Curing 742 Chamber Rust ©

 by Larry Ahlman



Maybe you've never heard of chamber rust -- the creeping cancer that destroys autoloading deer rifles. But if you own a Browning BAR, Remington 742 or a Winchester 100, it will pay to be informed.


Gathering your gear and packing for a deer hunt is lots of fun. But, it's hard to find fun when the hunt is over and you're putting it all back. Most hunters want to get this unpleasant task completed as quick as they can, so they toss their gear in the nearest closet.  DON'T DO IT  This shortcut could cause the demise of your favorite autoloading deer gun. The gun may have chamber rust and you're about to ignore it.


While walking the woods in rain and snow, moisture may have seeped down your  barrel, settled around the cartridge and formed rust in the chamber. Fortunately, the rust needs a few months to get a good hold.  If you clean the chamber promptly, you’ll have no problem.  But, let it go a long time and the rust can wreck your gun.


If you have a pump or bolt action, it's not a problem.  They can tolerate a fair degree of chamber rust. But an autoloader won't and here's why:  Imagine inflating a balloon inside of a pipe and trying to remove it. You can't remove the balloon until you deflate it.  This same thing happens in a rifle chamber.  When the gun is fired, the brass cartridge expands and locks firmly against the walls of the chamber.  During that moment, it's difficult to remove the cartridge. After the bullet is out the bore, the brass shrinks back to normal and the empty cartridge will easily extract.


With a bolt action or pump, the cartridge isn't extracted until after the bullet leaves the barrel and chamber pressure is gone.  But a gas operated autoloader works so quick that it starts extracting the fired cartridge while the brass is still locked against the chamber walls.


Manufacturers overcome this problem with a unique bolt design that delays the cycling until the pressure is 75% gone.  To handle the remaining 25% they smooth and polish the chamber to make it slick and easier to extract while the cartridge is under pressure. Correct operation of the gun depends on maintaining a polished chamber. If rust gets in, you'll have problems.


If rust is minor, the gun may still work, but not correctly. It will often fail to extract and frequently jam-- especially when a buck is in your sights. If rust is severe, the extractor can rip the back off the shell casing and cause the action bars to bend. If you continue shooting the gun, the condition can get worse -- even dangerous.




Once chamber rust sets in, there's no easy cure. If it isn't severe, Ahlman's can hone out the rust and re-polish the chamber.  However, our options are limited because we can't risk enlarging the chamber.


Manufacturers recognize the problem and try to warn consumers. Remington even packs a special chamber cleaning brush and excellent instructions with each new autoloading high power.  But, if you're like most, you rarely read instruction books and you probably tossed the chamber brush.  If so, that’s not a problem; you can easily make your own.


A 410 gauge shotgun brush is the right size for most chambers.  You'll need to bend the rod so the brush will go in. Place solvent on the brush and give the chamber a vigorous brushing. Then run a cleaning patch through the chamber and examine the patch. If it looks black or oily, your chamber is in good shape.


The Browning BAR, Winchester 100 and Remington 742-7400's are excellent deer rifles.  All they need is a bit of TLC in the chamber after the hunt and you'll get a lifetime of use from the gun.  But if you neglect the chamber, it will be a gun that you won't be handing down to your grandchildren.




Once the receiver guide rails are upset on a Rem. 742, there's no fix. We can, however, convert it to a pump -- similar to a Rem. 760. Even with a badly rusted chamber, the gun functions very nicely as a pump. So good, that after hundreds of these conversions, we've never had one come back for further adjustments. The best cure, of course, is to catch the cancer early and send it into remission. But, if it's too late for this, converting to pump is a very suitable solution.




507-685-4243 / 507-685-4244 • FAX: 507-685-4280


507-685-4243 / 507-685-4244



507-685-4243 / 507-685-4244