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Mil-Surp arms usually don’t have the caliber stamped on the arm, those that do tend to be in the minority.  If a government arsenal rebuilds a rifle, and changes the caliber, then the new caliber may be stamped on the rifle, however, there is no guarantee it will be so marked.   Israel seemed to be very conscientious about marking rebarreled M98 pattern rifles “7.62”.  However, I wouldn’t be surprised if there was one out there not so marked.                                                                                                                         

Often, when a government rearmed with a newer model rifle, older arms already in service were reworked.  Barrels were shortened, or stocks were changed so older arms would have the same outward configuration as current issue arms.  However, sometimes the newly configured older arm was left in the original caliber!   Spanish arms are a case in point.  Specimens of 7X57 M93 rifles will often be encountered with barrels shortened to 23.5 inches and fitted with a pistol grip stock, however, while these rifles look exactly like a Spanish M43, they have not been rebarreled to 8X57, the standard caliber of the M43!   

Almost 20 years ago, when Mil-Surp arms first were imported in large quantity, I was at a gun store that had rack after rack of surplus rifles.  They had a rack of South American Mauser’s tagged as all being one caliber.  However, looking them over I discovered several had not been re-bored or re-chambered!  The storeowner said they were all from the same shipment he got from the importer. Apparently, when the crates were filled in Latin America, no one checked to insure all were the same caliber.  At first glance, the rifles all looked the same.  One can only imagine what would happen if a cartridge with a bullet materially larger in diameter then the bore got chambered and fired in one of those odd rifles!      

I recently received an email from a gentleman that acquired a Siamese Mauser.  The question was; which caliber was his rifle chambered in?  Siamese Mauser’s appear in both 8X50R & 8X52R.   The reader was showing due caution.

After WWI, many European gunsmiths sporterized Mil-Surp Mauser rifles.  Often the caliber was changed to some obscure cartridge with an 8X57 head size and .323 bore, but little else similar to the 8X57.  Very often the new caliber designation was not stamped on the barrel.  Many of these weapons were taken as war prizes by returning GI’s.                                                                                                                                   

This 1/2 lb block of Cerrosafe is enough to do several chamber casts.

It makes sense to do a chamber cast of a rifle of unknown caliber.  But, sometimes it can be beneficial to do a chamber cast a rifle of a known caliber.  Of course it begs the question.  If the caliber is already known, why make a chamber cast? The chamber cast will tell us things that can’t be seen by looking through the action and trying to eyeball the chamber, throat & leade.

The subject rifle is an Enfield # 4 Mk II.  I know it’s chambered in 303 British.  The rifle is quite accurate, its barrel’s lands & grooves are about perfect.  .  However, it seems to have a somewhat long throat to the leade of the rifling. By making a cast of the chamber, throat and beginning of the rifling, exact dimensions can be determined.   Knowing the exact dimensions of a chamber can tell us a lot.  Accuracy issues, bullet fitting & seating depth concerns can be addressed once a chamber cast is made. The dimensions derived from a chamber cast will also allow one to have a custom bullet mould to be made expressly for that rifle. 

What we’re going to do is make a chamber & throat cast of this rifle.  Even though Cerrosafe melts between 158 and 190 degrees it’s still molten metal. While the process is quite simple, there are safety and practical issues to be addressed.  Let’s look at them.

My high-tech ladle!

► The Cerrosafe has to be melted.  It won’t do to melt the alloy in any item used for the preparation of food!  I made a melting pot / ladle from an empty soup can and a piece of scrap wood for a handle.  If at all possible, don’t heat the Cerrosafe in the kitchen or in your home.  Try to do it out-of-doors.  I used the barbeque grill.  A hot plate would work as well.   If you cast bullets with an electric casting furnace, I would not recommend that Cerrosafe be melted directly in the bullet-casting furnace.  However, a pot full of molten bullet alloy could have your homemade ladle set on top of the melted bullet alloy (like a double boiler) and that would melt the Cerrosafe quickly.

► The melted Cerrosafe has to be moved from the ladle to the chamber without spilling.  I thought about this.  How could I move the melted alloy through an action and into the chamber without getting burned or making a mess?                                                        

Then I thought, “Hey, this stuff melts below the temperature water boils at!  I can use a plastic funnel and some flexible plastic tubing.”                                                                

5/8 inch OD flexible plastic tubing can be had from any home center.  They sell tubing by the foot.   I found 5/8 inch OD was a perfect fit through the action of an Enfield.  It had just enough friction to hold exactly where I put it.   A plastic funnel from any discount store can be press fitted to the end of the tubing.  I left the tubing long so I could use a twist tie to secure the funnel tab to the trellis.  Now I see that wasn’t required.  I could have got away with just 3 inches of tubing sticking above the end of the receiver.

