Max bullet weight for a 40-82?

I was wondering what the max weight is for this cartridge. My rifle has a slow twist so it does not stabilize the longer bullets. Factory loads used 260grn bullets, which I use now. but I would like to go alittle heavier. There is already a mold I can order on Accurate molds. It is 300grn.

I have multiple articles on the caliber and the most people have went is 310 grns with good accuracy from what I can see. The bullet needs to stay under an inch in length to stabilize.

The rifle is an original 1886 MFG 1889.

You have to know what the ROT (rate of twist) is in your barrel. Weight can be regulated quite a bit by changing the ogive profile. A blunter ogive will be heavier than a say money type. Look at it as maximum length, the weight will increase by weight of the alloy mix and ogive shape.

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Originally Posted by Lead pot

You have to know what the ROT (rate of twist) is in your barrel. Weight can be regulated quite a bit by changing the ogive profile. A blunter ogive will be heavier than a say money type. Look at it as maximum length, the weight will increase by weight of the alloy mix and ogive shape.

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the twist rate is a 1-28. My barrel is 26 inches.

28 is slow!
You will pretty much max out at 0.9" bullet length.
Weight and speed will push it slightly either way but length is key.
Given a 0.9" cylinder from pure lead you'll get @330grains.

I ordered a mold from accurate Molds.

I just got my mold in yesterday and it looks really nice! I casted a few bullets and they came out nice.

Looking forward to a detailed shooting report. Accurate Molds is a very good mold maker. Which mold number did you order. Will you Loads testing, be black or smokeless
Rick