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Old September 25, 2019, 02:57 PM   #1
Nickmcpheron
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I need a ruling!!!!!!!

I have been looking at loading 38 special with unique for some time now. My current manuals state a maximum for 158 gr lswc from 4.3 - 5.0. The revolvers that will use this load are smith and wesson: m64 (4 inch HB), m19 (4 inch), and m66 (4 and 6 inch). With 158 gr swc from rim rock will a steady diet of 5 grs of unique be fine with these k frames? I have read most of John Taffin's articles but have also read about "new unique"

What say you?

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Old September 25, 2019, 04:26 PM   #2
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Sort of depends on the gun and bullet. Speer shows, for standard pressure loads, the 0.66" long Speer 158-grain LSWC seated to 1.440" COL has a max load of 4.7 grains of the current Unique, and 5.2 grains is maximum for +P pressure for the same bullet at the same COL. At that COL, the bullet would be seated 0.365" into the mouth of a SAAMI maximum length case. What I don't know is the length of your bullet or the COL you get with it, so I can't compare seating depths to see if your pressure will be higher or lower than Alliant found. Cast bullets are made of a less dense alloy than soft swaged lead bullets and they have a lube groove and a pronounced crimp groove, so they tend to be a little longer than their swaged counterparts. Where the crimp groove is located will determine the COL you end up with, assuming you use it.

So, more information, please! Bullet length and actual COL you will use. With that information, I can estimate the pressure difference and an adjusted load limit.

As to the guns, I don't believe you will see any safety issue with the +P in K-frames, but you should, nonetheless, work up to the load making sure you don't get any sticky case extraction. Sticky case extraction indicates you should immediately back the charge down 5%, as your pressure is expanding the chamber past the brass yield point and the steel elastic limit is not be too far away.

I don't think you'll find issues with throat wear at these pressures. I've seen it in my .357's, but not in .38's. The K-frame should tolerate it fine. Nonetheless, the revolver with the mildest loads lasts the longest. My old routine was to load wadcutters for the bulk of my shooting. I'd start out a range session with maybe a dozen full power loads, after which the wadcutters felt so comparatively soft and mild that I felt no temptation to flinch at all. Made for better marksmanship. Better still, though, is to take a heavy magnum out for that first dozen shots. Then everything feels mild afterward.
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Old September 25, 2019, 04:45 PM   #3
Paul B.
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I've shot 5.0 gr. of Unique in .38 Spl. for years, not only in K frame gun but in my J frame M60. Bullet is the Lyman #358156 gas checked SWC. My bullet comes out closer to 160 gr. than 158 in my alloy. The load hasn't been any problem in either gun. Both guns are still as tight as the day I bought them.
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Old September 25, 2019, 07:49 PM   #4
Nickmcpheron
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UncleNick:
Thanks for the help. Here is the info:
OAL 0.693, Meplat 0.230, Nose to crimp groove 0.324 Rim Rock 158 gr swc
I will use the crimp groove
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Old September 25, 2019, 07:51 PM   #5
Nickmcpheron
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Paul B:
I appreciate the reassurance. It is my understanding that the rim rock plain base swc I choose is very similar to the one you use.
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Old September 25, 2019, 10:42 PM   #6
Radny97
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I need a ruling!!!!!!!

Rimrock is the manufacturer used by buffalo bore for all their lead loads. Great tough bullets.
If anyone has ever shot a S&W chambered in 38 special loose using published loads I’m not aware of it. Most 38 revolvers can take a lot more pressure than what the cartridge can dish out. And by definition ALL of them can take the pressure of official published loads.
Don’t overthink this, it’s not like rifle cartridges. Your load is an appropriate published load. Load up a few and try them out. If you have sticky extraction then go back to the drawing board. If not, you’re gtg.


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Old September 26, 2019, 08:53 AM   #7
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Nickmcpheron,

The difference in seating depth is only 0.004", which is less than the 0.020" spread in case lengths, so the pressure difference is within the range you'd have from different case lengths anyway. Not enough to matter. Out of almost 17,000 psi, the spread, including the 0.004" difference with the difference in standard case length from min to max (1.135" to 1.155") is about ±350 psi. Given that current proof pressure is 27,000 psi for both standard and +P in 38 Special, you are in no danger of getting anywhere near there from the 5-grain load. The Alliant maximum of 5.2 grains of current production Unique for +P will apply and can be used as well.

It looks like your COL will be 1.469" seated exactly to that crimp groove in a case that is 1.145" long (the SAAMI tolerance midpoint, aka, the trim-to value).

