Author Topic: "73 Uberti Blow Up  (Read 5863 times)

Offline PJ Hardtack

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"73 Uberti Blow Up
« on: August 24, 2018, 06:42:56 pm »
At a recent CAS event, a friend suffered a catastrophic failure with his .45 '73 carbine. A round detonated, blowing the side plate almost off the rifle, the firing pin hitting him in the head. The linkage was destroyed.

He suffered a broken cheek, broken nose, his hard plastic safety glasses saving his eye. Had he not been wearing them, it is likely the pin would have penetrated his eye socket to his brain. The pin did carry on, narrowly missing my wife.

There is no way he could have put enough BP into a .45 Colt case to cause a problem. We figure that he put BP into his Dillon measure without fully draining the Tite Group first, the last few charges needing manual encouragement to drop. Nothing else makes sense.

He was taken to emerg, but returned within the hour to  soot the final stage of the match. That was pretty heroic of him. He figured that if he didn't, it would be a while before he got back up on the horse again.

This is the fourth accident I have seen on a CAS range, two of the others being Henry rifles where the user dropped the mag follower on loaded rds. In both cases, three rds detonated which did bad things to the mag tube. One shooter suffered brass fragments to his wrist.

The other was the case failure of a Dominion 44-40 balloon head case full of BP. In this case, the shooter had his glasses up on his hat, and the RO failed to notice. He got a face full of gas, but suffered no eye damage.

This sparked a discussion at our club re: the wearing of eye and eye protection. Believe it or not, in this day and age, we still have people that don't think they need eye and ear protection, not even for their kids. This is contrary to club policy and posted rules, but not strictly enforced.

Now it will be.
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Online Abilene

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Re: "73 Uberti Blow Up
« Reply #1 on: August 24, 2018, 09:32:48 pm »
Yikes, that's pretty scary!  Sure glad he wasn't hurt worse.  Do you happen to know how old the '73 was?  In particular, if it was one of the older ones with only a small pin holding the firing pin extension to the bolt.

Offline Coffinmaker

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Re: "73 Uberti Blow Up
« Reply #2 on: August 25, 2018, 07:50:55 am »

Some years back, Uberti started changing the design of the Breach Block (Bolt) and Firing Pin Extension Rod.  These changes were the result of several Out Of Battery detonations in Uberti 1873 Replicas.  The initial cause was, at the time there was a common practice of taking the Trigger Block Safety out of the rifle so the Speedy folks could eliminate something that might slow them down. 

At that time, the Extension Rod was retained by a tiny little soft pin.  In the case of an OOB event, the little pin would sheer and the firing pin extension tried to exit the rifle.  Usually hanging up on the Hammer.  Uberti reacted by increasing the size of the cross pin.  Someone still sheered the larger pin so Uberti went to the current design, with a slot cut in the side of the Rod and corresponding retaining plate secured by the actual Link Pivot Pin.  Bullet proof.  Ummmmm ...... not quite.  Recently, I saw the result of an OOB event that sheered the remaining steel tab from the front of the extension rod and spit the rod out of the action.  I was amazed.  Still am.

Nothing we build that is mechanical is FOOL proof.  Nothing we make is IDIOT proof.  Someone will always get around built in safety and manage to have an issue.  Or, deliberately eliminate the built in SAFETY.  Humans do that.  The thing to remember, in playing our super fun GAME, we play with REAL guns.  We shoot REAL ammunition.  We reload with REAL EXPLOSIVES.  BE CAREFUL OUT THERE!!

Offline Scattered Thumbs

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Re: "73 Uberti Blow Up
« Reply #3 on: August 25, 2018, 09:26:08 am »
I'm not getting it. Are these real blowouts. Or shots out of batery?

Offline Johnny McCrae

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Re: "73 Uberti Blow Up
« Reply #4 on: August 25, 2018, 10:43:59 am »
Thank you for posting this PJ

Quote
This sparked a discussion at our club re: the wearing of eye and eye protection

Quote
We shoot REAL ammunition.  We reload with REAL EXPLOSIVES.  BE CAREFUL OUT THERE!!

