Case Head Exits Rifle

[Jim Tarleton]

1) But did you fire the primer without a powder charge/bullet -- just empty case?

2) When the case head hit you in the forehead -- but the action was still closed -- did you mean just a piece of the rim?



.

Just the primer. I understood what you wanted me to do and why.

This is the rifle. It is a hoot to shoot, when it doesn't shoot back.

Jim

[Jim Tarleton]

I didn't answer all your questions.

It was the case head that hit me. I will see if I can find it and photograph it. It is a typical case head separation, about 1/4 inch long. The entire case head. It is not deformed in any way.

I have no idea how it came out, but I have a nice little half moon scar to show for it.

Jim

[Jim Tarleton]

I didn't see you reload data. I shoot a very old RRB (1882) and reload all my ammo.

The load was 43 grs 4895 and a 130 gr Spitzer with a Winchester LR primer. All cases trimmed to length and full length resized.

Jim

[MEHavey]

Something's got to be failing in the lockup.

This will result in the case's forward section/shoulder being anchored by pressure, and the case stretching as it tries to stay engaged with the breechblock face as it opens up. Bang! Instant failure just ahead of the web and the head kicks out-and-up off the inclined breech surface. The hammer (which is still released while you hold the trigger back) then moves forward under its mainspring and closes the breechblock up again faster than the eye can catch it.

There is no other way that much of a cartridge head can physically get out and the action appear still appear closed afterward.

And the only way that the breech can open with the hammer forward is for the circular breech locking cam under the breechblock in the picture/video here to be broken/off (hardly likely), on the edge of misalignment (or at a strange engagement angle), or the hammer/breech pins are somehow failing to keep things in alignment. The cam/engagement mechanism/surfaces are massive, though, and theoretical can't fail.

Have you pulled it apart to look at the pins/cam/block engagement angles after these instances?

http://upload.wikimedia.org/wikipedi...29/M1867_1.jpg

Field Strip a Remington Rolling Block Rifle - Video

[slamfire1]

The cam/engagement mechanism/surfaces are massive, though, and theoretical can't fail.

Somebody would need to model this action and determine what force it takes to force the breech block to override the hammer. Because that is what is happening.

The action is opening. The breech block is forcing the cammed surface of the hammer to move. I suspect there is enough spring in the action for these to occur. The breech block forces that hammer cam back, then the breech block opens, case head comes out, and then the hammer spring pushes the hammer and breech block closed.

You can't see it because it is happening too fast for your perception.

Under load, with a high speed camera, you would see things moving. Actions are not static, under load they stretch and move dynamically.

[Jim Tarleton]

Disassembly shows no sign of failure or wear. The pins are very tight, lockup appears very secure, and I have found nothing to indicate a failure of any type except for that little scar on my forehead. I have no problems with new cases, but once fired cases are a disaster. They all fail with few exceptions.

I was checking my notes when I was retrieving the load data, and in a 10-shot string of reloads, seven cases failed. Only one has ever caused a problem. None of the case head failures has caused gas to hit me in the face. Most of the case failures are not complete separations.

I "built" the rifle myself, and I did shorten (and re-taper) the barrel by one thread to eliminate any chance of excessive headspace (squared up the end of the barrel and finish reamed the chamber myself). When I finish reamed the chamber, I made one turn of the reamer at a time until the breach block would close on a GO. It has minimal headspace. When the block is in battery, it is actually in physical contact with the barrel face and the case head.

I know something occurred that was different from any other shot. A 1/4" long case head cannot pass between two surfaces less than 0.001" apart. But...for the case head to come out, the block had to be open, the hammer had to be retracted, and both went back into battery.

The only event I can conjure to create this sequence of events is that the hammer recoiled sufficiently to allow the block to move slightly to the rear and allow the case head to escape, but what force moved the block back into battery? THAT is the part that escapes me. The rifle has a thinned trigger spring (ala De Haas), and a primer could conceivably force the firing pin back hard enough to move the hammer, and subsequently the block. I just can't understand what force moved the block back into battery.

