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Post by bradshaw on Nov 4, 2024 9:53:55 GMT -5
Notes on Revolver Nomenclature
Some revolver nomenclature----such as frame, barrel, cylinder, trigger, etc.----is universally understood. Therefore does not need explanation. Even when a manufacturer applies its own term to a part, the shooter tends to understand:
Part that arrests cylinder to align a chamber to the bore
* Bolt---Colt.
* Stop or cylinder stop----S&W.
* Cylinder latch----Ruger.
Terms, from clear to confusing
Freebore, the absence of rifling between forcing cone and lands.
Freebore has been adapted from rifles to revolvers. Roy Weatherby, a pioneer of high velocity of rifle cartrkdges, used freebore to burn more powder and increase without spiking pressure. Weatherby’s intent was to increase velocity, not accuracy. Rod Sward of Interarms Virginian Dragoon fame incorporated freebore in the Silhouette Dragoon, specifically to increase accuracy. Freebore may be of any depth. Freebore does not specify a per-caliber diameter. In my view, freebore should be about .0005” per side more than groove diameter.
Since a revolver features a cylinder with multiple chambers separate from the barrel, provision must be made for a bullet which protrudes from the case, Technically, a chamber exit hole (throat) could be described as freebore. When chamber-to-bore alignment is perfect----runout .000-inch----a firm exit hole acts as freebore, supporting the heal of the bullet as the bullet shoulder crosses barrel/cylinder gap and forcing cone to engage the rifling. Most revolvers have lateral cylinder play at lockup, which, in the presence of lateral runout may be a good thing.
Alignment of a chamber to the bore is set by bolt notch on opposite side of cylinder. Specification package and manufacturing tolerances determine correctness of vertical & lateral chamber-to-bore alignment.
Forcing cone
The job of a forcing cone is guide a bullet into the bore without shaving or distortion This shooter considers the forcing cone a necessary evil, at once critical to accuracy, yet ruinous to accuracy when improperly cut.
Using the .44 as an example, freebore in a revolver barrel helps align the bullet ro bore axis when chamber-to-bore runout falls within .006”, or thereabouts. As expected, smaller bores are more sensitive to a given deviation.
Confusion sets in when an idividual applies his name or an appellation to a procedure unspecified. Confusion invites speculation, such as, is the wall of Taylor throating straight or tapered? Thanks to Lee Martin and now Larry Crow, I see Taylor throating is straight----which I call freebore----with low angle leade onto the lands.
The rifle community proved long ago the accuracy of a great barrel is ruined by a poor chambering job. The forcing cone in a revolver barrel commands the same importance.
David Bradshaw
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Post by bigbrowndog on Nov 4, 2024 12:52:38 GMT -5
Your post is timely David, as I have noticed that given my various 41 magnums using the same load produce various velocities, with wide ranging increases. Granted one is a shorter barrel,…4.2” compared to all the others at 7.5”. However each also has differing cylinder lengths, which to my thinking creates a differing length of free bore, since all rounds are loaded exactly the same. The velocity provided by the longer cylindered guns of the same barrel length are as much as 100fps difference.
I had been frustrated by how closely my 414sm compared to my Redhawk 41mag, when pushing bullets of the same weight. Top loads producing only 50-75 fps difference between the two, hardly a reason to burn 5-6 grains more powder for such a small difference. The 414sm utilizing all the room in the cylinder, the Redhawk having room for a longer OAL with the same bullets. I wondered if the “free bore” provided by the Redhawk was possibly the reason for the close proximity of the two velocities. My thinking was to try the normal 41mag/Redhawk load in the 414sm and see what velocity was provided. Perhaps the extended freebore would prove a diminishing return, at which point I will consider loading the round a bit longer by crimping in the lube groove and increase the powder charge by a half grain or 3/4 grain. Ironically the Redhawk will accept a loaded round of that length as well.
My goal is to simply see if a shorter OAL round loaded with the same bullet can provide the performance of one loaded to maximum length, I think this could almost parallel your “deep seating” methods. Possibly deep seating the .41 bullet in question into the SM case would provide the freebore and produce performance similar to the same bullet loaded at maximum OAL and be more efficient on powder usage.
Trapr
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Odin
.375 Atomic
Posts: 1,099
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Post by Odin on Nov 4, 2024 13:32:48 GMT -5
Trapr, your comments remind me of those talking of increased velocity of 45ACP loads when fired from a revolver as opposed to a semi-auto. This, even from the short 4.625" and 4.75" guns. Some suspect "oxegenation" at the barrel-cylinder gap for the increase in velocity, but the gap is otherwise seen as a source of velocity LOSS. The idea of freebore as a bit of a velocity accelerator is interesting indeed...
