BLOWUP!

[LongWalker]

Well, not exactly. 

Yesterday morning I went to test-shoot a rifle a friend is trying to trade off.  This one is a military rolling block carbine in 44-40, built on the No. 1 action, with markings from Mexico.  (These were also used as guard guns in some prisons here in the US, but guard guns aren't as cool as veteranos of the Mexican Revolution.)

The rifle checked out OK.  Chamber and bore looked good, some wear from cleaning from the muzzle.  Action locked up.  Ammo was an Ideal 42798 on top of a caseful of FFg.  Brass was many-times fired, and full-length sized to chamber in the various 44-40s my friend shoots.

On the 4th shot, I got treated to a faceful of burning powder residue and smoke, coming out of the now-open action.  The case ruptured and separated at the neck (we found the case neck in the chamber, didn't find the case head).  After some research, we think the back-half of the case slammed back on the firing pin, knocking the hammer back and allowing the action to open.  This failure mode has been discussed some over the years, but I've only seen something similar once before (that time, a case head separation in a roller in 43 Reformado). 

No injuries, thanks to eye protection and a covid facemask.  I suspect the case separation wouldn't have been as much of a problem in a Colt or copy, or a lever-action rifle: both do a better job of managing escaping gas. 

I suppose there are two lessons here, in addition to the reminder to always wear eye protection. 

First, particularly when full-length sizing brass, keep a close eye out for incipient cracks/case head separations.  The repeated use of this batch of brass, full-length sizing each time, had weakened it to the point it was ready to let go. 

Second, if you're going to shoot an old rolling block, it might be a good idea to check the amount of play on the pins, and possibly replacing them with oversized pins if needed.  When I disassembled the action and put the pins in their respective hammer and block, I was able to feel some "wobble". 

[AntiqueSledMan]

Hello LongWalker,

I would guess the case separation might have been influenced because or the breech opening.
I've had it happen with my Rossi 92 in .357.
Simply ejected a short case then had to remove the separated piece.
One cant over stress the need to examine brass, mine came in a box of used reloading equip.

AntiqueSledMan.

[ndnchf]

That is scary, but glad to hear you are ok. Not really a blow up, more of inadvertent breech opening.

I've been playing with rollers for nearly 40 years, but never had this happen. But I've read about it happening a couple times.  One thing to be aware of is the hammer spring strength. It is heavy, especially in military rollers. If it weakens over time or has been weakened in an attempt to lighten the trigger pull, it will be more susceptible to this kind of mishap. It is something to check on this rifle. 

Steve

[Tommy tornado]

I could see the brass being an issue.  .44-40 brass is very thin.  I find them with tiny cracks or splits often.  My current procedure with revolver brass is to wet tumble it now to give it a good cleaning.  It helps big time with finding cases going bad.  As mentioned glad to hear that no injury occurred.

[LongWalker]

Sorry for the delay getting back to this, amateur forensics takes a while.  I had to procure some new 44-40 brass to trade for the batch of brass that separated, and borrow the carbine for a week. 

As I understand it--and please check me on this, Ndnchf--the theory is that the case separates, the rear portion of the case moves back in the chamber wiith the primer striking the tip of the firing pin hard enough to drive it back and push the hammer open.  When the hammer is down, action is locked; when the hammer is driven back like this, the action is able to open.  No case separation, no action opening.  This is consistent with most of the blowups I've seen over the years.  I've seen actions locked but action rings split/barrels burst/etc. 

First, some ancient history.  When the .43 Reformado let go on me, the action opened AND the action ring split.  I contacted the best rolling block guy I knew at the time, the late Dave Higginbotham, to try to figure out what happened.  (Dave later founded the Lone Star Rifle Co, maker of the finest rolling block rifles made in modern times.)

