Thoughts On What The "Bore" Is

[leadman]

For as long as I can remember when the bore of a gun was mentioned it referred to the hole running length ways thru the barrel.
In recent years I have been seeing more statements asking if the original poster meant the land or groove size when the post referred to the "bore". I did some searching on the internet and several sites referred to the bore as the hole in the barrel that could be rifled or smooth.
My thoughts on this when I make a statement like "slug the bore" I am referring to the hole in the barrel. I was asked awhile back by a member here if I meant the lands or grooves.
If I state "30 caliber rifle barrel" I am thinking .300" to top of lands and .308" to the bottom of the grooves. Similar to people calling a .308" bullet a 30 caliber.
I, like most people refer to the bore size as the measurement from the bottom of one groove to the bottom of the opposite groove, at least on barrels with an even numbers of grooves in it. Or the maximum diameter of the hole in the barrel with other types of rifling.
Would like to read what others think on this subject.

[cainttype]

The bore is the smaller measurement made by the tops of the lands, the groove diameter is the larger measurement from the bottom of the rifling grooves... Think "bore-rider" cast bullet and things come into perspective.
A "30 Caliber" actually is a bore thought of at roughly .300", although their groove is a deeper.308" (just an example)... 35 cal, bore roughly .350", although groove is nominally .358", etc. ...

The term is used loosely at times, like "slugging the bore"... actually trying to find GROOVE diameter with a soft lead slug.
That difference can be very imprtant when choosing an appropriate mould for a firearm. Micro-groove versus standard rifling is a good example of why those measurements can be so important.

[ndnchf]

I agree with cainttype. Typically, when a barrel is made, it is "bored" to make the basic hole in the barrel. Then grooves are cut or swaged with a button. The term is used very losely and just to be clear, it's a good idea to clearly state what you are referring to in a post. There probably isn't a definitive, absolute correct answer and you'll get opinions both ways.

[Green Frog]

I refer to and expect to see "bore diameter" and "groove diameter" and unless one or the other is specified, the dimensions of that barrel's hole are in question. That's been pretty much standard in all the literature I've seen on the subject. (But then, I've only been at this about 50 years...)

Froggie

[Tatume]

Caliber and bore are the same: e.g. 30 caliber refers to a 0.300" bore, and uses a 0.308" bullet.

[Dusty Bannister]

Quoted "I, like most people refer to the bore size as the measurement from the bottom of one groove to the bottom of another groove, at least on barrels with an even numbers of grooves in it."

Not to my way of thinking. There is bore and there is groove, and then we get careless with "bore" condition, "bore" cleaner and "bore" scope. This has inadvertently resulted in folks new to the experience using the incorrect terms and confusion results. When persons new to the experience base their knowledge on what is read in forums, and not reloading manuals, it is time to make an effort to be clear in our use of terms. Our words will remain even after we are gone and should not need to have someone explain what we meant.

[Hickok]

This even goes back to the Civil War, where there was confusion between the Federal Ordinance Department and officers in the field as to whether the Sharps paper-cutter rifles and carbines used .52 caliber or .54 caliber ammunition.

Sharp's Rifle company listed them as .52 Sharps, as they used the bore dimension/rifling lands for naming their ammunition.

BUT, the boolit diameter was .54 caliber, because the grooves in the barrel were cut to this dimension. Now machining in those days varied, but this is close to what the Sharp's bore/lands and groove diameter was ideally to be.

[Eutectic]

Caliber and bore are the same: e.g. 30 caliber refers to a 0.300" bore, and uses a 0.308" bullet.

Not always Tatume..... Think of .44 caliber as an example.

Bore is one of those words in our language that has multiple meanings..... In machining, bore is a definition of an internal machining operation. The first step in making a barrel is machining a precision hole. When finished this becomes the top of the lands diameter if the barrel is to be rifled. Hence the bore diameter dimension vs. 'groove'. Bore is also the dimension of a machined hole. This is easier looked at as a shotgun (smooth) bore...... But bore is also a 'general' term used for the hole' in a rifle barrel which causes confusion.....

If that isn't confusing enough bore can also be the past tense of 'bear'!

I hope I haven't been a bore in this clarification!

Eutectic

[dnepr]

I tend to think of the machining operations you bore the hole first then cut the rifling deeper .

[35remington]

I agree with what is stated above....when people mention "slugging the bore" it is more properly meant that they are slugging the barrel. Two dimensions are obtained thereby....the bore diameter, which is the land to land measurement, and the groove diameter, which is the groove to groove dimension.

