Cases stretching, but headspace OK - a mystery!

[Alex Hamilton]

Hi, Guys,
Cases stretching and head separation when headspace is excessive is common, but I have a friend that is experiencing serious case stretching in 45-70 and 32-40 and neither rifle has excessive headspace. I don't know anything other than excessive headspace that can cause case stretching, so I should be grateful to hear if there are any other causes for this.
Many thanks,
Alex in UK.

[44man]

Not much except excessive loads. Easy to check head space. Put a layer of masking tape on the case head, (sized and trimmed or loaded round.) it should chamber, two layers should have a little resistance, three should not chamber.

[Digital Dan]

Hi, Guys,
Cases stretching and head separation when headspace is excessive is common, but I have a friend that is experiencing serious case stretching in 45-70 and 32-40 and neither rifle has excessive headspace. I don't know anything other than excessive headspace that can cause case stretching, so I should be grateful to hear if there are any other causes for this.
Many thanks,
Alex in UK.

Smokeless powder or black powder?

[leadman]

The headspace of those cartridges is measured at the rim so like the 303 British, has little to do with case stretching. You did not say what firearms these are chambered in but it is possible that the actions are "springing" from the loads being too hot.
Need more info like firearm, load, velocities.

[44man]

Lever guns stretch brass. Do not need HOT loads either.

[duck hollow pete]

Over size chamber or under size die has the same effect.

[Alex Hamilton]

Smokeless powder or black powder?
The 32-40 is M1885 Winchester High Wall and the load is 20grs of H4895, which I believe is on the low side, because of the unburned powder grannules left in the bore. The other rifle is Shiloh Sharps and that is loaded with black powder.

[Alex Hamilton]

The headspace of those cartridges is measured at the rim so like the 303 British, has little to do with case stretching. You did not say what firearms these are chambered in but it is possible that the actions are "springing" from the loads being too hot.
Need more info like firearm, load, velocities. The loads are not hot. Case full of black powder in 45-70 in Shiloh Sharps and 20grs of H4895 in 32-40 in Winchester High Wall. Your suggestion that the actions might be "springing" is very interesting. Are there any obvious symptoms to look for and can this be measured?
Many thanks,
Alex

[Bullshop]

Straight wall cases will stretch to the point of case separation if they are fired in a chamber that has lube in it.

Run a swab in the chamber with acetone on it to remove the lube then dry patch the chamber.
Keep the chamber dry and lube free and if headspace is correct the problem will cease.

[Digital Dan]

The 32-40 is M1885 Winchester High Wall and the load is 20grs of H4895, which I believe is on the low side, because of the unburned powder grannules left in the bore. The other rifle is Shiloh Sharps and that is loaded with black powder.


Are the charges compressed in the Sharps?

[44man]

Straight wall cases will stretch to the point of case separation if they are fired in a chamber that has lube in it.

Run a swab in the chamber with acetone on it to remove the lube then dry patch the chamber.
Keep the chamber dry and lube free and if headspace is correct the problem will cease.
Not true, lube will increase head pressure at the bolt. The brass can't grip the chamber so it comes back. Too much head space will have brass grip and stretch back to the bolt. Bolt spring in a lever gun just makes brass longer.
Remember the revolver S&W made for a bottle neck, they said to lube chambers. Kept case stretch from locking the cylinder.
It is the reason to never polish a chamber too much. You need grip on the brass.
Some autos even have fluted chambers to hold brass longer to reduce gun damage.

[blackthorn]

I think Duck Killer Pete is correct. My WAG would be there is either too much chamber clearance or the cases are being sized too much or a combination of the two. I am also making an assumption that those posters referring to "headspace" include "chamber clearance" in that designation?

[Alex Hamilton]

Are the charges compressed in the Sharps?No, the charges are not compressed and there is not much neck tension, because I have seen my friend seating the bullets by hand prior to firing.

[Larry Gibson]

Hi, Guys,
Cases stretching and head separation when headspace is excessive is common, but I have a friend that is experiencing serious case stretching in 45-70 and 32-40 and neither rifle has excessive headspace. I don't know anything other than excessive headspace that can cause case stretching, so I should be grateful to hear if there are any other causes for this.
Many thanks,
Alex in UK.

Alex

Case stretch and incipient case head separation is most often attributed to excessive headspace. With factory/arsenal ammunition that is most often the case. However with reloaded ammunition that is not the case.

What occurs with reloaded ammunition is the case, when fired, has expanded but does not the contract back to the original dimension prior to firing. Thus we think we must size the entire case to reload it. With some cartridges fired in some types of actions this is the case; most often with auto loaders. Resizing the case, full and even partial, is what causes the case stretch. Look at a fired case and you will see the case is expanded along the case body outward, especially in the web area. There you will many times see what is called the "expansion ring" and it is there that incipient case head separation most often occurs. You will see this expansion of the case with cartridges that are correctly headspaced to the chamber. When the fired case is FL or partially sized the die pushes the expanded part back in to size the case. Most all FL dies allow the brass, as it is squeezed in, to flow forward (RCBS X- dies are the exception). That is where the case stretch comes from most often. Since the brass at the web is thinned as the case body in front of it is expanded during firing it is not compressed back to it's original thickness during sizing it gets thinner with each firing/sizing until head separation occurs. The X-Die doesn't allow the case to flow forward and thus dramatically lessens the thinning process.