Dave ran through a series of questions:
1) Remington or other manufacturer? Remington
2) #1 or #5 action?  #1
3) Extractor type: sliding or rotary?  Sliding
4) Did I have the correct ammunition?  Chamber cast matched a .43 Reformado, ammo was original Rem-UMC 43 Reformado
5) Lead bullet or "brass" (brass or gilding metal jacket)?  Brass
6) Chamber/bore condition? Muzzle wear from cleaning, otherwise no rust
7) Action condition? Felt tight in the hand.  Trigger pull estimated at 13#, hammer draw to cock was heavier, no signs it had been messed with.
8.) Any remaining ammo? 8-10 rounds

At this point Dave asked me to section a couple of cases.  First one was sectioned at the case neck with a graver, to release the bullet without heat.  One the neck was sectioned longitudinally, the bullet should have been released--except it wasn't, the bullet and case neck were cemented together with corrosion.  The second case was sectioned full-length, showing a normal balloon case, much thinner throughout than I was used to seeing when I sectioned modern cases, with some corrosion.

After all that, his thoughts were that maybe the case neck--cemented to the bullet--went downrange with the bullet.  When the case separated at the neck, it slammed back on the firing pin (larger in the #1 than the #5), and drove the hammer back, allowing the action to open.  At the same time, the case split and the escaping gas hit the "weak" point in the chamber (the sliding extractor) and once started, split the barrel and action. 

That brings us to the 44-40 a couple weeks ago.  I compared the action to the 43 Spanish infantry rifle I have on hand.  The carbine's trigger spring had been replaced, resulting in a trigger pull of about 8#.  The action shows no other signs of modification.  The hammer spring was consistent with the hammer spring in my 43 Spanish (I'm not sure how to quantify the weight--pounds necessary to get a measured amount of deflection?).  As noted earlier, a bit of "play" could be felt in the action pins when not loaded by the springs. 

Headspace is good, chamber cast shows the chamber to what we would probably think of as "oversize" but that's not unusual for guns of the era.  (The cast would "chamber" in the original 44-40 Colt a friend shoots.)  The chamber shows no sign of damage (gas cutting, etc) from the case separation. 

As mentioned, I swapped new brass for the fired brass and remaining loaded rounds.  The loaded rounds showed the cases had been sized full-length.  Bullet was the standard Lyman/Ideal 42798.  Charge was slightly-compressed BP.  I pulled the bullets from several rounds, and sectioned the fired and unfired cases.  All showed signs of an incipient case head separation.  One of the fired rounds and one of the loaded rounds had cracked necks.  On inquiry, I learned the brass had not been annealed, and that the cases had been loaded "7-8 times". 

For now, I'm going with the original idea: the case head separated due to embrittlement caused by repeated sizing, driving the firing pin and causing the action to open. 

Yesterday morning, we put 20 rounds (loaded in the new brass!) through the carbine, w/o problems.  My friend has decided to keep it, he's going to fit oversized action pins, and use it with a dedicated lot of brass.  I'm trying to convince him to try neck-sizing the brass to limit the amount the brass is worked. 

[ndnchf]

I'm certainly no expert. But I do agree with you about the brass. That in conjunction with the worn pivot pins could contribute to case separations.

On the case head that seperated and blew open the action. Was the firing pin dimple on the primer deformed or otherwise not right?  I ask because this thought crossed my mind. When the firing pin hits the primer it creates a deep dimple. If the case separates and the head is driven back, the protruding firing pin tip would go back into that deep dimple, so it doesn't seem like enough force could be transferred to the firing pin to drive it back hard enough to kick the hammer back. Do you follow me here?

If the firing pin was driven back very hard, the tip of the firing pin retaining screw is all that would keep it from exiting the rear of the block. At a minimum, the tip of that screw would be mashed, dented or otherwise damaged by the blow. Did you remove this screw and inspect it and the firing pin? If so, and it looked normal, it seems unlikely the firing kicked back and pushed the hammer back.

Does the firing pin have a retracting spring? Some guns do. Some don't. Remington found that the springs could rust, jamming the firing pin in either position. If it jammed protruded, a cartridge could fire when the breech was slammed closed, but not locked by the hammer. The spring was eliminated on most later models unless a foreign government order insisted on it.

