Powder reduction when bullet contacts lands; is there a rule?

[oakbowerybarnes]

Marlin 336, .30-30, Lee .309-150-F when crimped in the correct groove is showing 1/8" long rifling marks on the bullet nose. ( .309-170 f is worse) Rifle has very short throat? Should I be reducing the charge by some specific percentage for this situation? Loads I'm using are light enough to not show any pressure signs, but may not be giving the result the original load was meant to. I am assuming that the load data was not developed in a rifle that was already engaging the bullet in the rifling. Gun shoots decent groups (not through playing with sizing, lubes, loads, etc.) so the engagement may not turn out to be an issue in the end. Closing the action, you can feel the pressure needed to get the cartridge all the way home.

[lar45]

I think that the pressure rise is more of an issue with jacketed bullets and not soo much with Cast ones.
I've gotten better accuracy with cast boolits when they are seated to just engage the rifling.
Checking the velocity with a chrony might give you an indicator if the pressure was higher with higher than expected velocities.

[FromTheWoods]

Are your cases the correct length?
Cartridge overall length within specs?

[btroj]

Unless you are close it max it doesn't matter.

What load?

[FromTheWoods]

If the case is "1/8" too long and the bullet's cannelure is designed for a 1/8 inch shorter case, then the overall length of the cartridge will be an eighth of an inch too long.

(btroj--Am I missing something here?)

Also, have you run these problem cartridges from the magazine to the chamber without them jamming?

I'm not as knowledgeable regarding reloading as are some members here. I know about extra length in lever guns from my problems years ago as a novice reloader. Loaded a few .32 WS cartridges that hung up in cycling.

Length is not in the poster's question. But if his cartridges are too long, that would explain their touching the lands.

I am following this thread because I too would like to know the answer to his question. I had bullets with rifling marks on them earlier this week, and didn't know if it was a danger or not, and how much it would affect accuracy.

[mikeym1a]

I thought it was desirable to have the boolit touching the rifling, to ensure a concentric start down the barrel. Or am I misreading something about this post? mikey

[Dan Cash]

OP, your greates concern with the situation you describe is difficulty in closing the action. If no difficulty, be happy as you have a desireable situation. .309 nose can be a bit large for a Marlin bore.

From the Woods, if you have cases too long, you have a dangerous situation which will spike prssures to dangeroous levels and adversely affect accuracy. Lever actions stretch brass so case length is worth watching.

[FromTheWoods]

Thanks Dan.

I've read various places that a thousandth off the lands is desired in most/many aspects. People have included accuracy and pressure as the reason for keeping it off the rifling. I've also read that some breech-loaders are most accurate when the bullet is seated in the lands. So--is it safe with cast bullets and maybe not safe with jacketed?

[oakbowerybarnes]

Sorry it took me a while to get back. The cases will chamber with no difficulty, the interference is only .002" on the bullet nose. The load was 10.6 grs. Unique with the Lee 150 flat nose. The complete rounds cycle through the magazine and into the action just fine. Just the pressure needed to seat the round and the obvious marking of the lands on the bullet to cause any concern. Again the load exhibited no high pressure signs and was OK accuracy wise. If no one thinks the issue is serious I will keep load testing without worrying about it.