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AR pistol with fixed Mag? (In mass )

amm5061

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I don't see why it wouldn't. Same diameter case. Similar OAL.
This. There's no reason why they wouldn't work. .300 Blk is just a .223 case necked up to take the .30 cal bullet.

As to not doing one for .300 blk, well, I don't have anything else that eats it, so for the first one I kept it simple. Theoretically you could do any caliber you want, you'd just need to change out the fixed magazine for a caliber appropriate one. Something like a Lancer with a single stack follower would work great for large bore rounds (.458 SOCOM/.450 Bushmaster/.50 Beowulf), though you loose the ability to use the side loaders for any caliber that doesn't use .223 as a parent cartridge. Top loading isn't that bad, and really only slightly more annoying than loading magazines the normal way without a speed loader.

Might do a .300blk one day, but right now I can't really afford to start stockpiling another caliber.
 

Dennis in MA

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I almost went 300blk. In the end, I decided to stick with 5.56. There is some decent ammo for it and I figured that was AOK. With the short bbl, you still get the terminal effects of the 5.56 at close range. This isn't a 50yd gun. It's probably not a 20yd gun. My house is only 40-ish feet at the longest point. In the back yard, I might get 100-120 feet from woods-to-woods. That would be extreme for this firearm.
 

Viper22

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I was on the fence too...at first I was leaning 5.56, as I wanted to say with a caliber I already had. BUT - The trade-offs seemed too great when going with a 7.5" barrel. Huge velocity loss, increase in noise, and I didn't want to go with a 10.5" barrel either. By the time you add a FH/comp then its close to rifle length.

Sooooo 7.5" 300blk it is. After pouring over data/videos/interweb opinions, the 300 blk has some interesting offerings in bullet weights and performance.

Went with:
Karri's Guns 300 Blackout 7.5" upper w/flash can & 9" MLOK rail w/hand stop
Karri's Guns BCG & Ambi CH
KAK Shockwave Blade & pistol buffer tube kit
AR Stoner LPK (w/WMD Guns NiB trigger)
BCM Mod3 pistol grip (on the way)
Fixed Mag Lower

Need to decide on optic, thinking 1-4x. Irons for now.
Also want to do a side-folder.
 
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Dennis in MA

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The nice thing is you can always get another upper. I might try it some day. I went the 10.5 route. Agree that 5.56 is not 7.5 worthy.

Do you people have any idea how much money NES costs me. Damn you people!! Lol
 

Viper22

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Take a look at the performance/gel tests of the 194 grain Lehigh Defense 300 Blackout offerings. Looks like a good HD option.
 

Viper22

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The nice thing is you can always get another upper. I might try it some day. I went the 10.5 route. Agree that 5.56 is not 7.5 worthy.

Do you people have any idea how much money NES costs me. Damn you people!! Lol
Yeah, just swapping uppers is easy enough. However, I've got a pinned/welded 14.5 - so a 10.5 really doesn't interest me too much. At they end of the day, they wouldn't be all that much different.

Now - looking at 458 SOCOM or 450 Bushmaster, that may be worthy of another build. IIRC there are 30rd mag bodies with a specific follower for the big bore rounds. Something like 10rds of 458 fits in a 30rd mag body. Just imagine how much of a thumper a 458 pistol would be!
 

Shawnyc

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Love 300BLK, wish we could have suppressors in MA though. If you keep loaded mags around make sure you label the caliber on them!
 
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amm5061

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Now - looking at 458 SOCOM or 450 Bushmaster, that may be worthy of another build. IIRC there are 30rd mag bodies with a specific follower for the big bore rounds. Something like 10rds of 458 fits in a 30rd mag body. Just imagine how much of a thumper a 458 pistol would be!
Tromix Restricted State, Compliant Magazines - Tromix Lead Delivery Systems

Pin one of those. .458 SOCOM is a fun round, but it does get expensive to shoot. Kicks like a mule, too. Tony also sells completed 8" uppers for .458 SOCOM, 12" uppers for .450 Bushmaster, and 10.5" .375 SOCOM and .50 Beowulf uppers. I've got a 16" Tromix barrel for my .458 SOCOM straight pull bolt action AR and it's more accurate than I am.

