6.8mm AR15 lower receiver different?

[sureshot]

I am starting to be interested in AR15 type rifles and am considering a 6.8mm
upper on a Bushmaster lower. While reading the Bushmaster catalog I noticed that the 6.8mm lower has a different order number than the 223 model? Anybody know what the difference is? My understanding of the whole 6.8spc caliber was that it is compatible with existing 223 receivers?

Anybody know what the difference is? My tendency is to go with the 6.8spc caliber for hunting purposes and then maybe pick up a 223 upper for range work.

[PatMcD]

Unless there is a difference in the buffer, I think they are exactly the same. I know you can buy a lower marked 6.8SPC, but it's the exact same as a .223 one.

[Cuda444]

The different part numbers, if nothing else, would be due to what is engraved on the side. Once says 6.8 SPC and the other .223/5.56. The receivers are totally compatible with one another. As far as the buffer goes, I think they are the same, but I'd have to do some research. Worst case, call Bushmaster.

[sureshot]

Thanks. May give Bushmaster a call unless someone here knows for sure. Why would the caliber be stamped on the receiver? it is a function of the upper only and they don't have different order numbers for all the other available calibers?

[Cuda444]

It's just the way it is, I guess. Even my Colt pre-ban has 5.56 cut into the side. In the same regard, the barrel is usually marked as well.

[Dan Carey]

The differences in the 223/556 and the 6.8 are few, first Stag uses a different barrel extension and bolt head and extractor. The rest of the parts are the same as their 223. Other manufacturers are using the same barrel extension as on their 556/223's and use a different bolt head and related parts. All the lower parts are the same, which includes the buffer and spring. The magazines are different.

[sureshot]

Thanks guys. So now that I know that they are the same, any general opinion on the 6.8spc caliber? Anybody in MA use one and if so, did you build it or did you buy it.

[1903Collector]

I bought an upper from Bushmaster in 6.8 and after getting a cycling problem squared away it's pretty neat. However unless you are going to reload for it it's going to cost a fair amount to shoot. I haven't fired mine much yet but it seems just as acurate as a 5.56 rifle. Also if you live in MA you will be limited to ten round mags. Recoil does not seem any harder that the 5.56 it's a fun gun to shoot.