► To get the best possible results the chamber & barrel must first be clean.  Clean the chamber & barrel in the manner you normally would.  The chamber, leade & barrel should be dry.  Use some spray disk brake cleaner to ensure a dry chamber.

► The chamber cast must mirror the chamber, leade and first inch of rifling.   That means the barrel must be plugged at some point.   I used a tape measure and measured from the back end of the chamber to a point including the leade and first inch of rifled barrel.  Remember; this means you will have to count the case length and about 1-½ inches for leade & rifling.  If you elect to not remove the barreled action from the stock, the point you identified can be marked with a bit of masking tape on the stock.   Then the distance from the point you identified & marked to the end of the barrel is measured.  Make note of this distance. 

Rubber bands hold the empty brass case in the correct position for a seated cartridge.  1 ½ inches additional is required for leade & rifling.

The cleaning rod with jag & patch will have to be inserted 21 ½ inches.

Fit a cleaning rod with a metal jag and a tight fitting cloth patch.  Make a mark on the cleaning rod the same distance as you measured in the last step.  You can use tape on the rod as well.  Alternately, Sinclair sells quality plastic Cleaning Rod Stops.  Each one is like a sleeve; it has a nylon setscrew to retain it on your center-fire cleaning rod without damaging the rod.  Large stops (for 27/30 cal rods) are part # 02-1020.

Cleaning rod with rod stop & jag. Rod stop has been set at 21 ½ inches. Tape could have been used in place of rod stop.

► Insert the patched cleaning rod into the muzzle up to the point of the tape mark.

► Since gravity is our friend on this job, it makes sense to have the rifle secured in a vertical position.  The funnel should also be in place and secured so it can’t move.  We want our hands free so we can quickly move the molten Cerrosafe to the funnel.  The most important reason to have everything secure in advance is; we want as much control as possible while pouring the cast.  That means both hands available to handle the ladle.   

You DON’T want Cerrosafe getting into the locking lug recesses of the action (if so equipped, like in a Mauser).  Doing so would lock the cast in place.  All we want is pour enough Cerrosafe to get the cast of the rifling, leade & chamber; nothing else.

Butt of rifle has been wrapped in an old towel. A bungi cord secures the rifle to the trellis. A twist tie is used to secure the funnel to the trellis. The tubing DOESN’T have to be this long. While you can’t see it in the picture, the nose cap of the rifle is supported on a block of 4X4.

► It seemed to me that pouring hot metal into a cold barrel would result in a wrinkled cast.  Anyone who casts bullets knows wrinkled bullets result until the mould is up to temperature.  So, I opted to first warm the barrel with my wife’s electric hairdryer before pouring the Cerrosafe.  Of course I secured her kind permission in advance before borrowing the dryer (Thanks Honey!).

Warming chamber with a hair dryer prior to pouring cast. Warm it for a good 5 minutes to get the chamber hot. Note end of plastic tubing has been pulled away from the chamber during warming process.

The ladle with Cerrosafe has been on the barbeque grill while the chamber is warmed. After the chamber is warmed, the tubing is quickly pushed into position, and the cast is poured.

The finished cast next to a .303 case, notice the long distance between the end of the chamber and the beginning of the rifling.  

► With everything in place; and the barrel warmed, the cast is poured.  Make note of the time.

► After 3 minutes the end of the cleaning rod can be tapped on with a small hammer.  The cast will come out of the chamber.  Cerrosafe shrinks and then expands.  After one hour readings can be taken with a caliper or micrometer and recorded on a drawing.

If a chamber cast is made to determine the caliber of a rifle, the cast’s dimensions can be compared to a reference book such as “Cartridges Of The World”. 

I’m considering having a custom bullet mould made for this rifle.  With the information supplied by the chamber cast, I can specify the exact dimensions to the mould maker.

Doing a chamber cast is simple and can tell us many things that simply cannot be ascertained by looking through a rifle action.  The unused portion of Cerrosafe will simply be stored in the ladle.  Cerrosafe casts can also be melted down & reused again & again if required.

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