I bought 1k 125 gn Thundercast bullets from RMR. My Lyman data shows 5.4 gn starting load of HS-6 and Hodgdon shows 5.9. 5.4 functions but is ultra smokey. Do I jump all the way to 5.9 as my next step? What do you think?
Sorry, was distracted and thought I had put that info in. 9mm mixed brass 1.125 with CCI small pistol primers. This particular projo will "plunk" all the way out to over 1.15. Fired out of an M&P 9C so 3.5" I will double check the cases when I get home.
Chances are it's just the bullet lube that's causing the smoke, especially if you're used to shooting coated or plated or jacketed bullets. In a short barrel like that I doubt you'll get less smoke with a heavier powder charge. Before upping the charge I'd make sure you have an adequate crimp. 1.125" is a good OAL that should feed in most any 9mm.
You might try a faster powder like 231, Unique or Titegroup, too.
Other than smoky, is there a reason to increase the load? Do you want more velocity or is the accuracy of the 5.4 gr. load poor? It you want/need to increase from the 5.4 gr load I would suggest going up in 0.2 gr increments for pistol loads. Make about 10 rounds of each load increment and see if you are getting whatever improvement it is that you wish. If your interest is increased velocity, you'll only know what is happening if you chronograph each load. Be safe and go slow.
As with every time this question appears, ask yourself this:
Did the two manuals have the same gun for testing?
Did the two manuals have the same bullet for testing?
Did the two manuals have the same lot of powder for testing?
Did the two manuals use the same lot of primers and the same case head stamp/lot?
Did the two manuals use the same COL?
Unless every answer is YES, I guess there will be a difference.
Looking at my data compilation, start loads for 124-125gn lead bullets and 540/HS6 range from 5.0-5.9gn and MAX loads (all pressure tested per manuals) range from 5.5-6.6gn, so your load is 0.1gn under max pressure in one manual. So, one manuals found that 6.6gn was max, so they used a 10-11% drop from MAX for a 5.9gn start; however, other manuals reached max pressure before even that START load such that, if your mix is similar to those manuals, a 5.9gn start would already be over-MAX in your gun with your mix of components.
I always start with the lowest starting load I can find and work up in increments--usually 0.2-0.3gn steps. So, I would have worked up 5.0, 5.3, 5.6, and 5.9gn and only gone up from there if accuracy was improving and there were no pressure signs.
Starting loads: look at your manuals. Most starting loads are selected as follows:
1) A simple 10-12% reduction from the max load
2) manual starts at a velocity, so all start loads are the same velocity
3) manual starts at a pressure, so all start loads are the same pressure
Start loads are not minimums nor do they represent loads that will function your gun.
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