Slugging barrel a must?

jonnefudge · June 15, 2017, 10:57 AM

Hi
I shoot cast 340gr Lee mold 457 with my marlin 45-70. It seems just fine with no leading. I have not slugged my barrel and wonder about benefits and possible hazards with shooting a wrong sized bullet. Too small or big what happens?

Thinking about buying that 459, 405gr hollow base from what I understand the hollowbase seals tight in the barrel? Will probably hunt moose with it.

Any input or tips is greatly appreciated!

/jonne

T. O'Heir · June 15, 2017, 11:52 AM

Slugging is about find the exact groove diameter. There really aren't any hazards shooting a cast bullet that is a couple thou off. Not enough pressure involved. Using a bullet that is 1 thou bigger is normal for cast bullets.
Too big and too fast means leading. More about the speed than the size though. A cast bullet will get squeezed by the steel anyway. Too small means the bullet doesn't contact the rifling enough. Causes bad accuracy and probably key holing.
Marlin uses .458" but if it's got their Microgroove rifling they supposedly don't like cast bullets unless they are .459" or so anyway.
You'll find your 340 grain bullet will be just fine for moose too. Bullwinkle is big but he's not that tough. Big moose have been killed up here with .30-30's. Accuracy is what's important. Not the bullet's weight.

HiBC · June 15, 2017, 01:00 PM

Undersize bullets particularly of harder alloy,allow gas leakage past the bullet.
The surface melts. You get leading and inferior accuracy.
You won't go wrong with .001 over groove dia.
So,YES! If you want to be successful with cast bullets,you need to know your groove dia. You will be ahead to also know the alloy you will cast. Custom mold makers are good at predicting shrinkage. For example wheelweight shrinks a little different if you add tin .
Bore dia matters,too.If your ogive is large,youll engrave chambering. Too small,its a "tippy" thing..even slump under the "G" force.They use a term "bore ride"

The Hollow base thing? Hmm. No experience!.My concerns/opinions...which could be wrong.That might be more of a muzzle stuffer thing.

You'll have to load/unload a core in your mold..I think it will limit you to modest loads.Get a bit zippy and that skirt will flare out on leaving the muzzle.
Tough on accuracy.Myself? I'd go flat base.

jonnefudge · June 15, 2017, 01:07 PM

Great input! How do I make a "slug" for slugging? Pure lead? DIY Mold?

mikld · June 15, 2017, 01:10 PM

There's an old saying; "Even a blind hog can find an acorn once in a while". If your bullets are shooting accurately without leading you're OK. If you are getting leading, poor accuracy or perhaps tumbling, then the barrel dimensions will be important in fixing the problems. Basically, as mentioned above small bullets tend to lead the barrel, and large bullets "normally" are no problem. I slug the barrels of all my firearms, even if they aren't going to shoot cast, and record the measurements, mainly because I just want to know..

Dufus · June 15, 2017, 02:09 PM

I agree that slugging a barrel for cast bullets is important, but more important is throat diameter.

You know your throat diameter and create a cast bullet that just squeezes into it and you will have a very accurate machine.

**Unclenick** · June 15, 2017, 02:15 PM

The only bad effect from either under or oversize bullets is poorer accuracy and more leading in the case of undersized bullets owing to gas cutting. Standard lead bullets are 0.001" over standard groove diameter for the guns they are meant to be fired in, but I find a number of revolvers and lever gun chambers tighten up some using bullet at 0.002" over, and Beartooth Bullets owner found the same thing in his revolver tests, IIRC. But by 0.003" over, they were shooting less well again.

Slugging your barrel will find tight spots you may need to lap out, but if you have no leading now, there isn't a lot of point. You've found your good combination already. You can buy pure lead slugs or sinkers from NECO, Beartooth Bullets, and Meister Bullets has slugging kits. You can always cast your own.

jonnefudge · June 15, 2017, 02:17 PM

Ok I see. Maybe stupid question but is there any difference to jacketed bullets if they have the same diameter?

**Unclenick** · June 15, 2017, 02:22 PM

Lead is softer so the start pressure is lower. Being softer, they upset at lower pressure so you can't normally drive them as fast (though some have come up with ways to do it). You usually use a lighter charge of faster powder with them, as a result. It is hard to cast bullets as perfectly uniform in mass as jacketed machinery can make them, so cast bullet benchrest records are not as tight as jacketed bullet benchrest records.

jonnefudge · June 15, 2017, 03:02 PM

Thanks guys for sharing your knowledge! I am really grateful.

g.willikers · June 16, 2017, 09:16 AM

Quote:

The only bad effect from either under or oversize bullets is poorer accuracy and more leading in the case of undersized bullets

Once again, Unka Nick sez it best.
I've found that a few simple tests should do.
Try some different sizes and see how they shoot and if they cause leading of the barrel.

Mobuck · June 16, 2017, 01:35 PM

I dunno, although I'm not a lead bullet fanatic, I have loaded and shot lead bullets for 1/2 century w/o bothering to "slug" anything.

