David Bradshaw Photos Vol. VI

[Lee Martin]

As usual I'll let David provide the commentary...



























-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[bradshaw]

1) S&W M29-2 with 8-3/8" barrel which shot High Revolver at the IHMSA 1978 International Championships. Along with a brass grip old model Super Blackhawk, this M29 toughed it out against single shots and helped create a separate category for revolvers in silhouette.

2 & 3) with forged, case hardened "combat" trigger, a worn or spare cylinder stop, and the red ramp sight, which S&W replaced with target front and a high, black blade at rear.

4 & 5) Newer Nickel M29-2 with the tournament gun. As blue revolver munched silhouettes, nickel revolver sought deer. (Blue with original red sight was a hunting revolver before silhouette came along.) Both are 2-inch guns at 100 yards.

6 & 7) S&W mahogany box, onto which dope was recorded after first stage of 1978 championships. Wind calculations started at 100 meter pig, which provides much better drift dope than shorter distance. Rams at 200 meters were started with 14-clicks left windage, ended with 18-clicks windage plus 1-foot.

8 & 9) Jay Tee Revolv-A-Gauge, developed by Sheldon Williams, to measure chamber-to-bore alignment and position of any misalignment.

10) Reading head----plastic indicator contacts chamber throat.

11) Indicator dial with knurled handle and button----press prior to inserting shaft in barrel.

12) Revolv-A-Gauge in M29 barrel. The "total indicator reading"---- .005"divided by two----yields .0025-inch chamber-to-bore misalignment. Average for this revolver.

13) M29 with Revolv-A-Gauge. Barrel was set back at S&W by Al Plaas to remove erosion. Plaas then overhauled lockwork and timing. Despite considerable shooting, revolver utterly reliable. And, thanks to Al Plaas, revolver is tighter than when it was made.
David Bradshaw

[cj3a]

Neat gauge.

[cj3a]

David, I have been thinking more about that gauge. Have you measured any line bored guns or a Freedom arms.

[bradshaw]

cj3a.... I've used the Jay Tee gauge on Freedom Arms, all or most of which guns (as I recall) showed CHAMBER-TO-BORE OFFSET of .000" to .002-inch, with .000" to .001" common. Line boring of the cylinder, as Lee Martin notes, starts the chamber pilot-hole with cylinder in frame. To complete the chamber, cylinder is removed and bored/reamed from the rear.

Line boring, properly set up, produces chambers on the bore axis.

It is not the only way to skin a cat. I've measured Dan Wessons which exhibit .000 to .001" or .002" offset. Likewise, some two-digit Redhawks. Years ago Smith & Wesson replaced the cylinder on a Model 19; chambers of the new cylinder ran .002" offset.

My brief tours of the factory at S&W, DWA, Ruger, Interarms, and Freedom Arms were made with eyes unskilled at encyclopedic absorption. Had I been looking through the eyes and seeing through the brain of Sig Himmelmann, I could tell you processes in blueprint detail.

Bill Ruger, Sr., said to me, "You can't do a damn thing without tools." Implicit in that is having useful tools and knowing how to use them. I read a biography of John Moses Browning, I think written by a son, in which someone claimed that Browning had "micrometer fingers."

However the better manufacturers make their cylinders, those mentioned above have proven they know how to make revolvers right when they want to, and that line-boring is just one technique for producing a proper cylinder. I have looked at revolver accuracy a long time. Having hit Tin Man 5x6 shots at 200 yards offhand with a Colt .45 4-3/4" Peacemaker built in 1897, I bear a profound respect for lessons learned in the old days, beginning with Try To Do Everything Right.

My Jay Tee Revolv-A-Gauge has two reading heads (.357, .375) (.41, .44, .45), with nylon shaft and head bushings for respective calibers.

Such a tool can isolate a badly misaligned chamber----or chambers----which then may be test fired and correlated to group on target.

I do not recall using the gauge in conjunction with a barrel crooked on the frame. I have shot Bangor Punta S&W M-586's----which, due to crooked barrels, lacked windage adjustment to get on paper at 15-20 yards.

The are some very accurate revolvers exhibit .004 to .006 offset. Everything else is good, including the all-important modest, concentric forcing cone.

It was giant and untested mistake when in the early 1980's Ruger and S&W cut excessive and sometimes sloppy forcing cones in a numb attempt to "correct" poor chamber alignment and to eliminate spitting. Killed accuracy or made inaccuracy worse, is what it did.
David Bradshaw

[Lee Martin]

You're spot on David. While line-boring is sound method I think folks over-emphasize it. It's become a buzz-phrase or sorts. Like you, I've owned or shot guns with 0.003 - 0.005" worth of offset and they drive tacks. If aligned within reason, say 0.002 - 0.004", I'll put the forcing cone, barrel, and the load ahead of it in the accuracy equation (of course the shooter trumps all of those)

Our line-indexing process has consistently achieved 0.0005" or less on throat to barrel alignment. And unlike line-boring we can cut the bore in one pass. So yes, there's definitely more than one way to skin this cat.

