Cerrosafe expands at 30 minutes to full dimensions

[ohland]

Misread [no, I followed!] the instructions. I will tell you that Cerrosafe will, at 30 minutes, be so tight that you cannot beat it from the chamber... Had to heat it up in the chamber and let it run out. I will go into town and buy a cheap, large ladle so I can control my pour.... The set-up was quite rustic and did not help.

Note to all: when you have puddled the chamber of a RB, you CANNOT pull the breechblock nor, obviously, the hammer... unless you want to drive out that 3/16 (?) inch pin that the hammer stops against. Pulling the bottom tang and pulling both pins is NOT enough.

:veryconfu

Hints For Using Cerrosafe by: Mike Watkins
http://www.brownells.com/userdocs/learn/bt002015.pdf

"Note the time the casting was poured. The casting will take only a very short time to solidify, usually within a minute. Wait 30 minutes and then remove the plug from the bore. Turn the muzzle upward and the casting will fall from the chamber. At 30 minutes after initial solidification, Cerrosafe shrinks slightly, so removal is very easy. "

At 30 minutes, it will not move. The muzzle casting I did was very resistant to come out at 30 minutes. But it was only about an inch and a half long, if that. Imagine a chamber cast for the 43 Spanish...

Tech Tip: How to Cast your Chamber using Cerrosafe by Bill Gravatt
http://bulletin.accurateshooter.com/2014/04/tech-tip-how-to-cast-your-chamber-using-cerrosafe/

"7. After the Cerrosafe has hardened, the chamber casting can be pushed out of the chamber coming from the muzzle end using a cleaning rod or a wooden dowel. It is recommended that you push it out within a half-hour of casting the chamber. We usually push our cast out within a few minutes."

[bangerjim]

Are you SURE you had the exact Cerrosafe alloy? I have two different eutectic alloys of Bi that melt at 140 and 170F and neither shrink like Cerro is supposed to.

[Gunlaker]

I push out all of my castings after one minute. The stuff will expand during cooling, eventually it will expand to well beyond the chamber dimensions.

There are a few different correction formulae out there. The best I've seen was published here a while back by a guy that sells some shooting related software.

Chris.

[ohland]

Are you SURE you had the exact Cerrosafe alloy? I have two different eutectic alloys of Bi that melt at 140 and 170F and neither shrink like Cerro is supposed to.

Dunno, I bought it from Brownells a few years back. I watched the Midway video on chamber casting with Cerrosafe, and watching Larry pop the casting out with a few firm taps from a cleaning rod suggests to me that 30 minutes is a tad too long...

Cut n pasted from Brownell's:
http://www.brownells.com/gunsmith-tools-supplies/barrel-tools/barrel-chamfering-accessories/cerrosafe-chamber-casting-alloy-prod384.aspx
"Unlike Woodsmetal which swells upon cooling and cannot be removed from a gun chamber, Cerrosafe shrinks during the first 30 minutes of cooling and then at the end of an hour, is EXACTLY chamber size. At the end of 200 hours it will have expanded approximately .0025". This factor is well known by all toolmakers and they will take it into consideration when making dies or reamers or gauges from your cast - if you will tell them the cast is of Cerrosafe. Cerrosafe melts between 158° - 190° F."

[ohland]

I push out all of my castings after one minute. The stuff will expand during cooling, eventually it will expand to well beyond the chamber dimensions. Chris.

After 30 minutes it's darned near immoveable. Just my (recent) experience... Got my SS ladle from Wally-Mart, now... breech block n hammer are out. Run an oiled patch into the chamber, then plug the bore ahead of the chamber. Heat up the Cerrosafe in the can, get it liquid, pour into ladle, set aside. Use the heat gun on the receiver to warm it up. Stick the RB in a wood jawed vise. Freshen up the Cerrosafe until liquid, then pour chamber. Wait two minutes and start tapping it out... And pray.

A lot less complex with the block and hammer removed.

[ascast]

yup ! remove soon, like within a minute of hardening

[Tatume]

... Use the heat gun on the receiver to warm it up ...

While I'm no expert on Cerrosafe, could this be the problem? When the receiver is heated it expands, and when it cools it shrinks onto the casting inside. Like I said, I'm only speculating.

[Nobade]

Yes, make your cast then push it out as soon as it is solidified. Wait 30 minutes and then measure. I do it every day, works great. If you time it just right you can measure things to a tenth (.0001) pretty reliably. As you learned, don't leave it in there or you'll have to melt it out with a heat gun!

-Nobade

[HollowPoint]

Using this stuff is really confusing to me. I tried using it when I was working with air rifles. I read and re-read the instructions. I even went online in search of videos on how to use it correctly.

I still ended up with a cast that was to small. And I tried every variation in the instructions that I found. I even made a cast of my chamber and immediately removed it from the chamber and proceeded to take measurements every ten minutes for a half hour just to see what kind of growth or shrinkage I was getting.

That wafer of cerrosafe has been sitting in my storage room ever since.

HollowPoint

[Gunlaker]

The expansion of the alloy, as noted in the instructions is not correct. The fellow i referred to in my previous post had a much more accurate correction formula. I believe his name is Tom Meyers, or Tom Myers. His posting was either here, or on the bpcr sub forum, maybe six months to a year ago. If you google his name and cerrosafe you might find it.Chris.

[Gunlaker]

This should help.http://castboolits.gunloads.com/archive/index.php/t-258324.html.

[dragonrider]

I usually give it about 10 minutes before I remove it. No difficulty pushing it out. I does not fall out as suggested above, but it comes out easily.