Then they mention, after "slugging their bore" which happens to be a standard .30 caliber barrel that their "bore dimension" is .308" for their barrel. In this they are wrong, as that's the groove dimensions.

"Bore size" or "bore dimension" when being technically correct for a rifled arm has never, ever been the groove to groove dimension. Those using the term that way have been incorrect.....and why they get corrected here is to get the terminology straight so we're all talking about the same thing in the correct way....and they weren't.

"I, like most people refer to the bore size as the measurement from the bottom of one groove to the bottom of another groove,"

If that's how most people refer to it, I would amend the above to state, "I, like most incorrect people, refer to the bore size as the measurement from the bottom of one groove to the bottom of another groove." At this point technically correct people step in.

As here.

Since bore size has a specific correct meaning of the land to land dimension in a rifled arm, best use "bore diameter" when you mean the land to land dimension, or "barrel diameter" or "groove diameter" when you mean the groove to groove dimension.

[mdi]

Since you've already gotten definitions of what "bore" and "lands and grooves" mean and their history, perhaps the "confusion" is from those making sure all words/phrases are used "correctly". To find groove diameter, one needs to slug the bore, as you cannot just slug the groove diameter or actual bore diameter. To find the internal diameters of a barrel, no matter how or when it was made, one drives a lead slug down the barrel (I know there are other ways to find these dimensions, but we're talking about "slugging the bore") and measures it. Those asking "is that bore or groove diameter?" are usually just being "Vocabulary Police"...

[Dan Cash]

Y'all pretty well defined "bore" as the diameter of the hole prior to rifling. One point about terminology that is constantly miss used is the term Caliber. If one refers to a .30 caliber rifle or gun, you are saying that the bore ahead of the chamber is .30 times as long as the bore diametyer. Properly stated, on would say caliber .30 meaning that the bore hole is .30 inch.

[TXGunNut]

For many of us casting and loading are precision endeavors. When we describe our loading and casting activities I think we should be precise in our terminology to reduce confusion and increase credibility.

[35remington]

To find groove diameter and bore diameter in a rifled arm, one needs to slug the barrel. A "slugged bore" reveals that you are going after the land to land dimension. When speaking of the dimensionality of a barrel one needs to specify just which dimensionality one is measuring.

When correct terminology is used correctly people understand each other. When it is not, often they do not.

[Digital Dan]

Bore = minor diameter
Groove = major diameter
Caliber = marketing hype
Cartridge = what most mean when they use "caliber"
English= the Devil's playground

[CajunRebel]

Hey, let's add some more confusion, e.g. 7.62mm versus .308 versus .30-06. Or .38 special being .357". :kidding:

[scottfire1957]

The "bore" is the hole drilled down the middle of the barrel. The "grooves" are added later.

[TXGunNut]

Hey, let's add some more confusion, e.g. 7.62mm versus .308 versus .30-06. Or .38 special being .357". :kidding:


...and then there's the 38-40 or 38WCF....but it's not a 38 bore, 38 caliber or 38 anything...except for 38-40 or 38WCF, it's a .40 cal. But then again, neither is the 38Spl....it's closer to 36. 35 Remington is closer to 36 caliber and the "mighty 44" is closer to 43. OTOH 7.62 mm is as close as we can get to 30 cal or .308. 45 ACP is pretty close to nominal diameter but the 45-70 (and 45-90, 45-110 ad nauseam) is actually closer to 46 caliber. 45 Colt is somewhere in between, and that's a wonderful place to be.
Digital Dan pretty nailed it, I'm just drunk and bored...

[W.R.Buchanan]

As a machinist I tend to want to be more precise in my verbiage, however the terms Bore and Groove have been mutated long before I got here and righting that wrong will never happen... The best we can hope for is an understanding between knowledgeable contributors so that the differences in nomenclature don't seriously affect the overall intent within the topics we talk about.

This is the same phenomenon as the Magazine/Clip misnomer that pervades the Liberal Media and Media in general.

It is caused by people who don't know what they are talking about in general, talking about things that they know nothing about specifically. However they speak to so many other ignorant people, that the terms stick and as a result questions like the OP's come up since some people actually have a desire to be literate with respect to a given subject..

Sadly being literate is no longer a prerequisite for being a journalist. The only requisites now are having an IPhone, a Twitter Account and a Mouth! Actual knowledge of the subject is not required, only the ability to use Buzz Words associated with the topic and convincing blather to influence those even less knowledgeable than the source... The current objective is not to increase awareness of a given topic, it is to create a movement either for or against a given topic. Strength in numbers being the motivation.

We all should know that a Clip is used to load a Magazine. IE; Enbloc Clip or Stripper Clip. It is not a Magazine, as in those cases the magazine is an integral part of the gun.

However when it comes to guns with removable magazines the terms have become interchangeable, and lets face it most of us are guilty of using the terms interchangeably.

When making a barrel,,, the blank is first "Gun Drilled" Which is the term used to describe any drilling operation that is more than 10 times the diameter deep. It is done on a "Gundrilling Machine" with a Special Drill invented I believe by the Hawken Brothers. It acts like a Trepanning Tool and keeps itself centered by cutting a circular Vee shaped groove in the face of the hole. Since there are no side loads generated the hole continues in line no matter how deep it is drilled.

I was in Thompson's Gundrilling in North Hollywood CA some years back and Mike Thompson (owner) showed me some blocks of 17-4 stainless that were 52" long. They had 1/8" holes drilled thru lengthwise and were within .002 true position when they exited. In other words they were dead strait! Drilling an 1/8" hole 52" deep is a pretty good trick,,, getting it to be strait is pure wizardry!

The drill itself is quite a neat piece of tooling as the shaft is round with 1/4 missing and a hole running thru the solid portion. This hole gets high pressure oil pushed thru it and the chips generated by the cutting surface are conveyed back up the open portion of the drill shank. In the case of the 1/8" holes the drill had 1500 psi on it.

To start the hole a pilot hole is drilled about 2" deep and reamed to size to match the Gun drill's size. The drill itself is also 3/4 of a round and there is a point protruding from the front edge of the drill even with the step . When the part is turned the drill actually cuts a circular groove in the front face of the hole. The chips are flushed up the drill shank.

Since the Drill is supported by the hole itself and the cutting portion does not induce any side loads to the cutter the drill follows the hole exactly and will continue to do so until you quit.

After the hole is drilled it is reamed to the exact size. This creates the "Bore." The resulting Bore is then rifled by either cutting grooves or swaging grooves(button rifling) or in the case of Hammer Forging a mandrel is inserted and the outside of the blank is beaten down to conform to the mandrels shape.

When talking "technical," about these things one has to be aware of the differences between Bore Size and Groove Size and be specific as possible.

When talking about non technical subjects like cleaning,,, Bore pretty much covers anything dealing with the hole in a gun barrel.

The term Caliber has become mutated by the gun companies so long ago that it doesn't necessarily refer to the bore size. Metric Calibers made in Europe tend to delineate bore size, but not so in the US. A .243 Win has a 6 mm bore which is @.236 and grooves of .243. however a 6MM Remington uses the exact same bullets. So who's right? Depends on what language you speak.

The gun companies are the ones responsible for all this cornfusion,and in their quest for the best and greatest new product they committed sins which are now set in stone in 3 different languages none of which translate to the same meaning.

Thus we will have to live with this forever.

Randy

[vzerone]

I might add that some barrel makers hone the bore after it has been reamed. Hammer forged barrels are a whole different ball game. Rifling grooves have moved towards a more shallow groove then they were decades ago. Many foreign barrel makers don't have the same bore and groove dimensions as us Americans do. Often there are quite a few different measurements within the same caliber. They pretty much follow the original manufacturer of firearms. An example is you'll find a difference in bore and groove dimensions between the American 6.5's, the 6.5 Carcano, the 6.5 Japanese, the 6.5x54MS, the 6.5 Swede, and many other 6.5's.

[BAGTIC]

That definition of "caliber" is normally only used for artillery and in that case should properly be stated as "calibers".

[BAGTIC]

Other countries have often used different bullet diameters as well. I can not recall if it was Whelen or Hatcher that commented that British, at that time, preferred bullets of a slightly smaller diameter than did Americans.

[303Guy]

The 38 special gets its name from the healed bullet 38 Short Colt from which the cartridge originated. The 38 Short Colt was anemic so Colt developed the Long Colt which no longer used the healed bullet but retained the name. The 38 Long Colt is the parent case for the 38 special.

[44magLeo]

They did the same with a lot of heeled, not healed, bullet cartridges.
The 44 rimfire was the start of the 44's It had a 44 diameter bullet that was a heeled design. It became the 44 American with a center fire case but still used the heeled bullet.
When Russians wanted S&W to build them revolvers they wanted an inside lubricated bullet. So instead of making the case bigger to accomodate a straight sided bullet they made the bullet smaller to fit inside the case. Thus a 44 Russian used a .430 diameter bullet but was still called a 44. The 44 Special and 44 Mag were just longer versions of the 44 Russian.
Then they even stretched them a bit more for the Super Mags, went to the extreme with the 444. They did add a bit of case diameter at the head, but still just a very long 44.
Leo