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Boomstick Bruce

inconsistant loads with TB powder

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10 hours ago, bgavin said:


This sounds like a good grounding wire would be beneficial.
Those loading in low humidity (winter heating) very well could be having static issues.

Thanks everybody.  So far, this has been a really informative thread.  Lots of experience and good deductive thinking here.  Provocative and useful posts.  

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All of my presses and PM's are hardwire grounded to a dedicated GND rod.

DO NOT ground to the house circuit.

OLG

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14 hours ago, Roscoe Regulator said:

There are references to "dirty", when what may be happening is that there is rarely enough pressure to form a 45 Colt case to the chamber. What does it hurt, if not in your face? By comparison, my 5.5" ported Redhawk 45 Colt is a different story shooting "Ruger-only" loads. Then my ejector may require a serious bump to dislodge the cases, which are still not shiny or clean at all but not the black we see in a cowboy load. That lately was with H110 and a 300 gr XTP using Hornady data. Wow!

Correct, the dirtiness of trailboss in the 45 is that most of us are running it lower pressure than needed to seal so you get blow back. I never minded it though, cleans up plenty easy.

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On 10/28/2019 at 4:36 PM, Springfield Slim SASS #24733 said:

I've heard people say that, but really, why would a Magnum load need a hotter flash? The powder is sometimes the same, just more of it. I always figured, maybe wrongly, the the primer cup was just stiffer to eliminate primer flow.  I'm sure someone here is in the industry and actually knows.

 

I don't think there is a simple answer. It gets a bit obscure, and you need to test.

 

Primers differ; different chemical composition, different amount of compound, and varying thickness and strength of cup. A little bit more internal volume can make a primer have inconsistent ignition.  Loading density does come into play, as does the ratio of the cases internal cross sectional area to height. Going from a 38 Special to a 357 Magnum case, just a wee bit over 1/8" longer can mean needing a primer change. 

 

A magnum primer may have a longer burn, (same compound, just more of it) or a hotter burn, (different compound). Every brand is different. 

 

For some magnum primers, yes, just the cup is thicker. The CCI 450 SRM primer has the thickest cup of all small rifle primers, IIRC. 

 

I don't think cowboy loads need a very tough primer cup, but some combos need a more powerful one. 

 

Here's a little fact; the pressure contained in the primer pocket is oft times greater than the pressure inside the case itself. My background in reloading was mostly rifle, and I looked at primers to estimate relative pressure (and measure the expansion at the presume ring, PRE). Reading small pistol primers for pressure signs is witchcraft IMNSHO. 

 

To try and make sense of what I was seeing, I loaded pistol cases with just a primer, no powder, no bullet, and fired them. I was seeing pressure signs similar to cases that were loaded with powder and bullets. I concluded that pressure from the primer explosion (priming compound is an explosive) was being sufficiently restricted by the flash hole that the pressure against the primer was greater than the pressure created after the powder ignited. The flash hole acts as a restriction in both directions, and it also act as a venturi, increasing the velocity of the primer flash.

 

About at this point I was developing a headache, but I was not deterred. I wanted to prove my theory.

 

I did more testing with firing only primers, but I increased the diameter of the flash hole in incremental steps. And, when the flash hole gets large enough, the primer no longer backs out, and it doesn't flatten either. I was satisfied with my proof. I loaded up some ammunition with these cases, they shot just like regular ammo, just no pressure signs for low power loads. 

 

My next step involved crushing all the cases with modified flash holes. With no access to a ballistic laboratory, i really didn't have any business messing around with flash hole size. 

 

One observation: when I fired a case with only a primer, invariably the cylinder was locked after firing. The primer would be set back and rotating the cylinder was difficult. At a point where the flash hole was pretty big, no primer setback. 

 

My point, if I haven't lost you about a paragraph or 2 back, is that the primer explosion is pretty intense, and depending on how much powder, and the type of powder, and the position of the powder, ignition problems still may be present.

 

I've mentioned this before, I test for this with a chronograph. I fire 5 shots with the powder against the primer for one string, and I fire the next string with the powder against the bullet. Ideally I want the average velocity of each string to be close to each other, and I'd like low Sd and Es for each string as well.

 

If I don't get the results I want, I try a primer change, either brand, or switch to a magnum primer if I've been using a standard one. And sometimes, changing the primer will make a huge difference. 

 

In a previous post I said that Trail Boss was a fast burning powder. There are faster burning powders as pointed out by OLG. I've looked at a few burn rate charts, some show TB to be around the Red Dot area, others show it near 231. I split the burn rates of pistol powders into Fast, Medium , and Slow. The mediums are around or from Unique to HS-6, slow are powders like Blue Dot and 2400. Fast are from around BE up to about 231. If one were to split the all the powders in fast, medium and slow, fast would end at or near Blue Dot, medium would be from 2400 to IMR3031 and slow would be from Varget to Retumbo. And that would be meaningless rubbish. I should have been more specific, my bad. The burn rate of Trail Boss is close to that of Green Dot.

 

Trail Boss is not like any other powder, IMO. When it burns it does so at relatively high(ish) pressures, for a very short duration. It is low energy, doesn't make much velocity for the pressure. It is really inefficient, not a powder you'd use if you were on a quest for maximum velocity. But for Cowboy ammo, perfect fit, low velocity with just enough pressure to seal the case in the chamber.  

 

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