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Posted: 5/25/2003 12:33:22 PM EDT
okay.i have a question/concern..i have a bushmaster pencil LW barrel..went to the range today and was function testin my mags..like 5 rounds out of each mag..i did bout 20 mags..and the barrel got hot enough to cook on.. it took a good 20 minutes to get reasonable temp..i am aware of military blazing up barrels (spent 4 years in marine corps) but those rifles/barrels are expendable..my stuff isnt. lol..jus curious if it gets that hot should i wait?? but my main concern is , if barrel gets that hot, is it possible to change the molecule structure..and diminesh accuracy..i have heard (this wasnt my case) that if ya have a tight sling on barrel and it gets hot that ya can acually bend barrel..dunno..jus wanna get an idea of what is goin on..thanks
Link Posted: 5/25/2003 12:36:11 PM EDT
[Last Edit: 5/25/2003 12:37:24 PM EDT by Lumpy196]
With a semi-auto you're far more likely to cause throat errosion rather than damage it in other ways.
Link Posted: 5/25/2003 1:12:12 PM EDT
okay..im jus use to shootin and cleaning guns..never got into doin much else until i built this AR..umm. what exactly is throat errosion and what causes it.(sorry for the noob ? )
Link Posted: 5/25/2003 1:30:23 PM EDT
The throat of a barrel/chamber is the distance from the end of chamber cut to beginning of rifling (rifling start point). Every time you fire the rifle a small amount of metal is removed from the beginning of the rifling. When the barrel becomes very hot, the erosion is increased drastically, and will wear out the throat (rifling beginning set-back) at a much greater rate. This translates into the distance that the bullet must jump (without twisting) before the bullet contacts the rifling and starts to twist. The father that the bullet must free run, the more chance there is for the bullet to engage the rifling off bore axes, or the rifling distortion upon engagement (imprinting). Bottom line is a long throat is curable by setting the overall length of the ammo at a greater length, but the overall length of any possible bullet is limited by the magazine with the ammo is feed from.
Link Posted: 5/25/2003 1:35:20 PM EDT
[Last Edit: 5/25/2003 1:59:36 PM EDT by Lumpy196]
It's the gradual eroding away of the rifling lands immediately ahead of the chamber throat. Metal burned away by the intensely concentrated flame from the powder at this point. It can lead to reduced accuracy and even the bullet being unstabilized (keyholing). It takes a lot rounds to do it in semi-auto fire, unless they are fired in large quantities rapidly.
Link Posted: 5/25/2003 1:45:08 PM EDT
thanks Lumpy196 & Dano523 for the great info..now i understand..okay then , with a bushmaster barrel rated 5.56mm, and me shootin 5.56 & .223, how i have been shootin is this..i put a mag in with 5 rounds and shoot : bang...bang...bang...bang...bang...Change mags..bang...bang...bang...etc.. im not shooting : bang, bang, bang, bang..(on occasion i do. lol) i mean are we talkin bout thousands upon 10s of thousands to wear on out..i never ever USED up a rifle b4, dont really wanna start..jus gettin tryin to get an idea of what is goin on..lol.
Link Posted: 5/25/2003 2:00:57 PM EDT
Read this to get an idea of the level of shooting were talking about here [url]http://www.galleryofguns.com/ShootingTimes/Articles/DisplayArticles.asp?ID=1205[/url]
Link Posted: 5/25/2003 2:10:38 PM EDT
AWWWWWWWWWWWWWWWWW!!!!!!!!!, very good reading..now time to change my range habits..thanks again..
Link Posted: 5/25/2003 2:12:41 PM EDT
Your barrel is chrome lined and the one in the Colt article is not. Chrome Lining [b]dramatically[/b] reduces throat erosion.
Link Posted: 5/25/2003 2:17:09 PM EDT
so i guess that is the joy of a chromed line barrel..last longer??? while the other one is a tad more accurate???
Link Posted: 5/25/2003 2:21:11 PM EDT
Unless you are doing extreme precision shooting, you will never appreciate the slight accuracy advantage but as you more than triple the life of your barrel and better protect it from the elements, you will most certainly enjoy the benefits of the chrome lining. A no-brainer to me or as Troy sez, "Go chrome or go home!"
