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Short necks=short throat life??

 
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  #8  
Old 12-23-2004, 03:47 PM
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Re: Short necks=short throat life??

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.
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  #9  
Old 12-23-2004, 03:57 PM
JR JR is offline
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Re: Short necks=short throat life??

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
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  #10  
Old 12-23-2004, 05:51 PM
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Re: Short necks=short throat life??

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
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  #11  
Old 12-23-2004, 11:56 PM
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Re: Short necks=short throat life??

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.
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  #12  
Old 12-24-2004, 12:02 AM
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Re: Short necks=short throat life??

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.
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  #13  
Old 12-24-2004, 03:48 PM
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Re: Short necks=short throat life??

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.
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  #14  
Old 12-24-2004, 05:43 PM
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Re: Short necks=short throat life??

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