357 Mag and Bullseye

[filmmaster]

If you bother to read the ctg information in your Speer manuals instead of just looking at the load tables you might learn something. They clearly state that velocities with their 158 gr swaged SWCs are kept low to prevent leading. The so called maximum load of 4.8 grs of Bullseye reflects that. Speer # 11 lists a maximum load of 7.1 grs of Bullseye with a 158 jacketed bullet which is in line with top data in other manuals. Read your manuals folks. Don't just look at the load data and ignore all of the "boring" information they contain.

Many manuals do not specify the actual bullet being used. Speer uses their swagged lead bullets, but admits the other data from other companies offer made with "cast bullets" will work just fine, just expect to be a lead miner after shooting.

Lee modern reloading 2nd edition gives 148 wadcutter loads, but doesnt even specify HBWC or DEWC in the book

 

[Warren Sear]

... But I don't know the cup to psi conversion...

There is no conversion. Two different methods used, and they do not directly relate to one another.

 

[pasound]

I use Bullseye for my .38 target HBWC and WC loads, Unique and Universal for my cast SWC .38 and .357 mid-range, and 110 and 296 for my jacketed and hard cast full power loads. Each powder to each use.

I use coated Missouri Bullets for both .38 and .44 loads, but Bullseye for plinking only. Better accuracy and velocity with a higher volume of slower powder.

 

[DWalt]

There is no conversion. Two different methods used, and they do not directly relate to one another.

That is correct, there is no conversion factor or formula. However, CUP will be lower than the peak PSI obtained from a piezo gauge for the same load. Just how much lower depends on a number of factors, but it is usually taken as being around 15%. Or another way to put it is that the copper crusher method does not actually indicate the true peak pressure, but gives more of an average pressure. Piezo gauges do read instantaneous peak pressure as their response time is so fast.

No ammunition manufacturer anywhere today (with the possible exception of some third world countries) uses the old copper crusher pressure measurement method as the piezo method is so vastly superior. As I have said in the past, using the copper crusher method is sort of like trying to tell time accurately by using a sundial.

 

[alwslate]

The difference between CUP pressures and PSI pressures will vary depending on the ctg. If you study the manuals you will see in the case of the .357 magnum loads listed as 35,000 psi and 42,000 cup are about the same. So the top loads listed in the old manuals do not exceed current pressure limits.

 

[Forrest r]

Nothing wrong with bullseye in the 357mag cases. Very consistent with good velocities for the amount of powder being burned.

Top row, 2nd from left (green bullet) a 158gr fn hp/mp 640 series
Bottom row center a 158gr fn hp/cramer "hunter" bullet

Playing around on the 50yd line with a s&w 686 6" bbl sitting using a pistol rest. These are 6-shot groups using both bullets pictured above and 5.5gr of bullseye along with 6.0gr of bullseye.

That's 2 different bullets using 2 different bullseye loads with the worst group being 2 3/16" outside to outside measurements on the bullet holes/6-shot groups @ 50yds.

 

[cowboy4evr]

I personally don't mind full magnum 357 loads and I shoot them the most . I shoot them in my 19's , 2.5" and 4" barrels . My 681 gets lots of them too . My 681 wears a pair of PC Magna's . I don't find it uncomfortable to shoot any of the above mentioned firearms with magnum loads . Proper stance is key ! Regards Paul

 

[Ole Joe Clark]

I tried unique and bullseye in the .357 loads, but quickly changed to 2400, 296 and I think, blue dot. Using powders that will fill up a pistol case is generally a safer load, no double charges. I used to love shooting some good hot, gas checked, cast bullets in the 686, and I was pretty accurate with it. I use the manuals, both old and new, sometimes just because I can cross reference them. I DON'T get my reloading data from the internet. It's easy to be safe and have fun shooting, but you must have a plan and stick with it.

Have a blessed day,

Leon

 

[Nevada Ed]

By the way............

if those coated 158 bullets don't work out,

I had good luck with coated 125 gr bullets with Bullseye and six other powders.

Have a Happy New Year.

 

[BC38]

That is correct, there is no conversion factor or formula. However, CUP will be lower than the peak PSI obtained from a piezo gauge for the same load. Just how much lower depends on a number of factors, but it is usually taken as being around 15%. Or another way to put it is that the copper crusher method does not actually indicate the true peak pressure, but gives more of an average pressure.

...If you study the manuals you will see in the case of the .357 magnum loads listed as 35,000 psi and 42,000 cup are about the same. So the top loads listed in the old manuals do not exceed current pressure limits.

I read these two statements back to back and it seemed that they couldn't both be correct. So I googled up this comparison chart that lists both values for 26 different rifle cartridges.
What I'm seeing is that in all but 5 cases the CUP number is consistently lower than the PSI number. And of those 5 exceptions 2 (yellow highlights) appear to have accidentally listed the same value in both columns and the other 3 (red highlights) the CUP number is higher.

Since there are 21 where the PSI value is higher and only 5 "exceptions" I have to wonder if the exceptions are the incorrect examples. Especially when there are more than one other example in the same range of values and they consistently show the PSI number as the higher value.

EDIT: Here is a link to the article where I got the table below
https://www.shootingsoftware.com/ftp/psicuparticle2.pdf
One thing I hadn't picked up on when I started this post is that the author points out on page 5 paragraph one that vecause this data is all for RIFLE cartridges, and that since they didn't test any HANDGUN cartridges one can't assume that the same correlations exist for handgun cartridges.
Another article I found here
CUP, psi & Reloading Data - Shooting Times
explains that the difference in cartridge shapes (bottleneck rifle vs straight walled handgun) and the cartridge lengths relative to where the sensor (copper crusher vs piezo electric) have to be placed in the test barrels for handgun cartridges has a bigger and different effect on the readings making the correlation less predictable.

So I'm going to do some more searching for a table of the same type contrasting PSI and CUP in handgun cartridges. Stay tuned.

 

[oysterer]

No, not Bullseye. Too fast a powder leading to high pressure. For full mag loads you use a medium to slow burner. Medium is HS-6, my absolute favorite. Another good classic is 2400, a slow burner. Those are the only 2 mag powders I have experience with. HS-6 is the best for medium power, no so much for full power. HS-6 goes well with magnum primers.

 

[ArchAngelCD]

Why oh why does a good thread have to be ruined by petty bickering? It needs to stop right now or I will have to lock this thread which I really don't want to do. If you want to bicker take it to email or a PM. I'm tired of having to say this.