don't see or feel any depression forming inside the chamber nearest to the notch. Check it from time to time for cumulative effect. At the pressures you are are running, the brass will spring back to shape pretty completely, so I don't know if you can count on it to mirror such an indentation, but monitor it over time anyway. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

October 9, 2017, 07:04 AM	#14
45 Dragoon Senior Member Join Date: June 14, 2013 Posts: 656	Hmmmm, if I were having a dedicated cylinder made for a S.A. of any caliber, I would have a Ruger type notch (thin, which extends the offset) and fit the bolt head for the new locking notch. That way, you build in strength/safety. (It's always best to fit the bolt to the notch, not the notch to the bolt.) As far as the Rhino, I knew there was a reason I didn't like the "firing" chamber being that close to my hand!! Mike www.goonsgunworks.com Follow me on Instagram @ goonsgunworks Last edited by 45 Dragoon; October 10, 2017 at 06:12 AM.