Tight neck chamber

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by jon12, Mar 1, 2004.


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  1. TOM H

    TOM H Well-Known Member

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    I still shoot tight neck rifles and my 22cal have tight neck .242 which is pretty standard and you do have to turn necks.

    Hammonds' Rifles - Chambering

    My 6ppc has .262 neck.

    I understand what your doing and it's easy to do. Only problem you have, if you need more brass you may not get it with same thickness.
     
  2. shortgrass

    shortgrass Well-Known Member

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    SAAMI specs on most call for .010" clearance. That's alot! Reamer makers might run their reamer bodies on the tight side, but rarely do they run necks tight. It's a safety thing. All ammo, commercially loaded or reloads, must fit into the chamber and be safe. Ammo fired in a chamber without sufficent clearance can give excessive chamber pressures to the point of being dangerous to the shooter, bystanders, and the firearm. I own and use several tight necked reamers per client request. The neck diameter is engraved in the same line as the caliber designation. If your rifle has a tight necked chamber you only need turn necks once. Some factory ammo may or may not chamber. To chamber and fire ammo of unknown neck diameter in a tight neck chamber is an invitation to a potential disaster. Tight neck chambers can be cut a couple of different ways. The neck portion can be incorporated into the reamer in the usual way. Or the reamer can only cut the body and a seperate reamer be used to cut the neck. The first method is the usual way, the neck is cut with the rest of the chamber, not as a sperate operation with a seperate tool. There is another condition known as a "no turn neck". In this condition a lot ( meaning a group) of brass is measured, with bullt seated, for neck diameter. The reamer maker alters the neck of the reamer for clearance to the gunsmiths specs( typically .003" to . 0035",,,, meaning .0015" to .00175" clearance per side. Usually not more than .005" clearance. If you're using more than .005" clearance why bother? It costs on the average $30 to have the neck altered on a reamer). The reloader then only uses this brass or brass with the same dimention for his loads.If the neck of your chamber has these tight of clearances don't roll your ammo in the dirt before trying to chamber it. Many tight necked match chambers have even less clearance. Typically .001"- .00075" (even reamer makers need a tolerance to work within). Tight necks of any kind are not for the novice. It takes a good understanding of the relationship of ammo to chamber before a tight necked chamber is ordered from your gunsmith. I spend considerable time with every client I cut a "custom" chamber for, both before the chamber is cut and after and I still get to remove a stuck, live round from a chamber now and then. Tight necks can enhance accuracy and give more loads per casing provided everything else is correct. They are not for everyone.
     
  3. elkaholic

    elkaholic Official LRH Sponsor

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    I admit I have not read thru this entire thread so bear with me if I repeat something. I am pretty sure that the basics have probably been well covered but I recently changed my mind on HOW tight a neck should be. I design and shoot a lot of wildcats , so I am usually working with necks more than most. Some of the parent brass MUST be neck turned, for various reasons. I use to think that the tighter, the better as long as it didn't get tighter than .001" per side in a hunting rifle, and that is too tight for most hunters! I recently did some testing with a powder that gave EXTREMELY low es, so was able to really see the affect of neck tensions, and neck clearance, on velocity (pressure). What I found was that everything I shot that only had .002"-.003" total clearance, the es went up along with the pressure, even with loads that were not high pressure loads. In the rifle that I was shooting (a 6.5 SS) things really settled down at .004"-.005" and accuracy was as good or better in every case. For long range use, es is especially important as most of you know. I know that I will likely get some flak over this statement, but that is what happened in this rifle. I think the more important issues are dealing with consistency of brass and chamber. Concentricity, uniform neck wall thickness, neck tension, trim length, etc. Of course there is such a thing as too loose, but I will be running a little more clearance than I use to run. ......Rich
     
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  4. AZShooter

    AZShooter Well-Known Member

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    Here is another variable when one uses a tighter than SAMMI chamber neck dimension:

    Neck wall thickness has an influence on how the brass can create tension. Thinner neck walls like .010" will not have the same tension as .014" even if the same reduction of OD necessary to hold the bullet in the case. I am certain that it has an influence on ES.

    The BR crowd tends to use thinner case neck walls and many of the smaller BR cases like the 6 BR come with thinner wall dimensions than our hunting magnums. Then those target shooters will use less neck tension to further lower the ES for less vertical at long range. There is no need to keep a bullet in place in the cartridge during recoil because most BR guys are single shot loading. Hunting rifles usually keep several rounds in the magazine where recoil has an influence on the bullet so having a thicker neck plus sizing with more reduction to the neck OD is necessary to keep the bullet in place.

    Elkaholic reminded me that I read something similar to what he said regarding using enough neck clearance, on Accurate Shooter forum regarding the 284 win:

    "Jerry Tierney, a past NBRSA 1000-yard champion and .284 Win “guru”, has observed that overly tight chamber neck tolerances can cause accuracy problems. Jerry says “some guys who were running minimal neck clearance .284 chambers weren’t getting the accuracy they expected. If you open up the neck to allow more clearance, say .0015-.002″ per side, that seems to solve the problems. I can’t tell you exactly why–maybe it allows a ‘cleaner’ bullet release–but easing the neck clearance has helped many .284 shooters get better results.”

    I recently ordered a 284 win reamer to my specifications. Asked for a .315 neck. I have a large quantity of Winchester brass with varying thickness necks. My plan is to turn the necks down to a .013" wall thickness which makes a loaded round neck OD of .310" or a .0025" clearance per side. This it a sporter weight hunting rifle.

    This is a great discussion we have had. Hope it all makes sense to you, jon 12.
     
  5. elkaholic

    elkaholic Official LRH Sponsor

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    Let us know how this goes for you. I am convinced .004"-.005" was better in my rifle........Rich
     
  6. AZShooter

    AZShooter Well-Known Member

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    I will make a note so I can let you know Rich. I won't be installing and chambering that 284 for a while.

