460 S&W Mag Case Separation

[BrotherMaynard]

I recently picked up this 5" 460V for a price that was on the high side of OK (the one below it is the previous acquisition, a 6.5" 624 no dash):

I heard a rumor that a gang of '56 Buicks would occasionally run amok in the area and I wanted to be ready in case it happened.

I did some research and figured I could make use of some 5744 I have on hand so I ordered some Hornady brass and 300 gr XTP pills. Unfortunately, I ordered the non-mag version of the XTP before I realized they are not the best bullet choice for this caliber. Based upon the data, I anticipated being below the max velocity (1500 fps) for the bullet so I elected to go ahead. I loaded 5 at 34 gr and proceeded in 0.2 gr increments to 34.8 gr (25 total rounds). The primers were CCI #34.

Off I went to my local outdoor range where it was cloudy and a sticky 77F. I loaded the first 5 and went to town. The 460 barked (a bit), bucked (a bit), and I smiled (a lot)...right up to the point I went to eject the fired casings.

Houston, we have a problem.

The spent cases ejected easily (at least what was left of them):


Needless to say, this caused a bit of consternation. The one on the far left appeared to show no signs of problems and when I stuck a bore scope into the case, it shows no signs of incipient separation. The others were toast.





With the exception of one fragment, the others fell out of the cylinder.

The primers looked OK:


The velocities (measured 12' from the muzzle) seemed reasonable:

1329 fps
1294 fps
1293 fps
1279 fps
1225 fps

I shut it down and returned home to do some sleuthing where I found multiple references to case separation when the cylinder chambers are not clean. Although I examined the pistol when I picked it up, I did not pay close attention to the cleanliness of the individual cylinder chambers. This turned out to be a fatal mistake for 4 pieces of not inexpensive brass.

I stuck a borescope into the individual chambers and discovered that the walls were covered in powder residue and lead streaks. There was also a ring of powder residue at the location where the cases separated. I am guessing that the previous owner had fired 454 Casull and/or 45 Colt without cleaning up afterwards. When I fired my 460 S&W rounds, the cases stuck and separated.

It took a bit of scrubbing but I managed to degunk the cylinder chambers. I loaded another 5 with 34 gr of 5744 and returned to the range where I was able to get through them as well as the remaining 20 in the ladder without a single case separation.

Note to self: spend the time to thoroughly inspect/clean the cylinder chambers on all previously-owned revolvers.

Coda

34.6 gr of 5744 turned out to be the best load so far with an average velocity of 1341 fps, an ES of 11 fps, and an SD of 4 fps with a group size of about 1.5" at 30':


This thing is a hoot to shoot but I find it really forces me to focus on the fundamentals.

 

[AJC1]

Wow that's a shocker. I want a 454 and the Sammi pressure spec is slightly insane. Basically rifle pressures.

 

[eddiememphis]

I don't understand how they all separated in the same spot. You say it was from a dirty cylinder and it was from shorter rounds. Your cases look like they separated much shorter than a .45 colt round.

How does a ring form that far back from the case mouth? And could this be a problem with rounds that fire with lower pressures- .357 in a .38?

 

[BrotherMaynard]

I don't understand how they all separated in the same spot. You say it was from a dirty cylinder and it was from shorter rounds. Your cases look like they separated much shorter than a .45 colt round.

How does a ring form that far back from the case mouth? And could this be a problem with rounds that fire with lower pressures- .357 in a .38?

It is a weird one. I plan to run it by Hornady as well and will update the thread if/when I hear from them. The dirty chambers is a guess but the only thing I did differently was scrub them clean before re-testing with the same load (brass/bullets are all from the same lots). From the Hodgdon data, I estimate the pressure to be around 51k for the loads in question. I would not expect a similar thing to happen with calibers that operate at lower pressures but I also did not expect this to happen with the 460.

Here are a couple of pics I got from the interior of the partially separate case. The separation point looks awfully suspicious.

 

[Jimfern]

I've never seen anything like that before. Thanks for sharing.

 

[edwardware]

First, that is exactly what straight-wall case head separations look like, so you aren't special (take heart!). The pin pushes the case forward while striking the primer, pressure rises expanding the thin front half of the case to grip the chamber, and high pressure forces the case head rearward against the recoil plate.

