This used to be at the Wisner's web page, the pictures are gone:
The first thing I would look at if a feeding problem seems to be the culprit, is the magazine. Feeding problems on these series of models can many times be traced to the magazine as with any semi-auto. Here the average hunter is more likely to leave the magazine loaded even when the gun is put away. Also the magazines will have been carried in a pocket where lint, twigs, dirt etc. can accumulate. With this debris internally the live round can be restricted as it tries to feed up into the chamber, possibly causing a malfunction. Also they can have became sat on & squashed so as to not allow the follower to come all the way up. You notice I do not use the word “Jam”, as it is so broad a term that it is essentially useless.
The followers from these semi-auto magazines will tax your imagination & patience to remove & then reconnect them back onto the trip latch. I would suggest that to clean the internal parts of one of these, that either you soak it in solvent & blow it out with compressed air at the same time depressing the follower. Or if you do disassemble one to get it clean, pay close attention to how it came apart.
The next to look at would be are reloads being used? Reloads are not bad, BUT the reloader needs to be WELL aware of proper sizing for semi-autos. This is completely different than for bolt action guns. A small base die needs to be used that sizes the WHOLE body back to original factory specs. Also if a crimp is used on the case, it will have to be trimmed accordingly so there is no bulge at the neck. This reloaded case MUST fall into the chamber. Also it is advisable to only reload them to be used for hunting 2 or maybe 3 times. As with this small base resizing will work the base & can create a case head separation of the brass after a few loadings. You can reload them more, but use these multi loaded ones for target practice. Believe me it is rather helpless seeing an animal you just hit, but did not go down & then run off with you holding a useless firearm. You have a case head separation in your gun & about all you can do is to just can stand there with your finger in your nose.
Another thing to look at if you reload is that the pressure level has to be near the factory otherwise the bolt will not cycle enough to eject. Read the reloading manual & try to pick a load at least in the mid range.
You guys that say I have reloaded for 30 years, therefore I know what I am doing does not mean a thing if it has NOT been for semi-autos that the reloader is in turn using themselves. Hell, I have been eating for 70 years but that does not make me a cook.
Another problem with these guns is that the chambers tend to get rusty. These extractors are a light metal "C" type clip with a small hole on one end that is used with a rivet to anchor it into the bolt head, & on the other side of this extractor there is a slight protrusion that has a sharp rear edge that acts as the extraction point.
At first the rusty chamber situation may just cause extraction problems. Then since things do not improve by themselves, the extractor may get bent & not be as efficient as it should be.
As things worsen, the gun can malfunction by not pulling the case from the chamber because of the internal rust in the chamber gripping the fired case & or the faulty extractor. If the rust job gets bad enough & the case is really stuck, the bolt will come back with enough force that it can rip the lips of the bolt face off. This then leaves no metal to hold the extractor into the bolt head. You now can have a really stuck fired case & a broken bolt head.
In the pictures below the barrel was almost ruined by neglect. The bore was bad also when I got the gun, but it was firing & extracting, much to my dismay. I was able to salvage this gun, by polishing the chamber with crocus cloth & fire lapping the bore, & the gun is still in service today.
A GOOD gunsmith/welder can weld the broken lips of the bolt & re-machine it back & reinstall a new extractor. If the chamber rust is not too bad it can be polished out with fine emery cloth wound around a slotted flexible shaft mounted in a 1/4" drill motor. It has been discussed on some message boards to not do this because it will change the headspace. Well, the gun is somewhat ruined now, whatever you do to get it operational makes it better than it was. Sure you may have made a slight change in the chamber, but using this method, you can not remove an excess amount. Also do not believe the BS about the chamber has to be slightly rough. Look at any new semi-auto & you will see a very smooth chamber. If it is somewhat rough, the extractor will indeed pull chunks off the case rim leaving the fired case in the chamber OR rip the bolt lips off that hold the extractor in place in the bolt. The roughness idea may have come from a retarded blowback pistol, which this is the case there, NOT HERE.
After many years of pondering why these guns were plagued with this phenomena & not the makes or models of others, the following answer finally came to me. It was the dedicated, hunt in the cold/rain, deer/elk hunters that seemed to have the majority of the problems. The sunshine hunters appear to not have any problems.
In the Pacific Northwest, elk season is later in the year when the weather is nasty, cold, rain, sleet & blowing. Also here the brush, replanted trees, & timber is thick, so the hunters usually get out in the brush in the morning, get wet & cold, and then drive around on logging roads in the afternoon to dry out & hope to see animals that some other hunters have put on the move. In the state of Washington, a loaded firearm in the vehicle is illegal, so they unload the gun, remove the magazine, & rest the muzzle on the floor possibly between the 2 hunters or in a gun rack for quick access.
