Hello
Factory duplication for a 158gr JHP can be done with 16.6grs H110/296 with a mag primer. This will duplicate both the Remington and Winchester loads.
Yes, 8.0grs Unique will be a little snappy.. 7.5grs would be more pleasant.
There's some irony in your statement, plus a few things of importance that need to be more fully discussed.
I have to go all the way back to the Hornady second edition to find a .357 Magnum 158 gr Jacketed bullet load using Unique. The test firearm was an 8 3/8" Model 27 (N frame). That edition was first published in 1973, but re-prints were made until 1979.
The start load was 6.1 grains with a velocity of 800 fps and the top end load was 8.0 grains with a velocity of 1100 fps.
There were no H110/Win 296 loads in that edition, but they do appear in the 3rd edition in 1980, while the Unique loads are no longer present. (That doesn't mean Unique is a bad powder in .357 Magnum, it just reflects the fact that newer editions of load manuals usually try to make room for newer powders.)
The 158 gr jacketed bullet start loads for H110 and Win 296 respectively are 12.1 grains and 14.1 grains with 1000 fps in the same 8 3/8" Model 27. The top end loads are 16.5 grains and 1250 fps for H110 and 17.0 grains and 1300 fps for Win 296.
If you fast forward to the Hornady 10th edition, they're using an 8" Colt Python The H110 / Win 296 loads for a 158 gr jacketed bullet start at 12.7 grains and 12.4 grains respectively, both with a velocity of 1000 fps. The top end loads are 15.6 gr for H110 and 16.0 grains for Win 296, both with a velocity of 1250 fps.
Two things to note here are:
1) Something to consider is that the 158 gr jacketed hollow point bullet used in 1973 wasn't the same as the 158 gr XTP hollow point used in 2016 in the 10th edition. Bullets in the same weight and diameter can still vary significantly in terms of their bearing surface, jacket hardness, jacket thickness and core hardness. These differences effect the "stickiness" in the bore, and in turn have an impact on the maximum average pressure of the load.
2) It's been known and acknowledged by Hogdgon for several years now that H110 and Win 296 are the same powder, made in the same lots and then just packaged with different labels.
What seems to be lesser understood, but something that is obvious in the load data, is that there is a significant amount of lot to lot variation in H110/Win296, particularly for a cannister grade powder. If you look at the 10th edition data above you'll note a .4 grain difference in the maximum load between H110 and Win 296.
Remember that by this time (2016) it was well known that these were nominally the same powder. What that is telling you is that there is a great deal of variation in H110 and Win 296 and that you need to work your loads up very carefully over that last grain or so when working up to a maximum load. H110/Win296 is a colloidal ball powder. These powders are popular with ammunition companies because they are quick and easy to produce, and cost less. Olin developed the process and that process is essentially to make large lots of powder, measure it's burn traits and then mix different lots of powder to produce a final lot that has the required burn specifications.
For commercial bulk powders, these specs are pretty wide and the ammunition company will buy a 10,000 pound lot and then work up a load for it.
Cannister powders used by hand loaders are made to tighter standards, but as you can see in the data, those standard are still wider than the norm for cannister powders.
Another example of the wide specifications in colloidal ball powders consider WC 844 and WC 846. WC 846 was used in M80 ball ammo (147 gr 7.52x51mm NATO), and it was also used in early M193 ball ammo (55 gr 5.56x45 NATO). However, it was only one end of the WC 846 specification that produced the required results in M193, so they split the former WC 846 specification into WC 846 and WC 844. WC 846 is more or less the commercial bulk equivalent of cannister grade BLC-2, while WC 844 is more or less the commercial bulk equivalent of cannister grade H335. Back in the day they all fell under the same, very wide WC 846 specification.
Despite this you'll still see folks giving a precise charge weight of WC 846 for M80 ball clone loads and a precise charge of WC 844 for M193 clone loads, when in fact there was never a precise load for anything other than a single 10,000 pound lot of WC 846. Some of those same geniuses will tell you that BLC-2 and H335 data can be used verbatim for WC 846 and WC 844. That's not the case given the wider specification for the bulk powders.