If you have excessive fore-to-rear slop of the cylinder on the crane (endshake) you can shim the cylinder rearward to reduce headspace. Elsewise, you'll need S&W or a true Gunsmith.

 

[Hartkopf]

First, that is exactly what straight-wall case head separations look like, so you aren't special (take heart!). The pin pushes the case forward while striking the primer, pressure rises expanding the thin front half of the case to grip the chamber, and high pressure forces the case head rearward against the recoil plate.

If you have excessive fore-to-rear slop of the cylinder on the crane (endshake) you can shim the cylinder rearward to reduce headspace. Elsewise, you'll need S&W or a true Gunsmith.

So would slicker (cleaner as well) chambers reduce separation chances? The front of the case possibly would not lock in to the chamber walls as well and reduce case stretching? Seems like a good reason for mirror polished chambers.

 

[Walkalong]

Chambers don't need to be polished, but they do need to be smooth and clean. I bought a Colt OMM in .22 Mag for cheap because it had been converted (poorly), from .22 LR. Chambers were terrible and cases were very hard to extract. Some work on the chambers and cases practically fall out now.

I'm glad a good cleaning fixed up the OP's issue, and it looks like it shoots quite well, but y'all can keep all that recoil.

 

[Typetwelve]

By chance, is that separation near the case length of a 45 Colt? For a very short time, I was running 45 Colt in my 460 and noted that it left a pronounced carbon ring inside the cylinder (one that just happened to be a serious pain to clean later). Long story short, shooting 45 Colt, then full 460 rounds, it left a major indent in all of my 460 cases where the carbon ring was. I'm pretty sure of that if I had continued to do that, it would have ruined the 460 cases in the exact same way.

 

[Mk-211]

If there's a carbon ring in the cylinder, are we seeing the Munroe effect?

The 460 round being more powerful, when fired the case is expanding to the cylinder wall. The carbon ring is being pushed into the case and causing the split.

I know someone here can possibly answer this.

 

[BrotherMaynard]

First, that is exactly what straight-wall case head separations look like, so you aren't special (take heart!). The pin pushes the case forward while striking the primer, pressure rises expanding the thin front half of the case to grip the chamber, and high pressure forces the case head rearward against the recoil plate.

If you have excessive fore-to-rear slop of the cylinder on the crane (endshake) you can shim the cylinder rearward to reduce headspace. Elsewise, you'll need S&W or a true Gunsmith.

My wife has referred to me as "special" since we got married...I'm guessing the context is different.

Thanks for the info/explanation. That makes sense. When I picked up the revolver, I measured the endshake to be 0.002" (max gap of 0.006" and a min gap of 0.004"). I did not measure the headspace but now I have an excuse to pick up some gauges.

 

[BrotherMaynard]

By chance, is that separation near the case length of a 45 Colt? For a very short time, I was running 45 Colt in my 460 and noted that it left a pronounced carbon ring inside the cylinder (one that just happened to be a serious pain to clean later). Long story short, shooting 45 Colt, then full 460 rounds, it left a major indent in all of my 460 cases where the carbon ring was. I'm pretty sure of that if I had continued to do that, it would have ruined the 460 cases in the exact same way.

I measured the split cases and the fall within 0.733"-0.739" (measured from the bottom up). There was a carbon ring around where the separation occurred; however, I cannot say whether it was pre-existing or occurred during the separation.

 

[cfullgraf]

Interesting information and good to know.

I've only fired a few 45 Colt rounds in my 460XVR but have not experience any failure of the full power loads in the 460 cases.

Since I have 45 Colt revolvers, I save the 45 Colt cases for them. I found a good light load that I can use in the 460 cases that reduces carbon build up in the cylinders.

I'll keep in mind to give the chambers a good clean after every shooting session.

 

[Cheesemaker]

This is interesting. I have had my 460 for 12 or so years. Initially, I would fire 45Colt and 454 Casull along with 460. I did have a few separations. I did stop shooting the 45 and 454s, I bought other firearms for those cartridges specifically I have not had separations since then. I never did think of them as related. Honestly, never gave separations much thought once I stopped having them.

Thanks for posting.

 

[25-20 WCF]

By chance, is that separation near the case length of a 45 Colt?…

The separations are nowhere near the length of a .45 LC or .45 Scofield case. They appear “close” to that of a .45 ACP…but that case wouldn’t work. The cases all separated at the same length because that is where the brass becomes thick enough to resist tearing.

…I would not expect a similar thing to happen with calibers that operate at lower pressures…

But it will and does happen with other calibers and at lower pressures. I’ve seen it with .357 and even .32 Long cases (the latter handloads fired in a .327) although I don’t know if those were due to dirty chambers or simply excess headspace and weak brass - not my revolvers.

Below are .357 cases fired with excess headspace:

 

[Slamfire]

Wow! About the first I have seen straightwall cartridges that gave sidewall separation.

Here is what I am going to claim. With nice and clean brass in a clean chamber, the front of the case swells out and fixes to the chamber. Friction and pressure keep the upper part of the case stuck to the chamber. Then, as pressures builds, the sidewalls stretch till the case head presses against the recoil shield. And, to make if more fun, your 460 S&W Magnum is operating around 65 kpsia with factory ammunition, and your reloads, could be 80 kpsia? Either way, the frame is stretching (elastically luckily) and that case sidewall is stretching even more as the gaps increase.

Stretching until it can't stretch anymore. Then it breaks.

The reason the high stretch mark is there is based on the time phasing of how the case flattens out with the pressure curve. The case does get thicker toward the head, you know.

I am going to offer a cure.

1) cut your loads till the case head separations go away.This should be the first thing any reloader should do, but from all the posts I have read, it turns out to be the last.

2) cut your loads till the case head separations go away, and then, lube the case walls before firing. You can leave sizing lube on, I use Johnson paste wax on rifle cases as it dries hard. Either way, you want to break the friction between case and chamber and have that case slide to the recoil shield. But, and this is important, cut your loads! If you lube your cases and still have god awful high pressures, than that lubricated case will really stretch that frame even more after lubricating. Your cases should last longer once they are lubed.

 

[edwardware]

So would slicker (cleaner as well) chambers reduce separation chances?

Yes.

The easiest solution is to leave a slick of case lube on the brass so the it slides just as you describe. . . I didn't recommend it because I don't enjoy the inevitable chorus of whinging from the didn't-pass-statics contingent.

The free body diagram demonstrating that the technique is safe is left as an exercise for the passed-statics crowd. As a hint: consider the yield strength of the brass in extension as a fraction of the force on the recoil plate.

I did not measure the headspace but now I have an excuse to pick up some gauges.

A micrometer, one of those separated heads, and a roll of scotch tape will get you quite close enough to diagnose the problem. You could also fire a primer-only case and measure primer extension.

 

[MEHavey]

that lubricated case will really stretch that frame even more after lubricating.

Slamfire, you and I are of the lubricated-case school of cure for most case stretch problems in rifles

[But] Do you really think the brass being allowed to stretch that very thin case wall will reduce shield
thrust to any significant degree in a revolver?

 

[BrotherMaynard]

Wow! About the first I have seen straightwall cartridges that gave sidewall separation.

Here is what I am going to claim. With nice and clean brass in a clean chamber, the front of the case swells out and fixes to the chamber. Friction and pressure keep the upper part of the case stuck to the chamber. Then, as pressures builds, the sidewalls stretch till the case head presses against the recoil shield. And, to make if more fun, your 460 S&W Magnum is operating around 65 kpsia with factory ammunition, and your reloads, could be 80 kpsia? Either way, the frame is stretching (elastically luckily) and that case sidewall is stretching even more as the gaps increase.

Stretching until it can't stretch anymore. Then it breaks.

The reason the high stretch mark is there is based on the time phasing of how the case flattens out with the pressure curve. The case does get thicker toward the head, you know.

I am going to offer a cure.

1) cut your loads till the case head separations go away.This should be the first thing any reloader should do, but from all the posts I have read, it turns out to be the last.