This could also happen in a very humid climate. In the colder weather the barrel will condense water on the inside & since the action is spring loaded and has no means of being held open without an empty magazine inserted, the average owner simply leaves it closed. The gun has gotten wet & COLD, now it is subject to a forced HOT air from the heater, in this close proximity to heat, the COLD steel condenses moisture on both sides of the steel. With the bolt forward under spring pressure & the muzzle down, when the barrel warms up the inside has condensation, this rises & is trapped inside the chamber. But the inside has no place to go.
If the drive home is long enough &/or the firearm stays there long enough, the outside condensation will dry off. At the end of the day, he then takes it home & may stand it in the corner to dry off. The condensed water inside of the barrel, then runs down & collects in the chamber area. Then possibly the gun MAY see an oily cleaning patch run thru the bore but the chamber is usually missed. This is not an area that the average hunter will even see if he runs a cleaning rag thru the barrel. Usually the bolts are closed on most firearms when being stored. This also traps any moisture inside the chamber. The gun is set away with the bolt closed until the next year with the owner thinking that they have done the right thing. The end result is a RUSTY chamber that we have seen MANY times, but did not understand what may have happened.
One of the most common problems with the Remington 740 & 742 is that after much use the receiver rails will get worn. These rails guide the bolt lugs on the movement both rearward & forward. The receiver is made of a soft metal since the bolt lugs engage the rear of the barrel for a positive lockup. The receiver simply holds the parts together.
This movement is under gas pressure on the rearward movement & spring pressure on the forward movement. At the rearward stop position the inertia of this bolt lug exerts extra pressure caming it against the receiver rails, pounding them enough that they get worn. There is a bolt latch on the 742 (this latch was not on the 740), this latch is supposed to lock the bolt head into the bolt carrier to help keep the front from over-rotating at the most rearward inertia's movement, but after wear on all parts, things seem to get sloppy & do not function as intended.
When this happens the bolt lugs, now slightly out of time, having been moving back & forth, may also chew up the front of the rails. Then the bolt carrier & lugs can get bound up & in extreme circumstances actually stop the bolt unit from cycling when the gun is fired, or binding it on the return stroke enough to stop it before it completely closes.
Under some circumstances the operating handle may drag, usually on the bottom of the receiver slot that the handle operates in. If this happens it is usually related to the above rail problem.
Since there are no new receivers available & the only used ones could be questionable in that may possibly be worn also, A GOOD gunsmith/welder/machinist familiar with firearms can usually salvage the receiver by welding the worn rails with a special long nozzled wire feed or heliarc welder. This receiver can then be re-machined to factory or tighter dimensions on a vertical mill using special long cutters. This is not a job for the average "gunsmith" however.
If you have to take the barrel extension of to do any rechambering or rebarreling you will need to make a barrel extension wrench. This extension is actually the barrels locking lugs. It is threaded & timed to the barrel so that the extension is indexed so the sights, barrel lug are all indexed for bolt lockup, headspace & everything where it should be. There is not any commercially available fixtures available to remove these extensions. If you try to use any other method, you will about 99% be assured of breaking the extension.
In the above photo, the inner slider is made to fit inside the barrel locking lugs. The 3/8" bolt locks the slider to the base. The bolt hole is also aligned with the barrel lug attachment bolt hole. In use, for removal the base is inserted over the barrel lug extension & the slider is then slid endwise into the lug recess. The bolt is inserted in just far enough to lock these 2 parts together, but not into the main barrel lug. Mark the relationship of the barrel to the barrel lug with a scribe mark on layout die. This will allow you to reinstall it in the same position.
Now Remington changed the threads at barrel date code (LO) from RH to LH to facilitate the extension not being backed off when used on the semi-auto guns. This will determine which direction, you trey to remove it from. You can nor put the barrel in a barrel vise, rap the removal handle in the proper direction & unscrew the extension off the barrel. They are usually on tight & require force to remove even after the initial bond is broken. Once it is off, if the barrel lug is stubborn & resists, you may screw the extension back on part way & do it over again but with the 3/8" bolt thru the lug & take both off at the same time.
Remington has also discontinued making extractors for these guns, #14669 which was 30-06 size riveted type & are the same that had been used on the 700, 740, 742, 760, 788. These extractors are riveted into the bolt & require a special rivet & tool to install. They however are currently available from Brownells in Iowa 1-800-471-0015.
Im thinking he left the rifle on the back porch in the humidity. 
