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Short necks=short throat life??

 
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  #1  
Old 12-23-2004, 01:09 AM
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Short necks=short throat life??

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
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Old 12-23-2004, 10:14 AM
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Re: Short necks=short throat life??

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?
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Old 12-23-2004, 11:57 AM
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Re: Short necks=short throat life??

Goodgrouper,

Myself along with several buddies (and a Brother I usually donít 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 canít 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
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Old 12-23-2004, 11:58 AM
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Re: Short necks=short throat life??

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)
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Old 12-23-2004, 12:30 PM
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Re: Short necks=short throat life??

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.
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Old 12-23-2004, 12:49 PM
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Re: Short necks=short throat life??

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

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.
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