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[Malamute]

A little less muzzle blast with the 5". 4" will be easier to carry.

I doubt most peope would be able to tell the difference in accuracy between a 4 or 5" auto.

[Mstrty]

That it. I own both. There is no other advantage. The only other difference that you didnt mention is a captured recoil spring in the 4" vs a full length guide rod in the 5". For target, HD, or action pistol get the 5" For concealed carry get the 4".

[Revoman]

You have pretty-much got it right, other than you should also get a slight bit more velocity too.

The sight radius is the main attraction though.

[osxgp]

Velocity is increased with a longer barrel. Accuracy tends to be better with a longer barrel as well. I think it boils down to what you plan to use the gun for. Target practice? 5" barrel. Home defense? Either. Carry? 4" or 5" barrel, but a shorter barrel with draw faster. However, everyone will have an opinion and those are mine. Good luck with your choice. I'm sure either will be a great choice for the most part.

[Old4eyes]

I have the XD9 in the service and the tactical. The tactical is easier to rack.
I have the XD45 in the tactical, it is easier to rack than the XD9 service. If you or someone you may be sharing range time / home defense duties is sensitive to the effort of racking, that might be a minor consideration.

Another minor consideration is if you mount a light on the pistol, most of the lights will extend beyond the muzzle of the 4" service and will be even with the 5" barrel. I've got TLR-1 mounted on the XD9 service and it gets dirty, and then it gets cleaned up. The light looks better mounted on a the Tactical, if looks are important to you. When I get more rounds through the XD45 Tactical to prove its reliability, it will be the night stand gun replacing the XD9 Service.

[appagohm]

Hmm... Unless your a professional you shouldn't notice the difference between the two. I have the 4inch service model. And have shot the tac model many times. From 50ft i can group 2 inchs with my service model xd 45. Really at the end it's up to you, both will be great, but if you ever want to carry it, you'd be glad you got the 4inch.