Measuring chamber depth?

[DonP]

I'm relatively new to reloading and I'm looking to improve the accuracy of a couple of my old C&R rifles. (mainly an '03 and Garand)

I read that the best accuracy comes from the bullet resting right at the start of the lands and grooves in the barrel when the action is fully closed and in battery.

I guess my questions for you more experienced handloading guys are:

1. Is that factual as far as enhancing the accuracy?

2. How do you measure the chamber size to determine the precise OAL for a round, like a 30.06, to achieve that kind of fit?

As always, any and all help and/or opinions is appreciated.

 

[WayneConrad]

I'm new at this too, so this is just opinion.

I read that you're not supposed to seat right on the lands, but a few thousandths away. The reason given is that seating against the lands raises chamber pressure higher than normal. I guess it has something to do with the bullet needing a bit of a running start before it has to engage the lands.

I've never tried to measure chamber size, but dad does it like this: Size a case. Do not prime it or add powder. Seat a bullet in it, but not very much. Now chamber it in your rifle. This will be hard, because you're using the action to finish seating the bullet by jamming it against the lands. Now carefully extract the cartridge and measure OAL. This is the OAL for that bullet to touch the lands in that chamber.

If the bullet jams itself into the lands such that you can't extract the case without leaving the bullet behind, I hear you can make one or two vertical cuts (leaving two or four narrow slots) in the neck so that the bullet is more easily pushed into the case when you are chambering the cartridge.

 

[donkee]

Try this link. It works great. I use this technique for rifle and pistol.

http://www.larrywillis.com/OAL.html

 

[Sharps Shooter]

There is a number of methods, but I'm a little on the cheap side and don't like to waste bullets (especially premium ones) or cartridge cases. I take one of whatever bullets I'm going to use and push it up in the chamber until it's against the lands. If you have long, skinny fingers it's easy to do. If your fingers are like mine, you might have to remove the rifle's bolt and use a short piece of wooden dowel to hold the bullet against the lands. Then, I take the rest of the wooden dowel and put it down the barrel so that it's sitting on the tip of the bullet. Now with a sharp tipped marker of some kind, I carefully make a mark around the dowel at the end of the barrel. I then gently push the bullet, which is probably slightly stuck, out, and let it drop into my other hand. Next, I re-install the bolt, close it and put the dowel back down the barrel. I then carefully make another mark around the dowel at the end of the barrel. Lastly, I measure the distance between the two marks on the dowel. I use a dial caliper for an accurate measurement. The distance between the two marks is the maximum overall length for the cartridge, using that particular bullet, with the bullet seated right up against the lands.
As Wayne stated, I too have read having the bullet tight against the lands can raise pressures. Besides, I have one rifle, actually it's my wife's 7mm-08, that doesn't have a magazine long enough to accept the cartridges with the bullets she is using unless I seat the bullets so they are about 1/16" off the lands.
As to your question about better accuracy with the bullets close to touching the lands - that's what I've read. The truth is, I have not experimented enough with different seating depths to say for sure. But it seems to work. I don't take a scoped, bolt action rifle hunting until I have it putting 3 bullets into an inch or less at 100 yards. And I've never achieved that using factory ammo.

 

[Lennyjoe]

I use a case that has already been fired. Roll the case mouth on the bench enough to hold a bullet snug inside it. Mark the bullet with a felt tip marker and install it in the case just a bit. Chamber the round and then remove it from the rifle. You will see if the bullet comes back out by the scrape marks on the ink. Re-seat the bullet if it moved, if not then measure the length of the round and thats the COL to the lands. Now seat the bullet .010 deeper and use that as a starting point. It's not a good idea to seat the bullet on the lands. Pressure will increase to the dangerous point if the bullet is seated up agains the lands. I learned the hard way.

Thats the poor man's way. If you got the extra bucks then I would suggest a Stoney Point set up to get the accurate COL.

Be safe.

 

[DonP]

Thanks Guys

That's exactly what i was looking for.

Don P.

 

[444]

This is the second time today I have recommended this book. But, if you want to get serious about this, buy this book: http://www.zediker.com/books/handloading/hlmain.html

Here is a link to an article that the author of the above mentioned book, published on-line. It is primarily about the M1A, but does contain some good info about the M1 also. http://www.zediker.com/downloads/m14.html