Question about building an AR

[JohnVH]

I dont believe the same magazine part, unless you modify it is my guess. Id bet you have to buy AR15 mags made to fit the caliber you have, thats how my grendel is.

[rock]

450 bushmaster is common here in Indiana, as it's one of the few rifle rounds legal, most use the same magazine with little complications.

[CastleRocker]

My uppers take three completely different magazines, (or should I say, different follower, and some adjustments to the feed lips).   In addition to having different bolts.   

My DTech 25 WSSM is single stack due to the diameter of the case.  (Ultra Mag, or Winchester Short Mag, or WSSM...big bolt for a fat case!)

My 6.5 Grendel and my new 6mmAR (just a 6mm Grendel), take their own magazine and a smaller bolt.

The 17/223, the 20 Practical, 5.56/223, and the 300 Blackout take the stock one. 

[Atroxus]

The more research I do, the harder time I am having picking a caliber. Currently the front-runners are .300 BLK, .450 bushmaster, .458 SOCOM, and 6.8SPC.

Anyone near Marysville have an AR in any of these calibers that would be willing to take me shooting? Maybe some hands-on experience will help me decide.

[Jekemi]

I strongly encourage anyone that is planning on building an AR to go to www.ultimatereloaders.com and read Gavin's several part video on building the AR. He does both the .223 and the .308. In addition, if you want to build an AR that you don't have to register consider buying an 80% lower with no Serial # stamped on it. You have to purchase a corresponding jig and have access to a very good drill press or metal lathe but you can build an AR that Obama and his gun-hating friends know nothing about. It is perfectly legal.

[Atroxus]

Anyone know what is the max energy I could expect a .300BLK to generate at 200 yards, assuming 16" barrel, 150gr Barnes TTSX bullets, and keeping loads within SAAMI pressure specs?

I am kind of leaning towards .458 socom for the extra punch. It is sooo much more expensive for upper components and ammo, that if I can get 900+ ft/lbs of energy at 200 yards with a .300 blackout I will probably go that route though. I am not a marksman, at 200 yards I can maintain about a 5" group with my .30-06.(I am sure that in the right hands the rifle is capable of better) So I don't ever see myself shooting at a live animal at ranges farther than 200 yards.