Cast Bullets in 9mm for Best Accuracy
... in a different thread ... Another poster tried some cast 9mm bullets sized to 0.358" and got better accuracy
Haven't you heard the sayings "Slug your barrel ... Bullet to barrel fit is king"? But there's more to accuracy than just bullet sizing and that's lead alloy hardness (or softness).
To me, accuracy of ammunition results from more efficient powder burn to develop consistent chamber pressure build/average max pressures to apply similar recoil force (On muzzle climb) and muzzle velocities (For bullet drop) round after round to produce smaller groups/less scatter on target.
Many reloaders load cast/lead bullets at reduced velocities to prevent/reduce leading of barrel and why there is a whole different set of slower published lead load data from jacketed load data (Because using jacketed load data would lead the barrel). And remember that gas checked bullets came into existence to prevent/reduce leading of barrel at higher velocities and modern jacketed/plated/coated bullets are essentially full-length gas checked bullets.
But using lower powder charges may not bump/expand the bullet base sufficiently to seal with the barrel to produce more consistent chamber pressures, which results in accuracy you seek.
When I was a reloading newbie shooting USPSA in 45ACP and 9mm, I tested not only various burn rate powders from Bullseye to HS-6, I also tested lead/plated/jacketed bullets. What I was told by many about "hard cast" bullets is they could be pushed to jacketed velocities. Then I met a local bullet caster who supplied match shooters in two counties and took me under his wing and taught me about lead alloy/hardness vs bullet leading/accuracy.
He told me harder lead alloy bullets around 20-24 BHN had to be pushed to near jacketed velocities to properly bump/expand the bullet base to seal with the barrel (
Expanding bullet base and compression of lube channel/lube flow form an "O" ring seal) to reduce leading and produce accuracy from more consistent chamber pressures. He used different hardness of lead alloy for his bullets (14-20 BHN depending on application) to supply his customers and for match shooters shooting Cowboy Action, he used lower BHN lead alloy.
When he retired, I switched to MBC as they used 18 BHN lead alloy and offered softer 12 BHN lead alloy for lighter/target applications (They did offer 10 BHN lead alloy bullets but not anymore). For most of my 45ACP loads, 18 BHN SWC (IDP #1) worked fine but not for my PT145 with oversized barrel that produced patches of leading. And when I tested softer 12 BHN SWC (Bullseye #1), even light 4.0 gr charge of Red Dot/Promo expanded the bullet base sufficiently to reduce/prevent leading of barrel and produce accuracy.
For 9mm, 18 BHN RN (SmallBall!) sized .356" for my .355" - .356" sized barrels produced full-length barrel leading with max Hodgdon lead load data for W231/HP-38 and accuracy was poor -
https://www.hodgdonreloading.com/reloading-data-center
- 9mm 125 gr Lead CN W231/HP-38 COL 1.125" Start 3.9 gr (1,009 fps) - Max 4.4 gr (1,086 fps)
I could have used .357" sized bullets but my tighter aftermarket match barrels would not have chambered finished rounds, especially with thicker case wall headstamp brass.
When even the start charge of Hodgdon lead load data produced some leading of barrel, I went looking for more load data and found 1999 Winchester lead load data and Speer lead load data -
https://reloadingdata.speer.com/downloads/speer/reloading-pdfs/handgun/9mm_Luger_125.pdf
- 9mm 124 gr Lead RN W231 (No OAL listed) Start 3.3 gr (910 fps) - Max 4.0 gr (1035 fps)
- 9mm 125 gr Lead RN W231 COL 1.130" Start 3.8 gr (911 fps) - Max 4.1 gr (982 fps)
And when I lowered powder charge to 3.8 gr, leading of barrel stopped and accuracy improved.
So if you are pursuing 9mm accuracy, in addition to bullet to barrel fit, consider lead alloy BHN, especially if you are using lighter target loads.
FYI, Z-Cast bullets use 14-16 BHN lead alloy and work well with lighter target loads as well -
https://www.jacobeagle.com/product-page/9mm-124-grain-rn-500-count
I run .358 sized Lee 125 gr RN in all my 9mm pistols ... I have a Promo load that runs about 850 fps, shoots very accurately
Fast burning Red Dot produced accurate lead loads for me in 9mm and I consider Promo modern Red Dot that meters like W231 -
https://www.thehighroad.org/index.p...ng-red-dot-in-9mm.894187/page-2#post-12041541