Dazed and Confused

[mmorris]

OK, I spent an enjoyable evening yesterday casting 500 LEE 158 grain tumble lube semi-wadcutters, and today I was making preparations to put the first 12 of them into some new brass over 3.6 grains of 231 (on my way up to 4.0), looking for 769 to 837 fps over (not through) my chrono so I can find the ideal load and commence flowing the 700 pounds of wheel weights in the barn down the barrel of my S&W Model 67-1, when I stumble across this here in the Wheelguns, Pistols and Handcannons area:


6. The cylinder exit hole should not be smaller than the size of the bullet you are sending down range. Have a gunsmith open up the cylinder holes so your bullets are not swaged down before they enter the barrel. This is also something you can do yourself. The ultimate boolit size is that which requires felt finger pressure friction when pushed through the Largest cylinder exit. The size chosen should not be so large as to cause a loaded cartridge to have any felt friction when placed into the Smallest cylinder

I know that the cylinder exits are .356 from earlier checks I did when I loaded some 125 grain LEE 9mm TL round nose bullets. They worked OK (no leading). Later I read that 125 grain bullets were not optimum for 38 special loads (maybe even harmful at some loads), and I decided to move up to 158 grain bullets.

So to re-check, I press a .358” SWC through the cylinder and find that it takes a lot more than finger pressure to reduce it to the .356” cylinder exit. Then I check a Hornady .38 FMJ at .3565 and I wonder what the overall effect of reaming the cylinder exit out to .3575-.3580 will be for the other bullets I may send down-barrel.

I have not slugged the barrel because I don’t have the jig to measure 5 groove rifling.

The Question
Is the quoted recommendation simply to aid those looking for the utmost in accuracy, or is it related to responsible reloading?

Do I ream the cylinder, resize the bullets or just blow ‘em out the barrel?

I don't want to resize, but I guess I will if I have to (yet more equipment and time before I :Fire:)

[timkelley]

Load up a dozen or so and go shoot them, worst thing can happen is a leaded barrel.

[mmorris]

Load up a dozen or so and go shoot them, worst thing can happen is a leaded barrel.

Thanks, will do.

[DanWalker]

Here's one thing that has proven to be a pretty reliable indicator of undersized throats for me.
If your groups tighten up as your velocity increases, you're looking at a swaging effect.
My guess is that at lower velocities and pressures, your boolit is getting swaged down as it exits the cylinder. It then tries to slug back up once it hits the rifling. It has been my experience that this will produce some leading in the forcing cone area, indicating that the boolit skids a bit before expanding sufficiently to restore the gas seal and fully engage the rifling. Accuracy can be pretty fair, even if this condition is present. You'll have a velocity window that's dependent on pressure, and boolit hardness, that will allow for good accuracy. Push your boolit too slow, or use too hard of an alloy, and you'll get the effect I describe. You'll probably reach the upper safe pressure limit of your firearm or the published maximum loading data, before you run out of boolit hardness, so stripping the rifling usually isn't an issue, unless you have to use an alloy that's REALLY soft to get the accuracy you want.
If you're happy confining yourself to the warmer end of the spectrum with your loads, you can probably find a workable combination of velocity and boolit hardness to give good accuracy.
If not, go to http://www.cylindersmith.com For less than 50 bucks, this problem will go away.

[bobke]

take a fairly soft bullet with at least .358 diameter, lightly lube your barrel and bullet and push it through the barrel, being careful not to deform same in the process. then take it and try pushing through chamber throats. if it's very tight or won't push through without some effort, the barrel's larger than your chamber throats and could benefit from reaming just slightly larger.
dan walker's comments about swaging effect are spot on and you'll likely find it much easier to achieve a broad range of accuracy with the proper relationship of bore and throat sizing than having to have a bullet size and resize itself in the transition from throat to barrel and really nail the bullet hardness issue to insure a correct seal of bullet in the bore.

[Edubya]

mmorris, you've been around since 2008, you know that everything that's written here or elsewhere is not a law of physics or any other absolute.
Everyone of my boolits get swagged down upon passing through the forcing cone. Most of them get a custom fit leaving the cylinder throat too. A .432 boolit will not gently pass through a .431" cylinder throat but somehow it seems to hit the targets that are presented to it.
EW