FYI ... Good info on Colt wheel guns .38 Special/.357 Mag.

[aharlow]

So i was doing a little research while waiting on my reloading supplies for my Colt Python .357 Mag. revolver. Come to find out that it is a little known fact that Colt used a nominal groove diameter of .353/.354 inch for all .38 Special and .357 Magnum revolvers. So in reading this I decided to checked the groove diameter on mine today and sure enough it was right on at .354 inch. Now the question i have is what sizer to buy for my Lyman 450? I was going to go with .358 because that seemed to be the majority of what others use if not sometimes larger. Well knowing what i know now i am thinking more like .356/.357 sizer and wanted to get input if .358 would still be ok or a bit too big. One thing i did learn today was it's always good to do some research on the caliber and manufacture of the firearm you are going to be reloading for and slugging a barrel is well worth your time as well as possibly saving you some money and headaches down the road. My alloy i cast with is COWW's +2% Tin at a BHN around 12 and i do not GC. I will be casting a NOE 150 Gr. SWC in HP/FN. Hopefully this also might help other's with Colt wheel guns who want to reload for them in the mentioned calibers above.

126190

[Poygan]

I normally size to .358 but found these rounds wouldn't always fit in my Python's cylinder. However, .357 fit every time. Can't address the accuracy because I didn't keep it long enough to speak to that.

[hanover67]

I have a Colt .44 special New Frontier that has a "tight" .427" barrel and .432" cylinder bores. I sized boolits to .429" and accuracy was OK. I've been told to size to the cylinder bore diameter, but I think squeezing boolits down 5 thousandths is a lot. I guess I could also use a real soft lead, but that runs the risk of leading. I'd really like to get a new cylinder that is .429" or .430, but that's out of reach right now.

[tazman]

Your next step is to measure the cylinder throats on your revolver. It doesn't do any good to size large if the cylinder is going to swage them back down when fired.
Best to size them the same size as your cylinder throats to reduce the possibility of leading.
A poor man's sizing check is to take a round boolit of known diameter and see if it will pass through the front of the cylinder. When you find a size that will pass through with firm finger pressure you are there. Make sure to test all the chambers on the cylinder. One or more may be different sizes. This can be fixed easily by having a smith ream them all to the same size.
Hopefully, in your case they will measure about .356.

[Guesser]

I cast, load and shoot several Colt 357 revolvers, Pythons, Mark V, Mark III, Trooper 357, Lawman Mark III. I size .358 and load/shoot. Have never had a chambering restriction or a pressure problem. I shoot the same ammunition in Smiff and Ruger 357's, it all works in all of them. My 3 Colt Officers Models in 38 Special also have the tight bores, I use the same bullets as in the 357 revolvers. Much ado about nothing. Take note!!!! There are no cautionary statements in your load manuals or anywhere else about sizing bullets for Colts. The one thing you will note is that the Colts will be more accurate by themselves compared to the off breeds; your contact with them makes them all equal.

[winelover]

Never slugged my Python barrel and just recently used pin gauges on it's cylinder. All the cylinder holes will accept a .360 pin guage. For years, I sized to .357 diameter, as recommended by RCBS boolit mold chart. Never was disappointed with the accuracy @ 20 yards. Could shoot the bull out of a NRA "Slow Fire Target" without using a rest. Of course, no leading, either.

Winelover

[aharlow]

Good to know Winelover and just what i wanted to know. I slugged my cylinder and measured with a caliper, not as accurate as your pin gauge, but got a reading of .3585 so yours is probably a more accurate measure. With bore diameter being .354 I am probably going to do the same and stick with a .357 size boolit diameter at first and give it a test. If i find some leading issues around cylinder throat and cone i'll try out a .358 sizer. Would .004 over bore diameter be ok if i would need to size to .358? Thanks for the help everyone!

[tazman]

Good to know Winelover and just what i wanted to know. I slugged my cylinder and measured with a caliper, not as accurate as your pin gauge, but got a reading of .3585 so yours is probably a more accurate measure. With bore diameter being .354 I am probably going to do the same and stick with a .357 size boolit diameter at first and give it a test. If i find some leading issues around cylinder throat and cone i'll try out a .358 sizer. Would .004 over bore diameter be ok if i would need to size to .358? Thanks for the help everyone!

