Obviously a lot depends on your situation. For example do you have other pistols or rifles for example. Assuming that you might not I would probably go with the Springfield XDM-45. And at the present good 45 ACP ammunition might be also easier to get than good 223/5.56 ammunition. Then there is which one you would use the most and which one would be good for home defense! Obviously the XDM for that application. If you have other pistols and do some varmint or predator shooting then obviously the Remington 700 would be a better choice. But as far as the 223/5.56 caliber ammunition in the present time you may want to review that! And consider like the Win. 243 or 30-06 which I have seen ammunition for both still available even at Walmart and other stores. But stores and dealers are completely out of 223, 308, 22LR ammunition "Always!" Or you are going to pay dearly even if you can find it! For example 223 ammunition that is "not top quality" for $1.00+ per round! WHEW! I spoke with a good friend of mine who is an executive at ATK who owns Federal and other companies and he sees "NO LIGHT" at the end of the tunnel at this time! Good luck on your selection!
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-- John F. Kennedy