So what does that leave? I'm not sure. The only other thing I can think of at the moment is recoil. If the hammer spring was loose, weakened or otherwise compromised, recoil and inertia could possibly cause the hammer to move rearward and unlock the breech.

So these are just my speculations and food for thought 

[LongWalker]

Unfortunately, I wasn't able to recover either of the case heads in question.  The Reformado case head was stuck in my glasses, but those disappeared in the ER and I was too dumb to think of them til later.  We were unable to find the 44-40 case head. 

I don't recall discussing the firing pin retaining screw with Dave, and have nothing in my notes about it.  I went over this afternoon and checked the screw on the 44-40; the owner is going to replace the screw and firing pin.  The screw tip was "smeared" as if hit a glancing blow by a hammer.  The shoulder on the firing pin is peened from the retaining screw.   I should have thought to check that, thanks for the reminder.  If he'll let me, I'll get pics of the pin and screw. 

Whilst driving around this afternoon, I got to wondering how much of a contributory factor tolerance stackup might be.  If the original tolerance on the partds, plus slop in the pins and wear on parts, could have made such an incident more likely.  This is something seen once in a while in old lever guns, where the hammer sometimes follows the bolt but if you cock the hammer slowly with your thumb it sets solid. 

Hmmm.  I've got plans to part out that 43 Spanish so it might make a good test subject.  I wonder if I could make a (possibly weighted) rod, drop it down the barrel with the action in a "fired" position, and cause the hammer to move. 

Anyone have any idea of the case head thrust of a 44-40 BP load?

[ndnchf]

Good point about the stacking up of tolerances. That is something easily overlooked but is very important. I don't know what the case head thrust of a 44-40 BP load would be. But there is a great web site devoted to the .44-40 that has a lot of the late John Kort's research and articles on it, as well as other related information from Bryan Austin. It might be worth a look.

https://sites.google.com/view/44winchester/44-40-Winchester?authuser=0

[greyhawk]

been pondering on this -- my son has two rollers (an original 22 and a repro 45/70)

trying to figure how a busted case could put enough pressure via the firing pin to open one of these

anything is possible I spose but thats not working for me

- however his (son's) repro broke a firing pin one time and a broken firing pin can "grow" if the crack is at an angle and one of the bits rotates in mid flight - also a broken pin can work for a long time if the bits stay (relatively) where they sposed to be (seen that on a winc 92 one time)

This whole thing is a darn good argument against resizing anything that will still go back in the hole it came out of

So yeah check his firing pin if not already done that......... 

[LongWalker]

Ndnchf- thanks for the link to the info from Kort.  I'd seen that before and was searching for it--the site has the best explanation/illustrations I've seen of case movement and primer movement.  I got to thinking about this last night in relation to the idea that case head thrust might be a problem, but that didn't make sense . . . .

The firing pin hits the primer, driving the case forward and starting the ignition cycle.  The primer is moved back out of the pocket by the force of the primer blast, then stopped by the breech face (the amount of movement is limited to the amount of headspace).  The powder ignites.  (This all takes about 1 millisecond.)  During this time, the case is held in place by friction, and the bullet is starting to move forward.  Eventually (about 3-4 milliseconds into the process) the case moves back, re-seating the primer.  This movement of the primer is why a revolver will usually lock up when a primed case (not loaded round) is fired: the primer moves back but is not re-seated.

There was at least one design from around 1900 and a few more during the '20s-'30s that used the primer thrust to unlock bolt-action rifles.  Garand and several others came up with designs for semi-automatics that used this primer thrust to actuate semi-automatic firearms.  In theory, I could see the primer thrust knocking the pin back and moving the hammer, but under normal circumstances I don't think it would be enough to overcome the inertia of the weight of the hammer.  I think in event of a catastrophic case failure, the primer thrust is increased by the force of the gas seeking to escape, and that under the right combination of circumstances, this is enough to move the hammer back enough that the breechblock is opened.  Wish we could have found the case head to see what it showed. 