I was thinking about this post while doing some reloading this morning and then realized I did not have my safety glasses on. This post was a great reminder for me to think about what I'm doing.
« Last Edit: August 25, 2018, 10:46:21 am by Johnny McCrae »
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Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #5 on: August 25, 2018, 12:08:32 pm »
The '73 in question is several years old. I'm not sure of what generation. The OOB question is a possibility - IF a BP load is strong enough to cause the problem.

Is it?
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Re: "73 Uberti Blow Up
« Reply #6 on: August 25, 2018, 12:51:39 pm »
The '73 in question is several years old. I'm not sure of what generation. The OOB question is a possibility - IF a BP load is strong enough to cause the problem.

Is it?

Any load with an OOB discharge can cause problems.  I've heard of bent levers.  But I have not heard of destroyed links and blown off side plates.  To me that sounds more like the loading error possibility you mentioned.  Hope he pulls the bullets of the rest of his ammo from that batch.

Offline Coffinmaker

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Re: "73 Uberti Blow Up
« Reply #7 on: August 25, 2018, 01:31:06 pm »

I think (That'll take a whole bottle of aspirin to fix), unless I could examine the rifle AND talk to the victim, the best any of could venture would be a WAG (Military acronym for Wild Ass Guess).  In the event of an OOB, the cartridge becomes a Grenade.  Nasty little bugger too.  However ....

Too blow the side plates would take a nasty detonation back in the action.  Based solely on the description, I would be more inclined (not on level) to postulate (didn't think I knew big words didja) the Ladle Tab let go and a round got back into the clockworks and detonated back in the receiver.  A full case of BP back in there could cause all sorts of havoc.  An OOB only has two ways for the blast to go.  UP and DOWN thru the Carrier Block Mortice.

However:  The Breach Block sheering the Extension Rod Retainer complicates the whole deal.  In the event is is an OOB, If the Breach Block (Bolt) recoiled hard enough to sheer the Extension Rod and Spit it out, It could easily bend/fracture the Links which could bow out against the Side Plates which are retained by a single screw and a couple of shallow Dovetails.

Either way, using your face to stop a charging Extension Rod is not something I would necessarily recommend.  Hurts.  Can hurt really bad.  Much rather it stay in the Rifle.  In any event .... Murphy has jumped up and clobbered someone real hard.  When it comes to mechanical devices, Murphy's Law is Supreme.  If it can go wrong, It Will.  At the worst possible time.  I am however, quite glad it wasn't me whom Murphy clobbered (Knocks firmly on Wood).

I'll now refresh my coffee while this little ditty posts.  Some slow it is.

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #8 on: August 25, 2018, 01:56:27 pm »
Thanks for the input, gentlemen.

I have passed on the comments to other witnesses and they will likely chime in on the OOB theory which seems to be valid.

It isn't just CAS where this sort of thing happens. I know of a case where a 9mm Colt Commander blew the grips and mag plate due to an overcharge of Bulls Eye. I found the gold Colt grip medallion on the ground during the investigation. His hand was shot full of wood fragments.

Years ago, a friend had the barrel of a cheap Italian ML blow where the stock tenon was inletted on the bottom of the barrel. His hand looked like he had held onto a grenade. He said he had not over loaded the gun.

Another friend recently had his .260 Rem blow up at the Cdn Nat. Sil. Champs in Saskatchabush. The rifle was destroyed and his left hand/arm badly damaged. He is expected to make a good recovery.

It is suspected that it was a low powder detonation and I've heard that his grandson might have been involved in the loading process.

Compared to a lot of injuries incurred in other sports, overall, we are doing pretty well.

