Best way to measure throat and bore?

[Markbo]

A thread in the lube section got me to thinking. (Uh-oh! :p )


Most of my sixguns have had the cylinders at least measured and most of those have been evened up - Ruger's seem to have an odd quality of having slightly different size cylinder throats.

So I have records for what all my wheelgun's cylinder throaths are. I do NOT have complete measurements/data for the bore and barrel throats. What is the best way to accurately measure those? Cerrosafe? Pound a soft bullet a little to make sure it is oversized and push it through?

I have read on here over and over that bullet fit is king to accuracy and I want to make absolute certain that I am using the right size for each gun.

And just a tiny bit off topic - what if I just use .454" bullets in all my .45s? I mean all of them I am shooting 800-1100fps and not pushing it. These could be my first cast bullets made of wheel weights so what... 11-14bnh???

I do have a couple 'hunting' guns that I want to shoot heavier bullets faster so what does the size/fit affect for higher velocities out of those?

[hornsurgeon]

i think the most important thing to know on a revolver is the cylinder throat. your boolit needs to be at least as big or slightly bigger than that. after that, i would worry about bore size. i think most people like their boolits about 0.001" over the cylinder size, and don't worry too much about the bore unless they are having issues. i think it's more important to look at boolit design and shape. most people, as do i, report bettter accuracy with a RF or WFN than they get with a RN or SWC, but there are others that like the SWC instead.

[Rico1950]

As long as your cylinder throats are larger than you measured groove diameter of the barrel,
shooting at cylinder throat diameter or .001" more will be fine.
If it turns out that the groove diameter of your barrel is larger than your cylinder throats, you've got a problem.

[hornsurgeon]

that is true, and then the headache of having to have the cylinder throats opened. they must be dead centered, and then you need to decide what dimension you want them. lucky for me, my gp100 has all cylinders within 0.0005" of eachother, and they are about 0.001" larger than the barrel. all is well. i also have paired that with a heavy RF boolit that has a nose that is 0.002" larger than the lands, so that also helps line up the boolit in the bore. it all adds up to an accurate gun/load.

[Potsy]

I have always been under the impression that slugging was the best way to measure bore and plug guaging was the best way to measure throats.
My probelm is, I don't own any plug guages and wouldn't have them on me when I needed them if I did.
Like today when I was trying to caliper the throats on a 25-5 .45 Colt. Measured .452 but probably closer to .4545-.456. I'm basing that on the fact that my Bisley throats calipered .449, but plug guaged .4515.

[sagacious]

And just a tiny bit off topic - what if I just use .454" bullets in all my .45s? I mean all of them I am shooting 800-1100fps and not pushing it. These could be my first cast bullets made of wheel weights so what... 11-14bnh???

I do have a couple 'hunting' guns that I want to shoot heavier bullets faster so what does the size/fit affect for higher velocities out of those?
.454" may shoot just fine in your 45's. Test it and see. It won't wreck anything, if that's what you're asking. If you're also loading for the 454Casull, in the long run you may be better off sizing those to exact bore diam or +.001 to .002". Expect around 10-11BHN or so for ww's. AC ww's work well for me in 45Colt.

You'll need to size for tight casemouth tension, for good accuracy, and to reduce/eliminate leading. The effect of those factors on velocity is of no consequence. Load for good accuracy and function, and do not worry about the last foot-per-second, as it means nothing in your application-- whereas the other factors do. Good luck.

[whitetailsniper]

i agree with fellow members,,, i found myself in same,with my bisley 41 rem mag. i wanted wfn bullets for hunting,so i bought verals wfn lbt mold,its a 250 grain wfn gc this bullet is a monster and on fist casting sesion ,i was excited to load some of these,after loading the problems started,they would not fit into my cylinder.the nose profile was .411 ,my barrel sluged out at .410. i took and measured the cylinder throats and found all 6 were differant and mostly came in at .410 i then knew at that point i had to make some changes,,the cylinder got opened to .411 the forcing cone was opened to except the wfn style bullets,i then went out and bought a .411 lube sizer die,and bought a factory crimp from MIKE VENTERINO( thank you mike) ive had other work done on my bisley as well ,springs,trigger pull, sights,hammer spring ect. all in all ive learned one thing- allways when buying a gun,specially a revolver, ck. and measure everything.as factory is not allways what they should be. i ended up getting machinest pin gauge set off ebay,,nice set for the price,and allways useful. just a piece of good advice---make sure who ever works on your guns,, knows there trade. to easy for a johnny come lately to say they can do ,,and find out they cant! i had a so called professional sass shooter,and so called master gunsmith start on mine, and when i cked up on them and there work,,, that guy wont touch my guns! try hamilton bowen,or others like him,and you wont regret it. good luck to you.

[Char-Gar]

The question is how to measure? Right?