Truthfully, if you want to go the shortie big bore route, I would get a tax stamp on a rifle lower. You're gonna want a good buttstock to help absorb that recoil. Also make sure you get a big bore style upper receiver. A standard .223/5.56 upper has to have the ejection port opened up slightly to allow reliable ejection of the larger cases, but a .450/.458/.50 upper has the ejection port already milled out a little more.


Agree that 5.56 is not 7.5 worthy.
I disagree--7.5" is perfectly fine with 5.56. Mine groups beautifully at 50 yards, and the only reason I haven't stretched it out to 100 yet is a.) laziness and b.) lack of time to get back to the range. It's an eminently workable CQB upper. Ideal for home defense, though with all carry and HD guns I would make sure to put a couple hundred rounds of your ammo of choice through it to ensure reliability and to know how it performs.

That said, I also went with a 10.5" that will eventually go on my SBR when I get the stamp back.
 

djbradles

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236433BE-467A-46A0-AB9E-4C248B69BFD8.jpeg
These two little rascals are jumpin in the womb and I’m getting sore from carrying them this long. Phewww! Due date is soon and I’ve setup a gift registry with Brownell’s. Do sign up before I give birth? It ain’t easy having babies ya know. I’ve named them “FDE x39” and “Tungsten Gray”.
 

amm5061

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Since fixed mag AR seems to be here to stay for some time (ugh)…would the Cross Armory quick pin and safe mag system be compliant with MA laws? Looks a lot better than having to use a MA loader

View: https://m.youtube.com/watch?v=MuAN52aQfgU
IANAL, but I'm gonna say no. Read up on the JC Arms case where the cops destroyed a fixed magazine to remove it and put their own standard cap mag in its place.

Any system that allows the magazine to be easily removed without some serious disassembly leaves you open to the same treatment.
 

Viper22

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Yeahhhhh.....that's not too "permanently fixed" IMO. While the MA Lock isn't the best looking way to fix a mag - There is no way to remove it without destroying some metal. It is still fixed in place when the upper & lower are separated.
 

djbradles

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Don’t pay attention to the royal mess up of them sending me a 5.56 lower instead of the 9mm lower that I ordered. That’ll get fixed. Other than that snafu I’ve been very happy with their products.
 

amm5061

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View attachment 284066 A quick dry fit with the 80 percent 9mm lower. I think this will turn out pretty darn good. Love the looks of it. Could do a pistol tube buffer instead but I do like the SBA3 braces. Preban glock fun mag stuffed in there for a test. Would look more balanced with a smaller mag. A reflex sight would do well or the Holosun one I use on another which is of very good quality. When it gets built it will probably get my own version of a fixed 10 rd glock mag with a drill, tap, and weld.
Let us know how top loading the Glock mag works. Keep a baseplate tool handy in case you get a jam.
 

Mountain

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This pipe dream GTG or a problem?
  • Pre-Healy lower purchased years ago on a 4473 but never built into anything. (not that pre-Healy means anything for a non-AWB build)
  • Install fixed 10-round mag, then assemble rest of the lower.
  • Pistol brace from one of the known vendors w/ ATF blessing.
  • 10.5" upper in 300 BLK.
  • EFA10 as a 30-cal non-high capacity pistol.
Mass OK way to do it? Thanks...
 

djbradles

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This pipe dream GTG or a problem?
  • Pre-Healy lower purchased years ago on a 4473 but never built into anything. (not that pre-Healy means anything for a non-AWB build)
  • Install fixed 10-round mag, then assemble rest of the lower.
  • Pistol brace from one of the known vendors w/ ATF blessing.
  • 10.5" upper in 300 BLK.
  • EFA10 as a 30-cal non-high capacity pistol.
Mass OK way to do it? Thanks...
It all depends on the lower. Was it pistol? If so then ok. Was it rifle? Then no go.
 

Mountain

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Then if 80%, 0%, multi cal go for it.

AFAIK when a lower is produced by a manufacturer it’s either rifle or pistol. I may be wrong on this.
If it was 4473'd as "Other" then you're g2g, but honestly I wouldn't waste a good pre-Healey ban lower on fixed mag. Save it and get yourself a virgin new production lower.
Sounds like a good opportunity for an 80%.
 
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