Interesting 357 magnum chrono results

[TargetTerror]

So I finally got around to chronographing my .357 mag and 38 special loads in my 6 inch 686 and 2 1/4 inch SP101.  Here are the results.  The chronograph was ~10 feet away from the muzzle.  I was using WSPM for 357, WSP for 38.  All cases were mixed headstamp, untrimmed, with a heavy crimp from a Lee FCD:

686
38 Special, 125gr Zero JSP, 5.1gr Unique - 890fps Avg velocity, 220 m/e

357 Magnum, 158gr Montana Gold CMJ, 12.5gr 2400 - 1076fps Avg velocity, 406 m/e

357 Magnum, 158gr Zero JSP, 15.1gr H110 - 1175fps Avg velocity, 484 m/e

357 Magnum, 158gr Zero JSP, 15.5gr H110 - 1168fps Avg velocity, 477 m/e


SP101
38 Special, 125gr Zero JSP, 5.1gr Unique - 764fps Avg velocity, 204 m/e

357 Magnum, 158gr Montana Gold CMJ, 12.5gr 2400 - 945fps Avg velocity, 312 m/e

357 Magnum, 158gr Zero JSP, 15.1gr H110 - 1070fps Avg velocity, 400 m/e

357 Magnum, 158gr Zero JSP, 15.5gr H110 - 1045fps Avg velocity, 380 m/e

357 Magnum, 158gr Magtech JSP loaded ammo - 1025fps Avg velocity, 367 m/e


I was surprised at the velocities for the 686.  I would have thought them to be a bit higher.  I was even more surprised at how little loss in velocity I get out of the SP101 - only ~100fps from almost a 4 inch shorter barrel!  That is astounding.  The Magtech's are also pretty astounding - they are just about a full-house 357 magnum load, and I will definitely continue to carry them.

I was also surprised at the performance of H110.  Because velocity fell off in both guns as I jumped from 15.1 gr to 15.5 gr, 15.1gr seems to be right around max pressure.  I'm not quite sure why velocity would actually decrease.  I think my crimp was uniform, but admittedly one might have been more aggressive, I don't know. 

Final note: try not to flinch when firing a snubbie with a full house load.  The metal poles on the chronograph don't like getting hit 

[Lone Star]

I was surprised at the velocities for the 686.  I would have thought them to be a bit higher.

Every gun is a law unto itself. It is not uncommon to see different guns with the same barrel length vary in velocity by 100-200 fps.

I was even more surprised at how little loss in velocity I get out of the SP101 - only ~100fps from almost a 4 inch shorter barrel!  That is astounding.

Don't be too astounded.  If your long barreled gun was producing lower-than-expected velocities, then the "low" velocity loss is easily explained.

I was also surprised at the performance of H110.  Because velocity fell off in both guns as I jumped from 15.1 gr to 15.5 gr, 15.1gr seems to be right around max pressure.  I'm not quite sure why velocity would actually decrease.

Perhaps it really did not decrease if they were loaded identically save the charge weight.  It is not uncommon to get non-representative velocity averages with a small number of shots and a large extreme spread in velocity.  Had you fired 100 shots with each load and compared the average of the 15.1-grain load with that of the 15.5-grain load, the latter would have shown a higher velocity.  Hodgdon shows 15.0 grains of H110 as a starting load with the 158-grain bullet.  It would be very, very surprising if 15.1 grains was indeed a maximum pressure load in your SP101.


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[Graybeard]

Back when I first started shooting the .357 Magnum the 158s were rated at 1550 fps. I can't verify they were doing it since I had no chrono in those days but they were made by Norma for Browning so I suspect they came close. I know for a fact the recoil level of them and what we get today are not even remotely the same.

[PaulS]

H110 and WW296 used to be loaded into the "knee" region of the powders load curve. What this means is that as you load this powder the pressure goes up normally until just past the maximum pressure and then very suddenly the pressure curve dips over a .2-.3 grain load range to a point where the pressure is well into the safe pressure range. Then as you add powder the pressure spikes well above the nominal pressure. That was in the 16.5 to 16.7 grain charge with a 158 grain bullet. If you dropped the charge by a grain you could end up with an over-pressure condition. The industry standard loads have dropped to the normal curve below the charges that are in the pressure knee. The first loads were also with lead bullets and the velocities were higher than you can get with jacketed bullets.
Add to all that the small S&W revolvers that had problems with full house 357 magnum loads and you get the commercial loads that we have today. The powders, according to Hodgdon and Sierra have not changed (more than batch variations) over the years so the load data that was developed initially are still good with the equipment and conditions in which they were developed. Ruger and TC guns can definitely handle the loads of initial development.
I have loads for my Ruger  that have velocities of 1470 fps with 140 grain bullets. The loads are over the current listed loads but have always worked well in my revolver since it was developed with listed data. I have spoken at length with powder companies and bullet makers and they admit that the data is still usable under the conditions that I use when reloading and in the guns I shoot them. This is a very gray area and if you have any problems when using the "old" data then you own the responsibility for the damage to your gun and any injuries that may occur. I do not recommend that you dig out the oldest books you can find and develop a load using that data but if you have a load that has been in continuous use with the old data there is no reason to change it just because the manuals change their charges. (as long as it has shown no signs of over-pressure in your gun and continues to work reliably in your gun.

[Catfish]

I know Bill is right about those Norma loads we used to get back in the 60`s. They would flatten the primer in every case. I still have some of the brass, and may even be able to find a part of a box of the ammo.