Cast alloy repeatability expanding bullet tests.
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Thread: Cast alloy repeatability expanding bullet tests.



  1. #1
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    Cast alloy repeatability expanding bullet tests.

    Most of us bullet casters judge our alloys by hardness/malleability factors, using many different methods of doing so...everything from hardness testers, to lead pencils, to the almighty sledge hammer!

    As those of you that follow my work know, I have been working on expanding bullets for the lighter loads in the SG 35. I started at 50/50 (wheel weight/pure lead) and water quenched that alloy from the mold and the results are posted in preceding threads. After studying the results I decided to move up to a 75/25 water quenched alloy to allow for just a bit less expansion, and greater retention of the lower part of the the bullet which would allow for a bit greater penetration potential.

    Like most casters I weigh my alloy components by percentage, and have always felt that my consistency from one batch to another has always been close, but as most casters know there are other variables involved that could change the outcome of the final product.

    So, to "measure" hardness in a different way, to check malleability at the same time, and to give me a measurable parameter to judge future alloy batches by, I decided to try a compression ratio test.

    For this test I used a hydraulic press, air powered, and, after some testing with the finished product (cast bullets) I found the outcome of this test and the repeatably to be excellent.

    After running a number of bullets of the same alloy through the test process I found that 400 psi was the sweet spot in all regards. It allowed me to "see" the bullet that I would shoot and hunt with compressed to about 50% of its diameter. I could visually check for malleability....no breaking or cracking of the alloy, and, I could measure the thickness of the compressed bullet and apply that measurement to the alloy being tested. By carefully and exactly applying 400 psi to "same" bullet alloy samples I found that the hydraulic press was very accurate giving a tolerance of + - .001, or a .002 parameter. For the purpose, I thought that was excellent!

    Pictured are the results of the first test with three different alloys....the 50/50 WQ, the 75/25 WQ and Wheel weight WQ.

    This process will allow me to test my alloys for "comparative" hardness and malleability against a set measurement parameter of "known" alloys. I will also be able to mix and test at the bench which will allow for instant repeatability of a specific alloy. The actual "hardness" of the bullet...the BHN......can be tested by normal processes for the purpose.

    Anyway, something of interest to me that will allow me to take the testing of my expanding cast bullet alloys to the next level, and I am sure it will aid in batch to batch alloy consistency.

    Thought this may be of interest.
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    It would be cool to compare a wide range of crush test bullets to the standard hardness tester and see if it would be a more precise hardness tester.

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    Good point rooter!!!! If the repeatability with this compression ratio test is consistent...which it has shown to be, then the next step would be to assign a BHN number to each sample. It would really only have to be done once, and then the compression ratio test could be used on subsequent batches and the BHN number should apply to "same" measurement results of the samples.

    I need to get a new pencil set to check BHN, and when I do, I will add the BHN number to each sample....that will be a good follow up test after the Compression ratio test is complete and will add validity to the test procedure.
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    another interesting test, cast up some, do all your testing and set aside the batch. test again after 6 month and a year. see if they age harden or soften as some casters claim.
    dpe.ahoy, sindbad and Flat Top like this.

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    Most of my cast stuff in the past has usually been pretty hard, somewhere in the area of 18-20BHN. As far as expansion goes it's something that I really wouldn't want to write home about, but at least the barrel never had lead deposits. Right now I'm using a softer lead, pretty much straight Isotope lead with a smidgen of Lino and Plastic coating them, or PC for short. I've done very limited testing, doing what I do there just isn't much time at the end of the day. I've done mostly pistol cals and not to many, but the full power 9mm with the PC bullets don't lead the barrel and expansion is.....just a tad more. The 357mag I just loaded this morning I'll be able to test later, right now I've only used the 158gr at 1200FPS with no issues. Expansion is better with the softer lead but I want more, little by little I'll creep up on the speed to see how it goes.

    PC'ing isn't really all that new, maybe a couple of years, but it does have it's benefits and I kinda like the stuff, real simple to apply. I'll move up to rifle cals later as time permits. Some folks PC there rifle bullets, some claim pretty good accuracy, even better accuracy after PC and then using the older method of lubing the grooves.

    dpe.ahoy, moofy07, sindbad and 3 others like this.

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    Grumpa; I have been using that 50/50 WQ alloy (pretty soft) that I have talked about in previous posts (for the SG 35) in my 44 Mag Blackhawk....250 Keith at 1000 fps with absolutely no leading at all...not even a speck. I throat my chambers and lap all my barrels (matter of fact I am in the middle of hand lapping a Redhawk now) and the Blackhawk that I shoot the 50/50 WQ bullets in is very accurate....also, the 50/50 alloy will show a bit of expansion at that velocity and the most important thing is that it should maintain a very high percentage of retained weight. I plan on doing a more thorough test of that alloy in the 44 mag when the weather breaks but from my preliminary testing that alloy looks good to go. I believe that alloy should do very well in the 900 to 1800 fps velocity range.

    The issue with revolvers and leading is usually found in the barrel at the barrel thread/receiver intersect. When they wrench that barrel in to the receiver at the factory it creates a constriction in that area...sometimes as much as .003 or more. When the bullet enters the forcing cone and then moves into the rifling that constriction swages the bullet down whatever the amount of the constriction is and then the bullet enters the balance of the bore undersized....so you get scrubbing and pressure blow by (gas cutting), and that creates leading. Jacketed bullet are a bit more forgiving in that situation, and the only way I know of to cure that problem when using cast bullets is to lap the bore. Once the bore is lapped and the constriction is gone, the cast bullets should be sized about .002 over the slugged bore diameter. Once that is done the cylinder chamber throats need to be sized (throated) to allow the .002 oversized bullet to barely clear the throat before it enters the forcing cone. When the bullet enters the bore, it is swaged to precisely fit the bore diameter, and eliminates scrubbing and gas cutting and accuracy improves greatly and the leading is minimized...or in some cases gone for good.

    I have never tried the fancy bullet coatings....just use Veral Smiths Soft Blue lube...and using the process I described above have produced some very accurate revolvers with minimal to no leading issues.
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    FlatTop, you got some pretty good ideas floating around. I'll be keeping up with this and subsequent posts and hopefully be able to get some consistancy in my alloys.
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  9. #8
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    Lipripper: I hope to wrap my testing up on Monday, so stay tuned!!! My 50/50 alloy worked well, but I think that a 75/25 alloy will allow for a bit more of the base of the bullet to be left after impact and penetration. I am looking for 1/3 of the bullet length to be undisturbed (the base of the bullet).....and I "think" that the 75/25 alloy will allow that. Check in on Tuesday, I should have the results on this forum if all goes well.
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