Hi All Around !

Recently found a MIB mod. 36 J-Frame dating to about 1976 in unfired condition (or almost unfired). While test shooting I discovered an odd problem with certain types of cartridges. Every now and then the cylinder would turn only with great difficulty (as if something acted as a brake). Taking a close look at the shells I discovered scrape marks on the floor of the cartridge rims, which, I think, could have only been caused by the hand. There is no other part there to interfere with the cylinder rotation. As if some shells don't quite have enough clearance to rotate into the firing position. The odd thing is that it is always the same shell, regardless of which chamber it is in, that doesn't seem to clear something. I replace all 5 shells and all is well. I reinsert that problem shell with 4 of the ones just used and it happens again on that shell. I go through the whole box of 50 and about 10 percent of the shells get stuck - and no matter what chamber I put them in. I use another manufacturer - like Speer or Win. - and everything is fine again. Please see attached pics. Does anyone have an idea what the problem is?

Attached Images

	PICT0164.jpg (86.2 KB, 108 views)
	PICT0165.jpg (67.0 KB, 121 views)
	PICT0166.jpg (62.4 KB, 271 views)

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QM3

Rim thickness varies a ton from manufacturer to manufacturer. That effectively changes your headspace (possibly reducing it to zero if the rim is thick enough). Possibly you are only having this problem with thicker rims?

My guess is that the same shell you're having issues with has a thicker rim.

If it were happening with different shells, but in the same cylinder, you'd look for a bent ejector rod etc.

Measure the rim thickness, if this one is thicker, and the problem doesn't happen otherwise, I wouldn't give it a second thought.

Possibly the hand is also protruding a tad bit too far into the frame but that is easy enough to fix with a stone and if it doesn't affect the major brands of ammo, I'd probably not give it another thought.

It is also possible that your cylinder has to tight of headspace. Use a stack of feeler gauges to measure between the back of cylinder and recoil shield where the firing pin goes through. Should be a bit over .060

Also make sure that the area under ejector star is absolutely clean. If the star is held back a bit it can cause binding.

It appears to me that the firing pin hole has a burr on it, possibly from the gun being dry fired, and this is what is creating the drag marks on the cartridge heads. The burr can be carefully peened back into place. DO NOT USE A DREMEL FOR THIS.

Probably nothing to do with OP's question, but
is it normal to see that much of the cylinder stop,
raising out of the frame (#3 pic)?

Just checked the headspace and it's within specs, area under ejection star is clean, in my opinion the hand is really not in a position to leave those marks on the shell bottom (but I can't exactly tell). I think Warren Sear is right on the mark. Although not visible, I can feel with my finger the area around the firing pin hole is not flush.

So if I should not polish it smooth, what tool should I use to peen it smooth?

The odd thing, however, is that not all the shells from one and the same manufacturer out of the same box have exactly the same rim-thickness. I cycle all the shells from one box and only about every tenth one doe not clear the burr (or whatever else interferes). Also tried a couple handfull of old winchester silvertips and all worked fine. REALLY STRANGE.....

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QM3

^^^ The burr can be peened down by a 1/4" steel rod with a flat or slightly rounded tip. Wrap the rod with electrical tape and insert it down the barrel, centered over the firing pin hole. Give the rod a few taps with a hammer and check your progress. You definitely do not want to over-do this, and it should not take more than a few taps to fix it.

Don't remove any metal; just push it back in place.

It looks normal to me.

The hand can not contact the case head, especially across the primer. That would have a potential risk of igniting a primer.

Yes the burr shown at the bottom of the firing pin hole is the source of the problem. Once it's removed, the variation in cartridge rim thickness, which is not uncommon, becomes a non-issue.

You mustn't peen it; the burr will just be burred back out by the firing pin all over again. It must be removed by stoning it off flush with the recoil shield.

In the photo it's clearly seen that the staking ring to stake the bushing in place was done off center.

If the firing pin bushing is proud of the recoil shield at the bottom, it's increasing the burr protrusion into the headspacing. As posted above, the bushing can be pushed back in place by tapping it in flush, with a flat tipped rod down the barrel.

And then peened around the bottom edge of the bushing recess with the edge of the same rod held at a slight angle.

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Jim
S&WCA #819

That is absolutely normal.

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Gunsmithing since 1961

WOW ! Now I also clearly see the burr on the enlarged pic as well as the off center bushing. I can remove the burr but it seems to me the the firing pin bushing is not easily moved around. How is the bushing set into the recoil shield? I have only basic gunsmithing tools. Perhaps I should take it to a professional gunsmith? The two I know work mostly on new post millennium guns and I hesitate to give them good old collectibles like this one.

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QM3

You can carefully remove the peened material with a fine stone or file. Be careful to remove only the peened material around the hole.

Hammer nose bushings are pressed into place after being oriented properly in the frame, and then staked in place. Your bushing is not off center, but the staking ring that is designed to keep the bushing securely in place is slightly off center. This issue is very common, where you will see the actual staking ring not perfectly concentric around the outside rim of the bushing cavity. Long term, this staking abnormality should not be a problem. The important thing is that the bushing is (and stays) properly oriented, (there is a cutaway at the back of the bushing that is at 12 o'clock) and it is (and stays) flush with the breechface.

S&W uses apecial tools to install the Hammer nose bushings, and most gunsmith's do not have the proper set of required tools, or the training on how to use them.

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Ret. LE, FA Instr, S&W Armorer

Really no need to take to a gunsmith!

First stone off the burr, that'll likely fix the problem. But also check the bushing to confirm if it's flush with the recoil shield by using a straight like a steel ruler. If not flush, first fire the gun with the thick base cartridges to see if the problem is resolved. You likely will not need to do anything more even if the bushing is not perfectly flush.

Good luck and let us know how it turns out,

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Jim
S&WCA #819

Thanks a lot everyone! You guys are great. With your help I think I fixed the problem. I carefully polished the burr away so the area around the hammer nose bushing is perfectly flush with the recoil shield. Now even the thicker rimmed shells pass without a scratch.

@armorer951: If I understood correctly, I can leave the off center staking ring as is, right? That's just a cosmetic issue but will not interfere with the operation of the gun.

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QM3

Blackpowder.....Yes sir, I believe so. Staking rings that are a bit "off-center" are common. The critical thing is that the bushing stays put.

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Ret. LE, FA Instr, S&W Armorer