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Offline treebeard

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Re: "73 Uberti Blow Up
« Reply #9 on: August 25, 2018, 02:41:00 pm »
Did the original 1873's have these problems with the firing pin coming back to hit the shooter? A lot of the originals are being shot a lot
and i have not heard that it is a problem. I suspect the originals were better built that the repro"s. this thread kind of makes me nervous about my Uberti 1873's. my max charge is 8.0gr of Unique which i choose out of Loaddata.com.

Offline Coffinmaker

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Re: "73 Uberti Blow Up
« Reply #10 on: August 25, 2018, 04:54:16 pm »

Hi Treebeard  :D  And PJ.

Some more stuff.  PJ, your up first.  There is no such thing as a low powder or low power detonation.  Physics.  Physics jumps up again.  You see, there are only so many Jules of energy stored in a given amount of propellant or explosive.  X number of Jules stored results in just X number of Jules released.  A low powder detonation just produces a Piffitt.  Or a whoomp.  No Boomba.  Nada.  Low powder detonations are an old wives tale.  It was not a "Low Powder Detonation."  The old wives tale started with people blowing up Single Action handguns.  The actual culprit was/is when a sloppy reload included TWO bullets in the same case.  The two bullets act as a bore obstruction and confine the gun gas in one tiny space.  Boomba.  No obstruction, no Boomba.  Simple (physics)

Treebeard it's your turn now.  NO.  Original '73s don't suffer this problem.  The design of an original '73 ignition system is completely different.  A Uberti has 4 pieces.  Breach Block (bolt), Firing Pin, Return Spring and Extension Rod.  They all flop around together.  Or apart if you screw up.  An original '73 has just two parts.  The Breach Block and the Firing Pin.  The firing pin and extension are one loooooong piece.  The firing pin is retracted by the links and is retained in the breach block by a rocker tab that doesn't break.  Neither Uberti nor Miroku copied the original design.  Stupid.  If your '73 was manufactured in the last 5 or so years, it should be nearly bullet proof although I did see one of the new design extension rods that failed.  It's simple.  Don't have an OOB detonation.  It won't be fun  :o

Here is the important part.  When the links are in correct parallel, the action is "locked" and the bolt is held in place by the links sitting in big lugs in the receiver and the back of the breach block.  Nothing moves.  All three pivots are aligned.  In an OOB event, the links are NOT aligned and are able to collapse.  Very very very RAPIDLY.  Fecal Matter Propagates.  The Trigger Block Safety prevents the hammer from starting the ignition sequence until the links are parallel.  Unless something or someone stupid, screws with it.  Kapish???  Oh, once the links start to collapse, the bolt accelerates to the rear real fast (Rocket Sled Time) and then comes to a stop.  Instantaneous Deceleration.  Then in accordance with physics, the Extension Rod shears the pin and continues to the rear, where one tries to stop it with one's face.  That hurts.  A LOT!  Don't have an OOB Detonation.

I'll now go get another cup of Java while this little dissertation posts. 

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #11 on: August 25, 2018, 05:23:47 pm »
A lot of people more knowledgeable than me would not agree with your opinion on this matter. I've read several times about 'detonations' occurring in revolvers loads using the classic 2.7 grs of Bulls Eye under a 148 gr WC.

Even in the event of a double charge, all you are going to get is one good "Bang!" and the cylinder will not come apart in a quality S&W .38/.357. Factory proof loads far exceed that, I believe. I don't think anyone is going to load a 2nd WC on top of the first.

I do know of a case where THREE rds were fired in a revolver before the shooter noticed the bullets were not leaving the barrel. He was shooting light loads and there was other firing going on around him. Net result was a bulged barrel.


Hi Treebeard  :D  And PJ.

