Case rupture - What did I do wrong???

[cw308]

Ocraknife
You sure opened a bag of worms. This was the last two rounds. Let's take a step back & start from scratch. Clean your firearm. Clean fired brass , size & deprime, pick out the shortest case, if in length llisted range, trim to that size all the cases, chamfer inside & out, flare the case mouth wide enough to hold the bullet in position, seat the primer to bottom ( getting yourself a pocket uniformer to uniform your pockets to the perfect depth & eliminate any seating problems) add your powder midrange on powder listed in load book to be safe, Install you case in the shell holder , screw the die into your press until it touches the case mouth & back out the die one complete turn, set the lock ring ,with the seated plug backed out, now install the bullet, lower the seating plug to your listed OAL, when the bullet is where you want it, back out the seating plug , Unlock the lock ring , lower the die until you get the bell out of the case with a slight taper crimp , there will be a slight shine around the rim of the case mouth when its right , lock the die in position .
lower the seating plug without moving the position of the die, when you feel it touch the top of the bullet lock your seated plug. Now you can seat & crimp in one step. To do this correct all your cases must be trimmed to the same length. You may know these steps already, if so sorry for the long post. I don't think your problem is as bad as most listed. Just go through the basic safe steps & keep us informed Hope I Helped, Chris

[Ocraknife]

Ocraknife
You sure opened a bag of worms. This was the last two rounds. Let's take a step back & start from scratch. Clean your firearm. Clean fired brass , size & deprime, pick out the shortest case, if in length llisted range, trim to that size all the cases, chamfer inside & out, flare the case mouth wide enough to hold the bullet in position, seat the primer to bottom ( getting yourself a pocket uniformer to uniform your pockets to the perfect depth & eliminate any seating problems) add your powder midrange on powder listed in load book to be safe, Install you case in the shell holder , screw the die into your press until it touches the case mouth & back out the die one complete turn, set the lock ring ,with the seated plug backed out, now install the bullet, lower the seating plug to your listed OAL, when the bullet is where you want it, back out the seating plug , Unlock the lock ring , lower the die until you get the bell out of the case with a slight taper crimp , there will be a slight shine around the rim of the case mouth when its right , lock the die in position .
lower the seating plug without moving the position of the die, when you feel it touch the top of the bullet lock your seated plug. Now you can seat & crimp in one step. To do this correct all your cases must be trimmed to the same length. You may know these steps already, if so sorry for the long post. I don't think your problem is as bad as most listed. Just go through the basic safe steps & keep us informed Hope I Helped, Chris

Thanks Chris. I'm happy to get all the info I can. I tend to prefer to seat and crimp in two separate steps however even though it takes more work.

[243winxb]

There is 1.5 thousands of an inch difference between one end of the fired brass and the other.

http://www.saami.org/PubResources/CC...0Automatic.pdf There is a taper to the chamber, .428" near the head, down to .424" near the mouth. The cartridge has a taper in the SAAMI drawing, but sizing with a carbide die, makes the case diameter all the same for the most part. Your brass may not produce the same measurements, but should be close.

[cw308]

Ocraknife
Two steps even better, just remember when ever crimping is involved, cases must be all the same length to do it right. Keep us informed. Be Well, Chris

[Ocraknife]

http://www.saami.org/PubResources/CC...0Automatic.pdf There is a taper to the chamber, .428" near the head, down to .424" near the mouth. The cartridge has a taper in the SAAMI drawing, but sizing with a carbide die, makes the case diameter all the same for the most part. Your brass may not produce the same measurements, but should be close.

Thanks! After firing my measurements were .426 at the head and 424.5 near the mouth. Now, I'm sure my $40 electronic calipers aren't as accurate as some but they may not be too far off. Are those numbers within spec?

[243winxb]

After firing my measurements were .426 at the head and 424.5 near the mouth.

Allowing for brass springback after firing, your numbers look good. Near the head, would seem to be a tight chamber (a good thing), but within tolerance.

[Ocraknife]

Ocraknife
Two steps even better, just remember when ever crimping is involved, cases must be all the same length to do it right. Keep us informed. Be Well, Chris

Will do Chris, thanks. I'd like to reiterate, I wasn't harmed at all and neither was the gun. This wasn't a dreaded kaboom. I feel like maybe the high quality of the Starline brass and the gun itself may have protected me from the overpressure. Still, after 30 years of shooting I've never had a case failure of any type so it was enough to put me on high alert.

[Longshot4]

Your plunk test should be level or a couple thow below the end of the barrel. Or do I have it wrong.
That case look like .010" below where it should be. That would be too short of a case that could be the reason for separation. Am I correct or am I wrong? Measure how far the head stamp is below the end of the barrel?

[cw308]

Ocraknife
First time for everything, no big deal, happens to all of us. I've seated a primer upside down. Called myself names nobody ever heard of.

[Ocraknife]

Your plunk test should be level or a couple thow below the end of the barrel. Or do I have it wrong.
That case look like .010" below where it should be. That would be too short of a case that could be the reason for separation. Am I correct or am I wrong? Measure how far the head stamp is below the end of the barrel?

Will do however, I feel stupid for asking this, but what exactly is considered the end of the barrel?

[243winxb]

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.

[Longshot4]

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.

[cw308]

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.

[Nick_C_S]

Since Hornady's 9th Edition is inaccurate, which manuals are the accurate ones?

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.

[Longshot4]

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.

[Nick_C_S]

Then look at thread#48 that is your photo.

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.

[Ocraknife]

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.

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

[Ocraknife]

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.

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.

[243winxb]

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

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.

[Ocraknife]

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.

What length should my cases be? I can measure that pretty easily.

[cw308]

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.

[243winxb]

Brass, Afters sizing , not shorter than .982" by SAAMI standards.

[Ocraknife]

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.

I just measured a couple they round out to about .986

[Mike Irwin]

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.

[Ocraknife]

It's the Schroedinger's Cat of the shooting sports.

This made me laugh so loud my cat probably won't be seen for days!