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Slugging a barrel
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September 11, 2023 - 7:32 pm
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I have to admit to having perhaps excessive apprehension about slugging a barrel.  There is just something about pounding and antique/vintage/collectable/valuable rifles that don’t fit together in my psyche.  Yet, I do like to fire many of my old rifles and I have no enjoyment of keyholes in targets or foot+ groups.  Given frequent variation in bore sizes, slugging a bore makes sense and often provides valuable information.  I’ve known that for years.  Yet I don’t do it.  I’ve seen various videos (e.g. Midway; youtube) and understand the six inch dowels, some case lube on the lead slug, using a rubber mallet and so on.  

My question today has to do how important is it to slug the entire bore.  A friend suggest pounding a piece of lead a short way into the bore (less than an inch) leaving enough sticking out of the muzzle such that you can simply grab it with a pliers and pull it out.  Would we expect the bore diameter to be a different reading there vs. what you have after pounding the slug through the entire length of the bore?  It’s not like rifle bores have a choke to them.

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September 11, 2023 - 7:46 pm
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The end of a barrel is the place I would expect to find the most wear and erosion therefore larger in diameter.

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September 11, 2023 - 9:55 pm
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I use a muzzleloading roundball that is larger than the bore and pound it through. Pound is probably an exaggeration; they tap right through. It’s really easy and it won’t get stuck or anything. For instance, on a .40 caliber barrel I’ll use a .440 round ball, etc. If you need a roundball let me know and I’ll send you one…or several.

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September 11, 2023 - 10:07 pm
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Given frequent variation in bore sizes, slugging a bore makes sense and often provides valuable information.steve004 said

  

Valuable info if you cast & can make bullets in size needed, but if you’re limited to factory bullets, how will you put that info to practical use?

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September 11, 2023 - 10:21 pm
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 Steve,

 It has been my experience the last 2 inches of the barrel has a lot to do with accuracy. I have owned old Winchester’s with poor bores that shot straight because  the last couple inches.were good enough to spin the bullet.

 If you push or shoot the bullet thru the barrel it will become as small as the best rifling, if that is not the muzzle end accuracy could be less. Maybe slugging the barrel by both methods is in order, pushing a slug thru and another in the end and pull out. One would think if the end of the barrel is to much larger than the rest of the bore making the bullet bigger is not in your best interest. T/R

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September 11, 2023 - 10:39 pm
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clarence said

Given frequent variation in bore sizes, slugging a bore makes sense and often provides valuable information.steve004 said

  

Valuable info if you cast & can make bullets in size needed, but if you’re limited to factory bullets, how will you put that info to practical use?

  

I don’t cast my own bullets but several small bullet casters offer a nice variety of bore sizes.  For example, for the .38/55, .38/56 and .38/72, one of the bullet casters I order from, offers a 255 grain bullet in .377, .378, .379 and .380.  

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September 11, 2023 - 10:44 pm
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Brooksy said
I use a muzzleloading roundball that is larger than the bore and pound it through. Pound is probably an exaggeration; they tap right through. It’s really easy and it won’t get stuck or anything. For instance, on a .40 caliber barrel I’ll use a .440 round ball, etc. If you need a roundball let me know and I’ll send you one…or several.

  

Brooksy –  that’s a kind offer and I may have to take you up on that – combined with your offer to let me try some of your .38-72 bullets.  By the way, what size ball do you use to slug a .38-55 or .38-72 bore.

While on the topic of .38-72, I did order some .380 bullets.  Recall I had tried some .375 bullets in my .38-72 and the group was very large with a couple bullets key-holing.  Anyway, the .380 bullets arrived and I loaded one up in a cartridge.  It won’t chamber.  I realize this can be another trick area.  Maybe that .380 bullet is the optimal size for my .38-72 bore, but that doesn’t mean the right bullet will fit the chamber.

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September 11, 2023 - 11:25 pm
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steve004 said

It won’t chamber.  I realize this can be another trick area.  Maybe that .380 bullet is the optimal size for my .38-72 bore, but that doesn’t mean the right bullet will fit the chamber.

That’s the common problem with “oversize” bores, & every BP bore I ever slugged was oversize, leading me to wonder if it was done deliberately, or just the result of loose control of tolerances.  You can inside-ream the necks of your cases to gain some clearance, but that may not be enough.  Or, breech-seat, as many match shooters of the period did.

