AR15 barrel profile question...

Discussion in 'Black Rifle Forum' started by ratf51, Jun 3, 2012.


  1. I have used the search function but nothing came up. If this question has been asked before my apologies.

    I am thinking of getting another AR, this time a rifle (I have a carbine/M4gery already.)

    My question: how much practical difference is there between a govt. profile barrel and a heavy barrel (20")? I know that the govt. profile would be lighter and, theoretically, the heavy barrel should be more accurate. But for the average joe, average shooter, not trying to do 300+ yard sharpshooting, but wanting something for range fun and shtf (heaven forbid) is one a better choice than the other? And if so, why?

    Thanks in advance!
     

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  3. ipscshooter

    ipscshooter Mostly IDPA now

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    Probably little difference, if any. The difference would be mostly a delta in heat xfer rate. I would be more concerned about twist rate vs. what weight bullet you plan to use.
     

  4. Accuracy is determined (in part) by barrel STIFFNESS. A heavier barrel is just a very simple way to make the barrel stiffer.

    Heavier barrels take longer to heat up (helping preserve accuracy under rapid fire) but also take longer to cool down (takes longer to return to maximum inherent accuracy). They also can cause more strain and fatigue on the shooter when shooting offhand for prolonged periods.

    Honestly, government profile is probably the way to go for a general purpose weapon. As IPSC said, you need to be more concerned about barrel twist, as well as type of barrel (stainless, chrome lined, etc) - likely more so than profile.
     
  5. Matthew Courtney

    Matthew Courtney Instructor #298

    3,644
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    Plank,

    All of the information I have seen shows that is is temperature variations that contribute to wider group dispersions, not merely being above ambient temperatures. In other words, a barrel shot repeatedly at 300 degrees would shoot similarly to the same barrel fired repeatedly at 75 degrees, or that poi shifts as temperature changes. What information do you have showing that it is higher temps which cause accuracy loss, rather than poi shifting as a barrel heats and cools?
     
  6. I'm referring to the barrel heating within a string of fire(ie: temperature variation shot-to-shot), not overall temperature.
     
  7. There is no way I would even consider an HBAR for general use. If you are going to tote it around and shoot it free hand then I think you'll be much happier with the lightest barrel commonly available.

    If it will be equipped with a high power variable and bipod and used from a bench or the ground then maybe an HBAR might be the best.
     
  8. FatBoy

    Millennium Member

    1,647
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    I had a HBar 20", man that was front heavy. Got rid of it for a Govt. I already had a heavy match SS upper for shooting groups and just wanted a plinker. Depending on what you want to do, will dictate your decision.

    FB
     
  9. Since I normally hunt with my ARs... carry them a lot and shoot a little, never burning through several mags at any one time...I prefer the lightweight/Superlight profile(s).
     
    #8 TxGun, Jun 3, 2012
    Last edited: Jun 3, 2012
  10. Matthew Courtney

    Matthew Courtney Instructor #298

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    Thanks for clarifying. :thumbsup:
     
    #9 Matthew Courtney, Jun 3, 2012
    Last edited: Jun 3, 2012
  11. Thanks for the responses. It is sounding like the govt. profile will suit my needs. So, follow on question: 1/9 twist or 1/7 twist-- I know that the 1/7 better stabilizes heavier bullets but the majority of my shooting would be with 55gr and 62gr bullets, with maybe the occasional foray into 68gr or heavier; so, between those 2 twist rates how much practical difference would there be for that type of shooting?
     
  12. 1/9 will generally stabilize <50-69 grain bullets, with the notable exception of some of the heavier solid copper projectiles (note: Bullet LENGTH is actually what determines the needed twist rate. With a less-dense design, like a Barnes solid copper bullet, you end up with a much longer projectile than the weight would make you think, which means it needs a faster twist), especially the 70 grain Barnes TSX.

    1/7 will generally stabilize ~55-77+ grain.

    Some 1/7 barrels don't do as well with 55, and some 1/9 barrels can stabilize up to 75 grain, depending on the individual barrel. The issues with 1/7 and 55 grain bullets seem to be more common in the longer bores, as the rifling has more time to act on the projectile.

    1/8 twist is slightly less common, but works with pretty much anything from ~50 grain up to around 80, and gives great results with most anything in between. Unless you intend to shoot a lot of tracers, 1/8 is really the ideal twist rate for non-SBRs.

    For plinking use, you'll generally want to shoot 55 grain. Green tip isn't a good choice for plinking - it's more expensive, less accurate, and tears up steel plates. For SD/HD use, the heavier OTM, JHP or soft point offerings are a better solution, and many will require a 1/7 or 1/8 twist barrel.

