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Thread: Barrels 101

  1. #21
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    Quote Originally Posted by Austin_Nichols View Post
    The statement in red is backwards. 416R is easier to machine than the chromoly steels.
    Well, I would say that which is "easier" (between chromo and 416) has a lot to do with the experience and preference of the machine operator, as well as what type of machine is being used -- but yes, many will say that they prefer to work with 416 vice 4150...

    ...but that is not what I said.

    I maybe should make it clearer though: Metals are (loosely) rated with a "machinability rating" -- and the base for this rating (1.0) is free machining carbon steel, alloys can be much lower on the scale, right off the top of my head, I think that 41XX is down around .50-.60 and 416R is well above that in the .80s?

    But, as this is a primer, I just thought I would make the general statement that 416 machines nearly as well as carbon steel, rather than say that it has a rating of .85 (or whatever)... then we are off on free machining additives and resulfurization, chip control, inclusions and break points, and then the door is opened to the dreaded sulfur stringers and then night of the living sulfur stringers and then...

    Quote Originally Posted by Austin_Nichols View Post

    Great write up!
    Thanks!
    The sun will rise tomorrow; itís your attendance of the event that is uncertain.

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  2. #22
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    Quote Originally Posted by K.L. Davis View Post
    Well, I would say that which is "easier" (between chromo and 416) has a lot to do with the experience and preference of the machine operator, as well as what type of machine is being used -- but yes, many will say that they prefer to work with 416 vice 4150...

    ...but that is not what I said.

    I maybe should make it clearer though: Metals are (loosely) rated with a "machinability rating" -- and the base for this rating (1.0) is free machining carbon steel, alloys can be much lower on the scale, right off the top of my head, I think that 41XX is down around .50-.60 and 416R is well above that in the .80s?

    But, as this is a primer, I just thought I would make the general statement that 416 machines nearly as well as carbon steel, rather than say that it has a rating of .85 (or whatever)... then we are off on free machining additives and resulfurization, chip control, inclusions and break points, and then the door is opened to the dreaded sulfur stringers and then night of the living sulfur stringers and then...

    Kino, are we not on the same page? Based on your own machinability numbers, 416 is clearly the easier of the two (meaning 416 compared to chromoly) to machine at similar hardness. Barrels aren't made from low carbon free machining steel so it really isn't relevant to compare it to 416R.

    For those that don't know...

    The American Iron and Steel Institute ran tests for machinability using AISI B1112 at 160 Brinell (a free machining low carbon steel) being turned at 180 surface feet and compared it to other materials. Its performance (set at 100%) is the basis for the ratings of other metals. Those materials with a rating of less than 100% are more difficult to machine. Those with a rating of over 100% are easier to machine.

    4140/4150 chromoly steel has a machinability rating of approximately .32 to .52 depending on hardness. But 416 is a free machining martensitic stainless and has a rating of anywhere from .24 to .88 depending on hardness.

    For comparison, Inconel is around .12, 7075 aluminum runs anywhere from approximately 3.2 to 4.8.
    Austin Nichols = Wild Turkey

  3. #23
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    Awesome post. Everything you wanted to know about barrels but were afraid to ask.

    I too would like to see some discussion about breaking in a barrel. I remember what Gale McMillan wrote on The High Road a few years back, but his opinion seemed to be a minority viewpoint.
    They had no right to win. Yet they did, and in doing so they changed the course of a war...even against the greatest of odds, there is something in the human spirit - a magic blend of skill, faith and valor - that can lift men from certain defeat to incredible victory.

  4. #24
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    Great stuff!

    Quote Originally Posted by Airborne12b View Post
    I know this is going to paint me as a noob, but I have to ask. I just built my first AR. This will not be my first time using the platform by any means, mind you. I have been isued probably 10-12 different AR variants over my time in the Army but none of these were NIB. The closest was the M4 that I was issued when I deployed to Iraq. As such I was never concerned with proper break in. For that matter I never remember in my time in the Army ever being told how to break in a new rifle. I am not sure if this is the best place to post this question but I figured that it being titles Barrels 101 that I would post it here. Thanks.
    It's my understanding that with chrome-lined barrels, there's no "break-in" other than just shooting it.

    You can find SS and unlined Chrome-Moly barrel break-in instructions on the web... there are several methods depending on the author. YMMV.

  5. #25
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    So from what I've read, Colt, LMT, CMT, BCM and the upper end (true mil-spec) manufacturers use 4150 and the more civilian recognized manufacturers like RRA, DPMS, Bushmaster, etc. use 4140? Just curious.

    I figure most of the 1/9 twist barrels will be the 4140, but as I've stated in other posts, I'm a tech junkie and "just want to know". Also, alot of folks use "Wilson" (Wilson arms) heavy match barrels and E.R. Shaw "heavy match" barrels, I assume they are mostly 4140 when supplied to RRA, DPMS, Model 1, etc unless they are the 416 SS?????

    Great post, very informative. Thanks for your time input into it.

  6. #26
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    Quote Originally Posted by Stik View Post
    So from what I've read, Colt, LMT, CMT, BCM and the upper end (true mil-spec) manufacturers use 4150 and the more civilian recognized manufacturers like RRA, DPMS, Bushmaster, etc. use 4140? Just curious.

    I figure most of the 1/9 twist barrels will be the 4140, but as I've stated in other posts, I'm a tech junkie and "just want to know". Also, alot of folks use "Wilson" (Wilson arms) heavy match barrels and E.R. Shaw "heavy match" barrels, I assume they are mostly 4140 when supplied to RRA, DPMS, Model 1, etc unless they are the 416 SS?????

    Great post, very informative. Thanks for your time input into it.
    BM uses 4150, just not the kind that the Military requires.



    C4

  7. #27
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    Probably a stupid question but what difference should there be between 1/7 and 1/9 twist in carbine barrel?

  8. #28
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    Quote Originally Posted by isakhnov View Post
    Probably a stupid question but what difference should there be between 1/7 and 1/9 twist in carbine barrel?

    The length of the gas system and the twist rate really don't have anything to do with one another.



    C4

  9. #29
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    Quote Originally Posted by C4IGrant View Post
    The length of the gas system and the twist rate really don't have anything to do with one another.
    C4
    I understand how it is made, question is what should I expect from two identical carbines where one has 1/7 and another has 1/9 twist? If nothing then why some manufacturers adopt 1/9 while other 1/7?

  10. #30
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    Quote Originally Posted by isakhnov View Post
    I understand how it is made, question is what should I expect from two identical carbines where one has 1/7 and another has 1/9 twist? If nothing then why some manufacturers adopt 1/9 while other 1/7?
    Well it depends on several things. For instance, a 1/7 twist barrel shoots 55gr ammo very well to about 100yds. Past that we see the groups open up a lot. Same with the 1/9 twist barrels. At about 100yds, 75/77gr ammo does pretty well, but as you go farther out, your group sizes can open up.

    So if you want to shoot heavier grain bullets at distances over 100yds, stick with a 1/7 twist barrel (which is what I shoot).


    C4
    Last edited by C4IGrant; 05-27-07 at 11:32.

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