Tight neck chamber

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


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  1. elkaholic

    elkaholic Official LRH Sponsor

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    Jerry.....004" is what I have settled on, and .005" doesn't seem to hurt me. I was going .002"-.003", but as I stated above, it was not working as well for me......Thanks/Rich
     
  2. J E Custom

    J E Custom Well-Known Member

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    That is perfect in my opinion. I use .004 if I plan on turning and.005 if I shoot factory only.

    I have had trouble with .003 and .003.

    Just my recommendation also.

    J E CUSTOM
     
  3. Mikecr

    Mikecr Well-Known Member

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    Personally, I consider anything >2thou over loaded OD as sloppy/factory.
    With 2thou clearance the neck will expand ~2thou and spring back ~1thou to pull from the chamber ~1thou over loaded OD. With a proper bushing of 2thou under loaded OD we squeeze down 3thou and spring back to 1thou under cal. You can & should go another 1/2thou squeeze and follow with neck mandrel expansion.There is absolutely no problem in this plan, and the necks would only need process annealing about every ~30 reload cycles. This can be extended way further with tighter clearances, so there is tension consistency here that most reloaders cannot achieve otherwise(without very very good annealing).
    Truly, necks with ANY clearance, will free release bullets with no affect to pressure. That is, you could have 0.000000001" of clearance, and while a cartridge that is not so straight will be in chambered tension, the neck will still expand to release the bullet.

    I consider required neck turning to provide <2thou clearance as 'tight'.
    Anything <1thou clearance is 'fitted'.
    I run a tight chamber with which I've fitted necks(<1thou). My load produces ~8fps ES as measured with 20' screen spacing on an Oehler. Pretty good from IMR4350 near SAAMI max(not over).
    I don't size these necks at all, will never need to, and with this the neck tension will never change.

    Certainly I know this isn't for everyone. But I also see calls for excess in clearances, including body, necks, and trim length, as more of paranoia and misunderstandings -than actual understanding.
     
  4. AZShooter

    AZShooter Well-Known Member

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    Mike,

    I am with you for every bit of your explanation. Well stated. A few comments/questions.

    Doesn't spring back vary somewhat with neck wall thickness? Do you use the mandrel setup with all your ammo? I would think on some just using the correct bushing would suffice.

    The 30 BR long also had a fitted neck (mentioned earlier) but I turned off another .0005" per side so I don't depend on springback to hold the bullet instead with I with a bushing. Accuracy stayed the same with fitted or bushing sized neck. Never considered using a mandrel. Only one I have is the K and M which might be the wrong dimension, don't know. Where do you get the mandrels? How do you determine what diameter you need?

    Finally how do you explain the comments:

    from Jerry Turney on the 284: 0015-.002″ per side gave a cleaner release and better accuracy.

    Or Accurate shooter that the 7 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."

    Or Elkaholic aka Rich's comment: I am convinced .004"-.005" was better in my rifle........Rich


    This is not to argue or an attack. I want to learn all I can. I know that so far I have not had any issues with any clearance I have tried. BUT I know that a fitted neck needs to be carefully monitored and everything must be right and clean. I also realize you can extend brass life if you don't work the necks by expanding and reducing diameters excessively.

    I find this a great discussion and have only read some of it in old issues of Precision Shooting which is no longer with us. We want more, we want more.......

    Ross
     
  5. Mikecr

    Mikecr Well-Known Member

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    Ultimately it's all about spring back, and wall thickness does directly affect this. So unless you hold a brass lot(all you'll need) of really uniform thickness, you should consider turning those within a reasonable thickness variance range(cull out the rest). This is where up front planning comes in.
    Brass springs back counter to last sizing, most immediately, and more of the balance over time. This happens with necks, shoulders, body, and even your seated primers creep over time.
    When you bushing downsize, the necks spring back outward away from that action(decreasing tension), and will continue over time. This may not be good for long term performance consistency, and the greater the sizing energy added, the greater the counter action -to a limit(~1.5thou).
    You don't need to downsize so much that a mandrel(I use Sinclair's) would actually upsize, and you *Rule 4 Violation* sure don't need to be upsizing necks with bullet seating.. Doing so will contribute to big seating depth variances, setup for big spring back variances(tension variances), and increase loaded runout. The mandrel is an intermediate step to relieve much of this(to reduce the amplitude of spring back energy/variance). The most consistent tension = the least tension = the least variances of it.
    There are BR shooters who turn a shelf in the neck for seated bullet bases to rest against. A planned precision donut. They don't need any tension, and therefore mitigate tension variance.
    Not practical for hunting, but fine for BR with bullets seated into the lands anyway.

    The Sinclair mandrel system is by far the best. And you can get carbide mandrels for it from PMA(who I believe designed Sinclair's entire turning system).
    I've installed a load cell in my expander die to measure force of pre-seating. This provides a more accurate relative tension indication than bullet seating force, as bullets are terrible expanders.
    This is not actual tension(spring back gripping force), but useful,, another thread.
    The sinclair turning/expander mandrels are also the correct size for reloading, where K&Ms are not.

