- February 2, 2017 at 8:32 pm #33256
I was asked over on CBA to pressure test some loads the boys have developed over there for use in solid frame 38 S&Ws. Posted this there and thought someone here might find it useful also. Not many around shooting the old 38 S&W. I bought the pictured H&R revolver many years ago for $5 at a local pawn shop. I was a LEO firearms and tactics instructor for a 3 county area. In disarming technique training toy guns didn’t last long and there wasn’t the plethora of fake training guns of today available. So I used the H&R. For all the rough handling it had it still shoots surprisingly well. Anyways, here’s the article;
38 S&W Pressure Tests
Earlier in this thread I offered to test some of the loads mentioned for pressure to determine what level of safety there was for the different strength of revolvers made for the 38 S&W cartridge. Ed Harris graciously sent me some bullets and the data for several test loads. I also had on hand three 38 S&W factory loads plus my own 38 S&W load I use in my Harrington & Richardson revolver.
The test handgun is a TC Contender with a 7.94″ long 357 magnum barrel. The bore is .347 and the groove is .357. A strain gauge is attached over the center of the chamber (as per SAAMI specifications). With a 38 S&W cartridge chambered the gauge is over the case just below the base of a factory seated bullet. The strain gauge is attached to an Oehler M43 PBL that is interfaced with a laptop computer which has the software. As you will note on the Oehler data sheets there is considerable data input on the conditions, test firearm and load information prior to testing. Each strain gauge is calibrated by the manufacturer and that is also input. I also use factory ammunition as a “reference”. Before each test the M43 runs a check on the gauge to ensure all is correct. A test cannot be done if that test is not correct.
The Contender has a 2.5X scope mounted and with quality 357 cast loads will put 10 shots into one raged hole less than 1″ ctc at 25 yards. However, with the shorter 38 S&W cartridge the bullet exits the case it is not supported as it is in a revolver by the cylinder throats before entering the barrel. In the Contender chamber there would be considerable space around the bullet in the longer chamber for probable misalignment before the bullet enters the leade. Previous testing showed accuracy could be quite good and very poor. Since I’m probably the only one shooting any 38 S&W out of a Contender that isn’t a problem those of you with bullets that properly fit your revolvers cylinder throats have. The test groups were cut out and pasted to the Oehler data sheets.
With low pressure loads the M43 PBL will not provide any measurements unless sufficient data is measured. This means any data from such shots will be “lost” including the velocity. To alleviate that problem I also set up a M35P Oehler in tandem with the M43 PBL screens to at least capture the velocity. It also is interesting to compare the measured velocity data. If the M43 PBL doesn’t measure all the shots in a test string the M35P still provides velocity information (generally a lower velocity shot wasn’t measured) for study. An example of that will be shown. The M35P print out is pasted on the Oehler M43 data sheet left of the “shot Data” and “Summary” data.
- February 2, 2017 at 8:35 pm #33257
The chamber on the Contender is to minimum specifications for the 357 magnum and most 38 S&W cartridges will not chamber. However, the R-P factory 38 S&W cartridges would chamber,,,,very tightly. I had on hand 50 new Starline 38 S&W cases and W-W and R-P 38 S&W fired cases. All of the Starline and most of the fired R-P cases would chamber when FL sized in a steel RCBS 357 FL die. With bullets larger than .358 seated they would not chamber. Thus all the test bullets other than the R-P factory that would chamber were sized .358 or .357. The R-P factory bullets measured .362 in front of the crimp and .354 on the seated bullet diameter. The W-W factory bullets were .350 – .352 on the seated portion. It is no wonder, as you will see, that accuracy was less than stellar out of my H&R with its .362 cylinder throats, .351 bore and .360 groove diameter.
In the following picture we see the bullets used: left to right; R-P factory, W-W factory, Western Lubaloy factory, Ed Harris provided the 36-125T, the 36-155D and the 36-151H and I provided the Lee 356-105-SWC. Also is a picture of the 3 bullets Ed provided loaded and another of the three factory loads.
CC! 500 primers were used. A roll crimp was used in the crimp groove of each bullet. All powder charges were weighed individually on a Redding scale.
- February 2, 2017 at 8:39 pm #33258
The following are the test results.
The R-P factory load was tested first as the rounds would chamber so it would give a “reference”. Previous chronograph results out of the H&R revolver showed the R-P to give 60 – 100+ fps greater velocity than other factory loads. It also had more powder; 2.2 gr vs 1.7 and 2 gr, than the W-W and Western factory loads. The MAP (Maximum Average Pressure) measured was 16,300 psi. SAAMI MAP for the 38 S&W is 14,500 psi. The SAAMI MAP for the 38 SPL is 17,000 psi and all 38 SPL factory ammunition I have tested (numerous actually) in this barrel fall below that MAP so the psi measurement is correct.
