Originally Posted by jwrowland77
I will be loading 9mm 115gr FMJ-RN ... can you use the data for the LRN for the FMJ-RN
Not really and I think that would depend on the powder. Look at the difference in 1999 Winchester powder charges below for 124 gr FMJ vs lead RN. Using lower lead load data for jacketed bullets may result in decreased chamber pressures from inconsistent/poor powder burn that will decrease the accuracy of your shot groups. However, if you look at 2004 Alliant load data below, you'll see that 125 gr FMJ and 125 Lead powder charges are comparable at the same OAL. Whenever possible, I try to use published load data and come close to matching the components used for my powder workup in my pistols.
Here are some load data for 9mm FMJ RN and lead RN bullets:
1999 Winchester load data
2004 Alliant load data
I'll be using Unique since I also have a 9mm, .380 and .38 Special I'll be loading for.
2004 Alliant load data lists 5.5 gr of Unique as max powder charge for 115 gr FMJ at 1.120" OAL. I typically use 1.125"-1.135" OAL for FMJ and would use 10% below max of 5.0 gr as my start charge and conduct my work up by loading 10 rounds of each at 5.0, 5.1, 5.2, 5.3, 5.4, 5.5 gr. (of course, you should always determine the Max/Ideal OAL using your pistol/barrel/magazine first - see below). When I range test the loads, I will first look for the charges that will reliably cycle the slide of my pistol, then accuracy trends while looking for pressure signs/issues.
As to OAL, you do not need to use the OAL listed on published load data as often test barrel fixtures (and not real pistols) are used to measure chamber pressures. Using published OALs WILL NOT ensure reliable feeding/chambering of finished rounds in your pistols.
Determining OAL should not be a guessing game and I use the following process for semi-auto loads whenever I use a new bullet:
1. Make sure resized cases drop freely into the barrel chamber. If not, adjust the resizing die to ensure the cases are resized full-length and fall in freely into the chamber. (If I can't resize a case on the second attempt by rotating the case 90 degrees, I consider the case wall too far stretched/thinned and will toss/recycle the brass).
2. Determine Max OAL - Make a dummy round (no powder/primer) and perform the barrel drop test with the barrel out of the pistol starting with the SAAMI max OAL until the dummy round falls into the chamber freely with a "plonk" and spin without hitting the start of rifling (if the round won't fully chamber, paint the bullet with dry-erase marker and rechamber to see where it is rubbing). To determine the amount of taper crimp to return the flare back to flat, I usually add .020" to the diameter of the bullet (So for 9mm .355" diameter bullet, .375" taper crimp and for .356" bullet, .376" taper crimp). Note: Some headstamp case walls are thicker and you may need to use even less taper crimp by .001" (so for .355" bullet, .375"-.376" taper crimp and for .356" bullet, .376"-.377" taper crimp).
3. Next determine Ideal OAL - Load the Max OAL dummy round in the magazine and manually release the slide without riding the slide with your hand. Incrementally decrease the OAL until dummy round reliably feed/chamber. Depending on the pistol/barrel used, Ideal OAL that will work reliably may be shorter than Max OAL. If you are reloading for multiple pistols, use the Ideal OAL that will work reliably in all pistols.
4. Once you determined the OAL that will work well for your pistol/barrel/magazine, next conduct a full powder work up to determine the powder charges that will reliably cycle the slide/extract spent cases and produce the most accurate shot groups by loading 10 rounds of each increment of .1-.2 gr from start charge and work towards max published powder charge. If I am using shorter OAL than published or different bullet that seats the bullet base deeper in the case, I will reduce the start/max charges by .2-.3 gr. If different published load datas vary in start/max charges, I look closer at the barrel length used (such as 4" vs 5") and other reloading component differences. When confronted with differing load data for the same barrel lengths and bullet type, I will side on the safety and use the lower published load data for my start charge.