Some more stuff.  PJ, your up first.  There is no such thing as a low powder or low power detonation.  Physics.  Physics jumps up again.  You see, there are only so many Jules of energy stored in a given amount of propellant or explosive.  X number of Jules stored results in just X number of Jules released.  A low powder detonation just produces a Piffitt.  Or a whoomp.  No Boomba.  Nada.  Low powder detonations are an old wives tale.  It was not a "Low Powder Detonation."  The old wives tale started with people blowing up Single Action handguns.  The actual culprit was/is when a sloppy reload included TWO bullets in the same case.  The two bullets act as a bore obstruction and confine the gun gas in one tiny space.  Boomba.  No obstruction, no Boomba.  Simple (physics)
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Offline Coffinmaker

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Re: "73 Uberti Blow Up
« Reply #12 on: August 25, 2018, 06:56:42 pm »

Not to be terribly disagreeable (wanna bet??) but WE are not discussing my opinion.  We are discussing science and physics.  There are numerable people who when faced with science as opposed to "Ralph's" so called experience will side with Ralph, even when he doesn't have a clue.  As a point ... ALL of the powder and ammunition manufacturers, and the military, have tried for years to get a low powder detonation that created damage or "blew up a cylinder."  Nada.  Nix.  Nine.  Has NEVER happened.  They have tried with the best and finest scientific equipment.  Not until a form of bore obstruction was introduced did bad things happen.  And YES, people have admitted to loading more than one bullet.  A fouled seating die grabs a bullet and hangs on to it.  Ralph the reloader places a bullet in the next case up for bids and the die rams TWO.  Several folks have been fortunate enough to catch this before a cylinder came apart.  Those Nabobs who claim 2.7Gr Bulls Eye under a single 148Gr WC simply don't know what they are talking about.  I have personally talked with military Ballistics guys as well as a Ballistics guy for Hodgdon who have confirmed NO ONE has ever created a Low Powder detonation without some form of obstruction.

When you talk about a double charge, a double charge of what??  There are powders out there that in a double charge, in any caliber, will destroy a cylinder.  Kindly remember, with a revolver, you do have a pressure release at the Barrel/Cylinder gap.  It can make a difference where the obstruction occurs.  Believe what you like.  Unless you can duplicate the effect in a pressure barrel, it doesn't exist.  For the most part, someone whom has done something wrong, doesn't actually know what they did wrong.  Just a REALLY BIG BANG and the gun came apart.  Unless your working with equipment that can measure what is happening in a pressure vessel, you don't even have a good guess.  It all happens in nano seconds.  Unless the individual talking and making claims is working in a Ballistics Lab, they really don't know what they are talking.  Just taking a WAG.

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #13 on: August 25, 2018, 08:47:02 pm »
Considering the length of a .38 WC bullet and the space it takes up in a .38 Spl. case, I think it  highly unlikely a reloader would seat one atop of another without noticing something was amiss, regardless of the type of press - single stage or progressive. A case without a bullet would make itself known PDQ.

I have been present only once when a cylinder came apart. It was a Ruger Super Blackhawk .44 magnum in the hands of a newbie CAS shooter. He assured us that his loads did not exceed 1000 fps. He had one very loud detonation on one stage and on the next stage, he blew his cylinder. God knows what kind of a load it took to do that, but it was almost certainly a double charge.

The suspected double charge I mentioned earlier was a double charge of Bulls Eye in a 9mm under a 124 gr FMJ bullet. The little Colt Commander did not like it.

It is also possible that he had not applied enough crimp and in chambering a normally charged rd, the bullet was deep seated. That would raise pressure.
« Last Edit: August 26, 2018, 02:55:23 pm by PJ Hardtack »
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Offline Coffinmaker

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Re: "73 Uberti Blow Up
« Reply #14 on: August 26, 2018, 03:39:34 pm »

Yessir PJ. 

