Help with correct bullet

[Bill]

I have a 1932 Krieghoff combination gun it is marked 8x72r my question is the barrel I,D.measures .309-.310 and the bullet measures.3185 - .319 which makes it 9-10 thous. diff. is it safe to shoot?

[sharps4590]

Slug the bore and measure the groove diameter. That's what you'll want to know. German 8mm is usually one of two, around .318 for the early stuff and .323 for a bit later. I forget the date the .323 was adopted but am certain it was before WWI. However, even after the war some rifle barrels were still installed at .318. If you're groove diameter is .318 your bullets are fine. If it's bigger, they'll shoot safely but accuracy will probably suffer. If your ammo is factory for 8 X 72R and you know for certain it isn't reloads it should also be fine. I'd still slug the bore so I knew.

[mike ford]

Bill,
To add to the information Sharps 4590 gave you, many older 8mm rifles have barrels with groove diameters between the .318 and .323 that he mentioned. Some of these rifles are able to use bullets larger than .318, some of them even .323. None of the 8x72Rs that I have checked will do this, and I have one myself.Also, because they have been consistent at .318" for groove diameter, they seem to be sensitive to case length. The way ammo is usually loaderd for them is to resize 9.3x72R cases to 8x72R.Because the 9.3 case starts out at 72mm, many people believe they are already the correct length.When they are reduced to 8mm, they lengthen. When such cases are loaded, the neck may "Jam" into the leade and won't release the bullet until the pressure becomes excessive.In extreme cases,the cartridge may not chamber with a .318" bullet.Failure to chamber may be a good thing, because it could prevent a high pressure cartridge from being fired.The cases should be trimmed to 2.84"
Mike

[Bill]

thank you very much for your information the problem i have is the groove diameter is .309-.310 and the bullets are.318 the difference of .008 -.009 thousands.

[sharps4590]

Ahhh...ok. When I read "the barrel ID measures .309 to .309" that sounded like a land to land dimension to me. I believe the bullets are too big. Pressure will go up considerably.

Mike has always said if the bullet one wants to shoot will slip inside the neck of a fired case it should be safe to shoot. However....I can't remember if that applies to jacketed bullets as well as cast so I'd wait til Mike chimes back in. You would have to have a fired case, obviously, and it's easy to pull a bullet to check.

[Bill]

http://www.germanguns.com/upload/showthread.php?1190-Help-with-correct-bullet&p=5734#

thank you very much for the information I am a little new to slugging a barrel can you explain thank you;

[Diz]

Bill,

How did you arrive at the dimensions for the groove diameter that you are calling out? If you slugged it and are measuring .309" - .310" then there may be something amiss. Eight to nine thousandths is a pretty big difference between groove and bullet diameters, especially for jacketed. If it was me I wouldn't shoot it until I could get this cleared up.

Thanks, Diz

[sharps4590]

Slugging the bore can be described by driving a lead slug through the barrel/bore. What you end up with is a mirror image of the bore. By measuring the groove diameter, the raised portion of the slug, you have the groove dimension.

There is many ways to slug a bore. I shoot a lot of muzzleloader so I have several different size round balls available. I think Mike and others use egg shaped lead sinkers. First clean the barrel then lightly coat it with an oil, almost any kind will do. I choose a round ball of appropriate size, in your instance I would choose a .350 round ball, set it on the muzzle and begin driving it into the bore. When it is almost flush....as in don't hit the muzzle with your hammer....take a punch or drift of an appropriate size and finish driving the slug the rest of the way into the bore then using a rod drive it all the way through, catching it on a folded up towel of something of the kind. Now you can acquire precise measurements of your groove diameter.

[Bill]

Thanks a bunch; not shooting was my feeling also because I sure thank a lot of my gun. Thanks again your information is priceless

[Bill]

Thanks sharps4590 ; without guys like you and your knowledge I would be lost and aggravated being there is no gunsmith close.Thanks again.

[sharps4590]

You're welcome Bill....I get pretty "lost and aggravated" all too frequently!!!!! I understand!

[Diz]

Bill,

It's all good information but I would add a couple of things. Use a brass rod if you can to drive the slug, it's easier on the bore than steel. Also, I use several rods of various lengths starting with the short one to keep the "springing" down to a minimum. One long one is like trying to hit the end of a piece of spaghetti. I like to start from the chamber end because it's safer for the muzzle and crown but everyone does it different. You shouldn't really have to pound it either but go slow and note if you feel any change in how hard or easy the slug moves. I find some barrels are tapered a little or have variations in ID and you can feel this if you are careful. It helps later when you are trying to get it to shoot.

Good luck, Diz

[mike ford]

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

[rtenenbown]

I used a OO size buck shot .33" diameter in my 8X57JR and it worked well.

[John]

When "slugging" the bore, would it make sense to slug it from the breech, but only push the lead slug a few inches into the breech end of the rifling. (Then, carefully from the muzzle - push the slug back out.)
This way, if the bore is slightly tapered, you will capture the "maximum" diameter. If you push the slug all the way, you will have the minimum diameter. Granted, in many cases the difference in the two may be slight, but if one wanted to match the bullet diameter to the max. groove diameter, this is the only way. Exaggerating here, but if the grooves were really deep at the breech, then you may get hot gasses blowing past the bullet (if sized to the smaller groove diameter near the muzzle) until it gets far enough down the bore to "seal."