no turn neck chamber?

[gcollins]

Howdy All,
Man this question I have, I really don't know where to post it, so here goes, and if it needs moved please do!
I am building a bolt action rifle in 260Rem AI I hope?
The barrel I have is a AI and 2 years later I don't think I am going to use it, I have found another 260 rem and I don't think it has the 40 degree shoulder chamber, I am sure I could rent a 260 AI reamer and in no time have the chamber to a AI. I have a couple friends that are machinist!

Now for my QUESTION: What is a no turn neck??the barrel I am looking for is a no turn?
Do I need to change my Cowboy name to Dumb A&&
Later
Greg

[Doc Highwall]

A no turn neck will be large enough that it will allow a loaded round to chamber. Example your case neck wall thickness is .015" and the bullet measures .264" giving a loaded cartridge neck diameter of .294"

SAAMI gives a max case neck diameter of .2970" and a min chamber diameter of .2980"

Here is a link for a SAAMI drawing.
http://www.saami.org/pubresources/cc_drawings/Rifle/260%20Remington.pdf

[B R Shooter]

Doc is right. In the competitive shooting games where accuracy is paramount, turning necks to fit a tight neck chamber is common. However, it does mean the user must turn the brass necks to fit this chamber. Many don't like doing this, too time consuming, or whatever. So, some reamers are made a bit tighter than SAMMI, but large enough where the loaded round has clearance. Lapua brass has a good reputation for good quality brass where the wall thickness is consistent. Most people who go for a no turn chamber are using a cartridge that Lapua makes brass for. Otherwise you end up culling a lot of brass.

[gcollins]

Okay,
Doc, I know about brass prep. The very first line of your reply says


A no turn neck will be large enough that it will allow a loaded round to chamber

Okay, then every factory chamber is a no turn?
Shooter, Okay I can see that being right if we were talking about Wild Cat chambers!

I am not trying to make fun of anyone, I still can't understand what Doc said. My point is, lets go to 15 different Wal Marts and I am sure that every 30-06 we looked at will chamber a round You guys know me: I don't make fun of anyone, I am just trying to understand? If, I am not understanding please help me.
Greg

[country gent]

With a custom chambering reamer is made you can specify neck dia. the reamer cuts to. Normally this is a dimension that gives .001-.002 clearence on factory loaded ammo or sammi spec ammo. This is the no turn neck you refer to, the standard factory type chamber. On a custom reamer for benchrest or serious match shootig a Tight neck or turned neck throat is specified this is .005-.007 smaller than the loaded sammi diameter of the neck for the given cartridge, meaning necks have to be turned before being oaded to allow .0005-.001 clearance in the chamber. This is a means of keeping the loaded round on center and true to the bore of the rifle as possible. Brass done for a tight neck is normally dedicated to that rifle. Some benchrest shooters fit to chamber is such that there is no need to size cases as spring back is more than clearence is. Its a a way of gaining that last bit of accuracy available.

[BK7saum]

A no turn neck chamber is usually chambered when a specific brad of brass will be used. A loaded round will chamber with minimal clearance, maybe 0.001-0.002". A SAAMI spec chamber is looser where the neck clearance is 0.005+" and all ammunition of that caliber will chamber.
With a no turn neck, if you change brands or even lots of brass, you will need to double-check clearance. Otherwise if too tight pressure problems might arise.

I have a no turn 6x47 lapua. I use lapua brass. Neck clearance is a couple thousandths.

[Doc Highwall]

A 6mm Br case has a .2717" max neck diameter for factory ammo. I have a 6mm Br that has a .266" neck chamber and a friend of mine has one with a .262" neck chamber. So with my .266 neck chamber I am turning the necks to .0106" giving me a loaded case neck diameter of .2642" or .0018"/2 =.0009" clearance all around meaning I have to keep my case necks clean if I want to stay out of trouble.

[B R Shooter]

A factory chamber will take any commercially loaded round, regardless of brand. So it's quite generous. Just looking at the difference in fired brass can easily be seen with the naked eye. and then there is the factory headspace tolerances, but that's a different discussion.

