5-Shot Build - Documented

[potatojudge]

Does anybody have a pic of a factory pawl from a 454 or 480 Blackhawk for comparison?

[Quick Draw McGraw]

Please, sir, I want some more. 😢

[princeout]

Apr 25, 2017 9:43:49 GMT -5 potatojudge said:

Does anybody have a pic of a factory pawl from a 454 or 480 Blackhawk for comparison?

Potatojudge,
I'm a little slow in noticing your request, but finally saw it and took a few pictures and some measurements.

Here is a wide shot of a couple of Ruger factory 5 shot pawls (left side) and a factory 6 shot pawl (right side).



Here is a closer view of one of each, with the 5 shot on top:



Finally,
This shot shows them overlapping, 5 shot on top.  This shows the extra length of the top portion of the pawl.



By my crude measurements, the top portion or tooth of the 5 shot pawl is 0.292" using a caliper held parallel to the long surface of the top tooth.  The same spot on the 6 shot pawl, measured in the same fashion, is 0.266",  Makes sense since the pawl has to rotate the 5 shot cylinder 72 degrees and the 6 shot only 60 degrees.

The distance from the bottom of the locating stud to the horizontal surface of the 2nd tooth was about the same, within a thou with, once again, crude measurements.

Tim

[Lee Martin]

Before I begin, I want to cover cylinder-to-bore alignment. Conventional wisdom says line-boring is the most precise method to index the cylinder throat and barrel’s bore. I’ll flatly tell you it isn’t. That’s no knock on the process or any of the fine gunsmiths that use the technique. If I built custom revolvers for sale, I’d damn sure advertise line-boring. It’s universally accepted as the gold-standard. It sells.

Line-boring is done in a horizontal mill using a frame/cylinder jig. A spud is first screwed into the frame which acts as the drill guide. The gun is held in battery and a centering drill spots the bore’s centerline. You can either drill one pilot hole per chamber and pull the cylinder or progressively increase the diameter. Regardless, with line-boring you can’t complete the pilot hole; otherwise you’d run into the breech face. Line-boring also requires a bearing block to wedge the bolt and a tightly fit basepin. That ensures indexing is consistent chamber to chamber. It supplements how the cylinder is kept stationary while cocked for drilling. Most of the work though is done by a jig which secures the frame and cylinder. While line-boring is quite precise, it presents some challenges;

• The frame jig must hold the action dead perpendicular to the mill’s head. If you decide to get into a line-boring, you’ll spend some time getting this right.
• The centering bit and pilot drill cannot be the exact diameter of the guide spud’s hole. If they were, they’d drag the edge. So they must be undersized by a thousandth or so. Alignment much past three zeros becomes difficult.
• The pilot holes must be re-indicated with a centering device to complete the bore (cylinder outside of the frame). Thus you’re drilling in two passes. This introduces the chance for slight misalignment upon re-centering (even as the drill follows the pilot hole)
• Frame and cylinder jigs are very rigid. However, they do not compare to the leveling capability and positive grab of a 100 pound, 3 or 4 jaw chuck.

By now, I’m sure some of you are shaking your head. Fine enough, but we’ve both line-bored and cut cylinders with the method outlined below. My conclusions are based on actually shop time, not conjecture.
__________________________________________________

Line Indexing

We didn’t invent the process, but my dad switched to line-indexing on his own in the 1990’s. After dozens of conversions, we found it easier and more accurate than line-boring. It all starts with sound cylinder fit. As illustrated in step #6, the bolt matches the frame slot and notches so there is absolutely no side-play. We also use the same oversized pin for indexing mock-up. Dad machined a frame mounted shank, made with extremely tight threads. It was center bored and honed to 0.2500” on the nose. Next he cylindrically ground a pointed rod, once again 0.2500” diameter. Key takeaways: 1) The point was indexed and zeroed to absolute center, and 2) The rod is so tightly fit there’s resistance when pushing it through the hole (unlike line-boring shanks which are a thousandth or two larger than the drill).

The homemade frame spud.



The shank is threaded into the frame and the rod is inserted. With the gun in battery, the rod is tapped and the fine indication point marks the cylinder face. This is repeated five times.



A Hartford Super Spacer is mounted on our Bridgeport. The chuck weighs 100 pounds and is accurate to seconds of a degree. The chuck had already been leveled to the table.



A Baker centering gauge is installed and the point is put in the indentation. Each mark on the gauge represents 0.0005”. The mill is turned on a very slow speed and the dial indicates misalignment. The table is adjusted in tiny graduations until the needle doesn’t move as it spins in the mark. Once it stays on the same dial mark, you’re indicated to 0.0000”.



