Printable View
Im just curious as to why no one has ever tried doing something to actually combat the constriction of the revolver barrel in the thread area?
Say a finish reamer down the barrel after assembly to kill any constriction.
Counter boring the barrel in that section before assembly to take up slack when assembled.
lengthening the forcing cone so that it goes through that entire section ...
Well that’s a perfectly reasonable question(s).
Answers:
Ream after assembling? Only cuts the lands but leaves the grooves constricted. Revolver then leads in the grooves.
Counter bore before assembly? Same as reaming above. Only cuts lands leaving grooves constricted after assembly.
Lengthen forcing cone? Its done. It’s called Taylor throating. It’s cutting a free bore section through the constriction and then a lead into the rifling. Some folks like it.
Not all revolvers have barrel constriction in the thread area.
Adding extra steps to the final construction of a gun costs money, and extra time. that would increase the costs of the gun. Guns are built with the concept that most of the ammo used will be jacketed bullets & not cast bullets. Barrel constriction is more noticeable to casters & not jacketed shooters.
And lastly,, it'd be easier to build a gun w/o the constriction IF,, IF,, IF,, we had gunsmiths working on guns instead of gun parts assemblers. But again,, a gunsmith type of employee costs a lot more than an assembler. And a gunsmith type of employee would slow down production. Slow production also costs more,, so a company can't afford to keep the stockholders happy. Most casual shooters never even know what barrel constriction is,, much less know it might be an issue.
So, it all boils down to MONEY!
I believe I have heard of those that use a firelapping kit to remove the constriction.
That's called a Taylor throat. I haven't heard very good things about them. Plenty of people firelapp successfully.
There is the near 1" of parallel freebore in a 45ACP revolver cylinder before the B/C gap and forcing cone and these are surprisingly accurate considering the flight path the boolit takes through the parts of the gun before it reaches the muzzle.Quote:
Originally Posted by megasupermagnum
I have a stainless Vaquero that the factory torqued the barrel SO tight to drift POI that they squeezed it down to .449" and trying to pass a snugly patched cleaning jag through the barrel required CONSIDERABLE beating with a good sized hammer, I nearly destroyed the cleaning rod. This one got Taylor throated and the .450" cylinder throats got reamed to .4525" this fixed this puppy right up!
If you have a stainless Ruger, with a fairly noticeable thread choke, it will require a pretty good amount of lapping as their stainless is VERY slow to lap. Some of the rifling will be damaged by the time you get the choke lapped out.
Round hole broach 0.0005" less than bore diameter to shave tops of lands to remove constriction. Lube with Brownell's Do Drill and smack through with lead hammer. Leaves mirror finish. Factory fix used in customer service when I was at Ruger. Better is to assemble barrel to frame with a UNEF class 2 thread which is not an interference fit, and then use 242 Loctite on threads. Avoid the thread choke in the first place.
My understanding is that in decades past, the gun makers practiced THREAD TIMING on both the barrel and frame. This allowed the sights to align properly at TDC, without having to gorilla-wrench the barrel on. Timing threads takes time, and machine operators who actually know how to do more than just insert the part and hit the 'ON' switch. That equals higher cost and slower production, which reduces profit. They figure that Joe Six-pack neither knows nor cares about these issues of properly timed barrels and no thread constriction, so they don't either. They "fix" (READ: swap parts or very reluctantly replace defective guns) things for the few that do care and seek remediation, and probably wish those folks would just go away.
I usually fire-lap the constriction out of the barrel.
Veral Smith wrote a great article for "Rifle" magazine back in the 1980s on this subject.
He used a Ruger Blackhawk .357 as his test subject. He discussed in detail the effect of crush-fit barrel threading. His remedy was to hand lap the barrel, in particular the threaded area.
The result was .359" throats and groove.
I think he used CH swage dies to bump up jacketed bullets.
To demonstrate the results, he showed before and after groups using a Ransom Rest.
He turned a 3-4" 25 yard gun into a Bullseye capable target pistol.
There used to be Taylor-throating for revolvers, which reamed a gentle taper into the threaded area so the boolit would be guided and swaged to the correct diameter before engaging the rifling. The write-ups showed great improvement, but it was also claimed that a properly (!) done forcing cone could produce the same result. I liked the Taylor-throating idea that everythiong didn't happen at once. Slap-dash, oversize and rough forcing cones and barrel constrictions aren't doing anyone any favors.
The thread form is part of the problem, 60 degree threads by their nature conspire to deflect toward the center at a place where the barrel is thinnest. Square threads don't have this problem, but they're too coarse and too much trouble for most revolvers. I think Colt used to use them on early 1873's but changed to 60 deg. later on.
I don't think your assumption is accurate. As you can read a number of solutions have already been posted. Also it has been observed in some cases the barrel can be simply unscrewed from the frame and the elastic nature of the steel allows for springback. Now go and install the barrel properly.Quote:
Originally Posted by BandeauRouge
With modern computerized machinery timing barrel threads is easy. Problem lies with variation in the revolver frames. At Ruger when I was there frames were checked by hand turning in a slave barrel which was supposed to line up within 3-5 degrees of top dead center when hand snugged. If more, frame was put aside and a 0.0015" pass taken off the front frame face on a Blanchard surfsce grinder. Problem was that assemblers in barrel shop were paid piece work and instead of putting frames aside for regrind they would use a cheater bar on the barrel wrench and grunt them on.Quote:
Originally Posted by nicholst55
On the SP101, GP and Redhawk fixed the problem by changing frame barrel thread from UNEF class 3A to a 2A so no longer an interference fit and used 240 series Loctite in assembly to keep barrels tight.