"Slugging" a barrel

[marcodo]

I suspect that this means taking an accurate measurement of the barrels internal dimentions.

Can someone remind me if the is an easy homemade way to do this?

 

[Sport45]

A lead round ball that's a bit larger than the bore can be driven through and then measured to determine minimum groove diameter.

I've driven swaged 38 caliber semiwadcutters through 30 caliber bores t measure them.

 

[DoesItMatter]

http://7.62x54r.net/MosinID/MosinSlug.htm

Very good tutorial, and common stuff around most garage's.

All I had to buy was the fishing weights and the dowel.

 

[rcmodel]

Beware the barrel with an odd number of grooves.

Some S&W and others use five groove barrels that are next to impossible to measure the resulting slug accurately.

You have a land on one side, and a groove on the other!

rc

 

[Jim Watson]

There was a guy, unfortunately since deceased, who had a collection of specialty micrometers and would accurately measure slugs sent in from odd number of groove barrels.

There is a procedure to do it with a V block, a rod of known diameter, and some calculations.

 

[marcodo]

I know this is probably not possible but my callipers have a piece tha can be used to measure the inside of things. I don't know what it's called but why can't that be used?

Sounds to easy to be true so I'll bet there is some problem with this.

 

[Jim Watson]

The inside measurement jaws on a conventional caliper are flat. The barrel is curved. A flat caliper jaw in a round hole will always give a lower reading than the actual diameter.

 

[rcmodel]

Yes, dial calipers have pointy jaws on one end for measuring I.D. of holes.

However, measuring the muzzle does not tell you what the bore diameter is further down in the barrel.

"Choking" where a revolver barrel screws through the frame may make it smaller there then anywhere else.

You could also have cleaning rod wear at the muzzle which makes it bigger then anywhere else in the bore.

Combine the two and the only way to measure a barrel accurately is by slugging it and measuring the slug.

rc

 

[Iron Sight]

So now I have slugged my bore.

Whats the rule for sizing my bullets at that point?

And Thank You.

 

[Jim Watson]

Could you let us in on the little secret of what gun, caliber, and barrel measurement you are asking about?

 

[Iron Sight]

"Could you let us in on the little secret of what gun, caliber, and barrel measurement you are asking about?"


I have no Secret gun, caliber, and barrel. You are saying each firearm has different standards for bullet sizing after the bore size is determined?

 

[FROGO207]

Basically this is true. Another factor is if it is a lead bullet or jacketed. The minimum and maximum diffrerential of the slug is most important ( ie how high/large and how deep/small the grooves go).

 

[Jim Watson]

You are saying each firearm has different standards for bullet sizing after the bore size is determined?

You bet.

The usual recommendation for cast bullets is .001" larger than groove diameter, but I am getting best accuracy in a .40-65 with .411" bullets instead of the theoretical .409" in a barrel cataloged at .408". Why? Because the chamber throat into the rifling is .411" and a full size bullet gives better alignment.

The real cast bullet experts consider both bore and groove diameter in selecting or designing a bullet. The bearing surface must fit the throat and fill the grooves, but also the nose section should be large enough to ride on top of the lands and guide the whole length of the bullet but without digging in.

Revolvers usually do better with a bullet diameter that fits the cylinder throat, even if it is not what you would pick from barrel dimensions.


You have less control over barrel fit with jacketed bullets but sometimes there is a selection you can make that will help.

 

[ants]

I think we're making it complicated too quickly.


The general rule, not the exception:


+.001 inch for lead bullets. That's the industry standard rule. But of course, you'll have to shoot some in your own gun to determine its accuracy as Jim Watson is explaining. You may have to go larger or smaller to obtain maximum accuracy in your particular gun.

 

[243winxb]

I think we're making it complicated too quickly

I agree, lead bullet are standard diameter same as jacketed. Basic is .001" larger than jacketed for handguns. 45acp=.452" 38 special=.358" 44mag=.430" One exception its 45colt, new guns=.452" Old Colt single actions=.454" Rifles will run on the larger side by .002" 308= .310" But never hurts to slug a barrel. Mr. Lee said >

Cast bullets size specification

Standard practice is to size cast bullets .001 inch over jacketed diameter, but there is not 100% agreement on this. Some of the sources state that cast bullets should be sized to groove diameter, others state they should be sized to chamber throat diameter, still others state to size to .001 inch under the inside diameter of the case mouth of a fired case. Take your pick...

Mr. lyman said>

Q: How do I slug my barrel?
A: Slugging is done by driving a soft pure lead slug through the barrel and measuring the raised grooves present on the slug. A lead round ball used for muzzle loading that is slightly larger than your caliber can be used for this.

Plus have your barrel lightly oiled.

 

[Remo-99]

Still don't know the application, while +0.001" is fine for pistol calibres. I do like to run lead +0.002" or more over the groove diameter in rifles.
The tightest groups I have so far, were from .311 sized lead bullets in my .308win, clover leaves at 100 yards using a sporter barrel and a bipod rest.

 

[243winxb]

Way to Much About Nothing. .001"

Take your micrometer and set it to .001" Have a good look at what .001" looks like. We really are making mountains out of mole hills worrying about it. Bigger is better than undersize for sure. An alloy lead bullet will swage into the riflling much better than a jacketed bulllet, so no big increase in pressure. As long as the round chambers, all is well. I feel the reason most rifle bullets shoot better, bigger is they fit the throat better, the round is centered in the chamber. Revolvers, not so much as the bullet must jump the gap between the cylinder to the barrel, then get funneled into the rifling by the forcing cone. Single shot or auto, might benifit from proper fit(larger) of the bullet in the chamber. Nothing wrong with slugging the barrel and trying different diameters to get the best, most accurate load.

 

[Iron Sight]

These instructions say go smaller than the Groove Diameter????

http://7.62x54r.net/MosinID/MosinSlug.htm

 

[rcmodel]

BS!

I think he is talking about jacketed bullets, and he can't get any that are .313".
SO he says .311" should "work well".

I doubt the "well" part, but they will work.

But .312" would work better, and if there were such a thing, .313 would really "work well"!

rc