Slugged my 357 Colt King Cobra

[bigdawg86]

So I slugged my King Cobra's barrel since I wanted to start shooting some lead that was given to me... I got a bore diameter of .353 and all my projectiles are .358 size.
I was quite surprised at the measurement I got, but upon doing some google research, I found that others have gotten the same measurement.

Now that I know where I am at, would it be recommended to size the bullets down?

I did a quick Midway USA search and found a Lee .356 sizer die... since I have only my single stage press I assume this is as close as it's gonna get.

What should I do?

[waksupi]

I would fit to the cylinder.

[bigdawg86]

So slug the cylinder and not the barrel?

[GP100man]

Yep it`s more important to have the cyl to match or just larger.001" than bore !

Think of the throat ,forcing cone & bore as sizers, alot easier to size down than up.

The Ole Man said think of shooting a lead boolit down a funnel .

[bigdawg86]

Got it thanks!

[MtGun44]

Groove diameter, I think you mean. Bore diameter is the top if the lands.

Also, what measuring tool are you using? Do you have experience with precision
measurment or new to the art? I'm a bit skeptical of .353 groove diam, and
expect it to be more likely a measurement error than that large a manufacturing
error.

Another issue is that Colt bbls have been reported to be choked, might be .357
or .356 or something at the back and tighter at the muzzle, maybe even as
tight as .353. This is typically an accuracy enhancer.

Bill

[bigdawg86]

Groove diameter, I think you mean. Bore diameter is the top if the lands.

Also, what measuring tool are you using? Do you have experience with precision
measurment or new to the art? I'm a bit skeptical of .353 groove diam, and
expect it to be more likely a measurement error than that large a manufacturing
error.

Another issue is that Colt bbls have been reported to be choked, might be .357
or .356 or something at the back and tighter at the muzzle, maybe even as
tight as .353. This is typically an accuracy enhancer.

Bill

Although I am not a grizzled veteran to "precision tools"... I don't know the name of the caliper offhand, but it is an analog caliper that I received from a late family friend that was a hardcore reloader so it's a quality instrument. I did measure a Speer .224 bullet and it was .224 on the money. I slugged from muzzle to breach so having a choked barrel makes sense. For kicks and giggles I did the same procedure on my Colt 38 Army Special with the same result. I am completely open to the idea that I did it wrong.

[bigdawg86]

In hindsite I am questioning if I measured from the actual rifling... ****. I guess I will remeasure when I get home.

[Moonie]

Calipers are not accurate enough for this kind of measurement, you must use a micrometer.

[mainiac]

Having never fooled with,nor slugged a colt barrell,i dont know how many grooves are in the colt barrell? If its an odd number,then that could be a reason for the undersize figure.Very hard to measure odd number of grooves,cause ya cant get on them perfectly 180 degrees apart.....

[Char-Gar]

I have seen lots of Colt 38 barrels run .354-.355 in the grooves. I have never known of one to be .353. I suspect your measuring is off a tad.

[white eagle]

Calipers are not accurate enough for this kind of measurement, you must use a micrometer.
nonsense a caliper is fine
you don't need .00005 or .0005,.005 is plenty close enough for what its intended

[BABore]

nonsense a caliper is fine
you don't need .00005 or .0005,.005 is plenty close enough for what its intended

Spoken like a man who knows precision measuring instruments.:veryconfu

Being close enough at 0.005" means his bore slug could be anywhere from 0.3505 to 0.3555.

You need a proper micrometer that read tenths or 0.0001". When slugging a barrel you should pound one soft slug all the way through the barrel so as to detect the smallest point. You should also pound a slug just into the muzzle, then back out the way it came. This slug should be the smallest diameter of the two. If it's not, then you likely have a constriction or choke point. Typically it's at the barrel threads. More than 0.0005" of constriction needs to be remedied by either hand lapping, fire lapping, or about 500 jacketed rounds. The bbl should be slightly choked at the muzzle. Constriction before the muzzle leads to leading and less than stellar accuracy.

Each cylinder throat should be slugged and compared. They should all be within 0.001" or preferably less to one another. Throat diameters should be anywhere from 0.0005 to 0.0020" over the bbl's groove diameter. Larger calibers seem to be able to handle throats on the large side of this better than smaller ones like the 357. If the bbl checks out ok, still size to the throat diameters within reason. A close boolit fit to the throat helps keep proper alignment.

[MtGun44]

LOL! ".005" is OK? Hope that's a joke.

No offense on your skills or tools, but this has been discussed by people here and
by experts in the industry and there are standards.

Checking against a .224 bullet is useful, no doubt, but not conclusive. Where I work
(aerospace weapons industry) you need to be able to accurately measure one more
significant digit than is required. This is necessary to be certain of the final digit.

Calipers are rated to +/- 0.001" so are absolutely not permitted for this work in my
industry and are certainly marginal for measuring accurately to 0.001" in any case.
You really need that extra digit.

If you really want for this work is a micrometer that is accurate to 0.0001". These can
be bought new from Enco Tool for well under $50. Look at their Fowler brand mics online,
often available on sale for $28 or so, a decent quality tool.

Feel is also an issue, lead can be tricky to measure. Even or odd number of grooves?

S&W uses an odd number and are difficult to measure accurately because of this.

Bill

[white eagle]

what I was referring to was the the placement after the decimal
you can substitute and number you want in its place
was for reference only
we are talking about cast lead boolits it really dont need to be .00015
:groner:

[Groo]

Groo here
The Colt Python was known for a tapered bore usually starting around .358 or .357 and
going down to .355 to .354.. In the old days this allowed 9mm jsp or jhp bullets to be used
for light bullets..
This might have followed through the rest of the line...
Ps Does it work??? I was at Thunder Ranch one year and hit a man size target 3 out of 5
at 300 yds with a 4in and 110 gr bullets..