-Lee
www.singleactions.com
"Building carpal tunnel one round at a time"

[bradshaw]

Lee.... you are absolutely correct that forcing, cone barrel, and load come before minor chamber-to-bore OFFSET, or misalignment. In my own crude experiments many years ago, I found that----given a short, concentric forcing cone----the bullet departs a slightly offset throat to enter the barrel suffering less OBTURATION than a bullet that tips and slams an oversize or off axis forcing cone.

Recovering bullets from snow, 50 to 150 yards from the firing line, revealed greater deformity of bullets slamming an exaggerated forcing cone. Snow is a great medium to gather a bullet without damage. (Excepting varmint bullets).

The simplest way to make a revolver shoot is to build it correctly in the first place. It is a rough game trying to catch up to dimensional sloppiness. Serious students such as Stroh and Bowen and Linebaugh and you, etc., and a manufacturer such as Freedom Arms get around this laxity by making a cylinder to a gun to correct a symphony of dimensional and alignment faults. (And I call Stroh and Bowen and Linebaugh and you and other top smiths "students" precisely because a good professor continues to learn.)

Bullets recovered from snow are another tool for the diagnosis of a misbehaving revolver.
David Bradshaw

[hammerdown77]

This is a question loosely related to the topic at hand, but I was wondering, in the presence of a less than optimal forcing cone geometry, will moving to jacketed or very hard cast, truncated cone style cast bullets mitigate the effects over shooting a standard SWC design cast at about 12-18 BHN?

[bradshaw]

hammerdown77.... Correction. Your topic----bullet selection----is very much related. By naming bullets, you have set yourself an experiment. Now all you need is a "good" revolver and, for comparison, a couple of "bad" revolvers.

This is why the forcing cone is so important: as the bullet departs the chamber throat, it must meet the rifle square, or as close to on-axis as possible, and continue on axis until completely seated in rifling. A bullet tries to line up the throat to the bore. (Think bull in a cattle chute.)

A hard bullet, which lacks the elasticity of a softer slug to "slug up," nevertheless may better retain its shape and therefore center of gravity. If I have to live with aberration in a revolver, I would choose a bit of chamber offset over a bad forcing cone or gross throats, either of which enable a bullet to tip between throat and rifling.

What is a bad forcing cone?
* tipped----off axis
* too steep
* too deep
* rough

When chamber offset measures in the .010"-.012" zone, spitting is very likely, with deformity (obturation) just about guaranteed. An oversize or fugitive forcing cone intended to compensate for misalignment only aggravates the problem, as the bullet slams into one side of the cone, to enter the bore asymmetrical. Thus fired, recovered bullets show long engraving on one side, short engraving opposite. Stood on its base, the bullet resembles the Leaning Tower of Pisa. Image this: bullet meets forcing cone at near peak pressure, tremendous gas expansion driving it forward.

My cure for a bad forcing cone is to remove the barrel, trim the shoulder on a lathe, timing the threads of course, set back barrel as for removing erosion; dress barrel mouth for minimum gap. Followed by... recut forcing cone on lathe. If you happen tom have a compression ring (thread choke), you cab ream 0.8-inch groove diameter freebore prior to recutting cone. And, freebore works with a shorter forcing cone.

One projectile especially susceptible to damage between throat and rifling is a bullet of JACKET-FORWARD construction, such as military ball, Full Metal Jacket. Unsupported and driven by magnum pressure, the skirt, or part of it, may blow into the forcing cone. This doesn't just occur in revolvers; it is known to happen in rifles or single shot pistols with the chamber cut to leave a sharp edge between neck and rifling. This absence of gentle leade will destroy accuracy in the best match barrel.

So I have answered your question with a picture. A picture which hopefully explains why I cringe when I hear writers advocate a forcing cone reamer as the road to instant accuracy.
David Bradshaw

[hammerdown77]

Excellent explanation David, thank you.

I think it would be a worthwhile endeavor to photograph forcing cones on different models Ruger, S&W, Dan Wesson, whatever, both old and new, and point out differences, good forcing cone geometries, bad geometries, etc.

I would like to take pictures of the forcing cones on several of my revolvers, but I'm not sure my camera or skills are up to the task. I will give it a try, and if results are good, maybe we can start a new thread of just forcing cone pictures.

[jwp475]

A deep and or oversized forcing cone is also responsible for velocity loss oin an other wise well set up revolver

[bradshaw]

jwp.... true. As for accuracy, revolver velocity is influenced by numerous dimensions beside barrel length:
* chamber, especially throat
* cylinder barrel gap
* forcing cone diameter & depth
* groove diameter

Obviously, cylinder gap is a major factor by itself. Also, chamber exit or throat diameter, as oversize throats bleed pressure.

Combinations which rob velocity:
* Large throats in conjunction with an excessive cone allow gas to blow around bullet into bore before enters rifling.
* Large throats in conjunction with tight bore.
* Large throats, loose gap, tight bore=major robbery.

A slightly loose bore may increase velocity.

Freebore modestly reduces velocity.
David Bradshaw

[jwp475]

+1....

[AxeHandle]

Here is a forcing cone shot of a 44 Hunter that has been Taylor Throated by Jim Stroh..

[buckheart]

Forcing cone of a 45/70 BFR