Seems like you are good to go.
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Old September 26, 2019, 12:51 PM   #8
Nickmcpheron
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UncleNick:

That’s awesome. Thanks again for the knowledge. I sure am glad I asked.
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Old September 26, 2019, 01:32 PM   #9
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5 grains of Unique is a tick over max for a .38 Special cast 158. A whole .3 of a grain according to Alliant. It's not to going to bother any .357 though. The Max load for a .357 158 grain cast bullet is 6.0.
The assorted OAL, Meplat, nose to crimp groove and any of those numbers make no difference of any kind. Neither do the revolvers.
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Old September 26, 2019, 04:50 PM   #10
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"Paul B:
I appreciate the reassurance. It is my understanding that the rim rock plain base swc I choose is very similar to the one you use."

The bullet I shoot is the Lyman #358156, a nominally 158 gr. bullet. I cast my own and they run closer to 160 to 162 gr. in my alloy. Always been quite accurate, even in the snubby. It'a also a very good bullet in my .357 Magnum over 14.0 gr. of 2400. Little to no leading in either cartridge.
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Old September 28, 2019, 06:41 PM   #11
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T. O'Heir,

It's still under the +P max though, and the OP just wanted to know if it would be safe in his K-frame guns and if it would put undue wear on them. Now, if he had an Airweight, this would be a different story.
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Old September 28, 2019, 09:54 PM   #12
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I was just about to post this question when I came across this thread,and I thought it might be appropriate.

I bought a Ruger GP100 .38/.357 about 20 years and have been shooting 125gr JHP with Unique 6.5gr as my .38 Sp load. No problems whatsoever with extraction. But I was looking data over from several sources as I investigated Titegroup and I cannot find ANY reference to a Unique load that high these days and I have no idea where I first found it.

It raised the question of danger obviously despite my having no indication of any problems. The 50th Ed of Lyman manual for .38 Sp. lists 6.0gr Unique w/ 125gr JHP as max with 16,700 CUP. I also shoot 125gr JHP with .357 cases using 17.0gr of 2400 and Lyman lists a max of 17.7gr delivering 40,600 CUP.

Clearly the 6.5 gr Unique load is delivering more than 16,700 CUP, but if the .357 load is 40,600 CUP is there really any danger with the excess .38 Special load?
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Old September 29, 2019, 02:33 PM   #13
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Alliant lists 6 grains for 38 Special +P, but 9.6 grains for a Gold Dot in 357 Magnum. QuickLOAD shows the greater start pressure of a JHP over the Gold Dot only takes about a 0.1-grain reduction to get a pressure match, so figure about 9.5 grains for the 125-grain JHP in a 357 Mag case. If both cases are loaded to maximum COL (the reason many bullets have two crimp cannelures or crimp grooves; one for each case) or they are under maximum COL by the same amount, the pressure won't be significantly different because the difference in max COL for the two cartridges makes up for all but 0.020" of their case length difference. So the volume the powder is burning in doesn't change much.

Bottom line, I estimate you are seeing pressure peaks of around 20,000 psi, which is above +P, but so far below 357 Magnum that you have no worries in your gun.

I will point out the CIP maximum pressure for 38 Special is 1500 bar, or 21,756 psi. I don't know whether Europe has fewer older guns in this chambering or not, but if you buy European full power 38 Special loads that weren't rolled specially for the American market, then you would be shooting at above this 6.5-grain load pressure anyway, even in a 38 Special chamber. With your gun, you have no worries.
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Old September 29, 2019, 11:11 PM   #14
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Thanks, Unclenick.

I shot 5 rounds each off a bench rest at 15 yards today with a 125gr JHP using Unique 6.5gr, CFE-Pistol 6.0gr (max 6.3) and Titegroup 4.3gr (max 4.5) and the winner was clearly Unique.

While I'm here, I thought it was on this thread but I can't find it, someone posted a comment involving 16,500 CUP was equal to 82,000 PSI. I recall seeing these formulas, even though it is claimed to be difficult to to draw a comparison;

PSI = CUP x 1.516 - 17902 with 16,500 CUP, PSI= 7112

CUP = 17902 + PSI/ 1.516 Using 7112, CUP = 16,500

Maybe the poster -or I -added an extra zero to that 82,000, but even 8200 doesn't come up in this formula Do you have any such formulas?
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Old September 30, 2019, 12:24 AM   #15
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I don’t know the formula but I can assure you that 16,000cup is not 80,000psi or vice versa. The lee reloading manual uses both psi and cup for different loads. It seems cup and Psi are very similar. Most loads listed at 16,000 psi are giving similar velocity to 17,000 cup pressure. Not very scientific just comparing what I can see. Hope this helps.
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Old September 30, 2019, 08:46 AM   #16
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I fund this on https://www.convert-me.com/en/bb/vie...php?f=2&t=6411

est » Sat Oct 26, 2013 2:11 pm

US Conversion (ANSI): PSI = -17,902 + 1.516 x CUP
European Conv (CIP): PSI = -2806.88 + 1.20911 x CUP

