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Thread: silent but deadly! mouse fart AR15

  1. #1
    Boolit Bub
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    silent but deadly! mouse fart AR15

    Hi folks, I need some opinions to help me make a decision. I'm building an AR15 for plinking and pest control, and I'm at an impasse deciding on a bolt and barrel. My two top choices are 300 blackout and 6.5 grendel. I intend to fire reduced loads for practice at my home range to avoid pissing off the neighbors. They work night shift, and don't appreciate excessively loud rifle shots when they're trying to sleep during the day. Standard velocity .22lr is no problem, as the range is 100 yds away from any buildings, but testing some full power smokeless cast boolit loads in my .45-70 definitely was a no-go.
    I intend to load sub-sonic, and cycling the action is not particularly important to me. Bearing that in mind, I'm looking at a 16inch .300 blk barrel, and a 24" 6.5 grendel barrel...the longest commonly available in both calibers to help lower muzzle pressure. Both barrels i'm looking at feature a 1:8 twist, so I should be able to stabilize moderately heavy boolits...which to me means 140-160gn in the 6.5 and 200-240 in the .300 cost and availability are appx. the same either way, and I like that both can be reformed from common military brass. At this point, I do not intend to run a suppressor.
    So what do y'all think will be less obnoxious? I'm leaning toward the 6.5 because of the longer barrel providing more expansion volume for the gas, and the projectile being lighter, allowing for smaller powder charges at the same velocity. However, if it's a poor choice for a cast boolit shooter, that opinion could change.

  2. #2
    Boolit Master


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    A 24" barrel on an AR is not going to handle well.

    If I needed a low noise CF option for plinking, I would use a .38 Spl at 800-1000 fps in a lever action. But with .22's readily available at $.04 a round, that is the best choice unless your "pests" are coyotes. You cannot reload for $2 a box.

    Another option to think about is a 9mm AR with 147 gr bullets.
    Don Verna

    NRA Endowment Member

  3. #3
    Boolit Bub
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    Thanks for the quick reply! I did consider the 9mm option, and my pests are primarily large groundhogs, raccoons, coyotes, and the occasional fox that eats my chickens. .38 special would not be a bad choice either, but I already have a stock and a built lower for an AR that I have almost no money invested in. Handling is of little concern to me at this point, it'll be fired primarily from a bench or prone, and I don't do any "run 'n gun" style matches or anything. I just like tinkering with guns, working up loads, casting boolits, and playing around with ballistics. In reality, I shoot far more .22 than anything else (3000+ per year), and I'm just looking for fun and a little something different. This is definitely not a gun I "need"

  4. #4
    Boolit Buddy JoeJames's Avatar
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    With a subsonic 223/556 you get @ a 40 grain bullet zipping along at 1050 fps, and if you had a 22 LR dedicated upper with 22 LR subsonic ammo you'd get @ a 40 grain bullet zipping along at 1050 fps. 300 BO or 6.5 would be a heavier bullet but at same speeds.

  5. #5
    Boolit Bub
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    yeah, that's the basic idea...get a little more weight moving downrange at 1050 or so...plus much better b.c. than the little 40 grain pill to help buck the wind...or at least be more predictable in the wind. There's some fine looking molds out there for both! Occasionally I'll take it out to the public range (300 yds) with full power loads, but that'll be maybe 30% of the time. I don't mind gas checking/powder coating to keep the bullet intact at real velocity.

  6. #6
    Boolit Buddy JoeJames's Avatar
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    Quote Originally Posted by pashiner View Post
    yeah, that's the basic idea...get a little more weight moving downrange at 1050 or so...plus much better b.c. than the little 40 grain pill to help buck the wind...or at least be more predictable in the wind. There's some fine looking molds out there for both! Occasionally I'll take it out to the public range (300 yds) with full power loads, but that'll be maybe 30% of the time. I don't mind gas checking/powder coating to keep the bullet intact at real velocity.
    I am loading my Rossi R92 44 Magnum with Oregon Trail .431" 240 grain hard cast bullets, 7 grains of Unique, 44 Magnum case + @1050 fps, but with a big ole boolit it makes a difference.

  7. #7
    Boolit Bub
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    One of these days I'll do a big straight wall rimmed case lever gun, but till then, I've got this half-built AR burning a hole in my pocket. lol one of my favorite loads for the .45-70 is a .45 round ball in front of a little bit of black powder, and a whole lot of filler. Quiet and accurate close-range, but it sure goes screwy after 50 yds. or so. Not recommended for anything but single-shot...burns dirty, and no real crimp to speak of. It does smack the ever lovin' tar out of groundhogs if you can sneak up close enough!

