Reloading 300 BO with .311 Cast Bullets

[Rottentofu]

I started reloading 300 BO with cast bullets. I read that cast bullets need to be 1/1000 - 2/1000 over groove diameter. (Not sure why is that, hopefully someone can provide me with more insight) The place I bought the cast bullets from sold .311 cast bullets and told me it should be safe to use on my 300 BO reloads. Just wanna get some thoughts from you guys before I start using those cast bullets. Thanks!

[jericho89]

The reason why you go over size is so that the bullet makes a good seal in the barrel and prevents leading. As for that size with your barrel, you need to slug your barrel and find out what the true size of your barrel is.

[Whiterabbit]

you already bought the bullets?

Perfect.

Don't bother slugging, etc (my opinion). Load a dummy cartridge and load it in the rifle.

If the bolt slams home, load and shoot. If you already have a load developed for .308's or something and it's super max, back off a smidge if you want. It's cheap security.

But most important, if it fits, it gets shot. And fittment means the chamber/throat, not the bore.

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If they do NOT fit, never fear! a lee push through sizer in .310, .309, .308 whatever is what you need to get these loaded and shot. But I wouldn't bother if with your brass, your chamber, these chamber up. 30-50ksi when you pull the trigger is sufficient pressure to size them down in the leade to fit in your bore just fine

[NapalmCheese]

Lead bullets are relatively soft compared to jacketed lead bullets, and it takes less to displace and engrave lead than copper. So, having a bullet that is 0.001 or 0.002 overbore isn't a problem and is, in fact, recommended. For the record, a lot of marlin .30 caliber rifles need to use 0.311 sized bullets because of their 'micro groove' rifling.

In otherwords, you're probably fine. Slug your bore if you want, otherwise start at low charge weights and see where it goes.

If you're new to cast lead bullets check out the castboolits forum (castboolits.gunloads.com) for help and info. What you want to see is no leading in the bore with a decent 'star' pattern at the muzzle after shooting a few lead rounds. Leading isn't the end of the world, but it's easier to avoid it than clean it. If you need to clean it just take a strand or two off a copper chore boy and wrap it around a bronze brush to clean your bore. It'll be clean in a few swipes.