[GabbyM]

Chambers I cut with the one reamer I own. A standard Clymer 243 A.I. Are tight enough that when I use oversized cast bullets. .245" vs J bullet diameter of .243". I need to neck turn to qualify the new dimension wall thickness. When using old brass. Which all my 243 brass is as I've already worn out a couple barrels with the 800 piece lot I have. Routine is before shooting used 243 win brass from one of the old factory chambers. They are maximum FL die sized in order to get the head space short enough. Bold will still close snug as that's the way I cut the chambers. Which is where the go gage just does close then I check with some sized old brass to see that my die will make them fit. I turn the necks to just qualify they are at the new brass dimension. I think that's .015" on a 243 Win. Then I anneal them and load with cast boolits to fire form the old 243WIn to the Ackley chamber. Then I anneal them again and place in lots using the 100 count plastic boxes I like. With the .015" neck a new .245" cast boolit will slip fit a fired case. Never tried it but if the necks were to be allowed to grow .0015" I'm sure you'd get enough bullet release tension on the fat ones to cause at least a shot to shot pressure deviation that would ruin accuracy. With the little powder charge I use under that 84 grain boolit if it chambers it will be safe to shoot IMHO but accuracy could be poor if your bullet release isn't consistent. My DPMS AR-15 bull barrel with 223 Rem SAMI chamber is pretty tight also. When I started sizing down old brass for it I had to buy a new FL die as my old one with several thousand mil surp cases behind it was worn enough it failed to size them enough. All my bolt gun hunting rifles around here can take a .004" oversized cast bullet just to get to a .002" bullet release diameter. My Win 94 AE only takes .002" over and will not chamber a .312" loaded round. Daughters Marlin 336 in 30-30 is the same way. So don't go by rule of thumb where people say they are all large because they aren't.

Any chamber advertised as a target grade no turn should be expected to be on the tight side of SAMI dimensions. Just because that's the standard vernacular. So you need to check all your brass to make sure it's not oversized in the neck. Easiest way to check them after you've found some oversized is to buy a neck turn tool and run them all over it. God brass that starts out new and is just neck sized then shot in the same chamber should not grow on you much. But if you've had to trim to length a few times they may be getting fat.

[gcollins]

I thought I knew what it was but, since I didn't know for sure I asked and it got answered. On my 22-6mm build I just can't use the action after I took it to a gun smith (if you can call him that) just ruined the action when he drilled it for scope mounts, so I am looking for a 93-95 small ring Mauser action thrower in a draw some where that you would sell? I put this out to anyone.
Greg

[Multigunner]

Rather than using a tight chamber neck the best method I've found is to neck size only and size only 2/3 the length of the neck. This centers the neck and bullet to the origin of rifling.
An added benefit is that the less the length of contact between neck and bullet, within reason of course, the less any difference in neck tension between one case and another can affect the pull strength.
The bullet release is smoother and more consistent shot to shot.

[flounderman]

I hope you are not looking for a 93 mauser action to put a 22-6mm on? the holes in the mauser can be welded up and redrilled as to your ruined action.

[B R Shooter]

Rather than using a tight chamber neck the best method I've found is to neck size only and size only 2/3 the length of the neck. This centers the neck and bullet to the origin of rifling.
An added benefit is that the less the length of contact between neck and bullet, within reason of course, the less any difference in neck tension between one case and another can affect the pull strength.
The bullet release is smoother and more consistent shot to shot.

The main reason for turning necks was to make the neck thickness the same all the way around. If you use a tubing micrometer and check the brass thickness, you can be surprised at how much it varies sometimes. By turning the thickness the same, then fitting the neck in a chamber where the clearance is minimal assures the concentricy of the loaded round to the bore.

Neck sizing only helps a great deal in many cases. At some point though, your brass will start to get tight and you'll have to resize.

[Doc Highwall]

A rifle chamber with minimal clearance in the neck eliminates overworking the brass.