Hardness vs velocity vs accuracy?

[pergoman]

I have been powder coating nearly everything for the last 2 years using Smoke's products and the shake & bake process with pretty good results. The one issue I have encountered is I seem to have a hard time getting bullseye quality accuracy above a certain velocity. This seems most prevalent in the 9mm ammo. For instance, I have worked up loads using several different powders with boolits in the 121-130 gr range that shoot very well up until 950 fps to 1000 fps at which point the groups start to widen. I'm trying to get 130 power factor loads for knocking down steel with bottom feeders. I'm thinking my allow might be a little too soft and is deforming at higher velocities in these mid-light weight projectiles. The same alloy in my 160 gr 9mm tips shoots well but I don't have to push them fast to meet my desired 130 power factor. These are moving at around 810 fps and knock steel down just fine. I shoot these heavy tips in my 929 revolvers.
Has anyone encountered and resolved this issue? I will be casting some of my favorite tips with a harder alloy which will make them a bit lighter as an experiment. I will coat them and see what happens. My standard alloy is around wheel weight hardness. I will add some lino to make it harder.

[popper]

Try WD after cooking.

[bmortell]

you can change hardness back and forth by just re baking 400 20m and either cold water drop or air cool, even if there already sized it still works good, just did this to the last batch I did, switched them all to hard

[fredj338]

Yes a change in alloy or bhn is needed when pressure go up. I can get 2"/25y accuracy with range scrap running pretty much max pressures. I coat & then water drop out of the oven. Bullets go about 13-14bhn.

[Lloyd Smale]

Ive been doing this for more then 40 years and 99 percent of the time harder shoots better in any properly dimensioned gun at any velocity. Alloys bumping up is old wifes tales ****. Only time it might be a benefit is in your way out of spec. think of it this way. Everyone chases the accuracy of jacketed bullets. and the copper jacket is much harder then any alloy of lead. When I shoot ppc and plate shoots and bullseye I practiced with softer bullets so I wouldn't use up my lino stash. But on competition days my 38 (pop gun loads) and 45acp loads were with bullets cast out of linotype or at least water dropped ww. Never bothered with any alloy softer then 17bhn when 1/10s of an inch mattered. That said your talking a 9mm and unless your shooting a high dollar or comp 9mm chances are its not a tack driver with any load. Theres much more in play here then alloy. Your gun may just prefer heavier bullets or have rifling to shallow to grab lead well at high velocitys. Like any other loading project just a primer swap, different powder, seating depth or bullet design might change things drastically. I had a 9mm sti trojan that was a tack driver with 120 rcbs round noses at 18bhn but shot the 115 rcbs into groups 3 times the size with the same alloy and powder and primer. Ive got a glock 43 that shoots a group buy 130 hp into 1.5 inches at 25 yards. Same exact load shoots 4 inch out of my 19. Switch the load and its the 19 shooting great groups and the 43 shooting minute of paper. All that said a harder bullet will about allways outshoot a softer one in any gun and semi auto pistols even more so because they all tend to have marginal rifling dept.