Over size forcing cone

[Sailormilan2]

How much effect does an oversized forcing cone have on accuracy? I have a S&W 629 6" with an over sized forcing cone. The forcing cone is so big, a Brownell's forcing cone plug literally drops in, with the upper step about .090" below the lip of the forcing cone. The cone will actually swallow the entire front driving band of a .452" cast SWC Long Colt bullet.
It appears that in order for me to fix the problem, I will need to set the barrel back at least 2 turns, possibly 3. Because of this, I got a brand new, unfired replacement 4" barrel to put in the place of the 6" barrel. Unfortunately, the replacement barrel has exactly the same problem.
I've been told that an oversized forcing cone won't have effect on accuracy, and then I've been told the exact opposite.http://i752.photobucket.com/albums/xx166/Sailormilan2/SWForcingCone6_zpspcmqt7ny.jpg (http://s752.photobucket.com/user/Sailormilan2/media/SWForcingCone6_zpspcmqt7ny.jpg.html)


http://i752.photobucket.com/albums/xx166/Sailormilan2/SWForcingCone4_zpsj8r4lrbx.jpg (http://s752.photobucket.com/user/Sailormilan2/media/SWForcingCone4_zpsj8r4lrbx.jpg.html)

[DougGuy]

If it's smooth and concentric, you have nothing to worry about. Taylor throating a revolver barrel does not have any detrimental effect on accuracy in fact it may improve a larger percentage where others it may make no difference. Taylor throating removes a LOT more metal than what your forcing cone has had cut out of the barrel. I cut semi extended throats in auto barrels and they shoot lights out. The longer leade in to the rifling serves to center and square the boolit up with the bore and it is led more smoothly into the bore than a short throat with steeper angled leade ins. Your forcing cone is pretty much doing the same.

How does it group? What are your cylinder throat diameters? Can you push a .432" boolit into the throats from the front? Having larger throats will ensure the boolits are not being sized down upon firing, which will definitely help it take advantage of the larger, longer forcing cone.

I think you may have better accuracy with a WFN or RF boolit style where the sides are smooth and rounded, not like a K type boolit with the shoulder and driving band.

[Sailormilan2]

All my cast bullets are sized at .430", and they pass easily through the cylinder throats. I am considering bumping them up to .431". I am a bit out of practice shooting the 629, but yesterday, using Sierra 180 & 240 JHP loads it was grouping about 4-5" at 25 yds. Which in my opinion is not good at all.
But, it has reamer marks, so it's not smooth, and I am very leery of cutting more since it's already large. Comparing it to my Model 28, the forcing cone on the 28 is very much tighter.

[johnson1942]

doug guy is the go to man but i also have learned one thing. a very very short roundnosed bullet with a 60 thousands wad behind the bullet. also switch to black horn 209 powder and fill the case full just behind the wad and bullet. it wont be a magnum but it wont be a wimp either. if you do this you will shoot holes in hole. also even if you lube your bullets and on a short bullet it may be only one groove., put them in a jar with a little lee alox in the jar and shake them around and set in the sun to dry. useing this method you will get bored with the groups so tight every shot. also check you crown. ive never and rarely like factory crowns. put a polished 79 and 1/2 degree crown on it and doing all the above you will never ever sell that gun. i really like reading anything doug guy post, he has taught me alot and helped my guns shoot holes in holes. making a gun shoot perfect is a matter of science and dog guy has the science down pat.

[DougGuy]

All my cast bullets are sized at .430", and they pass easily through the cylinder throats.

I am considering bumping them up to .431". I am a bit out of practice shooting the 629, but yesterday, using Sierra 180 & 240 JHP loads it was grouping about 4-5" at 25 yds. Which in my opinion is not good at all.
But, it has reamer marks, so it's not smooth, and I am very leery of cutting more since it's already large. Comparing it to my Model 28, the forcing cone on the 28 is very much tighter.

There would likely be the cause of the lousy groups, not the forcing cone. Honestly I think you'd be better off sizing to .432" and seeing if they will go into the cylinder throats, if so try it and see how it works, if not may I suggest having the cylinder throats reamed and honed to .4325 ~ .4328" and feeding the gun a diet of .432" boolits. Trying .431" is a step in the right direction as well, and probably work better than sizing to .430"

[johnson1942]

my 44/40 easily passes a larger bullet through the cylinder holes. all it needed was a forcing cone job, which i did and then it went from so so groups to what i call a one hole gun.

[Outpost75]

FWIW I have two Ruger Vaqueros, .44-40 and .44 Magnum which both have forcing cones which accept .45 Colt and .45 ACP bullets. The two .45 ACP and .45 Colt cylinders from my NMB convertible .45 both fit, time and index in both .44 Vaqueros which were built two years apart. Accuracy is NORMAL squirting standard pressure .45 loads down the .44 Mag and .44-40 barrels. I wouldn't worry about it in a strong gun. 25-yard sandbagged group squeezing .45 Colt Cowboy loads down a .44-40 barrel. My choice for a TEOTWAWKI gun which will take any ammo which falls off the tailgate of the alien spaceship is a .44 Ruger Original Vaquero with .44 Mag., .44-40, .45 ACP and .45 Colt cylinders. Squirt it all down the .44 barrel!!!!

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Velocity Test .45 Colt recylindered 5-1/2" S&W M1917 vs. 5-1/2" Ruger .44-40 Vaquero with .45 Colt NM Blackhawk cylinder

Ammunition__________________S&W converted M1917_________________Ruger Vaquero .44-40
____________________________New .45 Colt Cylinder_________________NM Blackhawk .45 Colt cyl.
____________________________Cylinder gap 0.004"___________________Cylinder gap 0.008"
New Winchester 255-grain lead___852 fps, 17 Sd, 40 ES_________________793 fps, 12 Sd, 32 ES
Old Western 255-grain Lubaloy___866 fps, 20 Sd, 52 ES_________________799 fps, 8 Sd, 21 ES
200-grain FN, 7.2 grs. Bullseye___945 fps, 14 Sd, 34 ES_________________912 fps, 14 Sd, 42 ES

[jrayborn]

Wow! Very interesting.

[S.B.]

I guess my question would be, what, possibly, could be the difference what size a forcing cone could make on accuracy? I mean it's the tapered end of barrel that is the lead in of barrel not the size of bore? Please explain?
Steve