    Clear as mud yet? :rofl:
     
    #11 WoodenPlank, Jun 3, 2012
    Last edited: Jun 3, 2012
  13. I couldn't hear you-- had my eyes closed. :rofl:

    It does get a little confusticating at times. Thanks for the clarification!

    (I like the Silver Bear 62gr stuff, it seems to shoot well and is inexpensive.)
     
    #12 ratf51, Jun 3, 2012
    Last edited: Jun 3, 2012
  14. bullittmcqueen

    bullittmcqueen Gunfighter

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    For your stated purpose, I would think a lightweight or gov't profile barrel in 1/7 would fit the bill. I have personally owned an HBAR upper and never saw the benefit. For the benefit of shaving weight you should not see a lot of accuracy drop-off (with a gov't or LW profile) if you're going to be shooting less than 300 yards/meters.
     
  15. Ya'll talk to me about the lightweight barrels-- how do they hold up? What are their drawbacks and strengths?
     
  16. There was just an article in Recoil magazine about the Daniel Defense V7 with lightweight barrel. They did a test and shot a 5 shot group at 50 yards which measured .80 inches. They then shot 90 rounds as fast as the could, then shot another 5 shot group at 50 yards. Group size was the same just a little low.

    After that test, and Daniel Defense cold hammer forged barrels, I would go with the lightweight barrrel.

    Adam
     
  17. Barrel quality is going to be the determining factor more than profile. Your heavier (stiffer) barrels will generally be more accurate but the difference is often very minor. If this gun is going to be carried at all, hunting, training, shtf, I would recommend a light weight or Government profile over a H BAR.
     
  18. Matthew Courtney

    Matthew Courtney Instructor #298

    3,644
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    Just for kicks, I ordered some tracers to see how they shoot from the 6920's 1/7 and the Sports 1/8.
     
  19. Matthew Courtney

    Matthew Courtney Instructor #298

    3,644
    2
    A more realistic test of practical accuracy would have been to fire one at a bullseye target, then do a mag dump at another target and repeat that until 5 shots were in the bullseye target. The group size of that 5 shot group would give an idea of what practical defensive accuracy one could expect. Holding a zero through a range of temperatures and conditions is a worthwhile attribute to some folks.
     
  20. ipscshooter

    ipscshooter Mostly IDPA now

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    I ran across the following a few years back. Not my info past the wavey guy, except the sig line. Take it for what it's worth. :wavey:

    pulled this info off the Bushmaster website. I picked up a Bushmaster superlite upper to go with my Bushmaster lower recently. Can't tell you how well it shoots yet longterm, (only put 30 rds through it so far), but, I like the way it handles and at 75 yds I put 10 rds into an apple sized group w/ the iron sights. Not bad for not having shot iron sights in years.

    Barrel Weight In Pounds ( for milled front sight subtract 0.2 pounds )

    Barrel length_________Heavy Barrels________ Fluted Barrels

    10"_________________2.0_________________1.9
    11.5"_______________ 2.2_________________2.0
    11.5/5.5"____________ 2.6_________________2.5
    14.5"_______________ 2.5_________________2.2
    14.5"AK_____________2.7_________________2.4
    14.5"MY_____________2.7_________________2.4
    14.5"AM (phantom)____2.7_________________2.4
    14.5"IZ______________2.7_________________2.4
    16"_________________2.7_________________2.3
    16" Dissipator________ 3.0_________________2.6
    20"_________________3.5_________________3.0
    24"_________________3.9_________________3.1
    26"_________________4.0_________________3.2

    Military Style Barrels

    14.5"M4_____________2.0
    14.5"M4AK__________ 2.2
    14.5"M4MY__________ 2.2
    14.5"M4AM (phantom)_ 2.2
    14.5"M4IZ____________2.2
    16"M4 Dissipator______2.3
    16" Superlight________ 1.9
    16"M4_______________2.2
    20"A2 (govt profile)_____2.5



    And, Weights of our Upper Receivers...
    A1 Type - 0.7 lbs.
    A2 Type - 0.8
    V Match (flat-top, also designated as A3 type) - 0.6
    A3 - 1.2 (including weight of A3 Type Removable Carry Handle)
    A3 Type Removable Carry Handle only - 0.6
     
    #19 ipscshooter, Jun 4, 2012
    Last edited: Jun 4, 2012
  21. Umm, no.
    First, most realistic, and legal, defensive applications are not going to require a mag dump.
    Second, with the fluidity and adrenalin of a defensive situation, you aren’t going to be able to obtain bench rest accuracy anyway so it doesn’t matter.
     

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