Did I slug/measure my cylinder and bore correctly?

[Stopsign32v]

So Here is what I did. Pure lead 36cal round balls and I hammered them into the face of the chambers and then back out (enough to where the cylinder would close but no further). I hammered a 36cal round ball from the muzzle of the bore to the rear. Measurements below...

Cylinders:

https://live.staticflickr.com/65535/51309957766_19c9013f9f_b.jpg (https://www.flickr.com/gp/113193676@N08/pGPTNQ)

https://live.staticflickr.com/65535/51310678984_492368bb52_b.jpg (https://www.flickr.com/gp/113193676@N08/E32J7T)

https://live.staticflickr.com/65535/51310154483_0f52c76686_b.jpg (https://www.flickr.com/gp/113193676@N08/z29512)

https://live.staticflickr.com/65535/51310154433_3523dd6126_b.jpg (https://www.flickr.com/gp/113193676@N08/oW994w)

https://live.staticflickr.com/65535/51310154478_2b767490d7_b.jpg (https://www.flickr.com/gp/113193676@N08/Vf210v)

https://live.staticflickr.com/65535/51310958020_50859a7121_b.jpg (https://www.flickr.com/gp/113193676@N08/538486)




Barrel:

https://live.staticflickr.com/65535/51309213682_c3e9aeb2a5_b.jpg (https://www.flickr.com/gp/113193676@N08/auV825)

[Rcmaveric]

Looks good to me. Thats tight tolerances. Thats exactly how I do it.

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[Stopsign32v]

So what do I do with this information? LOL And what is tight about it? I was surprised at the bore size.

[358429]

Your gun is made correctly.
I wish my SP101 was made correctly *mad face*

Now what you want to do is get a powder coated cast lead bullet that is sized 358 and then try to push it through with fingertip pressure using a pencil or ballpoint pen or wood dowel...etc

You want to feel light resistance.

If it falls through then it's too small, and if it takes a great deal of pressure is too big.

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[358429]

Tight tolerances means that all the chambers are sized the same, and the relationship between chamber throat and Barrel Groove is correct. Tight tolerances is a good Accurate Gun!

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[Mk42gunner]

In a perfect world, you want the cylinder throats to be equal to or larger than the barrel. Your's appears to be like this.

I would lube and size to .358" or 359" and start shooting.

The one thing that is questionable in my mind is the .351" dimension for the barrel slug. Did you measure across the large part (groove) or the small part (bore)? Keep in mind the slug is a mirror image of the bore.

Good Luck,

Robert

[Stopsign32v]

In a perfect world, you want the cylinder throats to be equal to or larger than the barrel. Your's appears to be like this.

I would lube and size to .358" or 359" and start shooting.

The one thing that is questionable in my mind is the .351" dimension for the barrel slug. Did you measure across the large part (groove) or the small part (bore)? Keep in mind the slug is a mirror image of the bore.

Good Luck,

Robert

Robert,

What I did do was slug another round ball and measured it. Same measurements but then I got an idea and while holding the ball I spun it slowly while keeping tension on the measuring wheel and it fluctuated from .3510-.3560. Not sure if that is helpful or not. I do believe I saw .3575 once but only once. Worth noting is the lead is so soft that each rotation you do this way the measurements on the high side get smaller and smaller.

Edit: Tried this again and saw .3575 twice so we will call the bore .3575 if that sounds right. I do not see a flaw at measuring the grooves this way unless someone else thinks I'm wrong.

[tazman]

Size your boolits to .358 and shoot them. Your revolver is set up very well.

[reddog81]

What happens drop a .358 bullet into the cylinder? Does it fall through or get hung up?

If it drops through I’d size at .359.

My GP100 is .357. I use .358 or .359 and they work equally well.

[Dusty Bannister]

When you measure the ball that you pressed through the barrel, the small reading is the bore and the larger reading is the groove. If the grooves are cut individually, there could be some variation in the depth. Ideally, the cylinder throats should be equal or slightly larger than the groove diameter. Many prefer to use a micrometer for this reading. Does your caliper round off the fourth digit to "0" or "5".

[243winxb]

The .351" barrel groove, if correct, may be a problem? Test fire. Target will let you know. 1

[Tim357]

Also IIRC, Ruger uses 5 lands and grooves in their barrels. I don't think you can accurately measure the bore with a caliper...

[ryanmattes]

Cylinders at a consistent .3585 and groove diameter at .3575 sounds about perfect. I'd try .358 and .359 and see which groups better.

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[243winxb]

Also IIRC, Ruger uses 5 lands and grooves in their barrels. I don't think you can accurately measure the bore with a caliper...

Good catch. The 5 groove slug need measured differently. I wrap a strip from a soda can tightly around the slug. Measure, subtract the thickness, x 2 of the metal, to get groove diameter.

I was thinking only S&W was 5.

[Stopsign32v]

I wrap a strip from a soda can tightly around the slug. Measure, subtract the thickness, x 2 of the metal, to get groove diameter.



What? I've read this 4 times and can't comprehend

[243winxb]

Just shoot the gun.

http://www.texas-mac.com/Measuring_Groove_Diameters_of_Odd_Groove_Bores.htm l

Shim-wrap method at link.

[blackthorn]

What? I've read this 4 times and can't comprehend

It is very hard to get a concise measurement on a 5 grove slug. Wrapping it with a strip of soda can material gives you a smooth, round surface to measure. Since the wrapped slug surface is now increased in thickness by the soda can (on both sides) you need to deduct twice the thickness measurement of the soda can material from the total to get an accurate measurement of the slug.

[reddog81]

I wouldn't worry too much about the .351 reading. As long as the barrel is smaller that the cylinder throats you'll be fine. It's highly unlikely the barrel groove diameter is actually larger than .3585.

The .351 measurement is due to the rifling having lands and grooves. The rifling creates impressions in the bullet. If you google "barrel rifle bore and groove diameter" and take a look at the images it should be clear.

[mdi]

Edit: Tried this again and saw .3575 twice so we will call the bore .3575 if that sounds right. I do not see a flaw at measuring the grooves this way unless someone else thinks I'm wrong.

I would consider the .3575" the groove diameter, and the .351" the bore diameter. Terminology may be a bit confusing at times. Bore diameter is the diameter of the barrel before rifling is cut (formed, etc.). The groove diameter is the diameter of the rifling that has been cut (formed, etc.). For us newer casters, cast boolit shooters the important dimension is the groove diameter and the throat diameter must be larger to prevent barrel leading and for good accuracy. I slug the barrels and throats of every gun I acquire and I start with using bullets the same diameter as the throats ("drop through", "push through", and "loose or tight" are not measurements and can mean different tings to different people. Measure and you will know). This has worked for me since '86 in 3, 38 Specials, one 357 Magnum, 3, 44 Magnums and one 45 Colt...

FWIW, I much prefer using a 1", "analog" micrometer for measuring slugs and bullets (I am a retired life long machinist/mechanic and I often use the same "spin method" as the OP. Works quite well for me).

[Mk42gunner]

It has been so long since I slugged my current GP-100 that I have no idea what the measurements were, or where the slugs got off too (probably got remelted). Nor do I remember if it was five or six groove rifling.

I do know that it shoots cast boolits sized .358" very well.

Robert

[Stopsign32v]

Sure enough you can count it right there at the muzzle. It is a 5 groove bore.