Short necks=short throat life??

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by goodgrouper, Dec 23, 2004.

  1. goodgrouper

    goodgrouper Well-Known Member

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    I read awhile back in a PS magazine (I think) about an article that was written in regards to short necks equal short throat life. I kind of brushed it off as something I just didn't want to believe in because it sounded too logical and I had several guns with short throats in my safe. But I have to re-evaluate this now as of recent happenings. My .22-.250 improved shot its throat out 3 weeks ago after only 1050 rounds. It was in a 3 groove barrel and had nothing but moly shot in it. It was cleaned every 30-50 shots and was never abused. This barrel had everything done to it to achieve max barrel life and it seemed to have died an early death. On the other hand, my uncle and I both have .220 swifts that have both been treated well, but are not 3 groove and have not shot moly much, if at all, and they are still kicking with well over 2000 rounds through them. The 22-250 improved shoots 41 grains of N550, and the swifts like 42 and 43 grains of H414 and W760. So my conclusion is that either N550's flame temp is as hot as a solar flare, or the swifts much longer neck keeps some of that hot gas in the case and out of your throat. This could also explain why a 6mm Dasher has 3 times the barrel life as a .243 win when they both shoot roughly the same amount of powder proportionately. The Dashers neck is quite a bit longer than the .243's. Has anyone else thought about this phenomenon or witnessed it??
    thanks-- goodgrouper
     
  2. Bob S.

    Bob S. Well-Known Member

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    Good question. I am certainly not an expert but wasn't the swifts reputation for burning out throats because of the powder used at the time? Longer neck than the 22-250 now comparable barrel life with the modern powders. I think the overall geometry/pressure has to do with how fast stuff burns out. Neck length certainly is a part of it but is not the only consideration. Seems that as we stretch the case capacity we sharpen the shoulder angle and shorten the neck so we can maximize velocity/pressure by using "more" hotter faster burning powders. Fast/reliable/cheap - pick any two. I'm not a smith but how does throat taper change when a cartridge is "improved"? Does it correlate to neck length? case diameter vs bullet diameter? Faster taper - less surface area - bigger effect any erosion will have?
     

  3. Waltech Jim

    Waltech Jim Writers Guild

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    Goodgrouper,

    Myself along with several buddies (and a Brother I usually don’t recognize) have been shooting, and shooting out, 22-250 barrels for years at prairie dogs. They say an expert is someone who has made all the mistakes one can make in a very narrow field.... I can’t say we are experts but I know we have made all kinds of mistakes.

    One of the things we observed early on is that barrel life (22-250) was a function of how hot your loads were and how quickly you shot (how hot you got the barrel). If a person shoots slowly this variable (excessive barrel heat) is eliminated and then the most important factor in barrel life becomes the load you are shooting. I recall your post on twist rate (12/19) where you state your loads were slightly loosening the primer pockets. With all due respect, I would have to seriously question this as a possible reason for the lack of barrel life. A load that loosens primer pockets is producing a plasma that will have no problems vaporizing barrel metal.

    Other things we have found through years of testing (making mistakes) is moly helps lengthen the number of rounds you can shoot before you have to clean. We have not found it to have a positive effect on barrel life, and it can be argued that it has a negative effect as some guys add more powder to make up for the loss in velocity that might happen when going to moly vs non-moly bullets. None of us are using double-based powders anymore. (observation)

    As for the length of case neck having to do with barrel life, the first thing that came to mind was the 300 WM. The short for caliber case neck is often mentioned, but I have never heard of the complaint it is a barrel burner. (I use a 300 WM on prairie dogs and it has throated approximately .005 in 2000 rounds. Not excessive in this hobby). JMO

    Merry Christmas and Happy New Year

    Jim
     
  4. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Goodgrouper,

    It is my opinion from what I have seen that other factors other then throat length influence throat life to a greater degree.

    From what I have seen doing research with rounds such as the 257 STW and 257 AM, it is throat diameter much more then any other throat dimension that effects the accuracy life of a throat. The tighter the throat the better, to a point. If you are using one bullet only then I like to cut throat diameters to 0.0002" over bullet diameter.

    If my customers want to use several different bullets, I cut the throat 0.0005" over the largest bullet diameter they wish to use.

    In all honesty, the larger the case capacity, the higher percentage of powder that will pass through the throat prior to ignition.

    Also, stick powders are much more abrasive to the throat and origins of the rifling then a Ball powder. The stick powders also tend to burn a little hotter as well.

    A nice sharp shoulder of at least 30 degrees will help contain the powder charge longer so mor eof it burns in the case but still some will burn in the throat section of the bore and even past that.

    I have found that as far as accuracy goes, the proper rifling design increases accuracy life even more. For example a three groove system will take longer for the origins of the rifling to erode then a 6 groove system simply because there is more steel in each of the rifling on a 3 groove design, which takes longer to erode.

