.2695 in a .271 too tight?

[jdw91]

Thoughts? I'm using a steel .267 bushing in a redding FL die with new Lapua brass- 6mm BR with Berger 80's and 105 VLDs.

After sizing and seating the top of the neck measures .2695 using a Hornady electronic caliper; The caliper measures to the nearest half of a thousandth i believe. I'm not sure whether it's more towards .270 or .269, but assuming exactly in between is this too tight? How much clearance do most allow? I don't have any turner's and the barrel is no-turn. It's a pretty tight bolt close but it will close.

Jake

[Budweiser360]

Without a quality set of calipers or a outside mic, I would not trust it and make sure it is a good .002"

[BillPa]

What does the chamber measure? Not what its supposed to be, but what it actually measures. That's the determining factor what the finished ( loaded) neck diameter should be.

Bill

[jdw91]

I'm not sure as I've never fired a shot and don't have the reamer dimensions but I was told from the man who chambered it that it was a .271 no turn... now whether it's .2710 or .2713 etc I don't know, but hopefully no where under .271,


Jake

[Savagebien]

I doubt you will have a problem. I just measured some of my 6br ammo, old lapua brass (cardboard box), and sierra 107's. Measuring with two sets of calipers i get .270 one measured .2695. My chamber is a .272 nk. I'd go ahead and shoot some if you haven't already, should be fine.

[xr650rRider]

See if the bolt will close on a round. If not too tight to close, you'll be alright for a shot. Then take one of you bullets and see if it slides in the fired case. If it's a snug fit, then your perfect. If the bullet won't go, you'll need to turn necks. Loose fit, then there is nothing you can do but most factory chambers are loose anyway.

[jdw91]

xr650rRider, that's quite the intuitive method. I'll give it a try.

I still haven't shot it yet but the gun will chamber the rounds with a snug bolt close. Could be just a bit of dirt in the chamber that i need to clean out, as the neck fits and the headspace is good.

I know I've seen posts by BR shooters who allow .0005 to .0015 neck clearance, so I assume it'll still shoot, accuracy aside? I've heard that if it's to tight the "sine" wave around the neck will be just more of a straight line as gas can't flow back next to the neck anywhere. Has anyone experienced this?

Thanks for the help guys,

jake

[BillPa]

I've heard that if it's to tight the "sine" wave around the neck will be just more of a straight line as gas can't flow back next to the neck anywhere. Has anyone experienced this?


jake


Sine wave around the neck huh? ;D

Actually, the neck must be able to expand enough to release the bullet. If not the bullet can't move, but everything behind it might!

Not a neck size problem as such, but the same effect, the results of an undetected donut. The donut basically crimped the bullet and restricted it's release. The primer pocket expanded,leaked and the hot gasses burnt the boltface of a nice Mod 70. ( Not one of mine BTW) Also notice the imprints on the primer cup from the dirt that was on the boltface and where the cup started to fracture. Luckily all the shooter got was a bit of stuff blown back in his snot box,but it could have be worse, much worse.

http://i42.tinypic.com/fvfvpf.jpg http://i43.tinypic.com/2nuq2jr.jpg


I know it "supposed to be" whatever, the same as one of my pre-chambered 250 Imp barrels was supposed to be a SAAMI spec .286" neck. I suppose .283" is close enough to .286". Whats .003" under anyway?

I'm not much for one to think, assume or guess what I'm dealing with, I like to know for sure. Its why I make chamber casts.
http://i29.tinypic.com/2ynkqdh.jpg

The cartridge is the previously mentioned 250 and a cast of the chamber below it. The cast neck diameter measures .283" so the brass is turned to a finished .281" with a bullet seated for .002" clearance to expand and allow the bullet to release.

You say it chambers "snug", but why? Is it the neck diameter, the headspace-head clearance, the cartridge body diameter to the chamber, bullet seating depth or its just a snug fit?

Bill

[82boy]

I know I've seen posts by BR shooters who allow .0005 to .0015 neck clearance, so I assume it'll still shoot, accuracy aside?

Most BR shooters set their brass up at .002 clearance. (Some use .003) You may have seen post of someone who shoots less, but I guarantee they get flyer's, and are having all kinds of accuracy problems, and they are not very competitive.

[jdw91]

Bill, I rechambered a few rounds after cleaning and they chambered easily- before the snug fit was a "snug" bolt close, hard to describe- not forcing it but pressure was necessary. Interesting about the donuts, I hadn't realized they can be such a safety hazard, thanks for the pics. Any links to a "how to avoid donuts" thread? Again, I'm trying to stay away from turning necks to keep costs down.

82Boy, I'm not sure if this is from a while ago or 6ppc is a different ball game,

http://benchrest.netfirms.com/Neck%20Clearance.htm

Thanks for the help guys,

Jake