marlin 336 misfire question

[T-Bird]

I have just acquired a marlin 336 circa 1970's to use for a cast bullet gun (like I need another). It is very accurate withthe RCBS 200fn but persists in misfiring about 10% of the time.There is always a shallow strike on the primer when this happens, but the times it fires the strikes appear normal.If I try the misfired round a 2nd time, it will usually fire. I tried putting a small washer behind the hammerspring to tighten it but this didn't help. any ideas would be appreciated but a trip to the gunsmith may be necessary. Shoot straight, T-Bird

[Trifocals]

Sounds to me as though you may have a broken firing pin.

[BABore]

Marlin 336's have a 2-pc firing pin. The front half, which actually strikes the primer, is contained in the bolt body by a roll pin. This is located under the extractor where it surrounds the bolt body. It can be removed with a couple screwdrivers, or a pair of needle nosed pliers. Use the plier tips to push on each ear at the same time. Wear safety glasses as these buggers can go airborn. The front portion of the firing pin slides back and forth in the bolt body with no springs. The reamed hole can be rough or filled with gunk.

The rear half of the firing pin is shorter than the front and also held in by a roll pin. There is a small piece of flat sping metal that forces it out of alignment with the front half of the firing pin until the locking bolt is brought fully onto engagement by the finger lever. The spring has a slight bend at its midpoint. One end of this spring is bent 90 degrees and fits into the rear firing pin via a small slot. Once alignment is achieved between the two pins, they can then travel forward to strike the primer under the force of the hammer. Sometimes the bend in the spring is too much and it causes drag. Gunk and drag may be the cause too.

As mentioned above, the locking bolt straightens out the rear firing pin when the finger lever is fully closed. You need to verify that is indeed fully closed for every shot. Cast boolits, that have tight engagement into the bore or throat, may also be the culpret. This is especially the case if you get any variance between mold cavities or seating length. There is also a small spring loaded plunger in the finger lever. A rough plunger, or too strong of a spring, may not allow the lever to fully engage the locking bolt.

Any new-to-me Marlin gets a complete teardown for detail cleaning and polishing of all of these details. The bolt is one of the worst items to tear down unless you have a padded vise and roll pin punch. They do have 1-pc firing pin available, but they do disable an important safety feature. Since you do get good primer strikes (dents) most of the time, I don't think the hammer spring is an issue. That said, new hammer springs are cheap and the after-market ones are mo-betta than factory. Older Marlins also have two different notches for the strut that compresses the hammer spring. For ones that don't, adding a small washer works to increase spring tension. Hope this helps.

[Denver]

It's the firing pin. Not necessarily broken. but because of the design, ( 2 piece) they're prone to get gummed up among other things. and will do as you said. Not all the Marlins I've had do it, but some have and as soon as they misfire they get the firing pins replaced with one piece pins and no more trouble.

[gon2shoot]

What they said.

I bought a 35 that had been sitting for a long time and had the same symptoms, degunked the fireing pin and she aint missed a lick sense.

[T-Bird]

thanks guys, I think I have a combination of gunked up pin and cast bullet tight in the chamber. I broke down the bolt (amazing what you can find out how to do on the internet) cleaned and reoiled it. I notice the oal was long enough that the bullet was engraving on the rifling. I am now about finding the longest length that will allow complete closure of the lever without effort. Hope that fixes it. I may be back here if not. Shoot straight, T-Bird

[BABore]

T-Bird,

With cast you typically want the boolit to engrave into the rifling. Not excessivily so, but just enough. Sometimes you need to close the lever smartly to get good lockup every time. Play with the seating length as the CG allows and let the gun tell you what she likes. That said, I have had some cast loads that like a little running room before they engage, Doesn't happen very often, just another trick in the bag.

[Throckmorton]

I had the same problem this year with my vry old marlin,and cleaning the pin a d it's chanels solved the problem on mine.
I was getting some pretty good primer hits that were just not firing,apparantly it takes the full force of the pin to set off the primers,and just a tad of gook can slow the pin down enough that ignition gets spotty.

[T-Bird]

BABore, the engraving that I was having was enough that you couldn't push the round all the way into the chamber with your thumb sometimes. I want to be able to close the lever all the way. heading to the range this afternoon will report back. THanks, T-Bird

[T-Bird]

Seems to have worked, 10 shots yesterday,no misfires, lever closed all the way with very slight engraving seems to be perfect oal. Oh and it shot well too. Thanks, I think it's fixed- I guess I shouldn't have said that. Shoot straight, T-Bird

[mikenbarb]

I had the exact same problem with my reloads but factory ammo worked perfect. It turned out the gun was dirty and the cases were being re-sized too much and I backed off the die a little and it solved the problem(Along with a good cleaning).

[Morrison Machine Shop]

Replace the firing pin. Check your ammo.

[shoot1forme]

Had the same problem in a 70's vintage gun. I boiled the bolt in water for 10 minutes or so then de-gunked it. Checked my loads and sure enough, my 173gr. C.O.L. cast boolits when loaded were slightly long and contacting the lands and grooves. I was also applying a "wee bit" too much crimp, slightly bulging the mouth causing the lever to close a little tighter than usual. This was causing the rear firing pin to not be lifted up enough to be in proper alignment, which caused some of the inertia of the hammer to be expended trying to overcome the rear firing pin mis-alignment condition. All these coditions were additive and would cause my reloads to misfire most of the time. Took care of these problems and "bingo," the Marlin hasn't missed a beat since. Hope this helps!