Hey all!
So thinking about buying a new upper for my colt ar15. What im not sure on is which caliber uppers are possible for an ar-15 lower with no modifications? I have seen there is no way a .308 upper will work (Dang 
) I am hoping to get one in a different caliber maybe 300blk or something else. Anyone have any clue on what the possibilities are? also any input on a caliber to go after?
Thanks guys! 
Here are the calibers available. Tell me what you are looking to shoot with it and I can give you some advice, I’ve got 5 different calibers for different needs. Good luck, and I’ll warn you that building AR’s is addictive!
AR-15 calibers[edit]
Rimfire calibers[edit]
.17 Mach 2
.17 HMR[1]
.17 Winchester Super Magnum[1]
.22 Long Rifle[2]
.22 Winchester Magnum Rimfire[1]
Centerfire calibers inch measurement[edit]
.17 Mach IV
.17 Remington Fireball
.17 Remington[1]
.204 Ruger[1]
.222 Remington
.223 Remington – Original AR-15 caliber: .223 cartridges may function in a 5.56×45mm rifle, however 5.56×45mm cartridges can produce excessive pressure in a .223 rifle. On the other hand, a .223 Wylde chamber is used on .223 caliber rifle barrels to allow them to safely fire either .223 Remington or 5.56x45mm NATO ammunition.[3]
.22 PPC
.224 Valkyrie (necked down 6.8SPC) [4]
.223 Winchester Super Short Magnum[3]
.243 Winchester Super Short Magnum[3]
.25 Winchester Super Short Magnum[3]
.25-45 Sharps
.277 Wolverine (6.8×39mm)
.30 Carbine[1]
.30 Remington AR[5]
300 OSSM[3]
300 AAC Blackout (7.62×35mm)[5]
.300 Whisper[5]
358 Yeti – Wildcat [6]
375 SOCOM
.40 S&W[7]
.410 Shotgun
.45 ACP[8]
.450 Bushmaster[1]
.458 SOCOM[9]
.50 Beowulf[10]
Centerfire calibers metric measurement[edit]
5.45×39mm[1]
5.56×45mm NATO – Original AR-15A2 caliber: can also safely fire .223 Remington[1]
FN 5.7×28mm
6.5mm Grendel[1]
6.8×39mm (.277 Wolverine)[11][12]
6.8mm Remington SPC[5]
7.62×37mm Musang
7.62×39mm[5]
7.62×40mm Wilson Tactical[5]
7.92x33mm Kurz
9mm Parabellum[2]
10mm Auto[8]
Calibers which will not feed but which are used in rifles where the receiver functions only as a trigger group[edit]
.50 BMG
.408 CheyTac
.338 Lapua Magnum
AR-10 calibers[edit]
Center fire calibers[edit]
.220 Swift
.22-250 Remington
6mm-250
.243 Winchester – same bolt as 7.62×51 (worn-down barrels can be re-bored to take 6.5 Creedmoor or 7.62×51)[3]
6MM Remington
6MM Creedmoor
257 Roberts
6.5×47mm Lapua
6.5mm Creedmoor – same bolt as 7.62×51, and can be formed from 7.62×51 brass
.260 Remington – same bolt as 7.62×51, and can be formed from 7.62×51 brass
7mm-08 Remington
7.62×51mm NATO – Original AR-10 caliber
.308 Winchester – considered interchangeable with 7.62×51mm NATO according to SAAMI.
.338 Federal
.358 Winchester
.45 RAPTOR
.500 Auto Max
What is the mission of the new upper?
Wow thats a lot more possibilities than i imagined! The goal of it is just to have another fun caliber for shooting steel at the range honestly. Maybe some varmit eventually but not a huge factor. Ive been looking at the .223 wylde which seems awesome but still keeps me in the same caliber. Also i do handload so i can adapt to some of the less popular calibers as well.
6.5mm Grendel sounds promising
6.5 grendel for hunting, and 300 blackout for target shooting. Along with your 223/556 upper, you should have most shooting scenarios covered.
Wow thats a lot more possibilities than i imagined!
The list above is not correct. It includes both AR15 and AR10 calibers. Since you have an AR15, the list is about half the above.
Also, possible is the key word. Many of the chamberings on the list have rarely been made to work well in an AR platform. For example, many have tried to get cartridges like the .22-250 and .220 Swift to work well, but success has been very limited. These are AR10 offerings, of course, but the point stands. Not everything that has been tried, actually works well.