There is where you need to experiment and find out what your gun likes. Sizing larger than cylinder size isn't going to help accuracy. Between there and groove diameter you just have to try it and see how it works.
I have never dealt with a difference that great.

[Gemsbok405]

Have an E series (mid 70's) 6" Python, and with a cast and sized bullet in .357 is a nice firm fit in cylinder throat. Bullets sized .358 will not go into cyl throat at all.

Said sized .357 CB is super accurate and no leading.

[Cherokee]

My Python ate 357 or 358 size and gave exceptional accuracy with all the loads I tried. I did try some 356 size once...only once because they did not shoot well. I never measured the throats but I knew the barrel was .354

[aharlow]

Thanks Gemsbok for the info! I just melted down some pure lead and poured it into a once fired 357 Mag case about half full and whacked it out with my bullet puller. I took the slug and put it through my cylinder and then took some measurements and i got a reading of .3575. Looks like .357 sizing is going to work just fine and since you mentioned that the .358 wouldn't fit in your Python i'm going to bet it won't fit in mine either. Considering my bore diameter is .354 i think .003 over will be the most i would want to go over.

[tazman]

Sounds like a plan to me.

[Char-Gar]

It is NOT a little known fact that Colt 38/357s run about .354 in the groove. It may have been news to you, but it is not to folks who have been shooting Colts for a very long time. For Colt shooters it is like water runs down hill.

Now to the important stuff...it doesn't matter!!!! You don't size your bullets to fit the barrel, but size them to fit the cylinder charge hole throats, which on vintage Colts run .359 or thereabouts. You will get best results with bullets .358 or .359.

You shoot .356 bullets in that revolver and you are looking for poor accuracy and possibly leading. You might get by with .357 depending on the pressure of your loads and the temper of your alloy, but .358 - 359 will do you much better.

I don't know about the fellow whose Python won't take .358 bullets, but I will guarantee the problem is not the size of the throat. Probably too much crimp or something else. Colt never bored a Python cylinder with throats that small.

Here are a few nice old Colts all of which have .354 barrel grooves and .359 charge hole throats.

[MtGun44]

As tazman and Char-Gar said - you fit boolits in a revolver to the cylinder throats,
not the barrel. Until you slug or measure with a pin gage what size the cylinder
throats are, you are just "shooting in the dark", so to speak.



Bill

[aharlow]

I understand you size to Cylinder throat but what i mostly want to know Char-Gar is if the cylinder throats above measure to .359 and you size your boolits to .359 is being .005 over bore diameter ok? Most people say they load cast boolits .001 to .002 over bore diameter. Just wanted to know if this is just a rule of thumb or just a recommendation. Sorry it's my first time loading for my Colt Python so it was not a known fact to me and thought maybe others might not be aware of this. Didn't mean to insult anyone's intelligence on the matter just trying to help. Thanks

[Char-Gar]

I understand you size to Cylinder throat but what i mostly want to know Char-Gar is if the cylinder throats above measure to .359 and you size your boolits to .359 is being .005 over bore diameter ok? Most people say they load cast boolits .001 to .002 over bore diameter.

If "most folks" are talking about revolvers, they are wrong. Revolver bullets size is determined by the cylinder throat and not the groove diameter. Colt revolvers bored like yours have been winning matches and protecting lives long before either of us were born with bullets .004 or .005 larger than barrel groove diameter.

Therefore when we shove .358 or .359 cast bullets through a Colt cylinder into a Colt barrel, we KNOW that barrel is .354. I have knowingly done so tens of thousands of times!

So, the answer is: it is OK! Most of the other folks in this thread have been trying to tell you the same thing, but in not as direct and blunt way as I have. I have never had much faith in most folks being able to take hints and suggestions and come to the right conclusion. Most folks tend to filter such things through their own prior thinking and assumptions unless somebody (me in this case) grabs them by the collar and get's their attention.

There is so much bad information, wrong information, and misinformation floating around on the web. This "slug the bore and size your bullets .001 - .002 more" is nonsense that is repeated over and over again until it is accepted as fact. The critical dimension for determining bullet size in revolvers is the charge hole throat and the throat/free bore in rifles.