Rod
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Post by bradshaw on Nov 4, 2024 14:15:52 GMT -5
Trapr.... a longer cylinder has two pronounced affects, especially at magnum pressures and magnum doses of powder:
1) Slow barrel face erosion.
2) Increase velocity by containing chamber pressure.
While I haven’t done a before & after experiment on the same revolver barrel, it’s my impression freebore slightly decreases velocity.
A magnum benefits from firm dimensions to keep pressure inside the gun and behind the bullet. For velocity, it more important for a revolver to hold tight as the bullet accelerates. Even more so, a .357 Maximum, or the .375, .414 (.41), and .445 (.44) Super Mags. For all the great chamber and bore dimensions of big frame Dan Wessons, the frame is not as rigid as the Blackhawk/Super Blackhawk, Redhawk or Super Redhawk. Talking about endshake during discharge. Indicative of this description, the DW is more apt to bind with gap is set too tight.
Certainly the ORCHESTRA of DIMENSIONS is simpler to establish on a single action than on a double action. Yet, Smith & Wesson put its finger on the challenge decades ago, as id Dan Wesson Arms, and Ruger on some of its Redhawks with .000" to .002” chamber-to-bore runout.
Like the .445 Super Mag, the .414 SM burns too much powder, with too much noise, for too little gain.
David Bradshaw
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Post by 45MAN on Nov 4, 2024 14:35:31 GMT -5
Trapr, your comments remind me of those talking of increased velocity of 45ACP loads when fired from a revolver as opposed to a semi-auto. This, even from the short 4.625" and 4.75" guns. Some suspect "oxegenation" at the barrel-cylinder gap for the increase in velocity, but the gap is otherwise seen as a source of velocity LOSS. The idea of freebore as a bit of a velocity accelerator is interesting indeed... Rod I WAS GOING TO MENTION THIS, HAVING READ THAT REVOLVERS CAN SHOOT 45 ACP FASTER THAN SEMI-AUTO's BECAUSE OF THE "free bore", i.e. THE THROAT, IN A CYLINDER. ALSO BECAUSE MY FRIEND MARK KEY WAS GETTING 2,000fps WITH A 325gr SWIFT A-FRAME OUT OF A S&W 460 BFR, WHICH HAS A RIFLE LENGTH CYLINDER AND PLENTY OF "free bore" FOR EVEN THE S&W 460. |
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Post by 45MAN on Nov 4, 2024 14:44:08 GMT -5
SO DAVID: NOW WE ARE DEALING WITH 2 DIFFERENT KINDS OF REVOLVER "free bore", i.e. CYLINDER "free bore" AND BARREL "free bore".
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Post by bradshaw on Nov 4, 2024 15:05:09 GMT -5
SO DAVID: NOW WE ARE DEALING WITH 2 DIFFERENT KINDS OF REVOLVER "free bore", i.e. CYLINDER "free bore" AND BARREL "free bore". ***** Rey.... as they say in New Orleans, “Yeah, you raaht.” Chamber throats (exit holes) may be thought of as freebore.... unless we agree freebore is intrinsic to the barrel. You refer to as “freebore" in a revolver cylinder. Manufacturers call it a chamber exit hole, or throat. I add the term leade to describe the ramp between chamber and exit hole. The term “leade” is borrowed from rifle nomenclature, the ramp joining chamber throat to land. The Ruger 03 has freebore measuring .800” from barrel face to lands. An advantage of a longer cylinder is seen between the S&W .357’s, the M-28 and M-19. Fed the same amount of the same ammo, barrel face erosion happens faster on the short-cylinder M-28. Odin.... the 5-1/2” Ruger 03 sees a lot of use with .45 ACP cylinder. Likewise, the 4-3/4" Freedom Arms M-83 with .45 ACP cylinder. Velocity of same loads is comparable, with the M-83 averaging 10-15 fps faster. All ACP loads are configured for my 1911’s. No reason to hot rod ACP for a .45 Colt revolver. the 4-3/4” M-83 and 5-1/2” Ruger 03 average the same load 40-70 fps faster than a 5” 1911. David Bradshaw |
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Odin
.375 Atomic
Posts: 1,099
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Post by Odin on Nov 4, 2024 15:31:39 GMT -5
I was only noting that the velocity differences, and variables involved in Trapr's experience with the 41 Mag. and 414SM seem to rhyme a bit with what shooters have noted when running 45 ACP in a revolver as compared to a semi-auto. That long freebore-esque throat may be helping to boost velocity. Interestingly, if I'm reading David's comments correctly, there may be a bit of velocity DECREASE with any type of freebore AFTER the barrel-cylinder gap (ie. taylor throating, etc.). But also as Mr. Bradshaw noted, the main objective with barrel freebore is increased accuracy. Any added velocity may be appreciated academically, but on a practical level isn't something one should waste time chasing... at least where this shooter is concerned.