    Most of the rounds I deal with a very large case capacity rounds for their bore and I will say that I am much more concerned with throat diameter and the style of rifling used then the length of the throat.

    Just my opinion from what I have seen. Again, I do nto deal with traditional BR rounds much so take this for what you will. All my rounds are throat burners if you will but all will also offer +1000 of accurate barrel life which for a big game rifle is plenty.

    Good Shooting!!

    Kirby Allen(50)
     
  5. TOM H

    TOM H Well-Known Member

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    There are afew things missing like bullet weight,velocity and twist. I own acouple 22-250AI and a 220swift and have been pretty happy with velocity and barrel life and so far on my 22-250AI I'm way ahead of you on rounds fired I also own afew other AI. I have found on my AI from 22 thru 7mm I normally gain about 200fps and increase powder about less than 10%. I did look up laupa reloading of the 22-250 with N-550 and a 69gr bullet was the only load for N-550. Without knowing any more it's hard to comment and only thing I can honestly say might be your reloads more than a short neck. I've always preferred the long necks over the short for more than one reason and when the case is AI to me that changes.
     
  6. goodgrouper

    goodgrouper Well-Known Member

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    Waltech Jim and others,
    Thanks for your posts. That is an interesting point you bring up about moly actually causing more throat damage because of having to bump up the powder charge. I did have to do that to maintain the "sweet spot", but moly's intended purpose is to reduce friction--at least that's what is advertised, but I'm starting to think it doesn't make as much difference as what they say it does. I have noticed that the 100 and 1000 yard benchrest clan praised it holy 5 years ago, and now you see less than 10 percent of the guys still running it. Funny how the tastes change.
    You also have a great memory. My post on 12/19 did mention that to get the "sweet spot" with that load, it was just starting to loosen the primer pockets with a fairly heavy ejector mark. But I didn't mention that my swift was the same way. They both kinda had that "magnum gun" quality of not wanting to shoot until they were running max. This article I was reading basicly found that the longer necks of some cartridges, combined with shallow shoulder angles (&gt;30 degrees) shot the hottest gases from ignition down the shoulder wall and into the neck on the opposite side instead of into the throat of your barrel. Thus, their conclusion was that 2 cartridges with the same flame temp, case capacity, caliber, and primer with different shoulder angles and neck lengths would give greater throat life to the longer necked case. A perfect example of this comparison is the 220 swift and the 22-250 AI.
    Fifty driver is correct about ball powders having slightly cooler and less abrasive qualities than extruded powders, but it shouldn't be enough of a difference to increase barrel life by half, should it?? I mean holy cow, it went from 1050 rounds to over 2000. I have a hard time believing that N550 is THAT hot. What's your thoughts?
     
  7. goodgrouper

    goodgrouper Well-Known Member

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    Roper,
    Thanks for posting. Here's the loads:
    220 swift= 43 grains of H414, 55 blitzking, win case, Fed 210 gm, 14" twist, 26 inch barrel, six groove, 3955 fps.

    22-250 AI= 41 grains of N550, 55 moly blitzking, fed case, fed 210 gm primer, 14" twist, 26.5" barrel, 3 groove, 3925 fps.
     
  8. brianwinzor

    brianwinzor Well-Known Member

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    Goodgrouper, I am using a 22/250 AI with the 28 degree shoulder in a 1 in 10 twist Shilen SS barrel. This barrel was previously used for the .224 Clark for 1600 shots, before being set back and rechambered.

    I am using the Sierra 69 grain HPBT moly, and have fired about 300 shots, which included about 130 rounds of load development with 9 different powders.

    About 3 weeks ago, I measured the distance to the lands with this bullet, and found that the distance was still 2.470 inches, so there had been no throat erosion. I didn't believe it, so I remeasured two more times and got the same result.

    All my rifles are potential throat burners, but I have learnt over the last 30 years to manage that problem.

    I would guess that getting the barrel too hot, combined with a high pressure load, are the most likely reasons for only getting 1050 shots of barrel life. Did you measure the amount of throat erosion at that point?

    I have found that most of my "barrel burners" develop between .150 and .250 inches of throat erosion by about 1500 shots. At this point there is usually about 70 - 100 fps less velocity, (200 fps in 1 rifle) and although accuracy has deteriorated, they still seem to capable of shooting around .800 moa, as long as they are cleaned regularly.

    I also try to use a ball powder where possible in my "barrel burners", as Ken Clark (who developed the .224 Clark) found in his research that it helped to extend barrel life, and have followed his advice.

    I am currently using 46.0 grains of Winchester WMR with the Sierra 69 grain bullet for about 3430 fps in my field loads. Hope this is of some assistance. Regards, Brian.
     
  9. JR

    JR Well-Known Member

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    If you watch the Simpsons, you'll know who Nelson is...Nelson says, 'ha-ha'..n550...I don't know why my throat burnt so fast..jazus..just as well lit them off with pure nitroglycerine, the flame temp is much hotter with teh 500 series double based VV..Yes will smoke a pole faster than most..

    JR
     
  10. rost495

    rost495 Well-Known Member

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    A 223 is not a barrel burner for sure. But since I shoot thousands of rounds of 223 a year, we took a look at one particular style and brand of barrel. Then looked at barrel life vs what others were shooting. Between Varget, 2520,RL15 and N540 and N550 I could tell no practical difference in life. Maybe 500 rounds max difference but it was not repeatable enough to say for sure that it was caused by N500 series powders. One thing I do know in 223 is that N500 likes to be driven to the edge before it performs well enough for me to be happy.

    FYI though I've gotten 4500-6500 rounds of life in cut barrels in 223 I've never gone more than about 3500-4500 rounds in buttoned barrels and remained happy. Thats with all kinds of powders.

    And then what happened to the thought that ball is less damaging on the throat area, but burns up the middle of the barrel? Could never tell one way or another. Just shoot what works is what we would do.

    Jeff
     
  11. goodgrouper

    goodgrouper Well-Known Member

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    Brian Winzor,

    I am glad you asked that question. As a matter of fact, last spring I had the barrel borescoped just out of curiosity to see what 750 rounds would do to a 3 groove barrel. It looked nearly new! There was slight "lake bed" appearance for about 1/16" in front of the leade and that was it. I thought it would last forever at that rate. But somehow in the next few hundred rounds it grew to 1.5" inches of lake bed. And no, it never got really hot, except once but nothing like I couldn't touch the barrel.
    I too have another .22-.250 AI, but it is an 8" twist and shoots 75 grain v-max at 3350. It started life as a .22-.284 on a 30" tube, and after it shot out I cut 3" off and did the Ackley. So that barrel has had roughly 1700 rounds down it and it is still going strong and I've only lost about .025" of the throat since rechambering. Incidentally, The barrel shot out on the .22-.284 at 950 rounds! It burned 10 grains more powder but held on to the throat to within 100 rounds of the other .22-.250 AI. But it (the .22-.284) had a longer neck! I really think that might help.
    As for the other comment about how your seating depth remained the same, mine did too! I never adjusted it at all for the entire 1050 rounds. It always felt and touched the riflings so much that once a loaded round was in the gun, I had to shoot it because the rifling would pull the bullet out otherwise. Then one day it went all to hell. My groups tripled in size and I couldn't find the riflings with the bullet anymore! What frustration.
     
  12. goodgrouper

    goodgrouper Well-Known Member

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    JR,
    Interesting. Thanks for posting. I was wondering if you could tell me the source in which you learned of the 5 series powders being so much hotter. I would like to read it! Rost495 says it isn't any hotter at all, and he had pretty extensive experience with it it sounded like. Damn that Nelson did it again.
     
  13. Brent

    Brent Well-Known Member

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    I know a smith who set up a test using a 6.5 WSM short neck, and another with a longer neck. The cases were formed with 300 Ultra Mag basic brass, so bodies were identical.

    The throat was shot out in the short neck in 100 rounds, about .100 erosion, or .001 per round.

    The longer neck was almost .400 in length and proved to have .007 erosion in about 700 rounds.

    Highpower shooters tell me that the 300wm is a throat burner compared to most any other round they use. Not hard to understand though. They shoot fast, and is probably the most extreme abuse a barrel sees. They say 800-1200 rounds is it for the 300WM in highpower. The guys I know all opt for a longer neck, sharper shoulder, lower case capacity with medium to high BC bullets depending on range.

    It is said that at the apex where the shoulder angle lines would intersect up in the neck area should be well below the case mouth, the further the better. This offers more physical protection, I believe, so the throat is not being directly sand blasted by the hot burning powder so much. There are formulas that determine what the optimal neck length is for a specific caliber and shoulder angle is, but a longer neck and sharper shoulder angle better keep this turbulance point inside the case neck.

    One more point on another note is that a longer neck will offer support and better alignment to the bullet for a longer time so it is more fully engraved by the rifling before it is allowed to move a few ten thou off axis at the rear. Often a short neck case will not even allow the bullet to engrave before it laves the neck, especially on short bearing length bullets and ones seated further from the rifling. The larger diameter the throat is, the worse this is in my mind. We can turn necks to within a tenth or two of chamber dia, while most freebore throat diameters are about .0005 over bullet dia., so a neck that supports well will be better (and adjustable) off in controling the base of the bullet for best alignment.
     
  14. trader388

    trader388 Well-Known Member

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    30-378 wby has a .373 neck length hehehe but it still is a barrel burner! /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/grin.gif