Subsonic .458 Socom

[Ike Clanton]

Data for this topic is very limited but I have been loading 14.3 grains of HS-6 with a 400 grain powder coated cast HP. Shoots well and expands like crazy but I worry about low case fill. I have recently picked up 8lbs of CFE Blk which has establish loads for supersonic with a starting load of 34.8 at 1502 FPS. In my 10.5 it’d be dang near 1300-1400 I’m sure.

Is is dangerous to download in an attempt to make a subsonic load? Doesn’t seem like I’d have to reduce it by much.

[MarkCO]

Originally Posted by Ike Clanton

Is is dangerous to download in an attempt to make a subsonic load? Doesn’t seem like I’d have to reduce it by much.

Since you don't know "why" the max and min are in the manuals, better to get a powder that has the velocity numbers you are looking for in their published load range.

Most often, the mins are there to make sure that the case expands enough to seal. If not, you get leakage which is not good for the chamber, nor keeping it clean. Velocities will be erratic and accuracy suffers.

Someone is sure to jump in and say reduced loads lead to detonations, which they don't, and won't. Those are old wive's tales that have been debunked but keep getting passed around like a jug of bad moonshine.

[Ike Clanton]

Well that’s good to hear about the reduced load detonations because it’s had me worried. Unfortunately with the 458 SOCOM I don’t think there are any published subsonic loads most are just word of mouth on forms which is obviously not ideal. Once it gets excepted by SAMMI maybe powder companies will become more adventurous

[44 AMP]

The main reason you rarely find data for extra light loads is simply because so few people are interested in it, and the people doing the load testing for the manuals, simply don't waste their time and money to research data that almost no one is interested in.

There have been detonations from reduced loads in certain calibers with certain powders, notably large capacity magnum cases and certain slow powders. They are quite rare, but some have happened. But the idea that ALL reduced loads are dangerous is bunk.

[MarkCO]

There have been detonations from reduced loads in certain calibers with certain powders, notably large capacity magnum cases and certain slow powders. They are quite rare, but some have happened.

Reports of, is not the same as have been. Never replicated, never verified.

[Sharkbite]

but keep getting passed around like a jug of bad moonshine.

HEY….i like bad moonshine!!!!!

[Unclenick]

Reports of, is not the same as have been. Never replicated, never verified.

They have, actually. It is just that most people don't know about it. See below.

Those are old wive's tales that have been debunked...

Before you throw caution (which costs nothing) to the wind, I would be very interested to hear the nature of the debunking evidence you've referred to. I've never encountered any actual debunking of this particular claim, but rather just the anecdotally-based assertion that because the claimant hasn't ever heard of or experienced or found reports of one of these events himself, they don't exist. It's a little like claiming that just because you've never witnessed a rogue wave sinking a ship means they don't happen. Scientists thought that was so for a long time, for lack of surviving witnesses or adequate predictive modeling, before modern instrumentation found incidents of them occurring. You have to bear in mind that when handloaders have a gun blow up, they are likely to believe they caused it with an overcharge or the wrong powder and then pull down the remaining loads. It's embarrassing for them and doesn't typically make the evening news, so data from the field is hard to come by.

However, in the laboratory is another matter. The late Dr. Lloyd Brownell, who did all of DuPont's academic research on powder and pressures, reported occasionally measuring pressures in his lab for powder charges in the 30-40% case-fill range that produced more than double SAAMI pressures, despite being "reduced" loads. He brought this up in a letter to the editor in Handloader as a rebuttal to a similar claim to yours, but as presented by a writer in a Handloader article in the late '60s or early '70s time frame. I have it somewhere on a CD of old articles about pressure that Wolfe publishing used to sell. Brownell pointed out these events are statistically rare in their frequency of occurrence. The erratic pressures produced at those load levels have standard deviations of pressure such that the likelihood of such events is very low. Just not zero. This means even higher pressures can occur, but still less frequently. One of the advantages Brownell had over other tests that I've seen mentioned, is years of funding by DuPont that allowed him to fire the many tens of thousands of rounds with pressure measuring that you need to shoot to have enough of these events happen to be sure you aren't kidding yourself. Most claims to the contrary, if not simple anecdotal claims that low charges are safe, turn out to be based on tests with too few samples to be likely to produce an example.

The bottom line is that there's no harm in erring on the side of caution, but there is potential harm in failing to do so, so the risk isn't equal on both paths. It also puts the debunker in the position of having to prove a negative, which is extraordinarily difficult and which is why I asked about the debunking.

[MarkCO]

Not throwing caution to the wind. I've done testing myself as well as reviewed all the data I could find from all of the supposed "experts" who said it could happen. 3 months of work for a case, hired by an attorney. It is an old wive's tale and the fact that no-one has been able to replicate with actual instrumentation says so. Spend some time researching the "roots" of the rumor and it becomes clear...in fact, it becomes concerning that so many people believe it can occur. Finished with yet another circular argument lacking any basis in science.

[Unclenick]

But Dr. Brownell, a PhD physicist, DID measure it with instrumentation and in a laboratory setting and more than once. Pressure instrumentation and absolute pressure measuring was his whole thing in the studies he did for DuPont. He did not reproduce it in the sense of making it happen on command. His whole point is that it is random and does not happen predictably or frequently. He wasn't looking for it the times it happened in his lab. It was an observation. But if you thought nobody ever did this, you simply missed uncovering his work on it.

This is the problem with trying to prove a negative. You don't know what you don't know until you happen upon it. I don't know how many rounds you fired in your testing, but in months it won't be as much as Brownell fired over many years of work. Yet firing tens of thousands of samples is the only way to encounter it.

[44 AMP]

It is an old wive's tale and the fact that no-one has been able to replicate with actual instrumentation says so.

this reminds me of more than one episode of the show "Mythbusters". If THEY were unable to duplicate a reported event, they would declare it a "myth" and they busted it.

Now, I won't argue that the likelihood of having a serious pressure excursion from an underload has been over emphasized, but that is a different matter than claiming that the event never has and/or cannot happen.

Its a rare phenomenon, and one that (as far as I know) no lab has been able to replicate ON DEMAND, but as Uncle Nick pointed out (and very well, as usual) it has happened, and has been documented by a lab with pressure measuring instrumentation.