I believe other cartridges listed require things like magazine modifications or full custom magazines. Others do not cycle in autoloading AR actions, they can only be fired in bolt action “AR style” rifles.
If we are talking only AR15 offerings that will fire in a semi-auto action, I’d consider:
Not on the list is the new .22 Nosler, which I think shows a lot of promise as a varmint cartridge. However, now that many have been made, some recurring problems are showing up, so do some reading before you buy.
The .224 Valkyrie also is very interesting, but this has been tuned for the heavier end of the .224 bullet spectrum, but that too has some interesting possibilities.
I have never understood the recreational shooter’s fascination with the .300 Blackout. I think the badass name has a lot to do with it. The military use for this chambering is obvious, but for the hunter and target shooter, I don’t get it. Range is limited, ballistics are terrible, there are vastly better and more versatile choices for hunting, and .30 bullets are big chunks of expensive lead for target shooting.
The 6.5 Gren is interesting and fairly capable. I would think there’s probably some opportunity to hop it up a little with handloads.
Grouse
Yeah, the formatting of my message wasn’t the best, but if you look closely you will see the mention of AR10 calibers and single shot calibers.
The 300 blackout round is a great personal protection round and also great shooting subsonic ammo with a suppressor.
The 300 blackout round is a great personal protection round and also great shooting subsonic ammo with a suppressor.
Yes, that is what is often said. As I said, I can see the military appeal to this round, big honking hunk of lead that fits a standard AR15 lower and can be fired well through a suppressor.
For recreational use, I can’t believe that 1 AR owner in 1000 has a suppressor. Would even 1 owner in 5000 have one? I know suppressors are something of a preoccupation now, but I doubt the vast majority of .300 Blackout owners have suppressors.
Subsonic ammo is always interesting, but not cheap if buying factory ammo. And the full-flavor rounds aren’t cheap either. I suppose it doesn’t matter a lot if you only shoot a few hundred rounds a year, but IMO throwing out a .30 caliber hunk of lead gets expensive and limits the recreational utility of a round unless you’re very, very dedicated to it.
If a person wanted a quiet, low recoil, and cheap practice or steel shooting round in an AR, I’d say the best bet would be to look at an AR in .22 rimfire. I know there’s no badass Tacticool name to throw around there, but if the goal is quiet and cheap…
Grouse
I have never understood the recreational shooter’s fascination with the .300 Blackout. I think the badass name has a lot to do with it. The military use for this chambering is obvious, but for the hunter and target shooter, I don’t get it. Range is limited, ballistics are terrible, there are vastly better and more versatile choices for hunting, and .30 bullets are big chunks of expensive lead for target shooting.
Shoot subs suppressed and you’ll understand the fascination.
Shoot subs suppressed and you’ll understand the fascination.
So do you actually have a suppressor? Post a video, I’d love to see this in action.
As I wrote, I can’t believe that any substantial number of AR15 owners who have 300 BO barrels also have a suppressor, so to me, this explanation alone doesn’t come close to explaining the popularity.
A suppressor would be very entertaining. I hope we can finally get over the Hollyweird fake perception that has been created of these as criminal devices and make ownership a common sense process. I’d love to go with a surpressor sometime, but the current hoop jumping, legal wrangling, and then the retrofitting of rifles would be a significant investment.
Grouse
For me, I found that a full power 300blk in a 7.5″ pistol, is a wonderful substitute for a shotgun zone deer gun. Other than that, it’s just something you can tell your buddies you have to sound tactical. I recently have given up gun hunting deer, but the combo has been very lethal for me in the past.
I’m with grouse. I’ve shot, owned and handled all sorts of different calibers in an AR platform and most are just gimmicks or tacticool talking points. .223/5.56 and .22LR are the ticket with AR’s. the 6.5 Grendel is neat and can be incredibly accurate, but I just don’t see the benefit for 75% of people.
I have a friend with a .204 ruger AR and he loves it. Unless you’re hand loading, the cost of ammo is enough to negate the ballistics benefit of the round, leaving you back at square one.
Depends on the age of your colt there are some compatibility issues with big pin vs little pin. Otherwise everything else should swap out.
For me, I found that a full power 300blk in a 7.5″ pistol, is a wonderful substitute for a shotgun zone deer gun.
You can do this in MN?