I also pulled bullets of the W-W and Western factory and loaded them and the factory powder charges into sized W-W 38 S&W cases that would chamber. Neither of those two factory loads produced enough psi for a measurement. It takes 5 – 7,000 psi to expand the case to put pressure on the barrel and another few thousand psi for a “strain” on the barrel to be measured. I have measured as low as 9,000 psi with this test barrel with target 38 SPL loads. However, given the expansion ratio and loose fitting bullet in the longer chamber the lowest psi measured during this test was 11,700 psi. Thus the W-W and Western factory loads were all less than 11,700 psi as were any other load that did not measure.
Looking at the time/pressure traces to the uninitiated they can be of concern. Those are quite normal for low psi loads where the powder is not burning that efficiently. A comparison of the average velocities between the M35P and the M43 demonstrate very good consistency. The accuracy of the R-P load was extremely good.
Ed Harris 1 test is the 36-125T bullet over 3 gr Bullseye (Alliant). That is a short stubby bullet that was presized at .357 and lubed with LLA(?). I feared accuracy would not be that good given the loose fit in the 357 length chamber and was correct. Nine shots went into 2.137″ but a flyer (note the oval bullet hole) enlarged the group to 3.2″. The MAP measured 15,300 psi.
Ed Harris 2 test is the 36-125T bullet over 7.0 gr 2400 (Alliant). It proved to be a very erratic load and the 3.86″ group demonstrates that. Obviously there is not enough bullet mass for 2400 to burn efficiently at this low of a load.
- February 2, 2017 at 8:42 pm #33259
Ed Harris 3 test is the 36-155D over 2.5 gr Bullseye (Alliant). The 36-155D is a very efficient looking bullet. It was presized at .357 and lubed with LLA. This is a very good load demonstrating excellent accuracy potential and a MAP of 16,600 psi which is very close to the R-P factory load. Note the 1st shot was out of the previously 2400 fouled barrel and was out of the remaining 9 shot group. Those 9 shots went into 1.32″ which is very good.
Ed Harris 4 test is the 36-155D over 6.2 gr 2400 (Alliant). Here we see while we may assume accuracy to be good based on 8 shots the 2 high flyers tell us something is amiss. The internal ballistics identify that something; again 2400 at this low of a load is not burning efficiently as indicated by the very large ES figures for velocity and pressure measurements along with the erratic time/pressure curves.
Ed Harris test 5 is the 36-151H over 2.8 gr Bullseye (Alliant). This is a very consistent load and note that by seeing how the time/pressure traces are smoothing out. Also note the low psi ES’s across the board. Hey, accuracy was pretty good too! The one high shot was the high velocity. The bad news here for the 38 S&W is this load is pushing into 38 SPL+P psi range
- February 2, 2017 at 8:43 pm #33260
Ed Harris 6 test is the 36-151H over 6.5 gr 2400 (Alliant). Here again we see the powder beginning to burn efficiently with low psi ES’s and much smoother time/pressure traces. Accuracy was excellent with 9 shots in 1.4:. The lone flyer, shot #9, was an abnormally low velocity. This load had the highest velocity and test MAP at 19,600 psi….definitely into 38 SPL+P range.
This test is my own 38 S&W load developed for the break open H&R and Iver Johnson revolvers. I use W-W 38 SPL cases trimmed back to 38 S&W length. WSP primers wer used. The bullet is the Lee 356-105-SWC which drop the bullets at .361 with COWWs + 2% tin alloy. I leave them unsized and Lube with LLA. They are loaded over 2.5 gr Bullseye. Out of my H&R hammerless revolver (3 3/16″ barrel) they hit point of aim out to 25 yards with very good accuracy. However, for this test so they would chamber in the Contender the bullets were sized .358 and the cases were sized in the 357 steel FL die. As we see from the Oehler M43 data sheet only one of the ten shot test gave sufficient psi to measure. That was shot #4 and the psi was 14,300 psi. The remaining nine shots then had a psi less than the SAAMI MAP for the 38 S&W (14,000 psi). Note, as mentioned earlier, the M35P printout (pasted to left of Shot Data and Summary gives the velocities for each shot. Thus we still have a record of the entire test string. Accuracy was very good with a 1.235″ group.
- February 2, 2017 at 8:45 pm #33261
The last test was to chronograph and test for accuracy the 3 factory loads out of my H&R hammerless revolver. I was quite pleased with the ES and SD of all 3 loads from the revolver. As we see the R-P gave 60 – 100 fps greater velocity. That was as it should be given the higher psi of the R-P load. Accuracy was very poor, consistently poor for all 3 loads actually, which given the undersized factory bullets didn’t surprise me. On the target the R-P bullets are in the lower circle, the W-W in the middle circle and the Western Lubaloys in the top circle. As the velocity increased the point of impact lowered as usual for a revolver.
And there we have the test results. My only caution is that with the exception of my load which was developed for the break open revolvers to keep under the SAAMI MAP that all the other tested loads, including the R-P factory load, were over the SAMMI MAP for the 38 S&W. A couple test loads were over the SAAMI MAP for the standard 38 SPL. Due caution should be exorcized to use those only in appropriate revolvers which are also chambered for the 38 SPL.
- February 3, 2017 at 1:04 am #33267kensParticipant
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how do you come to a calibrated breech pressure? What known standard tells you a control pressure that the strain gage correlates to the delta voltage?
