S121 headscratcher

[oafpatroll]

A cross post from GS.

I've been buggering around trying to get my 130gr cast and powder coated bullets to play nicely with S121 for a while and will probably do so till I'm shot of the stock of the stuff that i have on hand because I'm wired up for pig headedness.

Yesterday I ran 18 rounds over the chrony to check for consistency as I've found it to be extremely inconsistent in the past. 16 of the 18 were at expected velocity level (i.e. high 900fps range) with a spread of 90fps. The headscratchy part was that two of them came in at 1340 and 1427 respectively. Neither of those two shots felt odd and case ejection was right in the middle of the pile.

I did a bit of GRT this morning and it suggested that I'd need very nearly a double charge to achieve the higher of the two anomalous velocities and that peak pressure would be 2.6 times the absolute max for the cartridge.

While I don't claim that a pair of double charges are impossible it seems quite unlikely. I visually inspect every case for fill level before placing a bullet and weigh one charge randomly selected from every tube of the case feeder on my press. A double charge or anything close to it is very obvious in a 9mmP case and the 1/25 charges I weigh hasn't been out by more than a tenth of a grain in many thousands, possibly even 10's of thousands of rounds loaded.

I am going to pull the remainder of the batch to weigh the charges and I'll inspect the cases that came back from the range as i want to get to the bottom of this. I'm discounting chrony muppetry for the moment as I tested a few batches of 38 Spl and 357 loads during the same session and they were bang on velocity expectation and consistency.

[janfred]

Now I really need to know what chrony you are using.

If you are using an optical chrony, the high velocity can be explained by enough unburnt powder going past the screens to give you an erroneous reading. If this is the case, try placing the chrony a few metres further from the firing point.

Next question; how did the load shoot?

[oafpatroll]

Now I really need to know what chrony you are using.

If you are using an optical chrony, the high velocity can be explained by enough unburnt powder going past the screens to give you an erroneous reading. If this is the case, try placing the chrony a few metres further from the firing point.

Next question; how did the load shoot?

Shooting Chrony Beta model, i.e an optical one.

There was no discernable difference in any of the shots in the 18 round string and I was only aware of the readings after I was done as a mate was recording them for me. The significance of the velocities was lost on him. It's a snappy load but not in the same league as my SD carry ammo simulating one which is noticeably pepper.

I think it's extremely likely that it was as you suggest a chrony anomaly.

[oafpatroll]

Because I've never had pressure concerns with a pistol load an inspection of the primers escaped me as a diagnostic measure and someone on GS reminded me. I only shot 18 9mmP rounds and collected all the brass and just checked them. Perfectly convex primer edges and no sign of firing pin impact point cratering. The cases are all generously chamferred so any variation in the primer edges would be very obvious.

Given that there were no signs of significant over pressure events while firing and on afterwards on inspection i'm going to write this up to an optical chrony glitch.     

[Treeman]

The problem is at the chroni. What the chroni is experiencing to give a wrong reading is a whole world of if and also's.
I firmly believe a charge, slightly larger bullet diameter or slight blockage  or anything that is capable increasing pressures enough will talk back at you in many ways, primers recoil and sound.
There is really only one area for this anomaly and that's the chroni.

[big5ifty]

Years ago I had a shooting chrony. I packed it up and sent it back to Canada, where it came from. With a long , not very nice letter in the box.

I never did get a reply from anyone. It was good riddance from my side.

[oafpatroll]

Years ago I had a shooting chrony. I packed it up and sent it back to Canada, where it came from. With a long , not very nice letter in the box.

I never did get a reply from anyone. It was good riddance from my side.

I've had this one for a long time and had the opportunity twice to compare it's results to others including a Labradar. It's never read exactly what anything else did but it was close and consistent enough to give me confidence. This pair of anomolous readings are a first and if it does anything similar again i will give it to someone i don't like.

[Treeman]

Were these perhaps powder coated  bullets ?

[oafpatroll]

Were these perhaps powder coated  bullets ?

They were but so are the last 20k+ that have been shot through the 3 guns that were used yesterday over the chrony.

[Treeman]

They were but so are the last 20k+ that have been shot through the 3 guns that were used yesterday over the chrony.
[/quote]
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I am think powder coating fragments, either scraped when seating or not well bonded.
I doubt u put 20K+ over the chroni, this would not be something that would be anything when trying to hit a target,

[Tripodmvr]

How far is the muzzle from the chrony. The escaping gases can also trigger the chrony and give false readings. For rifle I normally place optical chronies at 5m. For handgun 3m might be good.

[oafpatroll]

They were but so are the last 20k+ that have been shot through the 3 guns that were used yesterday over the chrony.

*******************************
I am think powder coating fragments, either scraped when seating or not well bonded.
I doubt u put 20K+ over the chroni, this would not be something that would be anything when trying to hit a target,
[/quote]

Indeed, I didn't mean that I chronied 20k rounds but rather that the powdercoating isn't a newly introduced variable. At a wild guess I'd say that I've shot 200ish of the same coated bullet over the same chrony previously.

[oafpatroll]

How far is the muzzle from the chrony. The escaping gases can also trigger the chrony and give false readings. For rifle I normally place optical chronies at 5m. For handgun 3m might be good.

More than 5m. The cable is 6m long so probably 5.5m table to tripod. Same as I've always done it.

[janfred]

I don't know about others, but when I used S121 it left quite a bit of little yellow particles in my pistol. If enough of that came out the end of the barrel, it is quite possible that it could cast enough af a shadow to be picked up as a shot.

Another problem I used to have with the beta chrony was that it used to pick up erroneous shots when the guy next to me fired his .300WSM. Or anyone else with a muzzle brake.

[Tripodmvr]

A windy day is also not conducive to accurate chrony readings. I use a tripod and the wind causes vibrations which have an effect on the timing of the sensors.