Help with correct bullet

[sharps4590]

Sure, it can be done that way. Not a thing wrong with doing so. Sometimes I'll slug both the breech and muzzle end separately just to know but usually I'll pick up a couple inches of the breech end of the barrel with the chamber cast. Given some past experiences with rifles being marked one thing then having been recut to something else I always make a chamber cast.

Everyone has different experiences. Mine has been that slugging the bore in the described manner works fine. I've never had a leading issue and open sights is all I shoot, none of my rifles being set up for a scope except for two that are claw mount and I don't have the rings so accuracy is limited by my old eyes. I always size to at least .002 over groove diameter or shoot the bullets unsized so that's never been an issue for me. There's a whole bunch of "right" ways to do it.

[Diz]

I can only speak for myself on this but in my experience when slugging a barrel is if I see that it is tapered or has a loose spot, knowing where it is gives me a better chance at getting the thing to shoot later on. I have found that if it tapers to larger at the muzzle then it usually won't shoot very well no matter what you do. If it has a loose spot in the middle then sometimes it will be OK and sometimes not. It would be rather unusual for a high quality gun to have imperfections in the barrel but occasionally things happen. Slugging or a chamber cast that includes a couple inches of the bore will tell you all you need to get started. Thanks, Diz

[fuhrmann]

Bill,
Look at the adjacent thread about the Funk sporter, and go to the part about the conversions from 8x57I to 8x57IS. Hidden within this part of that thread is a pretty good explanation of my statements that you can use a bullet that fits into a case fired in the rifle in question( Vic, that includes jacketed bullets).Axel has reported that between the wars when 8x57IS was restricted, there was a period of time when Mauser chambered their 8x57I rifles with a larger neck area, to safely use .323 bullets in the smaller diameter barrels.Note, this doesn't apply to all makers or gunsmiths that chambered rifles, hence the test with a fired case.
Mike

Mike,

I have no own loading experience with 8 mm cartridges and I have thought long about questioning this statement.
But I think it can be misunderstood as "an (or even any) oversize bullet can be safely used if the chamber is wide enough in the neck area" and this is potentially dangerous and needs to be said.

Further I think there are quite some experiments that I would try with a Mauser 98 rifle, but not with a break-action gun.

Regards, fuhrmann

[mike ford]

fuhrmann,
That is why understanding of loading is necessary. Before the cartridge is fired, the pressure is zero.When the powder is ignited, it creates gases that cause the pressures build up from zero,to the maximum, somewhere down the barrel. As the bullet moves, it makes the avaliable space for the gases larger and the pressure doesn't build up until the gases can overcome the additional space avaliable for them. By this time, the bullet has entered the barrel and has been sized(by the barrel itself)to the groove diameter. The problem arises if the diameter of the bullet is large enough that the case neck can't expand to release the bullet and the additional space for the gases is not avaliable, until the pressure builds enough to overcome the restriction; at which point the pressure may be too high to be safe. You are correct that the break action guns are not as strong as a 98, but the theory still holds. It's just that the level of safe pressure is lower. This is why I always advise not to depend on the normal high pressure signs(flat primer, case expansion, etc.) with break action guns. Before these signs appear, the pressure is likely already too high.On the otherhand, I would never advise you to do anything you are not comfortable with.
Mike

[fuhrmann]

Mike,

I have no problem with a slightly oversize bullet that is reasonably soft and has not much bearing surface.
But if the bullet diameter is significantly more than the groove diameter and you are considering harder and longer bullets, that initial pressure will increase and there is no way to properly calculate and compensate this.
So why bother and take a risk?

The Germans had this unlucky duality of different 8mm army and hunting calibers for a long time and may have found some odd combinations that actually worked. But there may also have been combinations that did not work well.
In the 1940 RWS handbook (see the revision of page 43) there is a lengthy explanation of the new 1939 proof law, saying that the former state was dangerous and from now on there are unambiguous caliber designations (on guns and ammunition) and a regulation of minimum barrel dimensions to avoid accidents. I assume there was reason behind this and I do not see why to take the step backward here.

Now instead of discussing theory, I would like to hear a confirmation from the thread starter - what are the actual bore and groove diameters?
If .309 / .310 is the bore diameter (Felddurchmesser in German), this is around 7.85 mm and just fine (maybe a bit on the wide side) for a 8x72R using the "I" or .318 or 8.07 mm bullet.
Still too narrow for an "S" bullet, and to all my knowledge there was no "S" version of the 8x72R.
But if this is the groove diameter (Zugdurchmesser) then it would be completely "out of specification" and I'd rather think of using a .308 or .311 bullet now - very puzzling.
fuhrmann

[sharps4590]

This is where experience, judgment and careful measuring are a must.

[mike ford]

fuhrmann,
Go back to my first posting in this thread,where I said all the 8x72Rs I'm familiar with have actual .318 barrels( not the .319-.320 barrels common with other old 8mms).In other of my old 8mms(8x57I,IR, and 8x57R/360) I use .321 bullets, made for the 32 Win. Special(and make .318 bullets from these same bullets)which are 170gr and intended for 2200-2300 fps velocity. I let the rifle tell me what it wants, It will tell you if you listen to it.In my 8x72R a .318 bullet is as large as will easily enter a fired case, a .319 cast bullet will just barely go in.My rifle told me, this way, that it wants.318 only bullets.
I'm a little familiar with the 39 law, it set requirements on manufacturer of new guns(and ammo)and did away with the Treaty reqirements restricting the use of .323 barrels.It, for all practical purposes, ended the use of .318-.321" barrels( until recently, now you can have full length EL in old calibers). The sitution was dangerous as they said, but it was because many people didn't have any understanding at all of handloading or ballistics and didn't even know what cartridge their rifle was chambered for, to buy ammo for it. The 39 law was the first that actually required that caliber designation on all guns be the commonally used name.For practical purposes, it also banned many of the calibers rifles we collect and shoot today. If Hermann Goering(?) thought an old caliber was too old or weak, there would be no chamber dimensions estabilished for it. There were also very strict laws for ammo, but enforcement was almost impossible.They couldn't test each round, but if a certain brand of ammo kept blowing up guns, the makers of it would meet new people and be asked a lot of very pointed questions.
Once again, I will never advise you or anyoe else to do anything you are not comfortable with. If you want to use .308 or .311 bullets in your 8mm rifle, then "have at it"; after all it is your rifle, not mine.
Mike