Grouse
<div class=”d4p-bbt-quote-title”>Merican Eagle wrote:</div>
For me, I found that a full power 300blk in a 7.5″ pistol, is a wonderful substitute for a shotgun zone deer gun.You can do this in MN?
Grouse
Don’t let the secret out.
I love the AR15 platform. I bought an entry level .223 wylde and soon after purchased a 300blk upper to utilize as a brush gun. The .223 is more fun to shoot than a .22.
TheFamousGrouse wrote:
<div class=”d4p-bbt-quote-title”>Merican Eagle wrote:</div>
For me, I found that a full power 300blk in a 7.5″ pistol, is a wonderful substitute for a shotgun zone deer gun.
You can do this in MN?
Grouse
Don’t let the secret out.
X2 I do this as well with a 10″ barrel inside of 200 yards it very hard cal. to beat!!! it packs a little more punch than the 223 and also lots of hunting bullets to choose from in 30Cal.
<div class=”d4p-bbt-quote-title”>tornadochaser wrote:</div>
Shoot subs suppressed and you’ll understand the fascination.So do you actually have a suppressor? Post a video, I’d love to see this in action.
Mine’s in jail yet. Lane Scorpion S30. Should get the stamp in March. Demo’d one at a 3 gun match last summer and also did some prairie dog shooting with a 6mm creedmore with that can after we got our antelope in september.As I wrote, I can’t believe that any substantial number of AR15 owners who have 300 BO barrels also have a suppressor, so to me, this explanation alone doesn’t come close to explaining the popularity.
I’m not going to say that .300 blk is the best AR caliber ever, because it’s not, but it does have advantages, and opens up a different type of shooting/hunting option for those who try it out. I know 4 guys just in my office alone that shoot blk suppressed. The guy sitting next to me right now is waiting on his SBR stamp for a 9″ .300 blk build. Guys I know in MN like the caliber for AR pistols for deer hunting.
A suppressor would be very entertaining. I hope we can finally get over the Hollyweird fake perception that has been created of these as criminal devices and make ownership a common sense process. I’d love to go with a surpressor sometime, but the current hoop jumping, legal wrangling, and then the retrofitting of rifles would be a significant investment.
For me the benefit is hearing safe shooting of rifles. Hollywood quiet only gets close with rimfire cans. (those are a blast by the way.) The last 3 bolt action rifles I’ve bought were factory threaded, so no real issue retrofitting. The paperwork took me 25-30 minutes of lazily filling it out while BS’ing with the dealer. Good NFA/suppressor dealers have streamlined the paperwork process to the point where it doesn’t take much longer to do your forms than a regular 4473.
You can do this in MN?
Grouse
Yup. It’s a really good option. I have a 7.5″ barrel with a Noveske KX5 under a carbine length FF tube and a nikon 3-9×40. I use a KAK tube with a Sig PSB. Goes without saying, but follow all NFA rules in regards to forward grips and PSBs on pistols.
I put a 300 blk together with a 16″ barrel with the intent of making a small tree stand gun for deer…Been having a lot of fun reloading for it, got settled in on a load and bullet…A little more testing, and I should have it ready of the 2018 season…Currently has a Vortex Red/Green Dot on it, but intend to try a low power scope on it too.
Wow thats a lot more possibilities than i imagined! The goal of it is just to have another fun caliber for shooting steel at the range honestly. Maybe some varmit eventually but not a huge factor. Ive been looking at the .223 wylde which seems awesome but still keeps me in the same caliber. Also i do handload so i can adapt to some of the less popular calibers as well.
The Wylde is a chamber design by Bill Wylde. It has a longer throat that allows the use of 80gr bullets to be seated long for slow-fire in Highpower and F-Tr class (though when he designed the reamer, F-TR class did not yet exist). It just so happens that this longer throat configuration allows the use of 5.56 NATO ammo and still keeps pressures within SAAMI spec. Hence the reason of it’s growing popularity. It’s one size fits all chambering for the 223 Rem.
It really gains you nothing over a straight .223 Rem chamber unless you intend to shoot big bullets, seated longer than mag length.
There are other options as have been noted (22 Nosler & 22 Valkyrie). A 17/223 or a 204 Ruger are a possibility as well.
How bout this for lower compatibility parts, please forgive my feeble attempt at humor.
AR-M16FAFCG-c.jpg
6.5mm Grendel sounds promising
Yes!!!!!!
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