Case rupture - What did I do wrong???

Headspace 10 mm

Looking at the chambers maximum at 1.004" and the cartridge minimum trim length of .982" This allows for .022" slop. This would allow the case to stretch a lot on firing, but the extractor should restrict forward movement some. But most all chambers and brass are some where in the middle. Note that minimum chamber and maximum brass are the same at .992" No need to trim brass till it gets longer than .992" The taper crimp is more forgiving with a variation in case length. Not so with a roll crimp used in revolvers. If brass can stretch more than .010" on firing, its possible to have a separation. But not common as new brass is softer than work hardened brass from many loading. It will be interesting to know the cause of yours.
 
Last edited:
The end of the barrel (all though there may be another term for it) is in thread 48 to the right of the head of the case. By the way it looks like you have a burr across from the head. It seams to me that there is some serous slamming going on. There should not be a burr at that location.
 
Ocraknife
l think he's referring to chamber & free bore, that's the space in the barrel just before the rifling . You can use your chamber as a headspace gage. I like the Lyman headspace gage , has a step for min. & max. settings built in. Very easy to use. When reading his post , he talking about the base of the case should be flush with the front edge of the chamber. If the case is to long or to short the problem you had could happen with a load at the high end of the scale.
 
Last edited:
Since Hornady's 9th Edition is inaccurate, which manuals are the accurate ones?
Click to expand...

Well, you can try Speer #14. But oh, its max charge is also 12.0 grains, so I guess both must be wrong. :p

Here's my load work up data:

Bullet: Hornady 180gn XTP - Item No. 40040
Brass: Starline - new, or near-new
OAL: 1.255" - per plunk test.
All 10-round samples.

On 4/3/15:

11.2 grains
1142 f/s - G29
1173 f/s - G20

11.4 grains
1155 f/s - G29
1184 f/s - G20

11.6 grains
1165 f/s - G29
1206 f/s - G20

11.8 grains
1188 f/s G29
1230 f/s G20


On 4/17/15:

11.7 grains
1193 f/s - G29
1226 f/s - G20

11.8 grains
1191 f/s - G29
1241 f/s - G20

11.9 grains
1215 f/s - G29
1243 f/s - G20

12.0 grains
1222 f/s - G29
1268 f/s - G20

My notes state that all rounds shot without trouble or pressure signs. I chose not to go beyond 12.0 grains, as the rounds already showed potent velocity numbers (because 10mm rocks ;)). I decided on 11.7 grains to be my "set" loading for volume production. I have since loaded and shot over 300 of these at 11.7 grains o AA#7.

I can't speak for your load technique of course. But I can speak for mine. I've been loading for 32 years and I am thorough and consistent. Assuming proper load technique, I am confident that 11.0 grains is not an overcharge.
 
Take a look at thread #24 and understand what the references are. Then look at thread#48 that is your photo. I think you have a undersize case that can cause a separation.
 
Then look at thread#48 that is your photo.
Click to expand...

I agree. That round is not properly headspaced. Either the brass is too short (easy enough to measure); or the chamber is too long.

Whether or not that can cause the brass to separate, I don't know. I'll leave that for people smarter than me.
 
Looking at the chambers maximum at 1.004" and the cartridge minimum trim length of .982" This allows for .022" slop. This would allow the case to stretch a lot on firing, but the extractor should restrict forward movement some. But most all chambers and brass are some where in the middle. Note that minimum chamber and maximum brass are the same at .992" No need to trim brass till it gets longer than .992" The taper crimp is more forgiving with a variation in case length. Not so with a roll crimp used in revolvers. If brass can stretch more than .010" on firing, its possible to have a separation. But not common as new brass is softer than work hardened brass from many loading. I will be interesting to know the cause of yours.
Click to expand...

OK, this is weird! My unfired brass from this batch is .987 the FIRED brass is .980 which means my brass shrank!
 
Well, you can try Speer #14. But oh, its max charge is also 12.0 grains, so I guess both must be wrong.

Here's my load work up data:

Bullet: Hornady 180gn XTP - Item No. 40040
Brass: Starline - new, or near-new
OAL: 1.255" - per plunk test.
All 10-round samples.

On 4/3/15:

11.2 grains
1142 f/s - G29
1173 f/s - G20

11.4 grains
1155 f/s - G29
1184 f/s - G20

11.6 grains
1165 f/s - G29
1206 f/s - G20

11.8 grains
1188 f/s G29
1230 f/s G20


On 4/17/15:

11.7 grains
1193 f/s - G29
1226 f/s - G20

11.8 grains
1191 f/s - G29
1241 f/s - G20

11.9 grains
1215 f/s - G29
1243 f/s - G20

12.0 grains
1222 f/s - G29
1268 f/s - G20

My notes state that all rounds shot without trouble or pressure signs. I chose not to go beyond 12.0 grains, as the rounds already showed potent velocity numbers (because 10mm rocks ). I decided on 11.7 grains to be my "set" loading for volume production. I have since loaded and shot over 300 of these at 11.7 grains o AA#7.