**Unclenick** · June 16, 2017, 05:04 PM

You've never been tempted to put your fist through a bad target?

I think trying out bullets is how you find what your gun shoots best. To me, slugging is more a diagnostic tool for helping determine why a gun may not be shooting well.

HiBC · June 17, 2017, 08:58 AM

Slugging the bore ,IMO,is a way to save a lot of time and components by narrowing down what you are looking for.
Molds aren't cheap,either

mikld · June 17, 2017, 10:12 AM

I like to know my guns as much as my little pea brain can handle (I have an Enfield 303 with a .316" groove dia., I have a 9mm Tokerev with a 358" groove diameter, and I never would have found out why they lead and are inaccurate if I didn't slug the barrels). Sorta like knowing what size tires my truck uses or what size my pants are. Slugging is easy, and quick and I keep the supplies and tools handy (most have other purposes). Yes slugging is an important diagnostic tool but I also do it just 'cause...

g.willikers · June 17, 2017, 11:02 AM

I would never suggest passing up a chance to beat on something with a big hammer.
I would still prefer doing things the easy way.
Just try a variety of likely bullets in size and design.
You never know for sure which one will be the "one", regardless of the results from knowing the exact barrel diameter.

**Unclenick** · June 18, 2017, 11:20 AM

HiBC,

Good point on saving effort and cost. My trying-out approach has usually consisted of choosing a bullet mold for a purpose, then trying it as-cast, sized 0.002" over and sized 0.001" over. But I already had the sizing dies. I would not make the investment in all that stuff as a starting point for a new (to me) caliber, though. Slugging makes much more sense as a starting point for that and for someone who doesn't have all the tools already.

I always end up slugging out of curiosity, but not because it is always necessary.

g.willikers · June 18, 2017, 01:03 PM

In defense of trying bullets instead of or in addition to slugging, here's my experience with a 9mm.
I did slug the barrel, using lead fishing sinkers.
It measured between .355 and .356, kind of a tight barrel for a 9mm.
But the bullet that proved the best shooter by far was .357.
If I had stopped looking at say .356 i never would have found that amazingly accurate lead flat nosed truncated cone gem.

June 15, 2017, 10:57 AM	#1
jonnefudge Member Join Date: November 20, 2016 Posts: 76	Slugging barrel a must? Hi I shoot cast 340gr Lee mold 457 with my marlin 45-70. It seems just fine with no leading. I have not slugged my barrel and wonder about benefits and possible hazards with shooting a wrong sized bullet. Too small or big what happens? Thinking about buying that 459, 405gr hollow base from what I understand the hollowbase seals tight in the barrel? Will probably hunt moose with it. Any input or tips is greatly appreciated! /jonne

June 15, 2017, 11:52 AM	#2
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	Slugging is about find the exact groove diameter. There really aren't any hazards shooting a cast bullet that is a couple thou off. Not enough pressure involved. Using a bullet that is 1 thou bigger is normal for cast bullets. Too big and too fast means leading. More about the speed than the size though. A cast bullet will get squeezed by the steel anyway. Too small means the bullet doesn't contact the rifling enough. Causes bad accuracy and probably key holing. Marlin uses .458" but if it's got their Microgroove rifling they supposedly don't like cast bullets unless they are .459" or so anyway. You'll find your 340 grain bullet will be just fine for moose too. Bullwinkle is big but he's not that tough. Big moose have been killed up here with .30-30's. Accuracy is what's important. Not the bullet's weight. __________________ Spelling and grammar count!

June 15, 2017, 01:10 PM	#5
mikld Senior Member Join Date: February 7, 2009 Location: Southern Oregon! Posts: 2,891	There's an old saying; "Even a blind hog can find an acorn once in a while". If your bullets are shooting accurately without leading you're OK. If you are getting leading, poor accuracy or perhaps tumbling, then the barrel dimensions will be important in fixing the problems. Basically, as mentioned above small bullets tend to lead the barrel, and large bullets "normally" are no problem. I slug the barrels of all my firearms, even if they aren't going to shoot cast, and record the measurements, mainly because I just want to know.. __________________ My Anchor is holding fast! I've learned how to stand on my own two knees...