1. A slug is the best way to find the barrel groove diameter. Measure the same with a good micrometer and not a set of calipers.

2. A machinest adjustable hole guage or a set of pin guages are the way to go on the throats or the inside of any round hole. Again, don't use calipers if you want a precise measurment.

3. The same adjustable gages can be inserted down the muzzle and when measured will give the an accurate land diamter measurment.

I have owned a set of Starett adjustable hole gages since 1969 and they have been invaluable to me for gun work over the years. They are pricy, but will last several lifetimes if handled with care.

Calipers have their place such as measuring the length of things past the range of the micrometer or the outside of a true cylinder. But even the best of them will have a flat spot on the jaws, albeit very small, but enougth to give a less than precise measurment. I am talking about measurments down in the .0001 range. I don't even trust calibers in the .001 range.

[Ed K]

It is crystal clear to me why we want our throats just a touch (0.001") or so over bore diameter. With 20-40Kpsi that boolit is readily swaged down and the seal is very good. What confuses me is when folks say you want to size your boolits 1-2 thou over throat diameter. I've never tried that but don't you need a hammer to load our gun?

For example I remember Brian Pearce saying something to the effect of: "The USFA has nice 0.4525" throats which are ideal for the 0.452" bullets and 0.451" bore." That makes sense to me. The other does not.

[Char-Gar]

Ed... in most sixguns you can load a round that has a bullet several thousands larger than throat diameter very easy. Just open the cylinder and drop them in. The reason is the full diameter portion of the bullet doesn't enter the throat.

A bullet that is larger than the cylinder throat will size down as it passes through. You are in effect sizing the bullet in the pistol rather than a die. The increase in pressure will be nil.

The benefit of doing this is twofold...

1. You have a custom fit bullet for each cylinder throat.
2. You can use the ammo is several pistols that have different cylinder throat diameters.

The latter is a major help to those of us who shoot a number of sixguns. I have 4 Colt and 7 Smith and Wesson pistols in 38/357 caliber, with cylinder throats from .356 to .359. I size my bullets to .359 and load ammo. This ammo can be fired in any of the pistols with good results.

Would custom tailoring the bullets for each sixgun result in better accuracy? Yea, probably but it would take a bench rest or a machine rest to realize the difference. Nothing would ever be noticed in regular hand held shooting for 99.999% of the shooters. The ease of reloading ammo that can be used in almost any handgun far outweights any slight increase, if any, that might be realized through sizing bullets for the individual pistol.

The big problem is this makes things far to simple for folks who enjoy doing things the hard way.

[nicholst55]

Like today when I was trying to caliper the throats on a 25-5 .45 Colt. Measured .452 but probably closer to .4545-.456. I'm basing that on the fact that my Bisley throats calipered .449, but plug guaged .4515.

Mine run between .456-457".

[Ed K]

Ed... in most sixguns you can load a round that has a bullet several thousands larger than throat diameter very easy. Just open the cylinder and drop them in. The reason is the full diameter portion of the bullet doesn't enter the throat.

So if I were to size a Keith bullet a few thou over throat diameter the front band (which is ahead of the crimp groove, ahead of the brass and thus chamber if properly trimmed) doesn't enter the throat?

[MtGun44]

No, it doesn't - it goes part way up in the cone transition between the chamber and the
throat. Elmer wanted the front band to partially center up the round in this transition
area. Loading a round with a Keith design .001 or .002 OVER throat diam has always
fit just fine in all my revolvers.

Bill

[Char-Gar]

Ed... Yes they will fit just fine! Load up a few rounds , drop them in your sixgun and your questions will be answered. Nothing like actual experience. Before this Internet came along, that is how we did things.

[Ed K]

Definitely I'll have to play with some different combinations to try this out. I know my FA doesn't seem to want to chamber my bullets sized over throat diameter. That's just one - maybe others would. As I said I have more to do to sort everything out.

[TomAM]

Whether the front band enters (or gets stuck trying to enter) the throat or only the transition area depends entirely upon the width of the band.

[Char-Gar]

Ed... I know nothing about Freedom Arms handguns. I understand they are quite tight in all spec. They are too rich for my blood. I wouln't pay that much money for a hangun, even if I had it to spend, which I don't. I have to stick to cheap Rugers, Colts and Smith and Wessons.

[WARD O]

Like Ed K says,

I run .431 - .432 bullets in my Ruger 44 specials, if I try to load one of those into my FA M97 in 44 special, it will not chamber.

Ward

[Markbo]

:hijack: Focus people

So it sounds like with moderate loads and softer bullets (11-15bhn) I can try .454" bullets in all of them without any worries about pressures or leading. That might sure make it easier if I can get them all to shoot the same size bullets. ;-)

Now what the heck am I going to do with all those 1000's of 21-24bhn bullets? :?

[WARD O]

How do you measure the slug from barrels with an odd number of lands and grooves? Like Smiths?

??