500 s&w loads overpressure?

[Aannddrreeww]

Well i worked up some loads for a 400 gr. Solid copper bullet in 500 s&w. 17 grains of unique powder gave me the velocity i was after. No signs of high pressure going from 14.0 to eventually 17.4 grains.

I decided to load some rounds at 16.7, 16.8, 16.9 and 17.0 grains to see which were the most accurate. Extraction of the 16.7 grain loads were a little harder than usual but the 16.8 grain loads were even harder. I had to pound the extractor rod with palm of my hand to get them out. I didn't load any more after that.
My question is why would the cases get stuck this time, but not the last time i shot identical loads?

 

[WrongHanded]

Difference in powder lots? Different primers, or cases? New versus prefired cases? Powder scale discontinuity?

From my perspective, Unique seems like a poor choice for a 60,000 PSI cartridge with a 400gr (space consuming) solid copper bullet. Just my two cents of course.

 

[Aannddrreeww]

The powder was from the same 1 pound container. Primers were from the same case of 1000. The cases have been fired numerous times. These charges were individually weighed and double checked on a beam scale. Scratching my head.

 

[Zendude]

The powder was from the same 1 pound container. Primers were from the same case of 1000. The cases have been fired numerous times. These charges were individually weighed and double checked on a beam scale. Scratching my head.

Maybe the brass is getting weak from multiple loadings

 

[Aannddrreeww]

Difference in powder lots? Different primers, or cases? New versus prefired cases? Powder scale discontinuity?

From my perspective, Unique seems like a poor choice for a 60,000 PSI cartridge with a 400gr (space consuming) solid copper bullet. Just my two cents of course.

Just out of curiosity, why would unique be a poor choice in powder?

 

[WrongHanded]

Just out of curiosity, why would unique be a poor choice in powder?

Well, solid copper bullets are expensive. So either you've got bags of money hanging around, or you're looking for some high performance from these loads. Other than accuracy, that would also suggest making the most out of the cartridge with high velocity and therefore high pressure. Basically, not plinking ammo.

In a load approaching 60,000 PSI, Unique woul be considered by many to be a fast burning powder. Add a heavy projectile to the equation, and one that is taking up addition space for the weight by being made of a material lighter than lead, and Unique can apparently perform inconsistently.

Fast burning powders are poor choices for top end loads in high pressure cartridges with heavy projectiles. It's easy to accidentally end up with an overpressure situation.

Now I have no idea what your load actually is, but I won't even run Unique at max pressure with standard weight bullets in .357 .41 and .44 magnums. Certainly not with heavy for caliber bullets. And these cartridges are only in the 35-36,000 PSI range. I would find a slower burning powder, if I were you.

 

[Aannddrreeww]

Well, solid copper bullets are expensive. So either you've got bags of money hanging around, or you're looking for some high performance from these loads. Other than accuracy, that would also suggest making the most out of the cartridge with high velocity and therefore high pressure. Basically, not plinking ammo.

In a load approaching 60,000 PSI, Unique woul be considered by many to he a fast burning powder. Add a heavy projectile to the equation, and one that is taking up addition space for the weight by being made of a material lighter than lead, and Unique can apparently perform inconsistently.

Fast burning powders are poor choices for top end loads in high pressure cartridges with heavy projectiles. It's easy to accidentally end up with an overpressure situation.

Now I have no idea what you load actually is, but I won't even run max pressure with standard weight bullets in .357 .41 and .44 magnums. Certainly not with heavy for caliber bullets. And these cartridges are only in the 35-36,000 PSI range. I would find a slower burning powder, if I were you.

I wish i had bags of money. No, i live in california where you now have to hunt with lead-free ammo. Uniqie is just the powder i have a lot of. My revolver is a 4" version so i'm relying on slow, heavy bullets.

 

[WrongHanded]

I wish i had bags of money. No, i live in california where you now have to hunt with lead-free ammo. Uniqie is just the powder i have a lot of. My revolver is a 4" version so i'm relying on slow, heavy bullets.

Ah, okay. Well, out of interest what load data are you using? Is 17.4gr of Unique a max load?

 

[LaneP]

Did this take place as the pistol was heating up from the firing string?

I love me some Unique but in my experience it's better for medium velocity loads. Pushing it too far has given me some crazy pressure spikes.

I once took a .45 ACP Unique load from a 90's Speer manual and even though I was several tenths below their listed max, it was way over pressure in the pistol I was using, to the point the ejector was driving up a divot in the case. I immediately ceased and that was that.

 

[Aannddrreeww]

There is no printed load data for this bullet so i contacted lehigh, the manufacturer, and they told me i could use data for jacketed bullets of the same weight, just back it off .2 grains. 17.8 grains would be the max load according to the lyman book.

 

[Aannddrreeww]

Did this take place as the pistol was heating up from the firing string?

I love me some Unique but in my experience it's better for medium velocity loads. Pushing it too far has given me some crazy pressure spikes.

I once took a .45 ACP Unique load from a 90's Speer manual and even though I was several tenths below their listed max, it was way over pressure in the pistol I was using, to the point the ejector was driving up a divot in the case. I immediately ceased and that was that.

10 rounds. That's all i fired.

 

[Obturation]

I don't use unique for magnum cartridges, it's great for many things but pushing heavy bullets isn't one of them. I would suggest h110/w296 or even 2400, they're regular magnum cartridge powders and act predictably.

