What's causing this ?

[RU shooter]

I tried out a new load in my kahr cw45 today the load was a speer 185 fmj fn 6.0 gr Bullseye and oal of 1.245 a middle of the road load from the speer manual for their 185 hp . I did recently change the spring in it with one from a Glock 23 which I have heard people do without issue as the Kahr spring is known to have issues as my old spring did. I have fired other cast loads and not had these smoked case issues . So whatcha think is going on that is causing this heavily smoked case ? Too light a load ? Under sprung ? All feed and shot fine and about 85 percent were smoked the others looked fine .

[cwlongshot]

Generally yea, a light load not producing the pressure to make the brass seal the chamber...

BUT, sometimes its WHEN the pressure curve seals the chamer. If a lil late, it can have enough pressure but at weing “time” allowing smoke to soot the chamber.

You can try a different primer, different lod or even seating depth sometimes will change things.
Are you set on thsi powder?

I load Clays in my lighter cast loads in 9/40/45 and its very clean.

CW

[onelight]

Put your old spring back in and fire a few see if that was it.

[RU shooter]

Trying the old spring was my next option but I kinda know it's weak because every load even factory ball I shoot I get firing pin swipe marks on the primer . I haven't had this with the new spring . Like I said Ive tried some other light loads with 200 and 230 gr cast and hardly any soot on the case but these are charred up pretty bad on 1/3 of the case top to bottom as can be seen in the photo . Stupid jacketed bullets !

[243winxb]

The new spring changed the slide timing.

Try the old factory spring.

[OS OK]

What does your taper crimp measure at the case mouth?

I think you may be pushing your round out of the case some with the primer ignition and getting poor starting ignition pressure. With the round moving forward and creating more space behind it, I would think it would be like not having enough powder. BullsEye oughta light up a lot better than that.

The case is not sealing the chamber.