What is the test for coercing a jury to convict an appellant of involuntary manslaughter?

The government argues in the alternative that even if the jury was coerced, the error was harmless since appellant was convicted of voluntary manslaughter rather than first degree murder as charged. Even assuming that harmless error analysis can apply, ⁴ coercing a jury verdict is an error of constitutional dimension, in the face of which the government bears the burden of proving its harmlessness beyond a reasonable doubt. Coleman v. McCormick, 874 F.2d 1280, 1288 (9th Cir.), cert. denied, 493 U.S. 944 (1989). The government made no such showing. We do not know whether, given more time to deliberate, the jury would not have convicted appellant of involuntary manslaughter, or perhaps that they might even have acquitted him altogether.