2) cut your loads till the case head separations go away, and then, lube the case walls before firing. You can leave sizing lube on, I use Johnson paste wax on rifle cases as it dries hard. Either way, you want to break the friction between case and chamber and have that case slide to the recoil shield. But, and this is important, cut your loads! If you lube your cases and still have god awful high pressures, than that lubricated case will really stretch that frame even more after lubricating. Your cases should last longer once they are lubed.

Thank you for the suggestions/information. I would HOPE that I am not approaching 80 kpsia with the starting loads but absent a way to directly measure the pressure, I cannot say with certainty that I am not.

I am presently using anhydrous lanolin + 99% isopropyl alcohol for sizing lube and it has worked well so far for lower pressure calibers but I may have to make a switch for the higher pressure ones, particularly if it solves the problem AND extends the case life.

 

[BrotherMaynard]

Yes.

The easiest solution is to leave a slick of case lube on the brass so the it slides just as you describe. . . I didn't recommend it because I don't enjoy the inevitable chorus of whinging from the didn't-pass-statics contingent.

The free body diagram demonstrating that the technique is safe is left as an exercise for the passed-statics crowd. As a hint: consider the yield strength of the brass in extension as a fraction of the force on the recoil plate.


A micrometer, one of those separated heads, and a roll of scotch tape will get you quite close enough to diagnose the problem. You could also fire a primer-only case and measure primer extension.

Thanks. I will try that.

 

[243winxb]

isopropyl alcohol

Bad for brass. Use RCBS 2 on a pad. Sizing may stretch brass, if done wrong.


Fire new, different brand of brass in clean chambers. No oil on brass.
https://www.grafs.com/catalog/product/productId/17861

Had 44 mag separate in a Marlin lever action. Old tired brass.

 

[eddiememphis]

What I am reading is this-
The front of the case expands to seal the chamber. It was sticking to the dirty cylinder wall not allowing it to move backwards causing the separation.

So the carbon ring would seem to be coincidental?

Or could the buildup of carbon not allow the case to expand enough for the bullet to get past the crimp easily, resulting in an overpressure?

I also do not understand how the carbon ring was so far below the mouth of a .45 case.

Why was there a carbon ring at .735" when a .45 case is 1.285"?

 

[25-20 WCF]

…Why was there a carbon ring at .735" when a .45 case is 1.285"?

Because the case failure had nothing to do with firing a .45 LC case in the cylinder earlier. Rimless cases fail the same way in rifles for the same reason - excess headspace and case walls sticking to the chamber. Handloading 101. The “carbon ring” is there because that’s where the case failed, venting the combustion gasses out the cut in the case onto the chamber walls. The OP has solved his problem, which was caused from poor firearm maintenance by the former owner (perhaps this is why he sold the revolver) and a failure to completely clean the chambers later. This is neither rocket science nor a mystery.




.

 

[BrotherMaynard]

Bad for brass. Use RCBS 2 on a pad. Sizing may stretch brass, if done wrong.


Fire new, different brand of brass in clean chambers. No oil on brass.
https://www.grafs.com/catalog/product/productId/17861

Had 44 mag separate in a Marlin lever action. Old tired brass.

Thank for the tip. I was not aware of that. Thanks also for the pointer to Starline brass. That is my preferred brand. Nothing against Hornady brass but I bought it as Starline was not available when I needed it.

 

[eddiememphis]

Because the case failure had nothing to do with firing a .45 LC case in the cylinder earlier. Rimless cases fail the same way in rifles for the same reason - excess headspace and case walls sticking to the chamber. Handloading 101. The “carbon ring” is there because that’s where the case failed, venting the combustion gasses out the cut in the case onto the chamber walls. The OP has solved his problem, which was caused from poor firearm maintenance by the former owner (perhaps this is why he sold the revolver) and a failure to completely clean the chambers later. This is neither rocket science nor a mystery.

That is very helpful.

Are you saying had Maynard done a thorough cleaning of the gun before he shot it, this likely would never have happened?

Is there possible damage to the cylinder walls? Either from Maynard's rounds or the previous owner's possibly having had the same issue?

I am thinking of being told about "flame cutting" of the top strap after shooting hot .357s.

The scary and potentially dangerous issue with used guns is not knowing what the previous knucklehead was doing to it.