Link Posted: 5/25/2003 2:27:50 PM EDT
yeah thats cool...im slowly learning the "technical" stuff involved with this sport..i been at it awhile..but never looked at what makes em tick.so thats cool..i appreciate the advice..
Link Posted: 5/25/2003 2:28:14 PM EDT
[b]Great[/b] article. Damn!
Link Posted: 5/25/2003 2:31:05 PM EDT
[Last Edit: 5/25/2003 2:42:24 PM EDT by Lumpy196]
All of my AR barrels are chrome lined and I never give a thought to eroding the throat, or damaging anything with even rapid semi-auto fire (which I do quite often). My point citing barrel erosion was that it was far more likely to happen then heating a barrel up so much you cause it to bend with semi-auto fire. The only time Ive ever seen heat build up cause any damage to anything was a 11.5" barrelled M16 with a Surefire 500 forearm that was fired so much in such a short period the front sight post expanded to the point the taper pins worked loose. Not likely to happen with semi-auto fire.
Link Posted: 5/25/2003 3:08:29 PM EDT
I can't say on the barrel thing I had the same question but the 5 rounds in each mag is not a very good idea in my experience. My 20 round mag does fine with up to 15 in it but once you go past that point the spring gives and it can not push the rounds up, I just need to replace the spring. This happens with one or two of my 30s too but the mags are ancient used USGI mags so what can you expect. So I'd check them fully loaded as well.
Link Posted: 5/25/2003 3:25:36 PM EDT
yeah eventually i will..but with as many mags as i got , i need to start sumwhere..i already found a couple mags that were wiggin out on me..one of would not feed after 2 rounds..it was consistant,,shoot 2 and then 3rd wouldnt feed,,pull T handle and chamber round and then same thing 2 rounds and then FTF.
Link Posted: 5/25/2003 3:26:40 PM EDT
That was a good article. I definitely would prefer a chromed bore on any rifle I buy, though. My Bushmaster of course has a chromed barrel, and the accuracy I'm getting with it at 100 yards (with handloads) is ALWAYS better than the best group recorded in that article. Anything bigger than a 5/8ths inch group means I had the yips. I've put in ten shot groups as small as 3/8ths of an inch. I've had five shot groups that were just one ragged hole in the paper. CJ
Link Posted: 5/25/2003 3:57:39 PM EDT
Originally Posted By die-tryin: yeah eventually i will..but with as many mags as i got , i need to start sumwhere..i already found a couple mags that were wiggin out on me..one of would not feed after 2 rounds..it was consistant,,shoot 2 and then 3rd wouldnt feed,,pull T handle and chamber round and then same thing 2 rounds and then FTF.
View Quote
I would try the 'anti-tip' green followers to see if you can bring the mags back to function.
Link Posted: 5/25/2003 4:02:05 PM EDT
That is a outstanding read.I just learned some thing new.Thanx lumpy.
Link Posted: 5/25/2003 4:17:29 PM EDT
[Last Edit: 5/25/2003 6:12:37 PM EDT by die-tryin]
yeha they have the green followers, all my mags do..it may jus need a new spring,,the mag itself is GI and it is in good shape, nuttin out of the ordinary..no biggie..i still got 1/2 my mags to go function test,,woohoo..also hopefully sum other ppl may understand like i did..awww the wealth of knowledge...
Link Posted: 5/25/2003 9:22:35 PM EDT
I like the tech notes at www.armalite.com. They cover just about everything. www.armalite.com, click at the top to enter the site. Then way over on the left, in the blue, click on Tech Notes. Here's one, Technical Note 48, The Effects of Barrel Design and Heat on Reliability
Link Posted: 5/26/2003 4:29:25 AM EDT
lol..actually that is exactly what i was askin in my original question...the moleuclar structure of the barrel DOES change when overheated..lol..good reading.although my barrel is 16", but i understand what they are saying..
Link Posted: 5/26/2003 6:23:12 AM EDT
Don't worry about it too much. Shoot and have fun, within reason. Last time I went out I had my barrel smokin'. Uh-oh, I thought, that's my most accurate AR! But I don't shoot AR's to shoot at bolt-action rates of fire. Anyhow, just replace the barrel when this one wears out. By the time you get to that point you will probably be able to do it yourself.
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