If you are changing more than one reloading variable at a time, it's hard to tell what variable is affecting the outcome (recoil, case ejection, accuracy, etc.).
As rcmodel and Blue68f100 suggested, I would first determine the OAL that works well for your pistol/barrel then conduct powder work up.
LeftyTSGC said:
I want to see if using 4.3gr W231 with a OAL of 1.090 -1.100 would produce a better load than 1.125? Any suggestions or advice.
Using shorter OAL/COL than what your pistol/barrel will support will result in more high pressure gas leakage around the bullet when the primer ignites the powder and may result in less consistent chamber pressures/muzzle velocities and decreased accuracy.
For many 9mm RN bullets, 1.125" will work in most pistols but will leak more high pressure gas than 1.135". What's the best OAL that will produce the most accurate loads? That's determined by using the barrel drop test to first identify the maximum OAL and then function testing by feeding/chambering from the magazine to determine the working OAL.
Once you determined the working OAL, then you should conduct the powder work up from start charge to identify the powder charges that will reliably cycle the slide and extract/eject the spent cases and produce accurate shot groups.
I am still looking for any place that i can find the formulas to detrmine the power and CUP for each of my loads. Any one know where i can find info.
To
determine the power factor of your load, you'll need a chrono to measure the average muzzle velocities. Power factor is calculated by multiplying the weight of the bullet with muzzle velocity divided by 1000. Let's say your 125 gr 9mm load measures 1000 fps. Your power factor is (125 grain x 1000 fps) / 1000 = 125 PF.
Keep in mind that depending on variables like ambient temperature, muzzle velocities may vary so many match shooters develop loads that are slightly higher in PF to compensate for these variables that may lower muzzle velocities. So if you develop 130 PF loads, you will have some buffer to ensure your loads will meet the 125 PF requirement. If you don't have access to a chrono, you could use mid-range load data.
Hodgdon lists the following for the 125 gr FMJ bullet.
125 gr Sierra FMJ W231/HP-38 OAL 1.090" Start 4.4 gr (1009 fps) 24,600 CUP - Max 4.8 gr (1088 fps) 28,800 CUP
I use load data for 124 gr and 125 gr bullets interchangeably as most FMJ/JHP bullets vary by about 1 grain. Let's say your working OAL comes out at 1.135" but the load data was tested with shorter OAL of 1.090" which means the actual muzzle velocities will probably be slightly less than published. But even with the longer OAL, the mid range powder charge of 4.6 grain may produce greater than 125 PF. Let's say 4.6 gr charge produces 1030 fps. Then (124 gr x 1030 fps) / 1000 = 127 FP.
BTW, Hodgdon load data used 4" test barrel. Star 30M 9mm pistol has 119 mm barrel which is 4.68 inches. That means your pistol may produce higher muzzle velocities than the Hodgdon load data. So you may be able to use 4.4 - 4.5 gr powder charges and still produce greater than 125 PF.
Most of us do not have access to chamber pressure measuring devices so we approximate chamber pressures (CUP/PSI) with muzzle velocities we obtain from chrono.