Slugging the bore with Cerrosafe

[Jim22]

Hi, I've read a lot about slugging the bore of a firearm - Pour lead into the bore and then shove it out and measure. Is there a reason no one does it with Cerrosafe? It's not that expensive, is reusable, and less likely to burn a the fingers.

[godzilla]

It has always been my understanding slugging the bore meant pounding a slug of lead thru it. Cerrosafe you cast it then measure.

[country gent]

Normally a bore is sluggged with a round ball or slug slightly bigger and driven thru. Swaging it down to size.. Cerosafe is a material with a very low melting point that is normally sed for chamber casts and casts of cavities to show sizes and details. With cerosafe in the rifleing poured in molten you risk a mechanical lock.

[Stewbaby]

As stated, cerro is too hard at room temp and though it contracts at first may be hard to remove from the bore. Keep it in the chamber and throat. It also changes dimensions over time do you can’t ’archive’ it like you can lead.

[cas]

I've measured a bore at the muzzle with it. That's the thing, you're measuring just one spot. (which sometimes is enough)

[Nobade]

I do that almost daily in the shop. Tells you if the barrel has loose or tight spots, make it long enough and you can pick up twist rate changes and wait an hour and you can measure the groove diameter down to a tenth. (.0001). Just make sure you clean the bore really well first, any fouling will throw off the feel. This is a real eye opener when you first compare a normal factory barrel to a top quality one. Night and day difference in feel.

[waksupi]

I think cerrosafe would get too hard to easily slug a barrel.

[fredj338]

Hi, I've read a lot about slugging the bore of a firearm - Pour lead into the bore and then shove it out and measure. Is there a reason no one does it with Cerrosafe? It's not that expensive, is reusable, and less likely to burn a the fingers.

Yeah not sure where you heard that but you would likely never get that long lead plug or cerrosafe out once poured in.

[fredj338]

normally a bore is sluggged with a round ball or slug slightly bigger and driven thru. Swaging it down to size.. Cerosafe is a material with a very low melting point that is normally sed for chamber casts and casts of cavities to show sizes and details. With cerosafe in the rifleing poured in molten you risk a mechanical lock.

^^this^^

[44magLeo]

When slugging a barrel it should be done in several places. One is to drive a slug in the muzzle an inch or so. One slug driven in from the chamber into the throuat and start of the rifling and one driven all the way through.
The one in the muzzle tells you the bore and geoove specs there. The one fromthe chamber gives you the specs of the throat and the start of the rifling. The one driven all the way through gives you the specs at the barrele tighest spot.
The one in the chamber is often done with the cerrosafe. This one is used to determine the size of you cast bullet. The diameterr of the throat and the start of the barrel is the size you need to match, or be .001 over.
This spec is often larger than the rest of the barrel. From cutting the chamber and throat or from w ear.
A good fit here is what seal the bore to prevent gas blow by and engage ti rifling. If it is larger than the bore the bore will size the bullet as needed.
The one in the muzzle can indicate wear at this point from agressive cleaning fronm the muzzle. If worm enough the accuracy suffers. You often find this on old military rifles. This is often corrected by raming out the barrel an inch or more to cut back the worn rifling tp get good rifling. thus somewhat restores the accuracy.
Leo

[MOC031]

^^^ Yep, there's the full perspective on both slugging and using Cerrosafe.

The thing you CAN'T do with Cerrosafe (I think, I've never tried it) is drive it the length of the barrel to find the barrel's minimum dimension. Running a lead lap through a barrel, you can easily feel both the tight and loose spots until you get that nice, uniform feel from end to end.

[MOC031]

With cerosafe in the rifleing poured in molten you risk a mechanical lock.

It's a minimal risk, although I've ended up with that several times over the years, usually due to being in a hurry and/or not paying attention.

And there's no real risk, given the low melting temperature of cerrosafe. A few minutes of low temperature heat gun, just enough to heat the metal to the melting temperature of cerrosafe, and the cerrosafe runs right back out of wherever you shouldn't have gotten it in the first place.

One disadvantage of Cerrosafe is that, after that first hour or so, the Cerrosafe dimensions are no longer spot on. So if you want an archival cast of your rifle you can go back to years later, Cerrosafe isn't what you want. I make and record all my measurements of the casting about an hour after it's done; after that, the Cerrosafe goes back in with the rest of the alloy it came from.

[MarkW]

As mentioned, cerrosafe is too hard to slug the bore with but if anyone wants to try it and post results go for it. If something gets stuck just remember that it melts between 160-190F so boiling water is enough to melt it.

[country gent]

Ideally when slugging the barrel you drive one slug in from breech end 1 1/2"-2" and back out then one from muzzle 1 1/2"-2" this shows any taper in the barrel. then the last one goes thru breech to muzzle this shows the smallest dia in the barrels length. with this you know pretty sure what you have. The big reason for using pure lead is its a dead metal with very little to no spring back.

We used lead wire to check die clearances when building form or progressive dies. a thin piece of wire laid in and cycle press measure the flattened wire to make sure there was room for the stock. Its embarrassing to send the die out and have it go over center on the stock and lock the press up LOL

[Cast_outlaw]

I use cerosafe with a small wire and pice of rag to make a small cast usually 1 1/2” it shrinks after cooling allowing it to be removed relatively easily in the first 30 min then starts to swell to .0025 over in 2 weeks on a mathematical formal witch can be worked back from if times ar known or just weight it’s low melting point make it so you can remove a mechanically locked slug by placing it in boiling water to melt (been there done that) as cerosafe that I have melts at 150-189f

[MOC031]

you can remove a mechanically locked slug by placing it in boiling water to melt (been there done that) as cerosafe that I have melts at 150-189f
Or you could use a heat gun set on the low setting and avoid having all that water in there. To quote you, "been there, done that".