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AR build question

shawn1172shawn1172 Senior MemberPosts: 588 Senior Member
Hey guys. I'm planning a build with a short barrel and suppressor. I don't really know what to use for a barrel though. I've seen 7.5" and 10.5". I'm learning toward shorter because I'd like overall length with the can to be shorter than my AR with a 16" barrel. Would I lose much accuracy with such a short barrel? Would it complicate the build in terms of gas tube length? What about twist? Thanks for any info or advice.

Replies

  • ilove22silove22s Senior Member Posts: 1,372 Senior Member
    1172,

    what caliber?
    The ears never lie.

    - Don Burt
  • shawn1172shawn1172 Senior Member Posts: 588 Senior Member
    It will be 5.56mm. Mainly building as a CQB / HD rifle so it won't be used for any real distance. 100 yards max at the range but mainly closer.
  • CHIRO1989CHIRO1989 Senior Member Posts: 12,474 Senior Member
    7.5" should be just fine at 100 yds, mine is. Zee made the point to me to get a 1-7" twist so the bullet gets at least one complete revolution.
    I take no pleasure in the death of the wicked, but rather that they turn away from their ways and live. Eze 33:11
  • BigslugBigslug Senior Member Posts: 8,191 Senior Member
    You're going to want faster twists with shorter tubes to ensure your pills stabilize. Just cut to the chase there and go 1-7". Going 10.5" lets you play in the "standard" mil-spec parts zone of the Colt Commando, so I'd probably go that route.

    The thing with suppressors - you can optimize for the gun without it, and get too much gas when the can is attached causing the action to cycle harder, accelerating wear on trigger pins and such. On the other hand, you can build the gun with a small port to run with a suppressor, but maybe not get enough gas to run without it. In any event, plan for a face full of ammonia-ish powder vapors with a suppressed AR.

    If there's a variable port gas block for an AR, you should consider it for a project like this.

    Terminal performance of military 5.56 pretty much sucks out of short barrels - those rounds were designed to tumble and fragment at high impact velocities. Kinda counter-intuitive, but we did a gelatin test with AR's ranging from 24" down to 10", and as the barrel length and velocity went down, the penetration INCREASED because the bullets weren't able to fragment like they were intended to. Think of it as behaving more like a pistol round and switch to one of the premium expanders if you want any kind of decent result. You'll get some velocity back with the suppressor attached, but it'll never be a .220 Swift.
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • CHIRO1989CHIRO1989 Senior Member Posts: 12,474 Senior Member
    Bigslug, did you fiddle with any of the premium expanders when you were doing the gelatin tests, any preferences?
    I take no pleasure in the death of the wicked, but rather that they turn away from their ways and live. Eze 33:11
  • BigslugBigslug Senior Member Posts: 8,191 Senior Member
    CHIRO1989 wrote: »
    Bigslug, did you fiddle with any of the premium expanders when you were doing the gelatin tests, any preferences?

    I think I've witnessed Winchester and Federal bondeds at a couple of industry demos over the years. Had good field reports from a buddy who drilled through the skull of a 200 pound pig with a 62 grain Barnes TTSX factory load. Based on my experience with the .30 caliber version on deer, I'd probably choose that.
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • CHIRO1989CHIRO1989 Senior Member Posts: 12,474 Senior Member
    Bigslug wrote: »
    I think I've witnessed Winchester and Federal bondeds at a couple of industry demos over the years. Had good field reports from a buddy who drilled through the skull of a 200 pound pig with a 62 grain Barnes TTSX factory load. Based on my experience with the .30 caliber version on deer, I'd probably choose that.


    We are talking pistol length barrels, correct?
    I take no pleasure in the death of the wicked, but rather that they turn away from their ways and live. Eze 33:11
  • NCFUBARNCFUBAR Senior Member Posts: 4,324 Senior Member
    First my thought is about the HD application, go 7.5" since you'll be adding back about 6" with a suppressor. Also to keep it a little more compact try to go with a XM177 shorty style stock to save a few inches on the back side. As to gas system, SBR/pistol length systems topped of with a suppressor might be best service by an adjustable gas block setup. I have seen mid-length ARs do so much better when able to adjust the gassing from non-suppresses to suppressed and the shorter gas tubes I believe are even more finicky.
    “The further a society drifts from truth ... the more it will hate those who speak it."
    - George Orwell
  • BigslugBigslug Senior Member Posts: 8,191 Senior Member
    CHIRO1989 wrote: »
    We are talking pistol length barrels, correct?