Another thought - Had I time and money, testing velocity in 1911 barrels cut with various amounts of freebore would be an interesting experiment. I suppose with the right tooling, only one barrel needs to be sacrificed...
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Post by bradshaw on Nov 4, 2024 15:58:15 GMT -5
.... Another thought - testing velocity in 1911 barrels cut with various amounts of freebore would be an interesting experiment... ***** Odin.... one barrel. Chrono all your loads. Target simultaneous velocity measurement; if possible, 50 yards. Repeat with .250” freebore. Repeat with .500” freebore. Record everything. David Bradshaw |
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Post by bigbrowndog on Nov 4, 2024 17:12:51 GMT -5
Like the .445 Super Mag, the .414 SM burns too much powder, with too much noise, for too little gain.
David Bradshaw
Until I’d gotten the Redhawk, the increase in velocity for the 414sm, was appreciable compared to the normal 41mag. My comparisons were FA97 and SW657, both providing what most would consider typical 41mag velocity. The Redhawk completely negated my velocity increases from the 414sm, I am currently having JRH build me a long cylinder Super BH in 41mag. and it makes me wonder what that gun will produce even with its 5.5” barrel. I’m so disconcerted by the near equal accuracy and nearly equal velocity that I’m giving thought to sending the 414sm back to Jack for conversion to a 5 hole gun in an attempt to squeeze more from it. I will first see if this freebore or extended chamber length will provide any increase.
I’ll post my findings on my 414sm topic and here if you will allow my slight hi Jack of your topic, as my findings occur.
Trapr
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Odin
.375 Atomic
Posts: 1,099
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Post by Odin on Nov 4, 2024 17:24:06 GMT -5
Like the .445 Super Mag, the .414 SM burns too much powder, with too much noise, for too little gain. David Bradshaw Until I’d gotten the Redhawk, the increase in velocity for the 414sm, was appreciable compared to the normal 41mag. My comparisons were FA97 and SW657, both providing what most would consider typical 41mag velocity. The Redhawk completely negated my velocity increases from the 414sm, I am currently having JRH build me a long cylinder Super BH in 41mag. and it makes me wonder what that gun will produce even with its 5.5” barrel. I’m so disconcerted by the near equal accuracy and nearly equal velocity that I’m giving thought to sending the 414sm back to Jack for conversion to a 5 hole gun in an attempt to squeeze more from it. I will first see if this freebore or extended chamber length will provide any increase. I’ll post my findings on my 414sm topic and here if you will allow my slight hi Jack of your topic, as my findings occur. Trapr Just thinking out loud about what can be squeezed out of a standard frame... My apologies for the hijack. |
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Post by bigbrowndog on Nov 4, 2024 17:43:59 GMT -5
Odin, I saw no real load data there, just mentioning of velocities and projected performance.
Trapr
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Post by bradshaw on Nov 5, 2024 9:12:17 GMT -5
When freebore may help
Chamber exit holes, or throats, in a cylinder, act as freebore to support the bearing surface of a bullet----when a revolver's ORCHESTRA of DIMENSIONS are exact & correct. It may be redundant to freebore the barrel when the bullet is assured at straight path from cylinder to rifling. To this shooter, freebore or careful permutation should improve accuracy of a revolver with some misalignment. It might even benefit stability of a bullet launched through oversize throats.
As for correcting damage done by a bad forcing cone,or chamber exits too large to support the heal of the bullet as it crosses the gap, I’m not so sure.
If there was a downside to the Production rule in IHMSA silhouette----no modification, except for a trigger job with factory parts, blackened or painted sights, and aftermarket grips finished to a standard pattern (example: Pachmayr)----it was to prohibit experimental work. To get to the top required real accuracy from a stock revolver. This meant you might go through a slew of sixguns to reach top tier performance. Wallet groups and behind the line bullroar don’t impress a sharpshooter; only performance on the Firing Line counts. It’s this production consistency which propelled Freedom Arms into the winner’s circle. I’d be reluctant to freebore a gun which shoots this tight out of the box.
So, what are the candidates? Candidates for experiment should include revolvers with oversize throats, say .003” or .004” over bullet diameter, and up. If the barrel is good but its forcing cone is junk, don’t look for a cure from freebore----until you set back the barrel. If you over-advanced THREAD TIMING, with consequent bore crush at the barrel shoulder----compression ring, aka thread choke----pull the barrel, correct the thread timing to hand-tighten 10-degrees BTDC, followed by freebore.
When freebore may not help
* Orchestra of Dimensions already perfect.
* Bad barrel: oversize groove diameter; alternating tight & loose spots, etc.
* Combination of oversize throats, oversize groove, off-axis cylinder & bore, barrel crooked on frame, etc.
Hand tools are for brushing your teeth and shaping grip frames, not for cutting chambers, or freebore, or forcing cones.
David Bradshaw
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