 

[WrongHanded]

There is no printed load data for this bullet so i contacted lehigh, the manufacturer, and they told me i could use data for jacketed bullets of the same weight, just back it off .2 grains. 17.8 grains would be the max load according to the lyman book.

This is just my opinion, but I think that is incredibly dangerous! Especially with something as fast burning as Unique.

Now I can understand, you just did what they told you. But I can imagine they were referring to slower burning powders, or you ended up talking to someone who just parroted what they were told by someone else.

 

[243winxb]

Brass may not spring back after repeated firings. Measure the web area and compare to SAAMIs
Larger then .530" may be an issue?

 

[ArchAngelCD]

Just out of curiosity, why would unique be a poor choice in powder?

When I think about powders for the 500 S&W Unique usually doesn't come to mind other than with cast bullets for plinking. 60,000 psi is a rifle cartridge pressure number and today Unique is a medium speed pistol powder.I

Since you are building hunting ammo I would look at AA5744, AA1680, Enforcer and similar speed powders. The slower powders will allow you to generate the velocities you are looking for but with less snappy recoil. More controlled recoil is always better for hunting IMO.

 

[LaneP]

If this were my scenario I would back that down to about 16, test that and if all is well, consider it max. There are many variables that contribute to increasing pressure and some are difficult to explain (accumulated jacket fouling?), but regardless, hard extraction is a sure sign you're running on the high end of the pressure spectrum.

 

[mrawesome22-250]

They say Unique is very spikey. Meaning once it reaches a certain pressure, small increases in charge weight can equal huge increases in pressure.

 

[Walkalong]

Just out of curiosity, why would unique be a poor choice in powder?

Pretty fast for full power magnum loads, and the extra drag of the all copper bullet adds to it.

When I think about powders for the 500 S&W Unique usually doesn't come to mind other than with cast bullets for plinking. 60,000 psi is a rifle cartridge pressure number and today Unique is a medium speed pistol powder.I

Since you are building hunting ammo I would look at AA5744, AA1680, Enforcer and similar speed powders. The slower powders will allow you to generate the velocities you are looking for but with less snappy recoil. More controlled recoil is always better for hunting IMO.

Good advise.

 

[Aannddrreeww]

When I think about powders for the 500 S&W Unique usually doesn't come to mind other than with cast bullets for plinking. 60,000 psi is a rifle cartridge pressure number and today Unique is a medium speed pistol powder.I

Since you are building hunting ammo I would look at AA5744, AA1680, Enforcer and similar speed powders. The slower powders will allow you to generate the velocities you are looking for but with less snappy recoil. More controlled recoil is always better for hunting IMO.

When I think about powders for the 500 S&W Unique usually doesn't come to mind other than with cast bullets for plinking. 60,000 psi is a rifle cartridge pressure number and today Unique is a medium speed pistol powder.I

Since you are building hunting ammo I would look at AA5744, AA1680, Enforcer and similar speed powders. The slower powders will allow you to generate the velocities you are looking for but with less snappy recoil. More controlled recoil is always better for hunting IMO.

Do you think these powders would generate much velocity in a short 4" (3") barrel, or just in the longer barrel lengths?

 

[WrongHanded]

Do you think these powders would generate much velocity in a short 4" (3") barrel, or just in the longer barrel lengths?

They will at least get you to the same place more safely.

 

[mrawesome22-250]

The powder that produces the most velocity in a long barrel will generate the most velocity in a short barrel.

Accuracy should be priority number 1. Not velocity.

 

[Aannddrreeww]

Well it sounds like i'm using the wrong powder for this bullet LOL!
Unique does great with my 440gr. cast bullets, just not with copper. I'll try H110.

Thanks to everyone for your responses. I really appreciate it.

 

[gotboostvr]

I was using 15gr of unique under a 460gr WFNL boolit in my 3" comped 500mag which isn't exactly an apples to apples comparison, but I was splitting cases in pretty short order. Primers (Win LPP) looked good, not flattened and extraction was easy. Brass was a little dirty leading me to believe case splitting was due to too much roll crimp. VERY accurate and stout, but not strong recoil. No velocity data however.

Just sharing my experience with unique in the big magnum.

 

[Obturation]

I was using 15gr of unique under a 460gr WFNL boolit in my 3" comped 500mag which isn't exactly an apples to apples comparison, but I was splitting cases in pretty short order. Primers (Win LPP) looked good, not flattened and extraction was easy. Brass was a little dirty leading me to believe case splitting was due to too much roll crimp. VERY accurate and stout, but not strong recoil. No velocity data however.

Just sharing my experience with unique in the big magnum.

In your experience can too hard of a crimp cause cases to split? Curious cause I've had starline 454 casull cases split on first loading with a known good load I've used for years, I always crimp pretty dang hard on heavy magnums but maybe this could be the cause? I do notice the starline cases are much harder than federal or winchester cases - none of those have split with several loading.

 

[gotboostvr]

In your experience can too hard of a crimp cause cases to split? Curious cause I've had starline 454 casull cases split on first loading with a known good load I've used for years, I always crimp pretty dang hard on heavy magnums but maybe this could be the cause? I do notice the starline cases are much harder than federal or winchester cases - none of those have split with several loading.

I think so, I don't have any hard evidence though.

I've split more cases in 357mag with heavily roll crimped lead boolits which I don't push as hard as similarly weighted jacketed bullets with less of a crimp. I believe it's over working the elasticity of the brass.