Which caliber for which rifle?

[Dr. Tad Hussein Winslow]

Guys, here it is:

I AM getting a Robinson XCR. I will also later on be getting another AR15. One of these will be in 5.56x45 and one will be in 6.5 Grendel. The question is, do I:

1. Get the XCR in 5.56 and the AR15 in 6.5 Grendel, or
2. Get the XCR in 6.5 Grendel and the AR15 in 5.56

???

Why or why not? Any reason to pick one, or just doesn't matter? If I do go AR15 in 6.5 grendel, then which - Alex Arms upper?

 

[Z-Michigan]

Flip a coin. Or get one XCR with two barrels and bolts.

I'd lean 6.5 G for the AR since a quality AR with a free float barrel is probably a bit more accurate than an XCR, and last I checked the XCR's longest barrel option was 18.6" vs. 20 or 24" for many ARs. But really I don't think it matters much either way.

So is your signature line deliberately ironic?

 

[Dr. Tad Hussein Winslow]

Oh yeah, guess I need to change that.... I mean, not counting EBRs....

Well, is the 6.5 grendel not more optimized closer to 18" whereas the 5.56 makes more sense with a 20" bbl? Or more so vice versa? Which cartridge is closer to its "goldilocks" barrel length at 18", as would be the XCR situation?

 

[W.E.G.]

Get the oddball caliber for the AR.

That way, when you get bored with the it, you will have
a much larger potential market to sell it to.

 

[Z-Michigan]

6.5 Grendel does well, IMHO, only with 20" or longer barrels. I'm sure people will disagree, but in the shorter barrels I don't see it having much practical benefit over 6.8 SPC or even 7.62x39. With those two, and the short barrel 6.5 G, past 300 yards you will need a good rangefinder and some serious bullet drop skills (or a computer) to hit anything small. The 6.5 G gains enough velocity in 20" and longer barrels to add some distance to that and give it, again IMHO, some benefit over the other two calibers. Alexander Arms has detailed velocity and drop charts on their website that I recommend you look over, for four different barrel lengths. (When you read them, note that they assume an artificially distant zero - but they're still an excellent way to compare the effects of the different barrel lengths.)

The .223 gains velocity in barrels up to at least 24" but nearly all common loadings are so fast that trajectory is pretty flat anyway, even down to 14.5" barrels. I have a couple rifles with 16" barrels and, once again IMHO, this is pretty short. I think 18-19" is a good sweet spot for this round, and more never hurts.

If you really want a 16" barrel, the 6.8 SPC and 7.62x39 reach nearly their full velocities in that length. Cardinal Armory/Kotonics stated in their FAQ that there was little benefit to going over 16" and essentially no benefit to going over 18" in the 6.8 SPC. And in 7.62x39, the 23" barreled RPK's seem to have only about 50fps over the 16" barreled AK's - wow, roughly 7fps per inch, not much benefit! (Well within the shot to shot variation for that and 95% of other cartridges.)

 

[3pairs12]

I wish I had your problem. I would go 6.5 in AR also that if decided you were done with that caliber you could just sell upper pretty easily and still keep the Robinson.

 

[Dr. Tad Hussein Winslow]

Thanks all - particularly WEG and Z-Michigan:

Get the oddball caliber for the AR.

That way, when you get bored with the it, you will have
a much larger potential market to sell it to.

That makes sense. I'll run with the 18.6" standard length XCR for the 5.56x45, and go with a 20" AR upper in 6.5 grendel later down the road (assuming that I still have the Grendel bug at that time). I'll check out the Alex Arms ballistic charts.

http://www.alexanderarms.com/siteshopper.htm?cat=15

This version looks like what I want:

http://www.alexanderarms.com/siteshopper.htm?cat=15&item=33

 

[RockyMtnTactical]

Get the AR15 in 5.56 because spare parts and such are much easier to get and find for that caliber in the AR15.

Who cares about which caliber the XCR is in, you will not find spares either way.

 

[Dr. Tad Hussein Winslow]

Anyone else have a vote?

 

[cliffy]

AR-10 .243 Winchester will blow both out-of-the-water

Power with light-recoil belongs to .243 exclusively. Why bicker about varmint rounds? Ever see a premium 100 grain .243 Winnie Pooh hit something? It would make you want to drop your .223 Remington and run! Kalishnakov's are even less potent than .223 Remington at long range. I'd run from a .223 Remington, if I didn't hold a .243 Winchester in decided defiance. An M-10 rifle in .243 caliber is what our military truly requires to be top-dog. Stop pussy-footing around the obvious, and issue M-10s as I've dedicated them. One round of .243 equals the firepower of 3 5.56mms. Even I, with my defective heart, can stand the mild recoil of a .243 Winchester. I defy anyone to come up with a better rifle round concerning serious warfare. Been there: Done that SP/5 Flying Crewchief of the 60s Cliffy

 

[SimpleIsGood229]

I would definitely make the AR the one chambered for 6.5 Grendel. A quality AR is likely to be more accurate than the XCR at long range, which is the whole purpose of the Grendel.

The XCR is the combat carbine, so make it 5.56. Unless, of course, you'd use the Grendel as a fighting carbine and the 5.56 for long range (I don't know why you would, though).