The US formula above is the same as what I posted above PSI=CUP x 1.516 - 17902

Here's a much more detailed discussion: https://www.shootingsoftware.com/ftp/psicuparticle2.pdf
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Old September 30, 2019, 10:33 AM   #17
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I've loaded a lot more rifle 's than I have handgun's. Something that has always bothered me with loading handguns is the speed the powder's burn. in a handgun it has always seemed to me that .2 gr of powder could destroy a gun. That would be in a rifle a powder chg already way over max. Have loaded a lot of 38 spec with the 148gr WC years ago. 2 1/2gr Bullseye was my favorite load, low recoil and about as accurate as I could ever shoot. never a pressure problem but then again well under max load. Strange I guess this adversion to max loads in a handgun, I load over max in rifles all the time. Then again I never load very hot loads in shotguns either! Something about working with powder that burns that fast. I did load some fairly hot loads in 38 spec for carry loads years ago. 115gr JHP in what I'd understood then would qualify as Treasury loads. I shot them in a Trooper MKIII 357. Don't know if it would have made a difference but was afraid to shoot them in a 38.
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Old September 30, 2019, 10:42 AM   #18
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No formula is exact converting one system to another. They're empirical approximations

Best info on both systems is in the Purpose and Data link for the cartridge in:

https://saami.org/technical-informat...ami-standards/

Use the tables in each one to compare a given cartridge's CUP and PSI numbers. Then use the formulas in post #16 to see their numbers. Post in this thread all the ones that match.

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Old September 30, 2019, 04:50 PM   #19
cdoc42
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BartB., I couldn't easily find the table you linked, but there was a table in the "shootingsoftware" link I provided. It listed comparable ANSI CUP and PSI pressures. ANSI = American National Standards Institute.

I only compared the first 4 pressures and it is obvious they are not even close when using the suggested conversion calculation. For example,

222 Rem: ANSI CUP 46000 ANSI PSI 50,000 Calc= 51,834 PSI
22-250: ANSI CUP 53000 ANSI PSI 65000 Calc= 62,446 PSI

But lower is
2506 Rem ANSI CUP 53000 ANSI PSI 63000 The calculation would still be the
same as the 22-250 (62,446)

The difference between the listed CUP and PSI values ranges between 9% and 23% just for the first 4 values, so one cannot even, e.g., take a reported PSI and figure it's generally 9% more than the reported CUP.

The problem is in choosing a powder. Lyman's 50th book has CUP and PSI values listed for a given bullet weight in .270. So if I wanted to pick a powder for a 150gr bullet, for example, in their list, that provided the highest velocity at the lowest pressure, the powders that list PSI instead of CUP would have to be eliminated in my choices.
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Old September 30, 2019, 05:04 PM   #20
Bart B.
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Quote:
Originally Posted by cdoc42 View Post
BartB., I couldn't easily find the table you linked, .
Pages 12 and 20 in the pistol and revolver document in

https://saami.org/technical-informat...ami-standards/

Download then open this Adobe Acrobat. pdf file: SAAMI – Z299.3 – Centerfire Pistol & Revolver – 2015

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Old September 30, 2019, 09:15 PM   #21
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The formulas are not for converting between CUP and psi. They are formulas for the least-squares fit trendline of the correlation between the two that runs through the data. The actual numbers deviate all around that line. Moreover, as Denton Bramwell, who came up with the correlation for SAAMI numbers said, it was only valid for rifle cartridges at pressures of 28,000 psi or CUP and higher (For the 45-70, the CUP and psi limits are the same 28,000 units).

So, how did SAAMI arrive at the two MAP numbers for each measuring system? When Ken Greene was still SAAMI technical director he was kind enough to spend some time on the phone with me about this fifteen years ago or so. It turns out they used the older copper crusher system to develop reference loads and then just fired those same reference loads in the conformal transducer to see what the result was. Some examples that prove how squirrely the relationship is:

Code:
Cartridge      CUP       psi
357 Magnum    45,000   35,000
223 Rem       52,000   55,000
308 Win       52,000   62,000
So, what you are seeing are differences in the dynamic response of the measuring systems to everything from piston inertia to pressure needed to push on it through the brass in the transducer rather than through a drilled hole in the crusher (usually; and where not, a reference load is used to correct the error). The bottom line is these measuring systems are not concise, though the CIP claims it can get within 3% of absolute, at least in ideal condition.

There is a lot of fudge-factoring in cartridge pressures, and even with all that, every once in awhile you can get commercial loads that pierce their primers or widen their primer pockets to the point the spent primers fall out when the spent case is ejected. It's not a tight science.
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Old October 1, 2019, 06:25 PM   #22
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So, at best, might the bottom line be in my .270 Lyman example just assume the maximum load listed for each powder under a particular bullet is just that -the max - and skip over the concern about accompanying PSI and CUP pressures -?
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