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BLOWUP!

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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

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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. 

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