Maybe.  I cleaned and lubed the action on my .43 Spanish rolling block, paying particular attention to making sure the firing pin movement was unimpeded.  Then I closed the action and set the rifle at full-cock, and dropped a ~12" piece of 3/8" brass rod down the bore while holding the barrel vertical.  The hammer "bounced".  How much, and if it was enough to unlock the action, I don't know--it was enough to make me wonder. . . .  I don't know why the action on the 44-40 carbine opened, but I think the case failure played a major role.  No case failure, no problem: so if I ever get a 44-40, I'll probably stick with neck-sizing the cases and watching the brass like a hawk.

With a rolling block, we've got a couple potential problems that center around the firing pin: 

If the firing pin is stuck in the forward position (rust, fouling, peened metal), you can have a situation where closing the breech causes it to fire out of battery.  I've done some experiments with this using a deliberately jammed firing pin and primed brass.  It looked to me like if it happened with a loaded cartridge it would seriously mess up the thumb that was closing the breech block. 

If firing pin protrusion is too much, you can get pierced primers.  A pierced primer results in gas blowing back into the shooter's face, which is disturbing at a minimum.  From what I saw (I wasn't the shooter that time!) it looked like the blast out of the touchhole on a flintlock.  I don't like to think what it would be like without safety glasses.

Then there are the headspace issues.  Early chambers were often what we would think of as "oversize", to allow for fouling, ease of chambering, lousy ammo, etc.  Rimmed cases/chambers are usually pretty good on headspace, but in the rimless smokeless cartridges I've seen (7mm, 8mm Lebel) it looked like headspace was established by the bullet jamming into the throat of the chamber rather than the shoulder of the cartridge and chamber.

We complain and worry about this stuff now, but the designers/users of first-generation cartridge guns had other priorities, and didn't have the same knowledge we have today.  For instance, I'm not sure they realized the issue of gas handling in event of a pierced primer.  Rolling blocks do little if anything to manage gas in even of a pierced primer or ruptured case.  But back then they were dealing with different tech to make cartridge cases, still figuring out much of it.   As a kid, I knew a guy who lost an eye in WWI due to a pierced primer in a Springfield, something they later addressed with the "Hatcher hole", and eventually, with a hole through the extractor.

Then there is past wear and neglect..  A guy did a great writeup on re-building a rolling block here: http://www.bpcr.net/forum/viewtopic.php?t=3515

[ndnchf]

Did you mean to say "half cock" in this statement?:

"....Then I closed the action and set the rifle at full-cock, and dropped a ~12" piece of 3/8" brass rod down the bore while holding the barrel vertical.  The hammer "bounced".  How much, and if it was enough to unlock the action, I don't know--it was enough to make me wonder. . . ."

At full cock, the hammer nose would be 3/4" away from the end of the firing pin and the breech unlocked. I checked 3 of my military #1s at the half cock position. The hammer nose is just off the end of the firing pin.  I can see how a strong rearward blow from the firing pin could make the hammer bounce from the half cock position. 

Is there a chance that the mainspring of that rifle was swapped for a lighter mainspring? Or lightened in some way?  That could make it more susceptible to hammer bounce and with a case separation, more likely to kick back and open.  It would be interesting to measure the pull weight of the hammer as-is, then swap in another original military mainspring and measure the pull weight again to see if there is a difference.

Steve

[LongWalker]

ARGH!!!!!  Proving once again I'm an idiot, I wrote "full cock" when I meant to say "hammer down", as if the rifle was just fired.  I was trying to see if, and how much, the hammer could be moved by an impact on the firing pin.  I haven't had a chance yet to try this with the 44-40 carbine. 

The mainspring on the 43 Spanish is a replacement purchased from Bill Wescombe, maybe 25-30 years ago.  I'm pretty sure it is a standard military spring.