    I'm 99% certain that pig died in front of a 16" barrel, but yeah, I'd probably choose the Barnes load as (hopefully) the best performer in a platform that is seriously compromised ballistically - you don't have the velocity of a rifle, you don't have mass, and you don't have starting diameter. The Barnes is cool in that it opens up into a something like a 4-bladed archery broadhead - you get the frontal diameter without the frontal resistance of a full mushroom reducing the penetration. Being solid, milled copper, they aren't cheap, but performance rarely is.
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • knitepoetknitepoet Senior Member Posts: 20,968 Senior Member
    I assume you already have a registered SBR lower?

    BATFE takes a DIM view of putting a <16" barrel on a unregistered rifle lower.

    I have a 10.5" on my pistol, haven't done any bullet performance testing with it, more of just a range toy.
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • CHIRO1989CHIRO1989 Senior Member Posts: 12,474 Senior Member
    Wambli Ska wrote: »
    True, but you have THIRTY of them readily available... Never get why folks fixate on the potential performance of ONE round. This is NOT a hunting rifle...

    True, but in MN, if you put a 10 round magazine in mine, it is legal to use in a shotgun only area for whitetails.
    I take no pleasure in the death of the wicked, but rather that they turn away from their ways and live. Eze 33:11
  • bullsi1911bullsi1911 Moderator Posts: 11,071 Senior Member
    Don't go 7.5 if you are planning to suppress. All but one suppressor manufacturers say that a less than 10" barrel will void the warranty on the .556 caliber suppressors.

    Check around. The only one that i know of that rates thier cans on a 7.5 barrel is huntertown arms.
    To make something simple is a thousand times more difficult than to make something complex.
    -Mikhail Kalashnikov
  • CHIRO1989CHIRO1989 Senior Member Posts: 12,474 Senior Member
    bullsi1911 wrote: »
    Don't go 7.5 if you are planning to suppress. All but one suppressor manufacturers say that a less than 10" barrel will void the warranty on the .556 caliber suppressors.

    Check around. The only one that i know of that rates thier cans on a 7.5 barrel is huntertown arms.

    I only see suppressors with a minimum 11.5" barrels at their site.
    I take no pleasure in the death of the wicked, but rather that they turn away from their ways and live. Eze 33:11
  • BigslugBigslug Senior Member Posts: 8,191 Senior Member
    Wambli Ska wrote: »
    True, but you have THIRTY of them readily available... Never get why folks fixate on the potential performance of ONE round. This is NOT a hunting rifle...

    Because when that one round is out of a 12 gauge, you don't die of old age waiting for your rounds to be effective. You're right that it's not a hunting rifle - the rapid stop is WAY more important than it is on a deer, hence the fixation.
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • bullsi1911bullsi1911 Moderator Posts: 11,071 Senior Member
    CHIRO1989 wrote: »
    I only see suppressors with a minimum 11.5" barrels at their site.

    They must have changed the warranty.
    To make something simple is a thousand times more difficult than to make something complex.
    -Mikhail Kalashnikov
  • ZeeZee Senior Member Posts: 23,703 Senior Member
    I have a 7.5" and 12.5" AR pistol. For HD, the 7.5" is pretty hot snot. It's compact, maneuverable, more accurate than any pistol OR shotgun under 100 yards, carries ample amount of bad decision pills, and..........with proper bullet selection and placement, adequately effective at changing ones mind.

    As as to bullet selection. I've taken 2 deer with one shot from a 10" barreled AR. One through the heart with a 64gr GD that dropped on the spot and one through the lungs with a 77gr Sierra Match King that ran about 30 yards and fell over. Both rounds went all the way through and both shots were under 50 yards by a good bit, if I remember correctly.

    Currently, my 7.5" barrel is zeroed with 64gr GD. If that is unsatisfactory for someone owning a short barrel, any of the 55gr or less Hornady V-Max (TAP) line should expand rapidly enough at house distance to do what needs doing.

    Oh, a 1-7" twist is a must in my mind for a short barrel. Regardless the bullet weight. Why companies make a 1-9" twist pistol barrel is beyond me.
    "To Hell with efficiency, it's performance we want!" - Elmer Keith
  • shawn1172shawn1172 Senior Member Posts: 588 Senior Member
    Zee, what are your thoughts on a 7.5" barrel with a suppressor? Good to go or would a 10" run better? I'd prefer to go shorter but want to be sure of its reliability.
  • ZeeZee Senior Member Posts: 23,703 Senior Member
    I have never suppressed a 7.5" barrel. But, I have a 10.5" Piston Driven barrel that runs flawlessly suppressed and have played with suppressed gas systems of the same length without issue.

    No experience with shorter suppressed barrels.
    "To Hell with efficiency, it's performance we want!" - Elmer Keith
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