Mistakes abound.  We are, after all suppose to be human.  An error I was present for, I gave a new guy my load for 45 Colt, 200Gr Bullet and sent him on his merry way.  Jest before the next match, he went to a vacant berm to test his newly loaded ammo.  The report was earth shaking.  To quote Marvin the Martian (one of my favorite characters) it was an "Earth Shaking KABOOMB."  I immediately started walking over, but here he came, white faced, eyes big like an owl, hands shaking.  He wanted to know what I was doing, giving him a load like that.  I told him it wasn't MY load that did that, what did HE do.  He didn't do anything.  He had one of his bestest buds reload his ammo for the match.  Never mind, the cylinder was jammed against the top strap (Ruger Vaquero), I took three rounds home.  Turned out what was in the case was the equivalent of a DOUBLE charge of Tightgroup.  A double charge as listed in the book as maximum for a .44 MAGNUM.  the gun went back to Ruger.  Ruger said the Guns was just fine.  They even replaced the Cylinder (free) and included a note with the repaired gun "Do Not Do That Again."  Seems his best bud the "great" loader had left his press set for a different powder in a different caliber.  Nearly a disaster.  As an aside, I will no longer share my load data with anyone.  I also WILL NOT reload for anyone but myself.

I do know of several folks whom have managed to stuff two 250Gr bullets in a 45 Colt case.  One guy caught the error, one guy blew the top strap and top of the cylinder completely off a brand new Uberti SA.  The guy whom blew up the gun, found another round in his batch, exactly the same way.  Was really curious how he got two different empty (no bullet) cases in his batch.  Never thought to investigate.  Normally, these type errors occur with Progressive Presses and the operatior is trying to load at crazy speeds.  Trying to get 700 rounds out of a Dillon 650 in under an hour.  Atz pretty silly but guys do it all the time.

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #15 on: August 26, 2018, 08:32:51 pm »
I've got two Dillon 550B presses and an ancient RCBS Jr. on which I reload my BPCR calibres.

I make it a habit to stop reloading and take a break after every 100 rds. More than that and my attention starts to wander. I also stop immediately if my sequence is interrupted by the phone or my wife.

Then I clear the cycle and start anew. All learned by experience .....
"I won't be wronged, I won't be insulted, I won't be laid a hand on.
I don't do these things to others and I require the same from them."  John Wayne

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #16 on: August 27, 2018, 06:17:11 pm »
I just learned that the rifle in question was of the latest generation.

Also, it was the first rd fired in the stage which precludes the likelihood of a bore obstruction.

I'm not getting it. Are these real blowouts. Or shots out of batery?
"I won't be wronged, I won't be insulted, I won't be laid a hand on.
I don't do these things to others and I require the same from them."  John Wayne

Offline Slamfire

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Re: "73 Uberti Blow Up
« Reply #17 on: August 27, 2018, 10:19:07 pm »
 Man ! I hate squeeze & duck !!! I just got thru loading 100 rds. for my 40/60 " Chappie " ,, after reading this ,I'm going to go weigh my loads,, 50 are loaded w/ TB and 50 w/ H-4198 , for testing 200-300 yds. OOh ! ,loaded 50 one nite and 50 the next nite ,,cleaned my LEE PPM between powders ,, " still " ,,??? .

  Mr. Coffin, I ( again ) thank you  ( and others ) for your knowledge and in put ,, it helps to remind us ,,, like PJ said ,,stop if interrupted ,, one of the reasons I load at night  w/o a phone ( over cautious ,,  ??) .

 coffee's ready ,, Hootmix .

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #18 on: August 28, 2018, 10:48:44 am »
Just to add to your nightmares .....

A friend with a "Star" reloader (the pioneer of progressive presses) was on "automatic pilot" while reloading .45 CP rds. He was watching an action movie at the same time.

He noticed that the powder hopper was empty and had no idea when that happened. He ended up pulling the bullets of well over 100 rds before he started finding powder. That's a lot of whacks with a kinetic bullet puller!

How's that for being switched off?
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Offline wildman1

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Re: "73 Uberti Blow Up
« Reply #19 on: September 10, 2018, 04:52:26 am »
There is a modification for the 73's with the small or large pin retaining the firing pin extension. A set screw can be installed in the bottom of the back of the bolt that will go into a milled slot in the bottom of the firing pin extension. The retaining pin will still shear but the extension will no longer exit the back of the rifle.
wM1
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Offline August

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Re: "73 Uberti Blow Up
« Reply #20 on: September 10, 2018, 06:26:08 am »
It's always good to read about safety issues on a forum.  It keeps us on our toes.