I assume the strain gage on the barrel is but one leg of a wheatstone bridge, correct? Where is the other 3 legs?
I am not disputing your info, but asking how to come to a control measurement.
I worked instrumentation in developmental flight test, worked with gages, completion circuits, and troubleshooting of the circuits and calibrations. The bulk of our stuff was calibrated in a lab before we installed it on the helicopter. We put strain gages on the rotor blades, and all the other rotating stuff.
- February 3, 2017 at 2:14 am #33270Rattlesnake CharlieParticipant
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In the summer of 2011 a coworker had a solid frame S&W in .38 S&W. For real, it would not chamber a .38 Special. He asked me to load up something more effective than factory RN ammo for use on armadillos. His place in TX was overrun with them, and he was tired of them running off after being shot with the RN ammo or even .38 ACP HP. I had a single cavity mold for the Lyman 3602433, which is the correct diameter for his revolver as well as it is a full wadcutter with most of the bullet out of the case to maximize case capacity. I did some research and found the best load used IMR 7625. I finally found that at a farm supply store in Alamosa, Colorado. $26 and change. Anyway, I can’t remember the charge weight, but he did report that it anchored the armadillos much more effectively that factory RN stuff.
- February 3, 2017 at 3:01 am #33274
“how do you come to a calibrated breech pressure? What known standard tells you a control pressure that the strain gage correlates to the delta voltage?”
I do it just like the big boys do it.
When the ammunition and/or firearm testing technicians (ballisticians) install a new pressure test barrel or a peizo-transducer the transducer is first calibrated. In the use of the strain gauge each gage comes with a “factor” which is measured when it is manufactured. That “factor” is entered into the program (data sheet, center column). There is also an “offset figure input. That is based on the type of steel the barrel is. The thickness of the barrel is also measured and input. Additionally the strain gauge is located over the chamber as per SAAMI specifications. When preparing for a test the M43 runs a self analysis and if not correct it will not test.
When the big boys have a new test barrel they then use “reference” ammunition (SAAMI supplied if available) or a previous lot of ammunition (their own or someone else’s) in which the pressure has already been verified. They then test that and use the difference as an offset figure to get the psi of additional test ammunition. That procedure is specifically spelled out in the SAAMI guidelines. In my case, since I am not an ammunition manufacturer, SAAMI will not sell me “reference” ammunition and if they did the cost would be prohibitive. So I use the SAAMI specified alternate method; the use of previously tested ammunition.
When I set this 357 magnum Contender barrel up as a test barrel I purchased a box of Federal 357 magnum and a box of Winchester 357 magnum ammunition. I then contacted the technicians at Federal and Winchester and gave them the lot #s of the purchased ammunition. They graciously provided the MAP and test conditions for those specific lots of ammunition. I then tested the purchased ammunition and found the Oehler M43 measured MAP of the Federal 357 magnum was 200 psi less than the Federal measurement. The Winchester M43 Measurement was 300 psi higher than the Winchester measurement…….I called that close enough for government work.
Additionally, every time I set up the M43 I run a 10 shot test with my test .308W rifle using the same lot of M118 ammunition. Then in the case of this test I also ran 3 factory loads not only because I wanted to test them but as a “reference” also.
At this time I currently have 27 test barrels/firearms and all have been “calibrated using the same method as described. With those 26 barrels/firearms I can test 30+ cartridges + 2 shotgun shell lengths. That’s how I do it.
- February 3, 2017 at 3:09 am #33276
Back in my LEO days when I was the firearms and tactics instructor for 3 counties I was testing some Second Chance test patches of Kevlar for the purpose of convincing the COP that such vests might be nice to have……..
As per the suggested test procedure I affixed the patches to a 12″ thick bundle of magazines. All was going well until I used a S&W Victory model 38 S&W revolver with the daunted 200 gr “man stopper” load. The bullet bounced back off the Kevlar patch and hit me in the belly. It only left a welt…….only time I ever, or ever planned to, shot myself……..funny but it was that which caused the chief to buy the vests……..
- February 3, 2017 at 3:26 am #33278Rattlesnake CharlieParticipant
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Good laugh, I always thought those British man stopper loads were dreamed up by someone drinking way too much gin. The load I came up with was from this side of the pond. 150 gr, and likely right up there with .38 Special results. A full WC also performs much better than a RN. IMHO, of course.
- February 3, 2017 at 4:55 am #33281ScharfschuetzeParticipant
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Great write up Larry. Glad you didn’t blow that long suffering TC Contender up with those “excessive” loads! 🙂
- February 3, 2017 at 2:13 pm #33291
Oh yeah, recoil was so fierce with those W-W and Western Lubaloy factory loads I was watching the bullet flight to target through the 2.5X scope…….:rolleyes:
Note in the Standard Atmospheric Ballistics table the bottom figure is the computed recoil in ft/lbs. The test loads ran 1.1 to 2.1 ft/lbs of recoil……my 105 gr SWC load was a whopping .8 ft/lb……pretty darn impressive if you ask me…….;)
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