  8. #8
    AKA: GRMPS Conditor22's Avatar
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    you put a can on a 300 BO and go subsonic -w- 230+ grn and you don't need hearing protection.

  9. #9
    Boolit Bub
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    Yeah, I've heard one suppressed before, and it was super quiet, but that was with a very short barrel. Without the can however, that stumpy little barrel sure could bark. I'd rather not pay the 200dollar tax, and wait months for paperwork and all that nfa nonsense if a 16 inch barrel would accomplish my "less obnoxious" goal.

  10. #10
    Boolit Buddy


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    Pashiner...300 BO will fit you needs almost perfectly. Google some "bolt action only" loads for subsonic 300 bo they are bolt action only not because of pressure but because they won't cycle the bolt on an AR. You should be able to get some pretty quiet loads with bullseye ECT with bullets from ~90 grains up to 247+ grains. Then if you want the action to cycle just switch powder to full bore loads. Of you don't mind using your AR as a bolt action,your options are almost endless.

  11. #11
    Boolit Bub
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    Even subsonic loads out of my unsuppressed 300 BO AR are rather loud, probably about the same as a 45acp.

    Which makes sense after I thought about it for half a second.
    quando omni flunkus moritati

  12. #12
    Boolit Bub
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    I have both a 16in 300bo and a 24in 6.5 grendel. Without going suppressed I don't know how quiet your going to get. I'd think the 24in grendel would be able to get quieter with the extra barrel length. Kinda like a 22lr in a 5.5in pistol or a 22in bolt gun. No comparison in the noise difference with the same ammo. I don't know foresure though as I've never tried to run my grendel subsonic. As far as handling a 24in AR is no worries. I have 5 of them. The only one that is a bit bulky is the 6.5 creedmoor in the AR-10. A 24in AR-15 is similar to any bolt gun. I don't know what you have for parts for your build yet. But A Sanders side charging upper would be handy if your going to manually run an AR. Otherwise a charge handle with big levers would be useful. Good luck with the build. I'd love to see how it turns out and maybe venture there myself.

    Adam

  13. #13
    Boolit Bub
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    Thanks for the input guys! I just got back from the range with a borrowed blackout sbr, and it was definitely quieter with subsonic loads than it was full power. Still need earplugs, but nothing like standing beside a .30-06 or bigger. The lack of a supersonic crack really cuts down on the echo. The comparison to a .45acp sounds pretty accurate to me. It was more of a hollow "pop" than the piercing crack of a supersonic rifle bullet. I think this idea is going to work. Fast powders and long barrels seem to be the name of the game here. I'm currently experimenting with the Hastings metro-gun system and 12 gauge slugs loaded to around 900fps. From inside the house they're nearly inaudible when shot 100 yds away. For those who aren't familiar with metrogun, it's essentially a 3 foot extension for a shotgun barrel. It lowers the muzzle pressure, and thus reduces the blast. If I can effectively launch a rifle bullet at a similar speed from a 24 inch barrel, I'm looking at a similar bore to barrel length ratio. Hopefully that will translate to similar noise levels. Fast powders will probably be a key to success.

  14. #14
    Boolit Master
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    I got the NOE 80gr 223 to work subsonic, so a bit more thump than the 22lr version. Weight is where its at, when it comes to subsonic since velocity is fixed. But doubt small animals would really notice the bullet weight.

  15. #15
    Boolit Bub
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    Hmm...that's a pretty cool idea too. At 80 gn. It should carry twice the energy, and maybe get some tumbling action on impact if the stars align.

  16. #16
    Boolit Bub
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    After some careful deliberation, I went with the 24 inch barrel in 6.5 grendel. It's got more bore volume than the .300blk and the longer barrel should provide plenty of gas pressure dwell time for cycling the action with a variety of goofy loads. Once it arrives and I assemble the rifle, I'll get it running and tuned up with commercial full power loads, then commence my mouse fart monkey business...stay tuned!

  17. #17
    Super Moderator & Official Cast Boolits Sketch Artist


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    I added a can to my 300 B O I could not tell if it helped
    Reloading to save money I am sure the saving is going to start soon

  18. #18
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  19. #19
    Boolit Grand Master popper's Avatar
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    Pistol powder and light cast will make a pop only. Won't cycle but fun.
    Whatever!

  20. #20
    Boolit Master brewer12345's Avatar
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    I am planning to fool around with quiet .223 loads in a single shot this year. I will have to get a mold because I think a coated cast boolit will be a lot less risk of sticking one in the bore than a jacketed. Is this a trail boss application, or would any fast pistol powder work?

    Already have a 22 short only browning rifle that doesn't quite cycle CB shorts but is airgun quiet with them, so this project is mostly for grins and versatility.
    "If you see me running something has gone poorly, and you should probably run too." - any beekeeper

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