You should take one of the pure lead bullets and hammer it through the bore with a brass rod. This is known as slugging. Take a micrometer and measure the outside diameter the bullet after forcing it through. Odds are high it will be 0.308" but might be larger. Whatever number you get, add 0.001" to it. This will be the minimum diameter bullet you should shoot. Many guns find even better accuracy with 0.002" or even 0.003" over the bore diameter. I size to 0.309" for my guns and it works great. Odds are almost zero that a lead bullet sized to 0.308" will work for accuracy or not leading the barrel.
As an aside, I would not use the Lyman style lube dies. Use a Lee push through die. The long length of this bullet allows it to bend during sizing. This will prevent chambering. Ask me how i know. I had to melt down those 100 bullets.
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