June 15, 2017, 02:15 PM	#7
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	The only bad effect from either under or oversize bullets is poorer accuracy and more leading in the case of undersized bullets owing to gas cutting. Standard lead bullets are 0.001" over standard groove diameter for the guns they are meant to be fired in, but I find a number of revolvers and lever gun chambers tighten up some using bullet at 0.002" over, and Beartooth Bullets owner found the same thing in his revolver tests, IIRC. But by 0.003" over, they were shooting less well again. Slugging your barrel will find tight spots you may need to lap out, but if you have no leading now, there isn't a lot of point. You've found your good combination already. You can buy pure lead slugs or sinkers from NECO, Beartooth Bullets, and Meister Bullets has slugging kits. You can always cast your own. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 15, 2017, 02:22 PM	#9
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Lead is softer so the start pressure is lower. Being softer, they upset at lower pressure so you can't normally drive them as fast (though some have come up with ways to do it). You usually use a lighter charge of faster powder with them, as a result. It is hard to cast bullets as perfectly uniform in mass as jacketed machinery can make them, so cast bullet benchrest records are not as tight as jacketed bullet benchrest records. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 15, 2017, 01:00 PM	#3
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,289	Undersize bullets particularly of harder alloy,allow gas leakage past the bullet. The surface melts. You get leading and inferior accuracy. You won't go wrong with .001 over groove dia. So,YES! If you want to be successful with cast bullets,you need to know your groove dia. You will be ahead to also know the alloy you will cast. Custom mold makers are good at predicting shrinkage. For example wheelweight shrinks a little different if you add tin . Bore dia matters,too.If your ogive is large,youll engrave chambering. Too small,its a "tippy" thing..even slump under the "G" force.They use a term "bore ride" The Hollow base thing? Hmm. No experience!.My concerns/opinions...which could be wrong.That might be more of a muzzle stuffer thing. You'll have to load/unload a core in your mold..I think it will limit you to modest loads.Get a bit zippy and that skirt will flare out on leaving the muzzle. Tough on accuracy.Myself? I'd go flat base.

June 15, 2017, 01:07 PM	#4
jonnefudge Member Join Date: November 20, 2016 Posts: 76	Great input! How do I make a "slug" for slugging? Pure lead? DIY Mold?

June 15, 2017, 02:09 PM	#6
Dufus Senior Member Join Date: December 10, 2014 Posts: 1,965	I agree that slugging a barrel for cast bullets is important, but more important is throat diameter. You know your throat diameter and create a cast bullet that just squeezes into it and you will have a very accurate machine.

June 15, 2017, 02:17 PM	#8
jonnefudge Member Join Date: November 20, 2016 Posts: 76	Ok I see. Maybe stupid question but is there any difference to jacketed bullets if they have the same diameter?

June 15, 2017, 03:02 PM	#10
jonnefudge Member Join Date: November 20, 2016 Posts: 76	Thanks guys for sharing your knowledge! I am really grateful.

June 16, 2017, 01:35 PM	#12
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	I dunno, although I'm not a lead bullet fanatic, I have loaded and shot lead bullets for 1/2 century w/o bothering to "slug" anything.

June 16, 2017, 05:04 PM	#13
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	You've never been tempted to put your fist through a bad target? I think trying out bullets is how you find what your gun shoots best. To me, slugging is more a diagnostic tool for helping determine why a gun may not be shooting well. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 17, 2017, 08:58 AM	#14
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,289	Slugging the bore ,IMO,is a way to save a lot of time and components by narrowing down what you are looking for. Molds aren't cheap,either

June 17, 2017, 10:12 AM	#15
mikld Senior Member Join Date: February 7, 2009 Location: Southern Oregon! Posts: 2,891	I like to know my guns as much as my little pea brain can handle (I have an Enfield 303 with a .316" groove dia., I have a 9mm Tokerev with a 358" groove diameter, and I never would have found out why they lead and are inaccurate if I didn't slug the barrels). Sorta like knowing what size tires my truck uses or what size my pants are. Slugging is easy, and quick and I keep the supplies and tools handy (most have other purposes). Yes slugging is an important diagnostic tool but I also do it just 'cause... __________________ My Anchor is holding fast! I've learned how to stand on my own two knees...

June 17, 2017, 11:02 AM	#16
g.willikers Senior Member Join Date: September 28, 2008 Posts: 10,442	I would never suggest passing up a chance to beat on something with a big hammer. I would still prefer doing things the easy way. Just try a variety of likely bullets in size and design. You never know for sure which one will be the "one", regardless of the results from knowing the exact barrel diameter. __________________ Walt Kelly, alias Pogo, sez: “Don't take life so serious, son, it ain't nohow permanent.”

June 18, 2017, 11:20 AM	#17
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	HiBC, Good point on saving effort and cost. My trying-out approach has usually consisted of choosing a bullet mold for a purpose, then trying it as-cast, sized 0.002" over and sized 0.001" over. But I already had the sizing dies. I would not make the investment in all that stuff as a starting point for a new (to me) caliber, though. Slugging makes much more sense as a starting point for that and for someone who doesn't have all the tools already. I always end up slugging out of curiosity, but not because it is always necessary. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 18, 2017, 01:03 PM	#18
g.willikers Senior Member Join Date: September 28, 2008 Posts: 10,442	In defense of trying bullets instead of or in addition to slugging, here's my experience with a 9mm. I did slug the barrel, using lead fishing sinkers. It measured between .355 and .356, kind of a tight barrel for a 9mm. But the bullet that proved the best shooter by far was .357. If I had stopped looking at say .356 i never would have found that amazingly accurate lead flat nosed truncated cone gem. __________________ Walt Kelly, alias Pogo, sez: “Don't take life so serious, son, it ain't nohow permanent.”