.257 Bob cast projectiles

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Mauser lover

Jul 13, 2011
East KY
Hello, I am having trouble finding slugs for a .257 Roberts. I want cast lead, just to load some plinking ammo. I found some .25-20 boolits, but they are advertised as .259 diameter. Is this permissible to use in a .257 Bob? From my VERY limited experience with cast lead loading, they are supposed to be a thousandth larger than jacketed projectiles. Is two thousandths going to be an issue, or am I overthinking this?

My other option is to use a different gun to plink with, but what fun is that? Thanks for the help.
You are overthinking it. .259" will have a chance. Your barrel might be .258" anyhow, the advertising does not always match the measurements.
.259" should work fine. I use .311" in all my .30cals, and .314" in .31cal rifles (.303, .32cal pistols).

I use .225" in .22; 360" in .35, .402" in .40; .431" in .44(.429"); .452" in .45 pistol
.460" in .45/70.
Missouri bullet company offers those, i believe they also offer thr members a discount. I dont think youll have an issue using them in a Bob..
Yeah, those are what I found, but from Missouri Bullet.

Okay, school me briefly on gas checks, as compared against the "Hi-Tek" powder coating or whatever it is.

AAAHH!!! I wish I would have thought of THR as a "shooting club" last time I ordered from Missouri! I saw that they offered discounts for clubs, and thought, "bummer, I wish I was a member of a club"! Come to think of it, I have even seen them advertise their discount for THR on these forums somewhere...
Im no expert in cast bullets so hopefully one of the guys that really knows his stuff will come along. I load the mbc bullets to only about 1200fps in most of my applications. The one where i pushed it faster was my .458, and it leaded like mad...but then it did that at 1200 also, so its likely i just had poor bore fit.

I believe the gas checks are really ment to keep the gas from cutting at the base and melting the lead. The hitek coating is supposed to do similar but also provide some lubrication and keep the lead from contacting the bore.
Not real sure about gas checks but I think they allow cast to be shot at faster velocities. Hope I'm right about that.

Did a quick Google
Here's a link, pick your choice ....

I use them in 30-40 Krag and they work great for accuracy.
Okay, that was quite a bit of reading...

At what velocity do I need to have a check?
What is the limitation with a check?
Does one need a check with the hi-tek coating?
If so, what velocity is that?

The .25-20 should be using a .257" bullet too. However, I really can't see any cast bullet that's only 2 thou over that damaging anything though. Only issue possible is finding data depending on the weight of the bullets you have. Lightest bullet in my old Lyman book, for either cartridge, is a gas checked 69 grain. Roberts velocities with 'em max at 2275 fps with IMR4227. There's 90 and 100 grain gas checked data too.
Everything you ever wanted to know about gas checks should be in your manual.
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