Tolorance for 12 gauge shotgun slug

[Bob in St. Louis]

Hey all,
First off.... I'm new at this, so please have some mercy on me for what might be a dumb question in your eyes.
I've casted several dozen Lee slugs, the one ounce size. I had some issues with the first batch and damaged the mold in the process. One of the problems was that the mold wouldn't close fully. Obviously, this caused the slugs to be a bit fat.
I'm willing to get my mic out and check them all, but I'm curious what the tolerance is.
Thank you!
Bob

[Bob in St. Louis]

Home from work now, and grabbed the micrometer...
I measured a few from a batch that I was happy with, and they're in the .69 range. I grabbed some of the ugly ones. The ones towards the end where the mold wouldn't close completely and the casting seam was more noticeable, and they're in the .72 range.
At what point do I worry that I'm shoving the wrong caliber down the pipe?
How big is too big?
By the way, I've got a smooth bore, no choke.

[rancher1913]

push one down the bore, if you have to use much force they are to big.

[uncle dino]

Hi bob. I don't have a lot of experience with that slug. But I believe that lee slug is supposed to drop at about .680 and be shot in a wad. Depending on your barrel it may be too large to be shot with a wad and too small to be shot bare. But the .72 may work bare...try pushing some through the barrel. Might be a good place to start..d

[Bob in St. Louis]

Best I can tell with the mic, the end of the barrel is .730.
And I do believe Dino is correct, they're supposed to "fit through" in a wad.
Funny thing is, I've never been able to shove a slug/wad through, even with a bit of "umph" behind the stick (using published load data).

[longbow]

My Lee Drive Key slug mould casts at about 0.685" at the nose and something in the order of 0.665" at the base IIRC. In any case they are somewhat tapered to suit tapered wad petals.

I do not recall if I pushed any through my bore in wads but I do know that my best round ball and other slug groups come from a fairly easy push through the smoothbore barrel which is 0.730" diameter cylinder bore.

I would mic the wad petals and do a little adding to find total slug/wad diameter. you won't do any damage to your gun if they are somewhat oversize as they are designed to squish down through a choke if they meet one... assuming they are cast of soft lead. However, accuracy is likely going to be poor if the fit is too tight.

A general rule of thumb several people use is that the wad/slug combo should not be over 0.003" larger than the tightest barrel restriction. In your case that would mean max diameter of 0.733".

The 0.720" slugs are rather large. Is that at the seam or is that at 90 degrees from the seam? Regardless if they are that large they are too big for a wad and too small for the bore... and they will be oval. I'd remelt those.

In fact I would be inclined to melt down and recast any that are much over 0.685" mostly because you want the mould to be working properly and casting as designed when you load so you aren't making changes to suit poorly cast slugs. The 0.690" slugs should be safe to shoot but unless you use a thin petal wad they will likely be very tight and result in poor accuracy.

I'll assume you are using the Lee recommended load data, hulls and wads? Or data from a reloading manual? If you are new to loading slugs this is not like reloading for metallic cartridges. You want to be using published load data and don't make any significant substitutions. All the components work together and substitutions can have large effects on pressure (assuming correct powder charge) ~ hulls and primers especially. A primer change from a recipe can result in up to 3000 PSI pressure change.

Not sure what your mould problems were but using some sprue plate lube or graphite on the core pin and alignment pins (new style) or grooves (old style) will help in getting the mould to close easily. The old style with extruded Vee grooves can gall up if they are forced and not lubed. The new style with alignment pins should not be a problem that way, however, the core pin belt/groove should be lubed for both styles.

That's my take anyway.

Longbow

[duckey]

Push one down your bore (with the barrel off if possible) in wax/shot cup you plan on using. You will have to find the right match for your gun. You'll want some snugness but nothing that you can push through relatively easily.

[Bob in St. Louis]

Cool, lots of good information here. Thanks guys.
A few specific points from Longbow;

- I don't recall on the fatest one is the fat part was at the seam, or 90 off, but I was specifically checking them at various points.
- The load data I'm using is indeed from Lee, I've also got some from the powder manufacturers. I've not yet started assembling shells yet (I've dabbled with a couple recipes but want to nail down a good solid one so I can make batch after batch with no deviation).

[cpileri]

According to Jmaes gates, .001"-.003" over bore (groove) diameter will be best. What is your bore?

[Bob in St. Louis]

Best I can tell, it's .730, but I'm trying to get the jaws of a digital caliper in there.
Not sure that's the most accurate method.

[longbow]

Best to slug it then use a micrometer to check the slug however, 0.729" is nominal 12 ga. diameter and in my experience most modern shotguns are "close" (within a few thou) to 0.729" though some European guns can be apparently considerably tighter as can Ithaca Deerslayers.

Best to check but if yours is a modern gun made for the North American market it will likely be 0.729" +/- maybe a couple thou.

Yup, there it is again as Carl says, up to 0.003" over bore diameter (smoothbore or groove diameter for rifled gun). I think at 0.003" over your bore diameter you will have trouble pushing the slug through the bore. A thump with a mallet and dowel should start it fairly easily then it may push through. I have to say I have not done this as, like I said, I have found that an easy push through has worked best for me so if I find a tighter combination I use a thinner petal wad. I am not concerned about pressure here, just that with tight combinations I have had wad petal failures and poor accuracy.

Longbow

[cpileri]

best method to get barrel diameter is to slug it: take a soft lead round ball (or slug, but it will be more difficult) and push/tap it down the lubricated bore. then measure the slug.

[seppos]

I collected some data to the table, but evidently I lost the paper somewhere so I can not comment that.

S

[Bob in St. Louis]

Thanks fellas!
Good idea about shoving a ball/slug through, then measuring its diameter when it comes out the other end.
Pretty slick idea (wish I'd have thought of that).

[longbow]

An ideal slugging ball is 0.735". Tap that into the bore from the breech then back out and measure. If no choke then you can push it right through. A regular bore size Foster slug can likely be swaged large enough with a hammer blow or two to the nose then used as well.

[Bob in St. Louis]

I took a 1 ounce Lee slug, set it on the concrete floor and gave it a good whack with a three pound sledge to enlarge the girth.
I then, lubed it up and tapped it into the end of the barrel (no choke, smooth bore), then tapping it the rest of the way down using a dowel rod it fell into the breech.
To retrieve it, I then set the gun on my table saw, pulled the charging handle back, the slug dropped out of the magazine well, rolled across the deck of the table saw, and fell perfectly into the 1" "finger hole" on throat plate. This caused it to fall deep into the bowels of the cabinet, into a large mound of sawdust.
Perfect shot, hole in one. I actually laughed out loud at the ridiculousness of the event (perfect topper for a crummy day).
After removing the access panel and fishing through a few gallons of sawdust, I managed to find my needle in a haystack.
Where the wear marks were, it measures exactly at .7300.