The mark is spotted with a starter bit. This is followed by a 1/4” drilled hole front to back.



I then enlarged the hole with a 31/64” bit (0.4844”).



A 0.510” reamer makes the final pass. This reamer was ground by my dad and matches our .500 Linebaugh pilot; also home ground.



I purposely reamed the throat under final spec. We prefer honing the throats to the desired diameter, approximating the bullet. This allows us to achieve tighter tolerances and produces a superior surface finish.

Video of me reaming a throat. Forgive the shakiness, I was holding the camera as I feed the reamer.



The process is repeated 4 times after the indexing head is rotated 72 degrees. Integral to proper alignment is re-indicating each mark with the centering gauge.



Checking throat-to-bore alignment – saying one method is better than the other means nothing without empirical evidence. The best way to do that is with a centering device. You start with a frame shank sporting a hole that exactly matches the throat. For example, if the throat measures 0.5100”, the shank’s bore also has to be 0.5100”. The cylinder is fit to the frame, the shank is screwed in, and the gun is cocked while held in a vertical mill. Using another centering device that rides the surface of the shank’s hole, the headstock is slowly fed down and zeroed. As it transverses the cylinder gap, it enters the throat. Misalignment, or lack thereof, is shown on the dial. Meaning if it stays zeroed in the throat over 360 degrees, you’re dead nuts on. If there’s runout, it’ll show-up on the dial.

Bore alignment – line indexing or line-boring are tied to barrel installation. Remember, we’re talking throat to barrel bore alignment here. If you thread the blank and lathe the cone with any runout to center, you’re nixing the precision throat. A lot of guys index on the outside of the blank when adjusting the chuck. Forget that. Even the highest quality blanks exhibit a thousandth or two of O.D. runout to the rifled bored. And most of the pistol blanks we use show 0.002” – 0.004” runout over the entire length. I’m a stickler on this, but you really need to center the blank in the chuck by zeroing across every groove. When I barrel this thing, I’ll detail those steps.

A couple of things to back my point. Magnum Research uses line-indexing on their BFRs, albeit in a more automated fashion. We all know how well they shoot. And earlier this year I was talking to a friend who is one of the most talented gunsmiths I know. He doesn’t commercially smith, but has done everything from custom built benchrest actions to Ruger conversions. For a living he builds engine balancing machines that he and his brother designed….that speaks to his engineering prowess. Anyway, we were talking about line-boring Rugers when he said there’s a better mousetrap. I didn’t say how we did ours, instead giving him the floor. After five minutes of explaining his approach, it turns out he uses the same method we do to indicate bore centerlines. We’re not alone on this one.

-Lee
www.singleactions.com
"Chasing perfection five shots at a time"

[cherokeetracker]

There is also another well known Smith that does it your way. We had this discussion a couple of months ago. He will be building me a new cylinder for my Colt SAA. That is all I am going to say. Other than, that is the reason, he will be doing it, instead of anyone else. I back you 100% on this Lee.
Just curious,,, If it took you 1 or 2 days to make that cylinder? I figure 2 days.

Charles

[potatojudge]

Thanks Tim, those dimensions make perfect sense.

Lee, thanks for the writeup so far. I've heard you allude to line indexing being superior, but now the process and rationale are clear. Elegant solution compared to line-boring. I would imagine a 'smith that line-indexes could charge less than one that line-bores and get more guns done in a given period of time. I would be curious how the big names in the industry do it- both the boring and the barrel turning.

I'm curious to see how the barrel is done and if there's a need or method for truing the frame threads and the front face of the frame. Patiently waiting, but glad the BR game is back on track to make time for this project.

Related but slightly OT, a re-bored cylinder can't be line-indexed it would seem. Realistically, can they be line-bored with much precision? Lets say somebody was doing a long cylinder 45 Colt cut from a 357 Max cylinder, they blocked the action, and fit an oversize bolt to eliminate side to side play. What would be the next step in recutting the chambers potentially off-center from their original locations?

[cherokeetracker]

I do remember you doing this same thing with your 44spl Build on the Ruger forum. ( Line indexing the cylinder)
One day on this cylinder is smoking along in my opinion. This has been very interesting and a lot of fun, seeing it all take place and coming together.
Another question,,,, On the rod that is used to center punch the marks,, Is that just a piece of drill rod? Or is it something a little more special since he cylindrically ground the rod? Say something he hardened or did something special to it.

