Why the difference in sizing the .308

[xtrm41]

I've noticed the Lyman reloading manual has recommended the size for cast bullets are different for the same bore diameter. For example 30-30 Winchester with a groove dia. of .308 is sized to .308,
yet the 30-06 with a groove dia of .308 is sized to .309
Why the difference?

[khmer6]

You will find lots of variation in 30 caliber and 7.62.. Theres even. 310.. 311 312

[303Guy]

Which raises the question - why are they called 30 cal? The 30 refers to the bore and not the groove diameter which can and does vary greatly. I made the mistake once of buying a .311 mold for my 303 Brit - it's a .311 groove right? (.312 actually). It turns out the .311 mold was for 308's so the bore-ride nose was loose and they shot poorly.

[xtrm41]

If you order .30 cal. bullets from a commercial casting enterprise. what do you get? .308 or .309?

[kir_kenix]

If you order .30 cal. bullets from a commercial casting enterprise. what do you get? .308 or .309?

Most commercial casters let you choose a variety of sizes. Also, there is usually a option to choose the hardness and lube that you would prefer as well. It can be overwhelming how many different combinations one can come up with using commercial boolits.

[khmer6]

You always have to look at what they are sized to. A lot of commercial casters will custom size as well

[shredder]

Boolit fit in YOUR rifle is what counts. I shoot some soft plain base plinkers that fall from the mould at .312 sized to .311 in my 06 at 1100fps. I tumble lube them with the 45/45/10. My high velocity loads are sized .309, gas checked and cast from a harder alloy so they perform well at 1800fps. THese are lubed with lithi bee in the grooves. Your rifle will tell you what works if you ask it by slugging the bore (and throat). Keep in mind the pressures you are working with and resultant velocities. That means as the pressure goes up so must the hardness of the alloy

[blackthorn]

Quote (in part) ---the Lyman reloading manual has recommended the size for cast bullets are different for the same bore diameter. ---Why the difference?”

Call Lyman and ask to speak with a technician! Tell us what they say.

[geargnasher]

If you'd read the directions part of the manual you would know the answer.

Gear

[10x]

Slug your bore. Find out what the maximum groove diameter is and shoot a cast boolit that is 0.001" or 0.002" over the diameter of that bore.
I have found 30-30 bores with a groove diameter of 0.310". A cast boolit sized to 0.309 gave a 5" group, the same boolit that dropped at 0.312 and sized to 0.311 to crimp the gas check on would give groups of just over an inch with the same load.
If you shoot 303 Brit you will have bore sizes that run from 0.310 (0r smaller) to sometimes 0.315" or larger.
Slug your bore.
I have found that in a savage 340 in 30-30 caliber a 150 grain bullet sized to 0.309 shoots very nicely. The same bullet sized to 0.309 does not shoot good groups out of my Marlin micro groove barrel. That bullet sized to 0.311 (to crimp the gas check on) gives very good accuracy with all other things being equal.

A good micrometer is an inexpensive life time investment. You can get one for under $20.00. A caliber is also nice but the micrometer is easier to get an accurate reading.
Slug your bore with a soft lead round ball and measure. It may save hours of experimenting with loads that won't group.

[runfiverun]

they show that same picture in their pistol and revolver reloading manual too.

[Pat I.]

If you'd read the directions part of the manual you would know the answer.

Gear

Very helpful reply. There's no question as to who one of your mentors is.

[Larry Gibson]

".30 cal" refers to the bore diameter. There are always manufacturing tolerences + and -.

Larry Gibson

[xtrm41]

Duh, I'm always saying that same thing to other people myself, I'll do a little studying in the front of the book, Thanks!