    My 7mm/375 Ruger has .0035" per side with .002" neck tension.

    The beauty of either of these 7mms is that I could adjust the neck turning tool to skim off .0005" -.001 per side with ease to change the fit.

    -----------------------------

    FYI on Accurate shooter in the 7mm info page, they suggest that .003"-.004" is best for the 7 WSM.
    quote:
    "WSM cases need adequate neck clearance in the chamber for bullet release. Total Clearance of .003″-.004″ (both sides combined) will probably better than .0015″ or less."

    Also....quote:

    "Producing Better WSM Ammo
    Here are some advanced reloading tips gathered from successful 7mm WSM shooters.

    1. Turn the necks, particularly with Winchester brass. This will help with neck-wall uniformity and bullet release. WSM cases need adequate neck clearance in the chamber for bullet release. Total Clearance of .003″-.004″ (both sides combined) will probably better than .0015″ or less.

    2. Make sure you have sufficient clearance between the neck and the side of the chamber. Some guys running with super-tight clearance on the necks had persistant and frustrating accuracy problems and unexplained flyers. Adding neck clearance (by turning the necks) cured the flyers. Three or four thousandths total clearance (sum of both sides) will probably work better than one-thousandth.
    3. Proper case-mouth chamfering is very, very important for accuracy and optimal ES and SD. With these long bullets you want the entrance to the case mouth as perfect as possible.

    4. Experiment with shooting the VLDs OFF the lands. While the 180gr VLDs, typically, work best seated .010″ or more into the lands, some shooters have obtained excellent accuracy jumping their bullets .020″ or more. It’s worth trying.
    Very low ES/SD is possible

    5. WSM brass really stiffens with time. For best results you may need to adjust neck tension (switch bushings) after a few reloadings. Annealing can also help after four or five reloading cycles."

    unquote


    This must be where I got the neck tension ES information that I wrote earlier. So I chose the mid road for my thick 375 Ruger brass for its clearance base on the above.
     
  7. elkaholic

    elkaholic Official LRH Sponsor

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    Good info.....I forgot to mention that I also found that jumping the 140 hybrids quite a ways, rather than into or close to the lands, lowered es......Rich
     
  8. AZShooter

    AZShooter Well-Known Member

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    That is worth knowing Rich.
     
  9. TracySes23

    TracySes23 Well-Known Member

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    .242" neck diameter in your chamber? Are you sure? That only leaves a total of .018" over bullet diameter. That's .009" per side without any clearance. If you wanted .002" total clearance, you'd have to turn your necks to a wall thickness of .008". I turn the necks of my brass to a .012" wall thickness. Why would you want it that thin?
     
  10. shortgrass

    shortgrass Well-Known Member

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    Maybe that's what works for him. There are no set rules when it comes to clearances. What works best can and does differ from barrel to barrel, lot of brass to lot of brass, cartridge to cartridge.
     
  11. TracySes23

    TracySes23 Well-Known Member

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    I just asked a question, I was hoping he'd tell me why. Often times I hear an answer I've often overlooked.
    I had an 8 year old tell me something, I'd never considered. He answer was logical & completely beyond my particular logic.
     
  12. Mikecr

    Mikecr Well-Known Member

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    We should consider cartridge design and chambering similar to racing engine design.
    With this we should realize that each system is in a balance, and you can't really improve a balance with single changes(unless this alleviates an actual problem).
    You wouldn't change to higher compression pistons in an engine, 'discover' a loss of horsepower in that action, and then declare that high compression pistons = less horsepower..
    And going tight neck clearances ALONE(with no plan) can also be a bad idea.

    For example; Until you make straight ammo, tight clearances will contribute to chambered tension points. A tension point is like your thumb on the action tang(which throws shots). So when accuracy issues seem alleviated by loose clearances, the root cause was as likely the result of crooked ammo in that straight/tight chamber. Where ES get's better with a sloppy chamber, it's as likely a bad load combination and/or bad load development(with a tight neck clearance).

    There are significant potentials with tight neck chambering(like high compression pistons), but only combined with planning and commitment to reach a successful balance there.
    This means more than a reamer in your gunsmith's hands, and more than comparing sloppy chamber to tight with the same load.
     
  13. elkaholic

    elkaholic Official LRH Sponsor

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    Hi Mike.....what is the exact spec that you would consider to be Loose and/or sloppy?......Rich
     
  14. J E Custom

    J E Custom Well-Known Member

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    SAMME specs. normally require the ammo manufacture hold his max dimension to
    .006 to .007 thousandths smaller than their maximum chamber dimension.

    A good reamer manufacture will hold the SAMME dimensions and if you shoot factory ammo you will still be fine. But rarely will a factory chamber be SAMME spec. (it will normally be larger).

    The minimum clearance between a loaded round should be .003 thousandths if it is turned. the normal clearance should be .004 thousandths with turned necks. you can go with less clearance
    but pressure will appear early if everything is not perfect. on dangerous game it is recommended that this neck clearance be between .006 and .008 for chambering in poor conditions or life threatening circumstances.

    So if you get a SAMME reamer and have it chambered by a good gunsmith it should be good to shoot most factory ammo. if you want to turn all of the necks on your brass, I recommend that you do a minimum turning then push the bullet you want to use in it, measure the od of the loaded round and add .004 thousandths to that and have a reamer made with that size neck.

    To find out if your rifle has a SAMME neck, a loose neck or a tight neck simply measure the Od of several fired cases, subtract the neck thickness x2 and the bullet diameter and you will know how much clearance you have from a loaded round to your neck chamber.

    Note ; these neck dimensions are very important if you want to avoid pressure issues.

    J E CUSTOM