Can A Split Case Create A Chrono Error

[Adventurer 2]

I finally got a chronograph at the end of last year. I've been having fun shooting my reloads through it this year. It's a Pact. Yesterday, I was shooting a reload box of .357 125 grain bullets over 15.8 grains of H110. One of the rounds didn't sound or feel right. I stopped firing opened the revolver and extracted a split case. This case had been fired one time prior. I checked the chrono and it had a velocity of 2820 fps. The other shots on that string averaged 1244 fps. I thought, Oh sh.t, double charge. Looked at the revolver, couldn't see any damage. Wrote some info on a card and closed that box up. When I got home I opened that box up, pulled a bullet measured the powder - 15.8 grains. Pulled another bullet 15.8 grains. Tried to funnel the powder from two bullets into one case - overflowing powder. I can't imagine I would ever not notice that much powder as I have only ever used a single stage press. Probably the most that could fit in a case is 20 grain of H110 with a bullet seated.
Is it possible that the split case caused a reading on the chrono as high as 2820 fps?

[Adventurer 2]

I set the chrono up just in front of the revolver (I don't want to accidentally shoot the sensors).

[Shoney]

All things being equal, the split case would probably yield a lower velocity.

If the crimp were light and the bullet were set back, the result would be an over pressure load that could split the mouth and give a very high velocity/pressure spike. I guess you will never know for sure,

[WCW]

I’ve noticed the odd error with a chronograph when using a pistol if you have it set up relatively close to the muzzle, and every time it’s happened it has always been with a slow powder. I assumed it may have been a small particle that caused enough of a shadow for the screens to pick it up and throw off the calibration. They are not totally foolproof, and moving the chrono a little further away seems to have fixed things for me.

As far as the cracked case goes, I doubt too much pressure had much to do with it. I’ve had lots of cases split shooting soft-loaded wadcutters. If it was a nickel-plated case, splits can occur with a low case usage. There is likely to be far more going on than just a cracked case if you are using a powder fast enough to double charge a case, and you will definitely know something is amiss.

[SL1]

Adventurer 2,

Some things do not seem right with your information. First, 357 Mag loads for 125 gr bullets with H110 are maximum at 20 to 22 grains of powder, depending on which bullet and whose data you use. H110 max charges should not be reduced by more than 3% to avoid squib loads, according to Hodgdon. So, your 15.8 grains seems very light (18% to 21% reductions). Is it possible that your next-to-last shot was a squib that left a bullet in the barrel? (Did you see where THAT bullet made a hole in your target?) If you had a lodged bullet, I would EXPECT your barrel to blow on the next shot, but MAYBE not. Is there any apparent damage inside the barrel (obvious ring, maybe)?

The second thing that is puzzling is the very high velocity reading from the chronograph. You did not describe how your last shot "didn't sound or feel right." Was there a lot more sound than usual? Was there more or less recoil than usual? IF there was a lot more blast than usual, given that you said you put the chrono right near the muzzle, it may be that the shock wave of an excessive muzzle blast transfered to the steel frame of the chorno and shook the sensors enough to make the circuits fire. The measured speed would then be speed of sound in your steel frame (much higher than in air), or somewhat less if the second sensor fired on a later vibration cycle than the first one. Just a guess.

Another possibility is that the blast wave itself (in the air) caused the sensor circuits to fire. The initial velocity of the shock wave can be much higher than the speed of sound. It is usually higher than the speed of the bullet. (For recoil calculation purposes, it is assumed to be 4700 fps at the muzzle from a high pressure cartridge.) But, the shock wave disipates rapidly with distance. That is why bullet velocities are usually measured 15 feet from the muzzle, where even the blast from a high power rifle cartridge probalby won't affect the sensors.

SL1

[Adventurer 2]

I thought it was louder. All of the rounds fired left the barrel and hit the target. I do not notice any damage to the revolver.
I would hate to tell you how light of loads I have shot out of my 357 revolver in the past. Right or wrong, in the past some of the even lighter loads that I shot were extremely dirty and felt anemic so I quit shooting them. I shoot different powders in 38 special and that 15.8 of H110 in 357 mag seemed hotter than any 38 special I have reloaded and shot in the revolver. The chrono has confirmed that. It has been my bridge load between my 1894C, lever action, and my 357 revolvers. Per the reload data for the rifle 15.8 H110 is a medium loading. I know it doesn't reach the minimum loading for a handgun, but it sure feels like a magnum round when it is shot in a revolver. Is there harm in shooting these lighter 357 mag loads (faster than the exact same bullet loaded for 38 special) in the revolver? The smallest barell length I own is 5 inches.
I will move the chrono out further. I just wanted to make sure I didn't hit it.

[SL1]

The problem with light loads of H110 or Winchester 296 is that they don't get up to high enough pressure to burn well. That is what makes them "dirty". In a revolver, because its cylinder gap vents pressure, it is possible for the light loads to essentially quit burning early and leave a bullet lodged in the barrel. That (along with the dirty powder residue) is only a pain in the a** IF YOU CATCH THE SQUIB AND CLEAR THE BORE BEFORE FIRING ANOTHER ROUND. The hazard comes from the potential for not catching the squib and firing another round into the obstructed bore.

