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View Full Version : Redpill me on bore vs groove diameter teminology



Andy
12-27-2016, 03:15 AM
I have only been casting and reloading for about two years and I just realized that I may have had my head up another part of my anatomy for a good bit of that time, in regards to how I talk about "bore diameter" as it relates to cast bullets.

I know how to make a bullet that works in a given rifle/handgun so I want to be clear i'm not asking that question, I'm just referring to how we talk about it. I slug a barrel, measure the maximum diameter of all opposing projected areas and add .001 or .002 to that to decide my sizing diameter and everything works out fine.

Common advice is stated as: "make your cast bullet .001" or .002" over "bore" diameter. The extension of that advice is then to then slug your barrel and measure the maximum diameter of opposing "groove" extrusions (largest diameter measurement of a rifled barrel slug pounded through the barrel) with a micrometer. These being the only easily measurable locations with a normal micrometer on a slugged bullet.

I found this post from 2009 which clearly shows my question with a diagram: http://castboolits.gunloads.com/showthread.php?105843-Which-is-the-bore-measurement

Based on the discussion in that thread and common sense, it seems like everyone should be saying "groove diameter" not "bore diameter", but I feel like it is far more common to hear "bore diameter" said.

What gives, is this just people using the wrong terminology or am I mistaken?

Artful
12-27-2016, 03:51 AM
http://castboolits.gunloads.com/attachment.php?attachmentid=29162&stc=1&d=1296780333
Red line is groove Diameter and the bored diameter that you stated with is the bore hole and you cut more away to get a groove in the barrel.
Leaving the tops of the rifling undisturbed.

So for a .30-30 - you bore a hole thru the barrel blank at 0.300" (blue line) then come back and remove more material to form the rifling (boring deeper)
- if your rifling is cut 0.004 deep then you have a 0.308"

But people do like to mess with terminology and it's labels. :roll:

The other thing is that people fail to consider the chamber throat/leade
that goes into the rifling. Your cast bullet has to form a gas seal once it
comes forward into the barrel - you don't want gas blow by to cut your
boolit before it can get all the way into the rifling.

http://www.tmtpages.com/LinkSkyImages/forum_images/Bara%2030-30/30-30_Winchester_Barra_~_Neff_HR~Barrel_30-30_Winchester_R-P_Rot_Cutaway_Night_Owl_Mold_311-165-GC_RF_Rot.Jpg

DougGuy
12-27-2016, 04:01 AM
People are simply using the wrong word to describe which dimension they are referring to.

When the discussion is about sizing boolits to fit a certain gun or caliber, you should be using groove diameter as a reference point.

ironhead7544
12-27-2016, 06:46 AM
Just refer to it as slugging the barrel and no one will get his panties in a twist.

BTW, Lead Bullet Technologies makes slugs that work great and do not need to be hammered down the barrel. Well worth the cost.

OS OK
12-27-2016, 09:36 AM
183576183575Thank's Art...I was looking for a drawing on the net that showed this same type drawing for a revolver. These are the best I can find for a revolver but...No luck.

Tom Myers
12-27-2016, 04:04 PM
-



Here are two revolver cylinder chambers that were drawn using the Precision Bullet Design ~ Ultimate (http://www.tmtpages.com/#ultimate) software

http://www.tmtpages.com/LinkSkyImages/forum_images/Revolver%20Chambers/38-40_WCF-P~~TMT_Design_401-401-200.Jpg



http://www.tmtpages.com/LinkSkyImages/forum_images/Revolver%20Chambers/44_S&W_SPL_Colt~Cylinder~~A_TMT_Design_431-429-270.Jpg

Half Dog
12-27-2016, 05:25 PM
This is great information!!!

runfiverun
12-28-2016, 01:35 AM
still trying to figure out the red pill thing.
I thought one pill made you larger and one pill made you small.
then years later the blue pill made you larger.. and the red pills were Ritalin [which spell check says I have to capitalize]
now I'm really confused.

Artful
12-28-2016, 02:23 AM
https://www.youtube.com/watch?v=zQ1_IbFFbzA

Walla2
12-28-2016, 12:38 PM
It is alphabetical; First you BORE the barrel, then cut the Grooves. Works every time.

runfiverun
12-28-2016, 01:03 PM
ahh thank's Art.
so the red jellybean gets you into the other room.
maybe I need to watch more movies.

Ken in Iowa
12-28-2016, 03:28 PM
Great thread for many reasons.

Andy
12-30-2016, 01:52 AM
Thanks for the replies everyone, I understand the terminology correctly now and am glad to know how to use it in the future.

Boolseye
12-30-2016, 10:35 AM
Good info, thanks!
-BE

BlackoutBuilder
12-30-2016, 07:11 PM
That was very helpful.

Bookworm
12-30-2016, 10:37 PM
I thought one pill made you larger and one pill made you small.


.....And the ones that Mother gives you don't do anything at all.
Just ask Alice,
When she's 10 feet tall.

Walstr
12-31-2016, 12:05 AM
RE: Slugging Bbl; I had slugged my rifle bbls by loading a very light load, say 3gr Unique in my 45-70. After fun making noise & killing paper at the range, I fire this rnd with the intention it "gets stuck" in the bbl.; return home & punch it out; a beautiful slug indeed. p.s. This was a totally silent event, as the sound was fully trapped! Cool. 3gr Trailboss in my 45 Colt Vaquero worked as well. My 1st attempt got the boolit halfwat into the bbl, so I had to punch it back into the brass to free up the cyl.; a little clumsy, but as experiments go, no biggy.