The Colt Revolving Fire-arm Cylinder is a multi-chamber rotating drum that indexes a fresh loaded chamber into line with a single barrel each time the hammer is cocked. A spring-loaded hand climbs a ratchet on the rear of the cylinder to rotate it, while a bolt rises from the frame to lock the chamber concentric with the bore before the sear releases. This solved the single-shot bottleneck of muzzle-loading pistols. Samuel Colt's 1836 patent turned a foot-soldier sidearm into a 5- or 6-shot weapon and defined revolver geometry for the next 180 years.
Colt Revolving Fire-arm Cylinder Interactive Calculator
Vary chamber count and cylinder leade diameter to see the indexing pitch angle, bolt arc travel, and comparison pitches for alternate cylinders.
Equation Used
The cylinder pitch is the angular index from one chamber to the next. Multiplying that angle by the leade-circle circumference gives the bolt tip arc travel; because theta_pitch = 360 / n, the arc also simplifies to pi * D_c / n.
- Chambers are equally spaced around the cylinder.
- Cylinder diameter is measured at the bolt leade circle.
- Bolt arc is measured along the cylinder outside diameter between adjacent leades.
- Chamber counts are whole numbers.
Inside the Colt Revolving Fire-arm Cylinder
The Colt Revolving Fire-arm Cylinder, also called the Colt Cylinder Revolving Device for Firearms in patent literature, works by linking three separate motions to one input — the shooter's thumb pulling back the hammer. As the hammer rotates rearward, a pawl called the hand rises and pushes against one tooth of the ratchet machined into the back face of the cylinder. That rotates the cylinder by exactly 360° / n, where n is the chamber count — 60° for a six-shooter, 72° for a five-shooter. At the same time, a small spring-loaded bolt drops out of a leade in the cylinder's outer surface, lets the cylinder rotate freely, then snaps up into the next locking notch just as the next chamber arrives in line with the barrel. Pull the trigger and the sear releases the hammer onto the percussion cap or firing pin.
Geometry is everything here. The hand must lift the cylinder by exactly one chamber pitch — over-rotation jams the bolt against the side of the leade, under-rotation leaves the bolt sitting on solid steel and the cylinder won't lock at all. On an original 1851 Colt Navy the bolt notch is 0.080 in wide and the bolt itself is 0.078 in — that 0.002 in clearance is what gives the gun its characteristic 'click' on lockup. If you measure more than 0.005 in of rotational play at the chamber mouth with the bolt engaged, the cylinder is no longer concentric with the bore and you'll see lead spitting out the cylinder gap on firing.
The failures all trace back to wear on three parts. A short hand — worn or filed back at the tip — fails to rotate the cylinder fully, so the chamber arrives early at the bolt and the action skips. A worn bolt or rounded leade lets the cylinder over-rotate past the locking position. And a weak bolt spring lets the bolt bounce instead of snap, which over thousands of cycles peens the leades into shallow ramps and makes the timing problem self-accelerating.
Key Components
- Cylinder: The rotating drum holding 5, 6, or in rare cases 7 or 9 chambers. Bored on a precision indexing fixture so each chamber sits on a pitch circle concentric with the cylinder axis to within 0.002 in. Each chamber's axis must be parallel to the cylinder axis within roughly 0.001 in/in or the bullet will shave lead at the forcing cone.
- Ratchet: A star-shaped projection on the rear face of the cylinder, integral with the central arbor hole. Each tooth is engaged in turn by the hand. Tooth height typically 0.060–0.080 in on a Colt Single Action Army; a worn ratchet is the single most common reason a vintage Colt 'skips' a chamber.
- Hand (Pawl): A flat steel finger riding in a slot in the recoil shield, spring-biased outward. As the hammer rotates rearward the hand rises and pushes the ratchet tooth. On a properly timed Colt the hand tip leaves the ratchet at the exact moment the bolt drops into its notch.