Not yet mentioned in this discussion is the common problem of sticking firing pins on '73 rifles.  A firing pin that is stuck (bound) in the forward position can, and eventually will, set off a round as the gun is levered.  Visualize the firing pin being proud of the bolt face and coming forward onto the round laying in the elevator.  The round could discharge at any point while moving forward, to battery.

This is not a theory, it has happened to me.  The round (a 38/40 180 grain bullet, case filled with Shutzen FFF) went off early in the levering of the gun -- about the time the bullet started entering the chamber.  All but the back 1/4" of the case was turned to shrapnel.  The lever was bent significantly.

The firing pin getting stuck this way was the result of repeated dry firing without a snap-cap in the gun.  The firing pin peened a burr into one of the narrow parts of the channel and that burr locked the firing pin solid in the bolt.  (the mechanism is inertial on Uberti rifles and the only thing stopping the forward movement of the pin on a empty chamber is the shoulders of the narrowed channel in the bolt)  I subsequently learned that this is a common issue from the 'smith who had repaired several '73 rifles that had "blown up" over the years.  He said, in every case, the rifle was owned by a serious shooter who had done a lot of dry firing with it.

He went on to tell me that REGULARLY testing the firing pin for smooth and uninterrupted retraction, back into the bolt, was a standard test that every '73 owner ought perform during every cleaning episode.  I have done so ever since.  Up, until that time, I had never checked the firing pin for binding, I dry fired a lot, and never used snap caps.  Those three things have changed.

I got off without hurting any other shooters and felt very fortunate.  The gun had to be completely rebuilt, but I got a BIG lesson for my money.  Hope this lesson helps keep you safe.
« Last Edit: September 10, 2018, 06:29:50 am by August »

Offline Chance

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Re: "73 Uberti Blow Up
« Reply #21 on: September 10, 2018, 09:03:18 am »


I do know of several folks whom have managed to stuff two 250Gr bullets in a 45 Colt case. 

This statement fascinated me so I thought I would set out to intentionally duplicate it. Using a Lee 0.5cc dipper I put some sand into a .45 Colt case and pressed in two 255 grain bullets (250 grain not available). Picking up the cartridge it was immediately obvious that it was heavier than it should be (OK, the sand would be a shade heavier than powder). It would also have stood proud of the others in a box as the resulting cartridge had an overall length of 1.75". To get those two bullets into that case there would apparently have to be no powder in there at all.

Chance

Offline PJ Hardtack

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Re: "73 Uberti Blow Up
« Reply #22 on: September 10, 2018, 11:16:24 am »
August - thanks for the tip! I'll pass it along.

This theory makes more sense to me than any of the others.
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I don't do these things to others and I require the same from them."  John Wayne

Offline Trailrider

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Re: "73 Uberti Blow Up
« Reply #23 on: September 11, 2018, 12:27:50 pm »
Alright, Ladies & Gents...grab a cup of you favorite beverage, be seated and get comfortable. (There may be a quiz at the end of the lecture period).
First, I will agree that without seeing the rifle in question, analysis of the problem is difficult.  An OOB firing sound possible if not probable.  The original Winchester '73's design was far superior to the current batch of reproductions.  Slam fire due to inadvertent release of the follower on M1860-design Henry Repeating Rifles has definitely happened! My solution is to load with the rifle almost horizontal, and to firmly wrap the fingers of the other hand around the barrel/magazine prior to releasing the follower.