    Tight clearances do need well taken care of ammo and chambers. This will never be a problem for me, or for a long range hunter. My father taught me to respect guns, not only in safety and honorable possession, but in condition as well.
    My guns are pristine.
    As far as reloading, I control all local aspects of it. I measure and verify everything, always. I am not afraid of my abilities to do this, because it's habit to think about what I'm doing.
    My ammo is perfect.

    As far as other's notions and fears, I addressed this in post #26.
    Whenever someone implies this or that without supporting understanding of it, be sure there are logical reasons.
    The prize in it is not what they observed, but the reasons.
     
  6. AZShooter

    AZShooter Well-Known Member

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    Thanks for taking the time to write those details Mike.

    I particularly liked the comment that you want to start out with brass that is as good as you can find. "you should consider turning those within a reasonable thickness variance range(cull out the rest). This is where up front planning comes in. " I try to use Lapua when possible. One of my BR friends uses RWS for his 300 win mag rogue (improved) Swears by it.

    Good to know about Sinclair's mandrels.



    I find this level of attempted perfection very interesting. Two of my friends are 1000 yd benchrest guys with a few range records and one placed well in the Sacramento Nationals a few years ago. That guy no longer shoots, if you can believe it.

    I will copy this in a documents file for further reading right along with the stuff Virgil said in the Secrets of the Houston Warehouse story.

    Good stuff. Thanks again

    Ross
     
  7. J E Custom

    J E Custom Well-Known Member

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    Like others, I have an opinion on "Tight Necks" based on My experiences.

    Tight necks were considered one of the only ways to get the best accuracy in the past because of many quality issues with chambers, dies and brass. Now days, with the quality of the dies and with well prepped brass this is no longer necessary to get extreme accuracy. for Bench rest shooting it works well because maximum pressures are seldom reached or needed. in long range hunting/shooting velocity is more important and high pressure loads are normal.

    The main issue with Tight necks is normally premature pressure spikes that limit maximum velocity
    (No free bore has the same effect) Keep in mind that long range hunting/shooting has different requirements than other forms of shooting so the same rules don't always apply.

    If you have a good quality barrel , and a concentric and true chamber the quality of your reloads will produce great accuracy without dealing with the possible pressure issues and loss of velocity. Over sized brass will almost always increase group size whether it has a tight neck or not. In a well sized case that fits the chamber perfectly, nether the tight neck or the .005 + neck should touch the chamber. so the bullet is suspended, and ether way should not have anything to do with accuracy.

    If a person intends to shoot factory ammo a tight neck spells disaster because of quality control issues with the brass wall thickness.

    I have opened up many tight neck chambers to solve the many problems that come with them and do nor recommend the use unless one is a very competent re loader and understands the issues with tight necks for this sport.

    Just my opinion based on "My" Experiences over 50+ years of shooting/competing.

    J E CUSTOM
     
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  8. elkaholic

    elkaholic Official LRH Sponsor

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    VERY well stated Jerry! This is what I was referring to about long range being different that 100 yard benchrest, etc. 20' per second at 100 yards means virtually nothing with an otherwise good load, but at 1000 yards, it does! It is no different than saying one bullet fits all. Thank you for your expert opinion......Rich
     
    joep17 likes this.
  9. TracySes23

    TracySes23 Well-Known Member

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    I've never seen it as a problem with 22-250 Lapua brass. The last 100 cases I turned had a neck wall thickness between .014"-.015". I've personally never seen any brass that consistent unless it was culled before it was purchased at a higher price. I doubt I'll ever need to buy more brass.
     
  10. joep17

    joep17 Well-Known Member

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    What a great topic and a can of worms with 17 ways to look at this.

    For hunting rifles I never do a "tight" neck. However is do clean up all necks to get more consistent neck tension. Regular loading dies so weird things as you pull the case back down through the expander. Stretching the case, expander ball off center and more.

    For competition rifles I turn necks, use a bump die with inserts for that particular chamber like forester (they are available in 0.001 increments) and then use a 21 century expander to get consistent neck tension and concentricity. This is for competition rifles.

    For example, my f Class 308 has a 338 neck reamer. For my shooting, I make ammo for a completed 334 diameter

    I take Lapua brass, neck turn to 0.013" inch per side with a Sinclair tool and can only be measured well with a good ball micrometer.

    Then I use a 0.330 forester bushing, and then run a 21 Centuryexpander mandrel. Is it perfect? Probably not but works for me. Consistent neck tension and concentricity is paramount to long range accuracy

    Tight chambers have a place in precision rifles. I pick my spots carefully

    For hunting rifles I tend to be more careful.

    Hope this helps and it is only my experience and where I landed after years of experimenting.

    My other advice is that if you go down this route, buy your own reamer and take it to the smith for your barrels only. Mine just cut it's 5th chamber and I am wondering how long until I need another one.