- Bolt (Cylinder Stop): A small rectangular block in the bottom of the frame window that rises into a leade in the cylinder's outer surface. Pre-leade ramps cut into the cylinder let the bolt drop just before the next notch arrives. Bolt-to-notch fit is typically 0.001–0.003 in for proper lockup.
- Bolt Spring (or Trigger/Bolt Spring): On Colt single-actions a single flat V-spring drives both the trigger return and the bolt. Spring rate matters — too soft and the bolt fails to snap into the notch in time, too stiff and the leades wear faster. Replace with a hand-fitted Wolff or factory-spec spring; do not file the original.
- Cylinder Arbor (Base Pin): The shaft the cylinder rotates on. Diametral clearance between arbor and cylinder bore typically 0.0015–0.003 in. Excess clearance shows up as visible cylinder droop and is a fast route to lead-spitting at the cylinder gap.
- Locking Notches (Leades): Rectangular slots milled into the outside diameter of the cylinder, one per chamber. Each notch is preceded by a shallow ramp so the bolt rides up smoothly. On a worn cylinder the ramps deepen into a 'cylinder line' — a continuous drag mark — which is cosmetic but signals worn timing.
Who Uses the Colt Revolving Fire-arm Cylinder
The Colt cylinder principle reaches well beyond firearms. Any time a designer needs to present one of n stations in line with a working tool — and lock that station rigidly during a working stroke — the same pawl-ratchet-bolt arrangement appears under different names. The Colt Cylinder Revolving Device for Firearms is, in mechanism terms, a hand-operated rotary indexer with positive lockup.
- Firearms — Historical: Colt Paterson (1836), Colt Walker (1847), Colt 1851 Navy, Colt 1860 Army — all percussion revolvers using the original Sam Colt patent geometry.
- Firearms — Modern: Colt Single Action Army (1873 to present), Ruger Vaquero, Smith & Wesson Model 29 — all use a hand-and-ratchet indexer descended directly from the Colt design, though S&W uses a swing-out cylinder.
- Machine Tools: Manual turret lathe tool posts (e.g. Hardinge HLV-H 6-station turret) use an identical pawl-and-locking-bolt indexing scheme to present one of six tools to the workpiece.
- Theatrical Props & Film Armoury: Stembridge Gun Rentals and ISS Props maintain working Colt-pattern revolvers for productions; a mistimed cylinder is the most common 'won't fire' callout on set and is fixed by replacing the hand.
- Museum Restoration: The Cody Firearms Museum and the Royal Armouries Leeds restore Colt cylinders using period-correct hand and bolt fitting techniques rather than modern replacement parts to preserve provenance.
- Industrial Indexing: Rotary dial assembly tables on small-batch lines (e.g. Weiss TC150) use cam-driven indexing instead of a hand, but the locking-bolt-into-leade principle is identical to the Colt cylinder lockup.
The Formula Behind the Colt Revolving Fire-arm Cylinder
The single most useful number for evaluating a Colt-pattern cylinder is the chamber pitch angle and the linear arc the bolt must traverse before lockup. At the low end of the range — a 9-chamber pocket revolver — pitch is 40° and the bolt drops earlier in the cocking stroke, leaving less margin for hand wear. At the high end — a 5-shot snubnose — pitch is 72° and the cylinder needs more rotational momentum to carry the bolt over the leade ramp, so a weak bolt spring shows up faster. The 6-chamber 60° design is the sweet spot Colt settled on by 1851 because it balances rotation distance, ratchet tooth strength, and chamber wall thickness in a 0.36 to 0.45 caliber frame.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| θpitch | Angle the cylinder rotates between adjacent chambers | degrees (°) | degrees (°) |
| n | Number of chambers in the cylinder | count | count |
| sarc | Arc length the bolt tip travels along the cylinder OD between leades | mm | in |
| Dc | Cylinder outside diameter at the leade circle | mm | in |
Worked Example: Colt Revolving Fire-arm Cylinder in a Colt 1851 Navy reproduction restoration
A film armourer in Vancouver is re-timing a Pietta 1851 Navy reproduction that has started skipping the second chamber on fast cocking. The cylinder OD at the leade circle measures 1.625 in (41.3 mm) and the gun is a standard 6-shot. He needs to know the design pitch angle and bolt arc travel to compare against the worn cylinder, and to evaluate whether the same fitting procedure changes for the shop's 5-shot Remington Pocket and 9-shot LeMat replicas.