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September 11, 2023 - 11:46 pm
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There’s a company that manufactures slugs that are caliber specific called meister. They will send a box with about 50 slugs, 5 in each size in increments of .001. Example for .308 they may start at .305 and go to .310. They are stamped with a letter and the letter designates the size in thousandths. I have a box for each caliber from 30 to 45. They don’t make for 25 cal. Paul.

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September 12, 2023 - 12:49 am
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clarence said

Given frequent variation in bore sizes, slugging a bore makes sense and often provides valuable information.steve004 said

  

Valuable info if you cast & can make bullets in size needed, but if you’re limited to factory bullets, how will you put that info to practical use?

  

In Steve’s favorite caliber it’s a simple matter to slightly flatten a piece of OO Buckshot (.33) to slug a .32 or .30 bore. As Brooksey noted the .44 ball is useful, I’ve rolled a .45 ball on an anvil to make a lead cylinder to slug a .40 bore. A .45 ball can be slightly flattened with a good whack with a hammer on an anvil to measure .45 bores. Just make sure the ball is pure lead!

 

Mike

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September 12, 2023 - 1:29 am
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Forgot to add, one good reason for slugging the entire length of the bore is to feel loose spots indicating a bulged barrel. 

 

Mike

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September 12, 2023 - 3:44 am
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I’d probably try a .395 or a 440 ball to slug that gun.

I have three antique marlins in .40 caliber. They all slug .410 but will only chamber a .408 at the largest.  I cast 20 to 1 and load black powder and get excellent accuracy . No problem punching those bullets up to groove size with black powder. I was pretty freaked out about the small bullet size until I shot some and saw how well they shoot.

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September 12, 2023 - 5:32 am
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steve004 said
Anyway, the .380 bullets arrived and I loaded one up in a cartridge.  It won’t chamber.  I realize this can be another trick area.  Maybe that .380 bullet is the optimal size for my .38-72 bore, but that doesn’t mean the right bullet will fit the chamber.

  

Not sure about the 38/72, but I load a lot of 38-55 cast bullets sized to .380 (bore diameters on all the 38-55’s I have all slugged right at .380) and have found cartridges will not chamber unless you take it an extra step by running the cartridge back into the sizing die (decapping stem removed of course) and when you first feel any resistance give it a slight “bump” to compress the brass a bit at the case neck (Likely just flattening the minimal bit of roll of the brass at the crimp groove).   The difference between an go and no-go is 2-3/1000″, neck diameter when bullet is first seated is .395″, a minimum neck diameter of .392″ needed to chamber.   In this added step, it also helps to leave a little bullet lube on the cast bullet and have a little lube on the case neck to keep from further seating your bullet by a few thousandths shorter than the OACL desired. 

Just an observation.  Not saying this will work in the case of your 38/72, just that its worked for me over the years with the 38-55.  And, not saying it will work for others or that its not idiot proof, all things considered Smile (in other words, its at your own risk).   

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September 12, 2023 - 3:57 pm
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1892takedown said

steve004 said

Anyway, the .380 bullets arrived and I loaded one up in a cartridge.  It won’t chamber.  I realize this can be another trick area.  Maybe that .380 bullet is the optimal size for my .38-72 bore, but that doesn’t mean the right bullet will fit the chamber.

  

Not sure about the 38/72, but I load a lot of 38-55 cast bullets sized to .380 (bore diameters on all the 38-55’s I have all slugged right at .380) and have found cartridges will not chamber unless you take it an extra step by running the cartridge back into the sizing die (decapping stem removed of course) and when you first feel any resistance give it a slight “bump” to compress the brass a bit at the case neck (Likely just flattening the minimal bit of roll of the brass at the crimp groove).   The difference between an go and no-go is 2-3/1000″, neck diameter when bullet is first seated is .395″, a minimum neck diameter of .392″ needed to chamber.   In this added step, it also helps to leave a little bullet lube on the cast bullet and have a little lube on the case neck to keep from further seating your bullet by a few thousandths shorter than the OACL desired. 

Just an observation.  Not saying this will work in the case of your 38/72, just that its worked for me over the years with the 38-55.  And, not saying it will work for others or that its not idiot proof, all things considered Smile (in other words, its at your own risk).   

  

I have used this method before with a couple other cartridges. It wasn’t necessarily because the bullet was oversized for the chamber, but it did work.  Sounds like I need to try it in the .38-72.  And, I plan to try these .380 bullets in various .38-55 and .38-55 rifles I have.  I bet I’ll be needing to do something for at least some of them.  Thanks!

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