changing from ar-15 to ar-10
 

Is it necessary to change out lower reciever parts or just the upper ? :confused:

They are built on different sizes, so you cannot switch between the two. You have to have a matching upper and lower for the ar-15, and a seperate upper and lower for the ar-10.

You can get different calibers for the ar-15, but they have to fit within the magazine restraints of the ar-15.

There are lots of caliber selctions for AR-10s (and clones) too. I have DPMS clones in 243 Win, 260 Rem, 6.5 Creedmoor, 308 Win , 338 Federal, and 300 SAUM. (all factory offerings).
Many more are available as custom or semi- custom offerings. Basically anything based on the 308 or 300 SAUM case is available.

I completely agree, there are a lot of options for both the AR-15 and AR-10 platforms, I was just trying to explain that they are different sizes and are not interchangeable with each other. The AR-15 as a magazine fed rifle is limited to cartridges with about the same OAL as a .223. The AR-10 allows the user to step up to 308 class cartridges. (Obviously if you don't want to use the magazine you can use larger cartridges in the AR-15, such as 50 BMG conversions.

There are 3 parts out of the lower parts kit that are different on the DPMS LR308 series. They are the take down pins and bolt catch screw (it's a screw instead of a rollpin). The bolt catch needs to be tapered on the bottom edge to fit, but a file or grinder will make short work of that and it will still work in a standard AR15.
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MERCURY COUGAR SPECIFICATIONS

What are some good (upper) caliber options in .223/AR-15 class for deer size game out to 200 yards?

Thank you!!

300 Whisper, can load supersonic, 6.8SPCII, 6.5 Grendel, 458SOCOM, 450 Bushmaster, plus some specialty uppers such as the WSSMs and OSSM from Olympic.

Certainly not an exhaustive list but these are some you could start looking into.

Thanks for the list. I like a couple of those. I'd like to look closer at the 6.8 and the .450. The 6.8 might get the nod just for lack of recoil (I'm assuming). I've done my share of shoulder beaters over the years and, although I'm not sure if the .450 is a shoulder beater, I like the idea of getting a lot of range time in with the same caliber I hunt with.

Thanks!!

just to expand on your post, Olympic now sells what they cal the "Game stalker" line, these rifles are on the ar-15 platform, but are chambered for 243 wssm, 25 wssm, and their own wildcat the 300 ossm. which is the wssm case necked up to .308
I have heard it performs close to the 30-06

The 450 Bushmaster definitely has a heavy recoil for the AR15 platform. I was trying out about 40 reloads today and put a sock with some sand in it between the stock and my shoulder to make it more comfortable. A lot of people shoot it quite a bit without that, but if you are sensitive to recoil you might want to avoid it.

The 6.8 will have a little more recoil than a 223, but I would still consider it quite mild compared to a lot of other hunting loads.