Case life is greatly extended by neck sizing only as this alleviates the expanding and sizing of the case body, particularly at the expansion ring/web of the case. Partial sizing to neck size is generally successful on cases with a bit of body taper so the FL die does not contact and squeeze the body in. If it does the brass will flow forward.

In your friends case with the 45-70 and 32-40, since they both are tapered cases, he can probably back the FL die off 1 - 2 turns and just size the case necks. He can also invest in a neck size only die which at todays brass prices may be the best in the long run.

Larry Gibson

[Bullshop]

Not true, lube will increase head pressure at the bolt. The brass can't grip the chamber so it comes back. Too much head space will have brass grip and stretch back to the bolt. Bolt spring in a lever gun just makes brass longer.
Remember the revolver S&W made for a bottle neck, they said to lube chambers. Kept case stretch from locking the cylinder.
It is the reason to never polish a chamber too much. You need grip on the brass.
Some autos even have fluted chambers to hold brass longer to reduce gun damage.
Then we disagree on this point.

[Guesser]

I had the same problem with a RB in 43 Spanish. The dies were setting the shoulder back enough that it stretched the case and separation happened prematurely. I neck size just enough to get gripshun (pull) on the boolit and load in IAW powder requirements; no smokeless. My cases are good, haven't lost any in 4-5 years now.

[EDG]

Sized cases stretch diametrally to fit the chamber when fired.
Sizing cannot undo that stretching. The brass gets squeezed back to it original shape when sized but the material is not compressed it can only flow toward the only unconstrained part of the die - toward the case mouth.

Some dies squeeze a case grossly under sized. The dies can even vary from one die to another of the same brand.
Some of the worst variations come from calibers that were developed before SAAMI standards.

[44man]

Then we disagree on this point.
Not really but most calibers need case hold in the chamber. It is why we don't FL all the time, just enough for good chambering. Short brass grabs and stretches back to the bolt if there is head space. Solved by not setting shoulders back but rimmed brass is different yet rims are not all the same either. same as belted cases. belts vary. Bottle neck cases in rimmed brass or belted take to shoulder head space too.
A Sharps or High Wall will have no spring, as solid a gun you can get. Wear might increase head space so why cases stretch in those guns is beyond me.

[Bullshop]

Not really but most calibers need case hold in the chamber. It is why we don't FL all the time, just enough for good chambering. Short brass grabs and stretches back to the bolt if there is head space. Solved by not setting shoulders back but rimmed brass is different yet rims are not all the same either. same as belted cases. belts vary. Bottle neck cases in rimmed brass or belted take to shoulder head space too.
A Sharps or High Wall will have no spring, as solid a gun you can get. Wear might increase head space so why cases stretch in those guns is beyond me.

""" why cases stretch in those guns is beyond me.""
I have tried to explain that it can be because of a chamber wet with lube. The brass case will flow forward because it can not grip the chamber wall. This is especially true with a compressed powder charge where the powder column is gripping the inside of the case and trying to drag it forward while the outside of the case is sliding forward unable to grip the chamber wall because it is wet with lube.

[Digital Dan]

No, the charges are not compressed and there is not much neck tension, because I have seen my friend seating the bullets by hand prior to firing.

Not sure what your problem is with the .32-40, but the .45-70 might benefit from .040-.060" compression. More powder and/or fiber wads.

[fredj338]

It's not unusual for rimmed cases to stretch, the rim controls headspace. Less than max loads helps, but they are going to stretch, nothing to do about it.

[44man]

""" why cases stretch in those guns is beyond me.""
I have tried to explain that it can be because of a chamber wet with lube. The brass case will flow forward because it can not grip the chamber wall. This is especially true with a compressed powder charge where the powder column is gripping the inside of the case and trying to drag it forward while the outside of the case is sliding forward unable to grip the chamber wall because it is wet with lube.
I can go with that. Most cases should never have lube in the chamber. Yet most case stretch is from brass grip so the brass goes back to the rear to the bolt. Set shoulders back and you will get case separation at the expansion ring. But what causes a straight wall case to do that? head space on the rim so is it chamber lube? Don't want boolit lube on brass either.

[Bullshop]

In Parker Ackleys Handbook for shooters and reloaders he mentions in testing the 30/30 improved in a 94 Winchester with the locking bolt removed from the action. The idea is to demonstrate how the AI chamber eliminates back thrust to the breach face.
In his test without the locking bolt in place everything remained normal upon firing. The case grip to the chamber walls was enough to keep the case from backing out so did show reduced back thrust over the standard 30/30 case design.
Now I wonder what would have happened in his test if the chamber had been wet with lube. Would the results have been the same?
Without the locking bolt in place there is not much holding the breach in place.
A chamber wet with lube will cause increased back thrust, yes true but it also causes the brass to flow forward too because it can not grip the chamber walls. This I have seen demonstrated many times that a chamber wet with lube will cause case separation with straight wall rifle cases.
The OP stated that all was correct with the guns head space and I strongly suspect that lube in the chamber is what caused the problem.
Many people take good care of their rifles by cleaning and oiling them and feel it is good to leave a substantial film of oil everywhere. That is good accept not in the chamber.

[detox]

SPG lube is way less slippery than most all other lubes. I learned this when resizing/lubing linotype bullets in my RCBS Lubramatic.

Are there any other lubes that are not too slick?