Results 1 to 14 of 14

Thread: Neck clearence?

  1. #1
    Join Date
    Feb 2003
    Location
    CA
    Posts
    699

    Neck clearence?

    My loaded rounds measure a consistent .2715 for my barrel chambered in 6x47 Lapua. (I am using a 1" micrometer and checking it with a digital Mitutoyo caliper)

    The Bartlein barrel has a .273 neck diameter; therefore I have .0015 total clearance

    Fired case necks measure .2725.

    Berger 87 VLDH at 3190 fps have an ES of 0008 and a SD 0005. Fire forming loads are grouping excellent, using N-550.

    Pretty tight tolerances. Opinions please.

    THANKS!
    Last edited by John S; 04-13-2018 at 06:09 PM.

  2. #2
    Join Date
    Apr 2017
    Location
    Ames, Iowa
    Posts
    257
    Quote Originally Posted by John S View Post
    My loaded rounds measure a consistent .2715 for my barrel chambered in 6x47 Lapua. (I am using a 1" micrometer and checking it with a digital Mitutoyo caliper)

    The Bartlein barrel has a .273 neck diameter; therefore I have .0015 total clearance.

    Fired case necks measure .2725.

    Berger 87 VLDH at 3190 fps have an ES of 0008 and a SD 0005. Fire forming loads are grouping excellent, using N-550.

    Pretty tight tolerances. Opinions please.
    http://benchrest.com/newreply.php?p=808532&noquote=1
    THANKS!

    Your actual clearance between the case neck and chamber wall is .00075 As long as you are aware of the tolerance/s there should be no problem. After each firing, if twere me I'd seat a bullet in a dummy round and check neck diameter of the loaded round. If you feel resistance when you chamber a round, I'd be miking the round before I fired it.

  3. #3
    Join Date
    Feb 2003
    Location
    Houston, Texas
    Posts
    6,977
    Maybe a tad on the tight side.

    The trend in extreme accuracy shooting as of late has been "a little looser is better than tighter". I shoot for .002 in my 6PPC's and .0025 in my 30 BR when measured over the base of the bullet in a loaded round.

  4. #4
    Join Date
    Feb 2003
    Location
    Tennessee
    Posts
    4,842
    Yes, go a little looser. I don't know but I'm guessing that the .273 chamber diameter is stamped on the barrel rather than measured. The chamber neck diameter is likely a bit larger than stamped on the barrel but I had a barrel that was actually smaller. You probably won't blow up your rifle unless you close the bolt with a hammer but if the case neck is too tight accuracy will suffer. In my actual experience...accuracy will suffer horribly!

  5. #5
    Join Date
    Feb 2003
    Location
    CA
    Posts
    699
    "I think I will fire form the rest of my brass and then turn the necks", he said with a groan.

  6. #6
    Join Date
    Feb 2003
    Location
    Lower Dakota Territory
    Posts
    1,583
    An easy double check on loaded rounds is a neck bushing. If your loaded round measures .2715, get a Redding .272 neck bushing and slip it over the necks of your loaded rounds. If it goes...all is well. The Redding bushings work well, as they have no taper. -Al

  7. #7
    Join Date
    Feb 2006
    Location
    California...unfortunately
    Posts
    568
    John,

    If you want one, I can make you a .272 gauge if you don't have the correct size bushing.

    Justin

  8. #8
    Join Date
    Jul 2010
    Location
    The OC, PRK
    Posts
    14
    Quote Originally Posted by John S View Post
    (I am using a 1" micrometer and checking it with a digital Mitutoyo caliper)

    . Opinions please.

    THANKS!
    Waste of time to check a mic with a caliper. Calipers are only close. For total precision, use the mic, especially when measuring 10ths. If you want to check it, [the mic] buy some standards. I make my living using mics and calipers--I am a tooling machinist. Checking a mic with a caliper will tell you absolutely nothing.
    Jon

  9. #9
    Join Date
    Feb 2003
    Location
    CA
    Posts
    699
    Quote Originally Posted by musketjon View Post
    Waste of time to check a mic with a caliper. Calipers are only close. For total precision, use the mic, especially when measuring 10ths. If you want to check it, [the mic] buy some standards. I make my living using mics and calipers--I am a tooling machinist. Checking a mic with a caliper will tell you absolutely nothing.
    Jon
    The caliper check is used to insure I am reading the micrometer correctly. Sometimes my eyes don't pick up all those little lines and I need to check and double check, plus I could be dyslexic or the cataract is catching up on me. Thanks for your concern.

  10. #10
    Join Date
    Feb 2003
    Location
    CA
    Posts
    699
    Quote Originally Posted by Zebra13 View Post
    John,

    If you want one, I can make you a .272 gauge if you don't have the correct size bushing.

    Justin
    Thanks Justin. I'll need to dig through all my stuff for a bushing.

    "It's Bristol Baby"!!!!

    John

  11. #11
    Join Date
    Feb 2003
    Location
    Poetry, Tex.
    Posts
    6,060
    Quote Originally Posted by John S View Post
    "I think I will fire form the rest of my brass and then turn the necks", he said with a groan.
    Well John, I fireform before turning.