Given
- n = 6 chambers
- Dc = 41.3 mm
- nlow = 5 chambers (Remington Pocket)
- nhigh = 9 chambers (LeMat)
Solution
Step 1 — at the nominal 6-chamber configuration, compute the pitch angle:
Step 2 — convert that to a bolt-tip arc on the leade circle:
That 21.6 mm is the linear sweep the bolt tip rides along the cylinder OD between one leade dropping out and the next leade snapping in. On a healthy Pietta the bolt covers that arc in roughly 0.18 s during a deliberate cock — fast enough that the leade ramps must be smooth or the bolt will bounce.
Step 3 — at the low end of the range, the 5-shot Remington Pocket:
The bolt has to ride 20% further between locks. On a 5-shot the cylinder also carries more rotational inertia per cock, which feels like a heavier, longer hammer pull and means a tired bolt spring shows up as a missed lockup almost immediately.
Step 4 — at the high end of the range, the 9-shot LeMat:
Only 14.4 mm of arc between leades. The bolt drops earlier in the hammer stroke, the ratchet teeth are smaller and shallower, and the hand tip must engage the next tooth almost immediately after disengaging the previous one. There is no slack in the system — a 0.005 in shortened hand will skip a chamber on a LeMat where the same hand would still work on a 6-shot Navy.
Result
The nominal 6-chamber Navy needs a 60° pitch and a 21. 6 mm bolt arc — that's the geometry every replacement hand and bolt must be fitted against. Comparing across the range, the 5-shot Remington at 25.9 mm arc gives the most fitting margin and the 9-shot LeMat at 14.4 mm gives the least — which is why original LeMats are notoriously fussy to time and why most modern reproductions tighten the ratchet tooth count instead of widening tolerances. If your measured cylinder skips and you've already ruled out a worn hand, check three things in order: (1) ratchet tooth wear at the tip — a peened-over tooth lets the hand slip without rotating the cylinder, (2) recoil shield clearance to the ratchet — under 0.004 in and the ratchet binds on the shield mid-rotation, and (3) arbor-to-cylinder bore clearance — over 0.005 in lets the cylinder droop and the bolt misses the leade entirely.
Colt Revolving Fire-arm Cylinder vs Alternatives
The Colt cylinder is one of three classic ways to feed multiple shots from one barrel. Each has measurable tradeoffs in cycle rate, mechanical complexity, and reload time — and those tradeoffs explain why the Colt Cylinder Revolving Device for Firearms dominated 1850–1900 sidearms, why semi-autos took over after 1900, and why pepperboxes faded almost immediately after Colt's patent.
| Property | Colt Revolving Cylinder | Pepperbox (multi-barrel) | Semi-Auto Slide & Magazine |
|---|---|---|---|
| Cycle rate (aimed shots/min) | 20–30 (single-action) | 15–20 | 60+ (limited by trigger reset) |
| Capacity, typical | 5 × 6 chambers | 4–6 barrels | 7–17 rounds |
| Reload time (full) | 20–60 s percussion, 8–15 s cartridge | 60–120 s (each barrel) | 2–4 s (mag swap) |
| Bore alignment precision | ±0.002 in chamber-to-bore | Each barrel pre-aligned, no indexing | Single fixed bore, no indexing |
| Mechanism complexity (parts count) | ~14 in lockwork | ~8 (simpler) | ~25–40 |
| Failure mode | Timing drift — hand/bolt wear | Chain-fire across barrels | Stovepipe, failure-to-feed |
| Service life before re-time | 10,000–25,000 rounds | Indefinite (no indexing) | 5,000–10,000 rounds before spring service |
| Application fit today | Cowboy action, hunting, collector | Obsolete | Defensive, military, sport |
Frequently Asked Questions About Colt Revolving Fire-arm Cylinder
That's almost always a worn ratchet, not a worn bolt. The hand contacts a different tooth for each chamber, and on a gun fired heavily from one or two chambers (common with cap-and-ball shooters who load the same chambers every range trip) those teeth peen down faster than the others. The hand then under-rotates that specific chamber and the bolt drops short of the leade.
