Re-loading experts

densa44 · #1 08-14-2017, 12:03 PM

Elk, Dick, LC and any others I may have missed. I have a wonderful old friend who buys me guns and reloading supplies. Now that dog training season is coming to a close I'm cleaning up the shop to start reloading again. I found some 7.62 x 39 brass and a rcbs shell holder (very nice touch) and a box of 123 gr. bullets. It says 7.62 on the box. The bullets are Hornady Interlock. On close examination the dia. is NOT .308 but .310. I now notice that the reloading data I have give bullet diameters of .310, .311 and .312. The gun these are being made for is a very nice bolt action and is fun to shoot.

How come the different diameters? Does this make any difference? Not that it is germane to the discussion but over the last 50 years I've done much worse.

shooter12 · #2 08-14-2017, 12:24 PM

7.62x39 its never been a .308 cal. You can load 308 bullets in it and shoot , no problem, but the actual military FMJ would be .310 not .308.
Hunting bullets made for 7.62x39 could be .310, .311, .312.
Need to find which one your barrel likes best.

Very often though the military ammo shoots the best .
Cheers!

qwert · #3 08-14-2017, 01:30 PM

There can be wide variation of actual bore size, even in bores of identical caliber. This is especially true of military spec production.

I suspect you can save a LOT of load development components, labour, bore wear, and time if you first -

'SLUG your bore' by driving through a (well oiled) soft pure lead slug, with a brass rod,
then carefully measure the slug with a micrometer, (not any caliper)

IMHO, this is the ONLY (easy) way to determine what you have with any confidence.

When you have an ACCURATE bore size, it is a LOT easier to select a potentially accurate bullet.

Good Luck, YMMV.

elkhunter11 · #4 08-14-2017, 01:55 PM

The bores vary considerably in that chambering. Most bolt actions will shoot .310" to .311" bullets quite well, but the first Ruger 77s apparently had .308" bores, so those rifles would likely do better with 308" bullets.

densa44 · #5 08-14-2017, 04:33 PM

Welcome to the additional experts, nice meeting you. I don't think I'll try to slug the barrel. I'll bet you are correct but I'm not up to that.
I'll try what I have and see if just by luck they work well.

Since I've read your comments I'm thinking I'll use some of my "heavy" .22 bullets with sabots. They will give the coyotes the kind of welcome I'm looking for.

If it helps I think the rifle is a cz.

While I have your attention an other question, obviously the larger bullet travels down the barrel, what effect does a bullet too big for the bore have?

Flieguy · #6 08-14-2017, 04:44 PM

I'm not an expert, but a lot of military .30 caliber rifles are .310-.312

Notably, 303 british, 7.62x39, and 7.62x54r.

My enfield likes to shoot .312

slug your bore as mentioned to find the exact diameter of it, I like these:

https://www.westernmetal.ca/shooting...itions-bag-500

elkhunter11 · #7 08-14-2017, 04:46 PM

If the sabots are .308", which they probably are, the accuracy could be even worse than is normal with sabots. A lead core bullet .001" to .002" larger than the bore will swage down when fired, with a slight increase in pressure.

260 Rem · #8 08-14-2017, 05:01 PM

A "tight" bore will result in greater pressure...and increased pressure could limit the volume of powder used ... so potential lower velocities. It is my understanding that at one time, tight bores were popular in Palma matches... because the factory cartridges permitted in that game were thought to suffer from inconsistent bullet diameters. (I have tried a tight Bore Palma barrel and found it no better than any other).
A friend that competes in FClass had a tight bore "polished out" (my term) in order to get the velocity he required. With a second barrel (same aftermarket source), he started load development with a known recepie and damned near blew the action...fortunately only damage to the extractor.

Big Sky · #9 08-14-2017, 05:06 PM

Quote:

Originally Posted by densa44

If it helps I think the rifle is a cz.

I'm no expert, but if it's a cz527, these guys are.

http://cz-usa.com/product/cz-527-carbine-223-rem/

Quote:

Built to CIP specifications, our 7.62×39 chambers are ideal for shooting steel-cased surplus ammo. Designed to shoot .311 bullets, some American brass ammo may not perform as well as the imported steel-cased variety because of SAAMI brass dimensions and varying bullet diameters.

sns2 · #10 08-14-2017, 10:53 PM

If it is that nice little CZ owned by your friend from Calgary with the black lab, those .310 bullets will shoot just fine. That chamber is .311 and so you will be right in the money with those Hornadys. Use the .310 data and work up safely, as I know you do.