Slugging barrel a must?

J

jonnefudge

New member
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
 
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.
 
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.
 
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..
 
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.
 
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.
 
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.
 
The only bad effect from either under or oversize bullets is poorer accuracy and more leading in the case of undersized bullets
Click to expand...
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.
 
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.
 
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.
 
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
 
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...
 
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.
 
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.
 
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.
 
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