  12. #12
    Join Date
    Feb 2003
    Location
    Tennessee
    Posts
    4,842

    Frank Murphy's method

    220 Russian to 6PPC - FLM


    You need:

    --virgin Lapua 220R brass

    --6 PPC chamber with a narrow neck (often .262, but not always)

    --a 6 PPC FL die

    --two neck turners (yes, unfortunately, two, unless you actually like adjusting the damned things)

    --a 6 mm expander mandrel that is .001"-.002" bigget than the mandrel on the turner

    --a Wilson trimmer with the .220R shellholder and the PPC shellholder

    --deburring tool

    Steps consist of:

    --weight sort the brass, or not, depending on your religion

    --lube the inside of the neck (Q-tip, case lube)

    --run the brass over the expanding mandrel

    --check lengths. If your brass is like mine, they'll all be the same; this is the miracle of Lapua brass in action. If not, trim as little as possible to make them all the same length. Chamfer or deburr the inner lip of the case neck (outer doesn't matter at this point).

    --use a set of feeler gauges, if you like, and adjust the first trimmer to get you to within a half a thou or less of your goal for neck thickness

    --adjust the length of cut so that with your brass the cutter just kisses the shoulder when the case mouth hits the stop

    --use the brass that didn't weigh right to set up this process

    --lube the mandrel on the turner and lube the inside of the case neck

    --run a case on the trimmer; if its too tight, get a bigger expander mandrel and start over

    --give all the cases their preliminary turning, keeping everything clean and free of chips to avoid marring the neck surface

    --set up the second trimmer similarly to give a thickness of .0001 to .0003 over your ideal final thickness (it'll thin with the first few firings). After you've fiddled around for a while adjusting the trimmer, you'll see why I said tp get two trimmers.

    --run all the brass through this second turning. As this is the finish cut, use a somewhat higher speed and a very fine feed; you might want to run the brass twice.

    --use your ball mic or case checker to check for thickness and uniformity (sorry, I didn't put these on your shopping list)

    --degrease your brass, using hot soap and water (simple green works well--just boil the brass in a solution of this) or lacquer thinner or whatever. I use boiling detergent solutions when I'm feeling environmental, sovlent when I'm in a hurry.

    --if the neck won't grip a bullet when it comes off the turner, FL size and do not reexpand, for a firm grip

    --deburr case mouth. If you believe in a long taper internal chamfer, now is the time to cut it.

    --put a bullet in a case to make a dummy round. Check neck OD (it should be OK, but why take chances?), and check for fit in the chamber gauge if you have one, in the chamber (striker assembly removed) if you don't. Ideally, the prepared case will chamber freely as the case neck enters the neck of the chamber, indicating that you didn't make the neck too fat, but develop
    some feel as you close the bolt, indicating a close headspace fit between the round and the chamber. Usually, this won't happen, as the brass is manufactured not to be longer than spec and the chamber not to be shorter. If you trust "bullet jam" (see below) to hold the case back against the bolt face (I do for short headspaced PPC chambers), all is well. If not, over-expand the neck to something like 6.5 mm or 7 mm, then go back to the FL die and adjust to get a crush fit. I avoid this for the PPC, out of fear of what will happen with all that expanding and sizing of the neck.

    --prime, fill with your usual 6 PPC powder, using a long drop tube and vibration to get as much in as you can, bringing the powder up into the neck. This is counter to the usual advice to FF with reduced loads, but that advice is wrong: fire forming means deforming the brass beyond its elastic limit, and that calls for high pressure. As is, the case capacity is reduced though
    chamber capacity is not, and you won't be able to get in as much powder or produce as much pressure as you will with your subsequent PPC loads.

    --seat the bullet well out, for a good hard jam into the lands

    --fire the rounds

    --apply the primer pocket uniformer, and flash hole uniformer/deburrer if you care to--many feel these steps are not needed with this high quality brass

    --at this point, some people run through another neck turning; I don't think you need to, but opinions differ

    --I trim the case mouths and deburr here, just a thou or so, to be sure everything is square.

    --Done.

    As I said, opinions about how to do this are like hemorrhoids (you know the joke), and I only say that this way makes sense to me. Others may do it differently, and I'll probably do it differently too, a few months from now.

    FLM

  13. #13
    Join Date
    Feb 2003
    Location
    Tennessee
    Posts
    4,842

    Here's the deal...

    There are two ways to look at neck thickness. One is loading at home and shooting them one time before you go back home. The other is shooting and reloading at the range under time pressure. Any clearance is absolutely OK in the first case since the case neck can't get too thick before you have time to check and correct it. The other case is where you don't have time to re-turn your cases and even if you did I assure you it would goof you up to no end.

  14. #14
    Join Date
    Jul 2005
    Posts
    352
    Time for a chamber casting and some careful measurements.

    I have a couple of barrels I use for varmint shooting that have tight necks.
    A stock case will not fit in the chamber.

    Necks are all turned to 0.0100 thickness.

    the dimension on the barrel was checked with a chamber cast before the first round was made and fired.

    I go for about 0.0010 of clearance all around, so 0.0020 diameter.
    Accuracy with a Panda action is very very good.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •