bore slugging question

[Olsherm]

I have slugged several of my bores but was never sure whether to measure the "grooves" or the raised up lands.Will someone please advise me as I have heard it both ways? Thanks olsherm

You cannot very well get a micrometer into the grooves!

 

[Sal1950]

You measure the raised "lands" of the lead slug. Like on a 357/38 if the weapon is to spec they should measure .357. But that is on a weapon with an even number of lands and grooves, on weapons with odd numbers it gets tricky as you can't measure at 180 degrees.
Sal

 

[WESHOOT2]

I ONLY use a quality ten-thou mike for this.

 

[Wireman134]

I have slugged several of my bores but was never sure whether to measure the "grooves" or the raised up lands.Will someone please advise me as I have heard it both ways? Thanks olsherm

You cannot very well get a micrometer into the grooves!

The grove of the barrel is the largest dia. of the slug. Thats what you measure.

 

[Jimbo357mag]

A recent 3-part article in 'Handgunner Magazine' on slugging a bore. It is a short read.

http://findarticles.com/p/articles/mi_m0BTT/is_2_37/ai_n58532609/?tag=content;col1

http://findarticles.com/p/articles/mi_m0BTT/is_2_37/ai_n58532610/?tag=content;col1

http://findarticles.com/p/articles/mi_m0BTT/is_2_37/ai_n58532611/?tag=content;col1

...Jimbo

 

[Wyandot Jim]

I have slugged several of my bores but was never sure whether to measure the "grooves" or the raised up lands.Will someone please advise me as I have heard it both ways? Thanks olsherm

You cannot very well get a micrometer into the grooves!

The grove of the barrel is the largest dia. of the slug. Thats what you measure.

Yep,
Think about it. If barrel lands measure 357 or 451 and bullet is 357 or 451 she no spiny. Has to go into the groves to spin:wink:
The old cap and ball Colts were called 44 cal but were 45 cal. Ruger carried this over to the Old Armys.
Reason is the barrel was drilled to 44 then the groves were cut to 454. So why it was changed when the centerfire 45 1873 SAA came out is a mystery to me. Yea I know the 44 Russian come in to play also as a first 44.
Jim

 

[5of7]

I have slugged several of my bores but was never sure whether to measure the "grooves" or the raised up lands.Will someone please advise me as I have heard it both ways? Thanks olsherm

You cannot very well get a micrometer into the grooves!

The grove of the barrel is the largest dia. of the slug. Thats what you measure.

Yep,
Think about it. If barrel lands measure 357 or 451 and bullet is 357 or 451 she no spiny. Has to go into the groves to spin:wink:
The old cap and ball Colts were called 44 cal but were 45 cal. Ruger carried this over to the Old Armys.
Reason is the barrel was drilled to 44 then the groves were cut to 454. So why it was changed when the centerfire 45 1873 SAA came out is a mystery to me. Yea I know the 44 Russian come in to play also as a first 44.
Jim

Actually I think that many of the early .45s were .454 and at some point in history it was reduced to .451........or so. 8)

 

[Wyandot Jim]

Actually I think that many of the early .45s were .454 and at some point in history it was reduced to .451........or so.

Yep After the Colt 45 ACP came along or there abouts.

 

[Driftwood Johnson]

Howdy

Rifling groove diameter for 45 Colt was specified at .454 for the entire duration of the First Generation, from 1873 until production stopped just before WWII in 1940. When Second Generation production started up in 1956, the spec for rifling groove diameter was changed to .451 in order to be the same as the spec for 45 ACP.

Here is a photo of some slugs. You can clearly see in this photo that the deep cuts in the slugs, represents the lands of the rifling. The high spots represent the grooves.

When slugging a barrel, be sure the slug completely filled the rifling grooves. Look for lengthwise drag marks on the slug, particularly the areas that represent where the grooves were. The bullet on the right is a soft lead bullet that I often use for slugging 45 caliber barrels. The arrow on the bullet at the center is pointing to drag marks that show the slug completely filled the rifling grooves. The slug on the left does not exhibit these drag marks, so the lead did not completely fill the rifling grooves. Measuring the slug on the left will not necessarily reflect the true diameter of the rifling grooves, since the slug may not have completely filled the grooves.

I always measure slugs with a standard dial caliper. Pure lead slugs like these are soft enough that just the process of measuring them can deform them, obscuring the measurement if trying to use a micrometer. I find a dial caliper is accurate enough for me, I can interpolate the tenths as accurately as I need, by reading the dial.

 

[Olsherm]

Now I am confused as one says measure the grooves and one says measure the lands.I always thought the deep grooves were "the grooves" and the raised up part was the lands??????? Thanks olsherm

I don't think those tin cans or buckets will ever notice the difference.HA HA

 

[Driftwood Johnson]

When a barrel is made, first a hole is bored. Then a tool goes through and cuts rifling grooves deeper than the original hole. After the rifling has been cut, the remaining raised portions of the hole are called the lands, the grooves are called the grooves.

This illustration should help explain that. The high spots the blue arrows are pointing to are the lands. It is called out as the bore diameter because that is the diameter the hole was originally bored.

When a bullet is fired through a barrel, it is deformed. The lands bite into the bullet, to get a grip on it and spin it. But the diameter of the bullet should be wide enough that it completely fills the rifling grooves.

In my previous photo, the red arrow is pointing to one of the high spots remaining on the slug after it was forced through the barrel. Those high spots are what filled in the rifling grooves. So in order to determine the groove diameter of the rifling, one measures across the high spots of the slug.

This method works when there are an even number of grooves, as in the illustration. If there are an odd number of grooves, measuring across the diameter of the bullet will not give a good reading because you will be measuring from high spot to low spot on the slug.

 

[FergusonTO35]

Question: when slugging a bore with a cast boolit, is it good practice to apply any kind of lube to the bore and/or the bullet?

 

[Driftwood Johnson]

Question: when slugging a bore with a cast boolit, is it good practice to apply any kind of lube to the bore and/or the bullet?

Howdy

Most will tell you it is a good idea. To tell you the truth, I have slugged plenty of barrels dry with no lubrication. But it certainly does not hurt.

These days I usually run a patch soaked with gun oil through the bore. Then I will run a dry patch through to soak up the excess, just leaving a fine coat of oil before I drive a slug through.

To tell you the truth, I have never really noticed any difference driving a slug through a dry barrel or a lubed barrel. But I lube the bore a bit just in case.