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Now, back to the irony bit that I started with:
"Factory duplication for a 158gr JHP can be done with 16.6grs H110/296 with a mag primer. This will duplicate both the Remington and Winchester loads.
Yes, 8.0grs Unique will be a little snappy.. 7.5grs would be more pleasant."
First, there isn't really an exact load such as "16.6" grains of H110/Win 296 that will duplicate factory performance. Remember the 0.9 grain difference between the maximum loads for the two of them in the Hornady 10th edition data? You can't have a 0.9 gr lot to lot difference and claim there is a precise load that duplicates factory performance. You're going to have to work that up yourself.
Second, that 8.0 grs of Unique isn't going to be nearly as "snappy" as a comparable load of H110 or Win 296. Setting aside for a minute that H110/Win 296 loads have gotten a lot hotter over the years, and using Unique and Win 296/H110 loads that produce the same velocities, the Unique load will always have a lot less recoil.
The reason for this is that the bullet is not the only mass being ejected from the barrel - the powder is also being ejected and it's being ejected at about 3 times the velocity of the bullet. That powder has the same mass and produces the same recoil regardless of whether it is unburnt, partially burnt or completely converted to gas and plasma.
If we go back to out 8 grains of Unique launching a 158 gr bullet at 1100 fps, and then select a H110/Win 296 nominal load of 15 grains that is in the ball park needed to produce the same 1100 fps in the same 8 3/8" in barrel, you'll have 5.37 ft pounds of recoil energy in a 2.5 pound revolver compared to 6.95 ft pounds for the H110/Win 296 load.
The irony is not just that the H110/Win 296 load is "snappier" than the Unique load, but also that the shooter will swear up and down that the H110/Win 296 load is faster because it produces more recoil, even though the actual velocity of the bullet is identical.
I'll also throw out an observation made over 20 plus years of handloading .357 Magnum with Unique and other powders in short barrel .357s and chronographing those loads. Contrary to
popular internet and gun rag rumors, a maximum load of Unique won't give up much if any velocity in a short barrel revolver (2"-3") compared to a slower burning colloidal ball powder like H110/Win 296, especially as the bullet weights get lighter (140 gr, 125 gr, 110 gr). The Unique loads will however have a lot less felt recoil.
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I'll also suggest a great deal of caution when using "maximum" pressure .357 Magnum loads.
The data above was developed in N frame, or N frame sized revolvers. If you develop a load in an N frame and then shoot it in a K frame you'll more often than not find the cartridge sticks in the chamber. In fact, if you develop a load in an N frame to the point the case starts to stick, and then shoot the same load in a K frame you'll have to tap pretty hard to get the case out.
That's why most manufacturers are not in fact loading the .357 Magnum to it's full pressure limit.
Personally, I'll work up a load in a .357 Magnum K frame only to the point the case starts to stick, and then back off to the point where it no longer sticks. For a self defense load, I give that priority over an extra 50 fps or so, as I prefer the ability for a fast and clean ejection and reload, especially with a short barrel .357 with a less than full length ejector rod.
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The things you need to take away from this are:
1) SAAMI changed the maximum average chamber pressure for the .357 Magnum from 46,000CUP (around 43,500psi) to 35,000psi in 1993. Which was about a 19.6% reduction in pressure. This was a result of more accurate measurement with piezo electric rather than copper crusher instrumentation, and recognition that the old .357 Magnum standard might have been a bit warm for a steady diet in K and J frame revolvers.
Most load manuals will reflect that change when you compare old and new manuals, but it's not an exact date as SAMMI only publishes updated data every 6 years or so. It's also a voluntary standard.
2) H110/Win 296 is the same powder, but it's made to a wide specification compared to most other cannister grade powders and you need to use caution when developing maximum loads, especially when you are substituting any components. You need to start at least one grain below maximum, and you need to start well below that if you are using generic data or are substituting a different brand of bullet.
3) Regardless of what the manual says, you need to pay attention to the load in your revolver, and when it starts to stick in the chamber, it's telling you that you're getting so much elastic expansion in the chamber that it is allowing more expansion in the brass than the brass can recover from, causing it to stick in the chamber. It's your sign to back the load off.
