Neck Clearance - How Much?

[rcw3]

Just curious how much neck clearance you feel is right for a 6mm long range rifle where you neck turn. .002", .003" .004", something else?

Robert Whitley

 

[dreever]

I use .00085 to a side in my 6BR.

Danny

 

[mikecr]

My 6br necks are .0015" under chamber. Just the way it turned out to clean up lapua brass.

 

[tightneck]

I think .002 total is good, .003 probably would'nt hurt. But I sure dont have a micrometer that'll measure necks to the 50 millionths...or access to an environment to make such a measurment.

 

[jb1000br]

Robert, in 1KBR, I have heard as high as 2thou/side,4 thou total) and usually not lower than 2 thou total,1 thou/side)

I am not fond of either, so I split the difference

3thou total,1.5thou/side)

sometimes closer to 2.5 thou, depending on how patient I am setting the neck turner...but definitely closer to 3thou total, than 2 thou total...

JB

 

[aJR]

hi all,I think it's a mistake to take for granted that the reamer will cut the neck section of the chamber to the same size as quoted on the reamer print.. Each time i set up for a new barrel/ cartridge i measure the neck id with a hole mic..If you don't have one gradually trim the case, seat bullet and trim/seat again until U can just get the cartridge in to chamber,U can see the scrape marks on the turned neck and feel the resistance till it clears just right .. This measurement is the 1 i use for the clearence,on a 6mm = 2 thou over the loaded dia,7mm = 2.5thou and 30 cal = 3thou as a minimum.. If you use a minimum U should chase it as the shots stack on because the brass flow thickens the neck ..JR..Jeff Rogers

 

[Ogre6br]

is this for a competition rifle or a hunting rifle??

and does it make any differace what the application is?

would you have different neck clearance for a walkabout V's a full blown BR comp rifle??

why??

how much clearance is too much and is it on a sliding scale? or for example "6 thou" is too much and it doesn't matter how far over you are after that beacause it's to much.

Does neck tension and neck clearance have a relationship to accuracy??

thanks

later
P

 

[onehole]

Hi all I have cut all my brass to give 1.5thou total clearance on a loaded round and with heads that have a pressure ring the clearance gets a tad more less again.These close fittings have not produced any problems but it was important to establish from the very start what the actual chamber measurement was and not to go on what size the reamer should have made it.My pacnor 6br was delivered as a 264 but my riflesmith measured it out at 264.5 and I later confirmed this by very carefully cutting back a case to this dimension on my mic and to witness very very light scratching from the neck of my chamber on chambering a case.On a previous rifle [6ppc] 272 neck I was running standard sako brass showing at least 5 thou total clearance but it would still shoot crazy little groups so go figure that one.On balance I would still prefer to get close as possible if only to satisfy the 'psyco' thing and if we are bothering with tight neck chambers we may as well take full advantage of the potential gains in accuracy.cheers onehole.