Let me start by saying I am NOT, and likely NEVER WILL BE, an authority on this particular subject.

I have read a lot over the years about the differences/dangers/whatever of the two standard 8 m/m "bore"sizes, the .318" and
the .323" - - -

Now,recently, I have come on a well established information source (which would normally be considered impeccable among shooters) which says the actual BORE size was/is the same for both, but the GROOVE sizes are different. It also says that at one time it was very common for factory ammunition to be loaded with .3205" diameter bullets, which performed very well in both.

Any of you AR folk ever hear either of those two statements anywhere?

Whaddaya think? Credible or not?

/

Alf-That pretty well duplicates the info to which I was referring.

So, based on that info, have you heard anything about .3205" bullets being commonly used in factory SPORTING ammo, to be suitable to both groove diameter bores?

BTW, how do you expect to get a good spirited argument discussion going if you're gnna start out by putting FACTS on the table?

Nice "debate" so far, but now I'll throw another wrench into the works. Whatever possessed SAKO to make and sell their 8x60mm FN Mauser rifles? Why would anyone make a 0.318 bore rifle in the 1950s? Was it just to make life difficult for more people? I know my reloading surely became more difficult when I discovered I had purchased a true .318 bore rifle instead of a standard 8x60S !!!!!!!!

LLS

AC, Your question couldn't have come at a more opportune time as one of our [gun] club members showed up at the range last week with a J-Bore Mau. sporter: double set triggers, integral bbl. rib, Hawken-like wedge in the forestock. After speaking with him about it, he told me he got case head separations after firing "moderate" handloads in it. (I know I should have asked for particulars, but didn't.) Upon further inquiry he revealed (a) that he had used .323" jacketed bullets and (b) that slugging the bore revealed that it was ~.318". I tried to convince him* to use .318" jacketed bullets or ~.320" cast ones in the future, hoping such things could be found. While he's not exactly a reloading newbie, he's not all that sophisticated either. Btw, his was the first J-bore I've ever seen.

*One would think that head separations on new brass would be convincing enough!

Yes but, wouldn't head seperation of his handloads be a consequence of excess headspace and or incorrect resizing?
I've heard swaging down doesn't increase pressure all that much.?

quote:

Originally posted by JAL:
Yes but, wouldn't head seperation of his handloads be a consequence of excess headspace and or incorrect resizing?
I've heard swaging down doesn't increase pressure all that much.?

In my experience, if you work up the load with the bigger bullets, it is no more dangerous or impractical than using the smaller diameter ones, at least for 3 to 5 thousandths of an inch difference. Having said that, it is only common sense to use the correct nominal size of bullets if they are at all available and there is no overwhelming reason to do otherwise.

That part about being able to build loads using bigger bullets is particularly true with lead bullets. They are "barrel-sized" easily. I got best accuracy with my first .30-BR benchrest gun by using 196 grain linotype bullets. They were sized to .3146" diameter, and were shot through a .3082" groove diameter bore.

Were not gentle pressure loads either, moving that 196 grain bullet at 2,301 ave. fps M.V. from a case that only holds roughly 33 grains of stick powder.

I doubt his case separation had anything to do with using too large bullets. I think you could have well "nailed" it when you brought up excess headspace....whether inherent in the rifle chamber, or induced by setting the case shoulder back too far when sizing the brass for reloading.

But then I wasn't there, so that is just my GUESS.

AC & JAL, I didn't witness the split cases or the rifle being fired. However, by the end of our conversation, we both realized it could easily have been a headspace problem.

A couple things; because they were cheap,as I, I've loaded and shot many 125gr. .310 dia. bullets in a number of .308 barrels with no ill effects what-so-ever.

Some where in my memory bank I recall reading in the National Rifleman circa late froties to early fifties about a 6.5 Arasaka being rechambered to 30-06. I know not how. the individual was fireing military or commercial ammo with no noticeable ill effects except a retrived bullet was longer and thinner. roger