I can't speak for your load technique of course. But I can speak for mine. I've been loading for 32 years and I am thorough and consistent. Assuming proper load technique, I am confident that 11.0 grains is not an overcharge.
Click to expand...

Thank you, however to be clear, I was using jacketed flat points not XTP bullets. I don't know if that makes a difference or not.
 
OK, this is weird! My unfired brass from this batch is .987 the FIRED brass is .980 which means my brass shrank!
Click to expand...
After sizing, they should get longer. When i set the sizing die, i keep a gap between the shell holder and bottom of the carbide die, the thickness of a nickel coin. But if your chamber is small, may not work for the 10 mm.
 
Take a look at thread #24 and understand what the references are. Then look at thread#48 that is your photo. I think you have a undersize case that can cause a separation.
Click to expand...

What length should my cases be? I can measure that pretty easily.
 
Ocraknife
Correct, your brass got wider. When you resize the die squeezes the case making it longer. Its good to measure the outer diameter of your fired case. That will tell you your chambers diameter plus .001 due to brass spring back . that's normal. The die brings it back to SAAMI specs. Size your brass & measure OD to see how wide your case gets do to your chamber.
 
Last edited:
Take a look at thread #24 and understand what the references are. Then look at thread#48 that is your photo. I think you have a undersize case that can cause a separation.
Click to expand...

I just measured a couple they round out to about .986
 
Important point that needs to be made about reloading information.

It is VERY rare for two loading manuals to agree on upper, lower, and max loads and pressure readings.

I'll say that again...

It is VERY rare for two loading manuals to agree on upper, lower, and max loads and pressure readings.

Every manual manufacturer tests their own combinations in their own equipment, with their own guns, and with their own selection of components, which invariably gives a spectrum of results.

In reality, EVERY manual is both right AND wrong.

It's the Schroedinger's Cat of the shooting sports.
 
OP, what type of crimp are you using? Can we see a pic of your crimp? My concern is that you are roll crimping or over crimping, and some of the rounds may be going in too far which could cause a failure. The 10mm auto like other auto rounds is designed to headspace on the case mouth. In extreme instances the wrong crimp could cause serious problems, especially in high pressure situations.
 
OP, what type of crimp are you using? Can we see a pic of your crimp? My concern is that you are roll crimping or over crimping, and some of the rounds may be going in too far which could cause a failure. The 10mm auto like other auto rounds is designed to headspace on the case mouth. In extreme instances the wrong crimp could cause serious problems, especially in high pressure situations.
Click to expand...

I am the fan of bullet hold; I want all the bullet hold I can get, and then there is R. Lee. R. Lee said there is no such thing as too much crimp. There was a time bullets were staked with punches. And then there was that scare, seems for what ever reason bullet were being welded to the case neck. All I wanted to know was the poundage, I wanted to know how many pounds it took to release the bullet. No one knew because they were using tensions with no way to measure it outside of interference fit.

After that they struggled for a term that could be used in place of bullet hold, like bullet grip. retention etc..

F. Guffey
 
OK, this is weird! My unfired brass from this batch is .987 the FIRED brass is .980 which means my brass shrank!
Click to expand...

I hear that all the time; reloaders claim there brass gets thicker and or thinner when they neck a case up and or down. And I always say my cases get longer and or shorten when necking up and or down.

I always say no one measures before and again after; but if they did they could start a new saying like: the case gets longer and or shorter and at the same time the case gets thicker and or thinner. Before the Internet Lyman claimed the distance from the shoulder to the case head increased when the body of the case was sized. Years after that Redding claimed they had a body die and I said 'FANTASTIC' because I knew there was no way to size the body of the case without shoulder support.

F. Guffey
 
Guys I think we are over thinking this.
Flame me if you feel the need but let look at this.
He fired 23 rounds before case failure occurred.
The last 2 rounds failed.
If the chamber was to long or the brass to short he should have had a rupture before the last 2 rounds.
Also remember all the rounds will pass a plunk test.
Pistol: S&W 1076 4.25" barrel
That is a good quality gun.
I would be inclined to load 25 more rounds just like the last and see if the failure repeated again at the end of the string of 25.
If so this is a chamber issue.
 
I believe I have close to 1,000 + once fired 10MM auto cases. None of them are Star-Line but I wonder how many different ways are there to make a case.

If someone examined the separated cases they would find the case head side of the separation has a tapered cup up to the point the case separated, after the separation they will find the case thickness is uniform. I know, you are all confused. But it is possible the thin part of the case locked onto the chamber and there was not enough pressure to cause the thicker case head to expand meaning when the case left the chamber the front of the case was locked onto the chamber.

Anyhow; if I had this problem I would change something that effected timing and I would use other cases.


F. Guffey
 
You must log in or register to reply here.
Back
Top