Chamber neck size

[JustDennis]

A real novice here. Have taken 6mm BR Lapua brass and necked it down using 22 Rem BR dies. Then neck turned and and run through the sizing die again. The result of this is the necks of all my brass are now all between .2485" and .2495",and trimmed to length of 1.516").

The question: when I order a barrel, what diameter should I have the neck of the chamber reamed out to? Or how much space should there be between the neck of a finished round and the surrounding chamber??

Thanking you for any assistance...

 

[dreever]

the rule of thumb is from .001,tight) to .002 above your loaded round neck diameter measured at the bullets pressure ring if a flatbase.
What does your loaded round measure?

Danny

 

[Forum Boss]

Dennis, you've done all the hard work. You've asked a sensible question.

Take the bullets you plan to use and seat them in the necks. Measure the neck diameters with bullets seated. Be sure to check right at the tip, and the base of the neck as well as the middle. You'll want a neck diameter in your chamber that is .002-.004" larger than your loaded rounds. Some PPC guys go with a very tight "fitted" neck, but we think you'll be happier with a neck at least .002" larger than your loaded round.

Normally the barrel maker won't be cutting the chamber--this is something your gunsmith would do. He and you can decide on the best chamber-neck diam based on your intended application.

If your 0.2495" dimension is for a round with bullet seated, we'd probably go with an 0.252" chamber. FYI, a .272" chamber works for for loaded 6BR ammo that measures 0.270" at the middle of the neck.

 

[750k2]

Just curious what your neck thickness was before you turned them -,just necked down)??

 

[rhino]

Loaded ammo diameter plus .002 is I think minimal. However many people prefer a .003 clearance.

So if you got a .292 loaded ammo, then your chamber should be .295.

Of course everyone has a different idea...but too tight is no good as well as too loose.

RHINOUT!

 

[WayneShaw]

Getting ready to order a 22BR reamer, so I took a 6BR Lapua case and ran it thru a 22 neck die. Set up my neck turner and started turning the neck down until I had a clean neck, no more. I then seated a Berger match bullet and miked the neck, it was .2495". So I'm going with a .252" neck on the reamer. Also, when you neck down the case, the mouth wants to bell some, so a little trimming is in order. I'll order a 1.560" case length, and a trim of 1.555" will be just right.