Diagnostic check: cock the gun slowly and watch the bolt drop on each chamber. If the bolt drops in the leade dead-centre on five chambers and ahead of the leade on the sixth, the ratchet tooth feeding that chamber is short. Fix is a new ratchet (on Colts, the ratchet is integral to the cylinder, so it's a cylinder replacement) or TIG-build and re-cut by a qualified gunsmith.
No, and the gun is on its way to a hand-skip failure. The bolt should drop into the centre of the leade, which means the cylinder must rotate the full 60° (or 72°, or 40° depending on chamber count) before the bolt rises. A 2° shortfall on a 41 mm cylinder is roughly 0.7 mm of bolt offset inside the leade — the bolt is sitting against one wall of the notch instead of centred.
The cause is almost always a hand that's too short, either from wear or from over-zealous fitting. New hands are sold long and stoned to fit; if the previous gunsmith took 0.005 in too much off the tip you'll see exactly this symptom. Replace the hand and re-fit from oversized.
For a frame under about 1.5 in cylinder OD, go 5-shot. The math from the worked example shows why: at small diameters the chamber wall thickness between bores becomes the limiting factor. Six chambers in a 1.4 in cylinder leaves under 0.060 in of wall between adjacent chambers, which is below the safe minimum for any cartridge over .32 caliber.
Five chambers at 72° pitch gives you ~0.090 in of wall in the same diameter, and the longer bolt arc (25.9 mm vs 21.6 mm) is actually easier to time because the bolt has more dwell time before it needs to snap up. Smith & Wesson J-frames and Ruger SP101s went 5-shot for exactly this reason.
The cylinder line is a continuous drag mark around the cylinder OD where the bolt has been dragging during rotation instead of being fully retracted. It is cosmetic on its own — every used Colt has one — but the depth and width tell you about timing health.
A faint line under 0.001 in deep is normal break-in. A line that's deeper outside the leade ramps than at the ramps means the bolt is dropping early (worn bolt cam on the hammer) and dragging across solid steel before reaching the leade. That's a re-time job, not just a cosmetic issue, and ignoring it accelerates leade wear into a self-feeding failure.
Black powder fouling. The ratchet face and the recoil shield form a tight pair — typically 0.004–0.006 in clearance — and BP fouling builds up on both surfaces within 20–30 rounds. Once the fouling layer exceeds the clearance, the cylinder binds against the shield and the hand can't fully rotate it.
The fix during a shooting session is a wet patch behind the cylinder every 18–24 rounds, or a drop of Ballistol on the arbor. Long-term, check that your arbor-to-cylinder clearance is at the loose end of spec (0.003 in not 0.0015) — period Colts ran looser specifically to tolerate fouling, and modern reproductions sometimes ship too tight for sustained BP shooting.
Yes — same mechanism, two names. 'Colt Cylinder Revolving Device for Firearms' is the descriptive phrasing used in Samuel Colt's 1836 US patent and in some museum and academic catalogues. 'Colt Revolving Fire-arm Cylinder' is the modern engineering name. Both refer to the indexed multi-chamber cylinder driven by a hand-and-ratchet and locked by a spring bolt against the frame.
References & Further Reading
- Wikipedia contributors. Revolver. Wikipedia
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