Older reloading manuals tended to show much reduced loads for H-110, even when they carried warnings about not reducing WW-296 at all. (The two powders are alledged to be nearly identical products of the same factory.) Now that Hodgdon has acquired Winchester Powders, they have started showing identical load data for H-110 and WW-296 (even though previous data almost always showed H-110 to be a tad slower than WW-296) and they now say neither should be reduced by more than 3%.

There are better powders for loads that are a little over .38 Special +P levels, but well below 357 Mag max loads. Alliant 2400 and Blue Dot come to mind. I can't get to my manuals at the moment, but I would consider Unique, SR-4756 and Universal as other possibilities. I am just not sure the last 3 safely get to your 1244 fps without checking the manuals. I know they would be cleaner.

SL1

[Mal H]

First, no way you can get 2820 fps with a 357 handgun even with a triple load of powder. So the error was indeed a false chrono reading. I'd bet it was a combination of factors: you were much too close to the chrono for good readings even under normal circumstances; hard to say what caused the false reading, but I'd go with the muzzle blast effect.

The problem with blaming the blast in your case is that the reading is generally lower than it should be when the blast is involved. The gases trip the start circuit and the bullet trips the stop, so the chrono thinks it took a long time for the bullet to traverse the start/stop distance. However, a plausible explanation is that the gases tripped both the start and the stop. That would explain the excessively high reading.

I agree with SL1 in that 15.8 gr of H110 is a pretty light powder load for that weight of bullet with this one exception - what type of bullet are you using? Jacketed or lead/plated? If the latter, then it might be a good load weight.

[Adventurer 2]

The bullets were jacketed. I said the chronograph was right in front but the actual distance was about 3 feet from the muzzle. Not far enough, though. I think going forward I won't share loads between the rifle and the revolvers. I am also going to rechronograph all of the rounds I've been taking notes on since December. This was the first reading I had that was insanely out of the ballpark and the split case concerned me.

[SL1]

Getting back to the split case, I doubt that it was caused by too much powder. You can pretty well stuff the case full of H-110 under a 125 grain bullet and still not exceed the pressure limit by much if anything. (Some old manuals show "compressed" loads for H-110 under 125 grain jacketed bullets, but Hodgdon has told me over the phone not to compress their ball powders, so I would not do it intentionally. If the condition arose unintentionally, I would think that you would have noticed it when seating the bullet on a single stage press.

I am assuming the "split case" was a long axial split in the middle of the case body, not a mouth crack or a circumferential split near the head. If so, that would indicate a case that was loaded too often, got brittle, and split. You can load cases until they split at the neck without any ill effect on the gun, although it will probably have a noticeable affect on accuracy. Spitting a case axailly now and then in the middle of its body probably won't harm the gun either. But, if you are getting more than a couple of cases that fail that way in a batch, I would suggest scrapping the whole batch, or at least relegating them to low-pressure loads if you want to shoot them all until they actually split.

On the other hand, if the split was circumferential or was axial but went into the case head area, then it is more serious.

SL1

[Adventurer 2]

It was a long axial split in the middle of the case body. You are right - two charges couldn't fit into the case and I would have had to have taken powder out to get a bullet into the case.

[Mal H]

One thing we've all forgotten to ask is what brand of brass was the split case?

I've had brand new brass split axially in the middle, not good, but not all that uncommon either. I just toss 'em and forget 'em. I've had splits from both Remington and Hornady brass. Don't believe I've had any from Win, Fed or Starline.

It's the splits like SL1 mentioned where you have to start looking at things like head spacing, especially with rifle loads.

Oh, and 3 ft is much too close for your skyscreens. I would suggest a minimum of 5 ft., and 10 is even better. 10 ft is the minimum for rifle loads. Your 3 ft. distance tends to make me think the gas-blast-triggering-both-sensors theory is what did happen.

[Adventurer 2]

Remington brass.

[saudst]

I realy got a kick out of your situation because it happened to me years ago the 2nd time I had my chronagraph out. I had some 120gr. reloads to chronagraph and the first shot read 4800 and something! I remember the adrenlin rush as I looked down at the bolt thinking my hand and gun should be hamburger. My chrono was about 6' from the barrel, it must have been the gasses. I'll never forget it as long as I live and can smile about it now, but it was prety intense. like they said, move the chrono 4-5 long paces out and no more anxiety.

Be safe, Tim.

[Unclenick]

I expect the split case caused the start pressure for the bullet to be reduced, so a larger-than-normal for that light load quantity of unburned powder ejected and tripped the screens.

Another good reason for not having the screens that close is the powder residue and smoke will gradually fog the sensor lenses and reduce the unit's sensitivity.

The 3% number for H110/296—the same powder according to Hodgdon's tech—is lower than its lot variation. In revolvers in good condition you will have a bit more room than that. Indeed, Winchester used to publish a fixed load for this powder (no start load or range) of 16.6 grains for the 158 grain JHP bullet. Hodgdon's site gives you 15 grains to start and 16.7 grains maximum. That start load is a 10% reduction, not 3%, though maybe they mean you can take another 3% off their starting load? I don't know.