Jim

[MEHavey]

The hammer moved it back into battery, Jim, as you still had the trigger pulled and the sear was disengaged.

Put the full-up/stronger spring back in.

Believe it or not I had a similar problem last week with a S&W Model-19 which had had its mainspring cut down to smooth out the action. Primer setback could then push the hammer to back out enough to allow primer flow right back to/into the firing pin hole and lock up the cylinder on every full-up/40,000psi .357Mag load.

Putting the original mainspring back in solved the problem.

In the Model-19 it was an annoyance. With the rolling block's dependence upon hammer position to lock up the breech, that sounds like a potentially fatal annoyance.

[Jim Tarleton]

Somebody would need to model this action and determine what force it takes to force the breech block to override the hammer. Because that is what is happening.

The action is opening. The breech block is forcing the cammed surface of the hammer to move. I suspect there is enough spring in the action for these to occur. The breech block forces that hammer cam back, then the breech block opens, case head comes out, and then the hammer spring pushes the hammer and breech block closed.

You can't see it because it is happening too fast for your perception.

Under load, with a high speed camera, you would see things moving. Actions are not static, under load they stretch and move dynamically.

The breach block of a RRB cannot force the hammer back in any way. Once the hammer has progressed to the point where the breach block is above the curvature of the hammer, the block can only move back if the hammer is retracted. There is no cammng surface.

Jim

[Jim Tarleton]

Somebody would need to model this action and determine what force it takes to force the breech block to override the hammer. Because that is what is happening.

The action is opening. The breech block is forcing the cammed surface of the hammer to move. I suspect there is enough spring in the action for these to occur. The breech block forces that hammer cam back, then the breech block opens, case head comes out, and then the hammer spring pushes the hammer and breech block closed.

You can't see it because it is happening too fast for your perception.

Under load, with a high speed camera, you would see things moving. Actions are not static, under load they stretch and move dynamically.

The breach block of a RRB cannot force the hammer back in any way. Once the hammer has progressed to the point where the breach block is above the curvature of the hammer, the block can only move back if the hammer is retracted. There is no cammng surface.

Jim

[Parashooter]

Well, your data and technique may show why you're getting head separations.

1. That's not really a mild load. Quickload estimates it near 45,000 p.s.i. (and that estimate could be significantly lower than the actual pressure generated in your rifle with your components).

2. If you're full-length resizing in a regular 7x57 die, you're probably producing cartridges with significant end-play, even in a minimum chamber. Remember, it's not the gun's headspace dimension that counts, it's the fit of the case between breechblock and chamber. Many mass-produced dies size for about .006" end-play in a minimum chamber. Ignoring action flex, that's .018" stretch for three firings - an amount close to the failure limit of much commercial brass. Add the flex inherent in the RB action and some cases won't survive two uses.

You can alleviate the stretch by reducing the powder charge to a more moderate level and sizing cases just enough to allow action function, striving for zero end-play. Also, useful 7x57 cases can be formed from heavy .30/06 military brass using your regular sizer and trimmed to length with any common trimmer setup (preferably powered). Such cases have heavier walls than most 7x57 commercial brass and will withstand more stretch.

I suspect that the sequence of events that allowed the case head to escape was -

1. The over-stretched case separated at about peak pressure and moved rearward at high speed, unrestrained by the now-detached case body's friction with the chamber.
2. The primer, as part of the head, struck the firing pin with sufficient force to drive the hammer back enough to clear the breechblock's locking surface. Finger still on trigger kept sear from engaging.
3. Residual pressure could then blow the block open enough to allow the case head to escape.
4. With the case head gone, no internal pressure remained, allowing the hammer spring to return hammer and breechblock to the normal fired position.



While this seems a highly unlikely string of unusual events, it's the only way I can imagine the case head could escape unless some part of the action were broken, missing, or deformed.