Charles

[Lee Martin]

Jun 13, 2017 22:03:11 GMT -5 potatojudge said:

Related but slightly OT, a re-bored cylinder can't be line-indexed it would seem. Realistically, can they be line-bored with much precision? Lets say somebody was doing a long cylinder 45 Colt cut from a 357 Max cylinder, they blocked the action, and fit an oversize bolt to eliminate side to side play. What would be the next step in recutting the chambers potentially off-center from their original locations?

You’re correct. Re-boring a cylinder can’t be done as described above. If the throat is way out, indicate through a frame spud that matches the hole you’re attempting to make. Once centered, either use a boring bar in a vertical mill or straight line-boring. Dropping a drill into the throat won't work....unsupported drill bits just follow the original hole.
___________________________________________

Charles – we can fabricate cylinders in a day; everything but heat treating that is. I’ve taken my time on this conversion. Whenever I get a free Sunday afternoon, I make some progress. Yesterday I cut the rim recesses and chambered it. Look for an update soon.

-Lee
www.singleactions.com
"Chasing perfection five shots at a time"

[Lee Martin]

I start by flipping over the cylinder and re-indicating each hole. A centering device sweeps all 360 degrees of the bore and the table is adjusted to zero runout. Again, this must be done on every throat.



A 0.610” endmill was selected to cut the rim recesses. Starline .500 Linebaugh rims mic 0.603” – 0.605” in diameter. I always want a little extra space to prevent grit from binding headspace. Upon cutting the first 0.060” recess, the endmill proved dull. It was re-sharpened on a tool and cutter grinder.



Milling the rim recesses. A depth stop was set at 0.060” in from the face.



The case measures 1.400” in length. Average rim thickness is 0.0602”, so the reamer is fed a minimum of 1.338”. I always go a little deeper and chose 1.360”. Another depth stop is set on the quill.



Before chambering, all five holes are again swept using a centering gauge. This confirms zero runout. You’ll recall, the chambering reamer is home ground and the pilot matches our throater. The finisher is held in a floating reamer holder.



Testing a case.



The fully chambered cylinder.



Next time I’ll harden it.

-Lee
www.singleactions.com
"Chasing perfection five shots at a time"

[Joe S.]

Nice!

[alukban]

I am enjoying this thread so much th aI feel like I should be paying you!


What level do you use?

[Quick Draw McGraw]

Question: This is gonna be a .500 Maximum, right Lee?

[Lee Martin]

Jun 21, 2017 22:19:43 GMT -5 Quick Draw McGraw said:

Question: This is gonna be a .500 Maximum, right Lee?

.500 Linebaugh.

-Lee
www.singleactions.com
"Chasing perfection five shots at a time"

[Lee Martin]

Tim – appreciate the pictures of factory pawls, 5-shot versus 6-shot. One thing I want to callout - there is no such thing as standard 5-shot pawls. The geometry must be matched to the cylinder ratchet; and not all 5-shot ratchets are created equal. They can vary in diameter, orientation, and cog relief.

Thanks to Tim, we see Ruger lengthened the first leg on their 454 and 480 SBHs. When custom smiths, us included, started doing 5-hole conversions, we didn’t have long pawls (and building them up isn’t recommended). In order to get 6-shot pawls to function, we dropped the ratchet timing a few degrees (counter-clockwise to TDC). The caused the hand to engage quicker, but also necessitated the following:

1) The bolt has to drop faster. This is done by increasing the hammer plunger’s protrusion
2) Because the next cog advances sooner, the second leg is filed back to prevent bind. This was illustrated above in step 13.

On the left, a .500 JRH BFR. On the right, a .480 Bisley SBH.



Notice how the BFR’s first cog sits lower relative to the .480’s? In fact, it’s tangent to the chamber, whereas the Ruger cog intersects the hole. The difference would appear even more pronounced if the Blackhawk was in 50-cal.

The 480’s longer hand reaches higher to begin rotation. The next cog’s orientation is also closer to TDC at this engagement. This allows it to clear the pawl before the second leg projects. I could go on forever about timing these things but won’t bore you guys. My only point is this - there’s a narrow window in which revolvers operate and each part has to be coordinated.

-Lee
www.singleactions.com
"Chasing perfection five shots at a time"

[Quick Draw McGraw]

This thread has given me a real appreciation for gunsmiths and explained why 5-shot conversions are so expensive. I have to admire your hard work, Lee, as well as your dedication to excellent craftsmanship. This will not be a half-assed, passable-quality revolver!