Now, as to "detonations":  By ordnance definitions, a "detonation" is an explosion that produces a shock front in excess of 25,000 ft/sec. There is insufficient chemical energy in small arms smokeless powder to cause a "detonation"!  HOWEVER...in smokeless powder bottleneck cartridges, especially ones that have sharp shoulders and are overbore capacity, reduced loads of slowburning smokeless powder can cause overpressure conditions strong enough to exceed the ultimate tensile strength of the brass cartridge, thus releasing high pressure gas into the action, with bad results! What causes the high pressure with reduced loads of slowburning powder is creation of a shock wave that, if the powder is in a certain configuration in the case, can reflect off the front of the shoulder in the case. When such a shock wave reaches the smoldering or partially burned powder, the pressure increases, which, in turn, increases the burning rate of the power. This increases the pressure, which increases the burning rate exponentially until the cartridge ruptures. This phenomenon has been known by Naval Ordnance engineers since at least the 1960's and probably before.
Moral: DO NOT ATTEMPT TO REDUCE LOADS OF SLOW-BURNING POWDERS BELOW THE RECOMMENDED CHARGES!  If you want reduced loads, go to a faster-burning powder!

Revolver blowups:  There are three potentials for overpressures in revolvers: 1) Double-bulleting due to failure to notice what's happening either by the handloader not paying attention to what he/she is doing; or malfunctioning of a progressive loader. (I have never had the latter happen...because I don't use a progressive press!)
2) Double-charging of a smokeless powder, either through carelessness or malfunctions.  However, experiments have shown that some double charges may not result in destruction of the gun!  Just be careful!
3) A phenomenon of premature shotstart in revolvers, where the bullet moves out of the case, and into the forcing cone where the bullet stops, allowing the pressure to build up until the case ruptures, allowing high pressure gas to do a number on the gun!
Now smokeless powder requires between 5,000-7,000 psi (NOT CUP!) to commence stable burning. If the bullet starts to move before this pressure level has been reached, the pressure will drop until the remaining powder is smoldering, but no extinguished. If the bullet lodges in the forcing cone and stops, so that the barrel-cylinder gap is blocked, the pressures will rise. This will cause the burning rate of the powder to increase, increasing the pressure, etc., exponentially.  Depending on how sloppy the chamber is compared to the cartridge case prior to firing, the increasing pressure will expand the case until it ruptures, releasing hot gases that act like a cutting torch on the steel of the chamber wall. With many .45 LC guns, the oversized chambers allow the cartridge to initially lie against the bottom of the chamber. If the bullet stops in the forcing cone, as outlined above, the case will usually stretch upward until it ruptures at the 3 o'clock and 9 o'clock positions, releasing the flame and cutting the chamber walls. The pressure also causes the top of the cylinder to come off, usually taking the topstrap with it.  Experiments I ran some years ago, measuring pressure-time curves in .45 LC ammo, purposely loaded to allow premature shotstart, without causing destruction, as well as experiments by others, confirm the presents of the pressure spikes and drop off until the bullet hits the forcing cone.
There is a simple way to prevent this phenomenon: Insure that "bullet pull", the force needed to move the bullet out of the case is high enough so the powder gets burning fully enough to move the bullet: Reduce the diameter of the expander plug sufficiently so there is good friction between the case wall and the bullet; AND CRIMP, CRIMP, CRIMP! Roll crimp the case mouth into a crimp groove enough so you can see and feel it, but not so much as to collapse the case or bulge the case wall away from the side of the bullet!
Now, I will entertain questions until the end of the class period. Go ahead! Flame away!  ;)
Ride to the sound of the guns, but watch out for bushwhackers! Godspeed to all in harm's way in the defense of Freedom! God Bless America!

Your obedient servant,
Trailrider,
Bvt. Lt. Col. Commanding,
Southern District
Dept. of the Platte, GAF

Offline Dave T

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Re: "73 Uberti Blow Up
« Reply #24 on: September 11, 2018, 02:41:50 pm »
I have to support everything Coffinmaker and Trailrider have said. While reading this I tried to remember how many "blow ups" I've been present for. It's well over half a dozen in 50+ years of shooting and competition. In every instance I saw or heard about it was eventually determined to be a reloading error. Double charges in progressives that don't auto advance, changing powder type without resetting the measure, and just not paying attention (watching TV while reloading is a classic).

Dave