My son in law is going into a career in gunsmithing.His experience as an Army Ranger/sniper for 14 years helped him decide on his avocation now that he is out and has his pension.
I'm considering buying him a gunsmithing lathe,or even the lathe/mill combo like the Grizzly G0791.My question is about any experience any of you with such a machine may have.I know Grizzly machines are made in China and use NSK bearings,reviews I've read are almost all positive.I'm thinking this could be a good entry level set up.

I would recommend a dedicated lathe. Preferably one specific to gunsmithing. While the combo machine can do multiple things, they do none as good as dedicated machines.

I have a smithy granite 1324. I bough it used several years ago. While it does good work, it has it's shortcomings. The lather part works good. The mill part has a lot to be desired. The tool head is WAY to high above the table. Even with a tall vice, I still have to lower the spindle almost all the way down to get a bit close enough to the workpiece to mill anything.
The lathe seems to work fine. The biggest complaint I have is no way to support something on the backside of the machine (like a barrel). So I have not tried any barrel work yet because of this.

Do not buy a lathe/mill combination, buy one or the other.

Grizzly has amazingly affordable equipment that is designed for the home hobbyist or light production use. I don't consider them to be commercial production quality machines.

The idea that you can be a pretty nice new lathe with DRO for <$6000 is amazing to me. I own a well used Webb-Whacheon 17x40 lathe that is considered top tier and they are still being manufactured today. A new unit costs $35,000 +/-. Used models in great shape run $8000 to $12000. The problem with industrial grade equipment is the size and weight. My lathe weighs 4500 pounds. It resists any attempts to move it.

Manual lathes haven't gone the way of the dinosaurs yet, but they are headed that way. Virtually all production shops use CNC.

Long time machinist/Gunsmith here. The advice about staying away from the multi purpose machines is spot on, they lack rigidity and repeatability- both essential to quality machine work.
Invest in a quality gear head lathe, it is the only machine in a shop capable of replicating itself and it is the most versatile machine a machinist/'smith can own. 13-40 is a common size and well suited for 'Smithing work.
Look for a narrow headstock machine with a spindle bore size as large as possible, 2" will accommodate just about anything a "smith will encounter.
Yes it will be heavy but that is a good thing, lightweight lathes lack rigidity and are prone to vibration which can wreak havoc.
Try to stay away from Chinese machines if you can for obvious reasons, I have seen too many posts and references to quality issues, repeatability and accuracy issues.
My personal machine is an ATRUMP 1340 of '95 vintage that I found on CL for $2500.00. It tips the scales at 1700# and is Taiwanese with Meehanite Iron and flame hardened ways. It is a very solid, accurate and repeatable machine.
My machine at work is a Clausing Colchester 8000 series, again of Meehanite iron and flame hardened ways. Solid machine as well, the only scary thing is parts can be tough to find.
We also have a Grizzly G9036 and it cannot remotely come close to either of the machines I mentioned. It's not a good sign when you go to change the oil in the headstock and you get about a tablespoon of sand from the casting process out
DRO is not a necessity and I actually wont use one for 'smithing work, I am focused on my cut and don't want to look away from the work. Dial indicators on mag bases will work just fine.
Another consideration is power. Don't even consider a 110/120V lathe, insist on 220/240V machine and preferably a 3 phase machine. They are more efficient electrically and just cut smoother.
The cost of the machine is just the beginning, he will have as much if not more invested in tooling as the cost of the machine.

Look into precision Mathews lathes.  If I remember correctly they are supposed to be made in Taiwan not prc and are similar to grizzly prices.

If I'm not mistaken, PM and grizzly have a lot of the same machines made in the same Chinese factories. PM seems to have more Taiwan machines though which are definitely an upgrade. It comes down to which company you want to potentially work with warranty wise. PM will be a little more expensive, but I've heard nothing but phenomenal things from their CS. I've heard good things about grizzly too, but a few more odd issues than PM.

Some good input gentlemen,thank you.
I like idea of getting something new or newer yet I find myself checking out older model South Bend machines.We have one at work that has been getting the job done since the 1960's(before my time).
Anyone ever go on a parts hunt for older machines?I'd hate to get an old,well made machine only to find I can't get replacement parts for it if I need them.
Bridgeport machines are fairly common for sale on line,same concern though,can I get replacements if needed.
The idea of a combo machine doesn't sound inviting.Never had any experience with them and don't plan on it either at this point.

I got the size one down from the gunsmith lathe.  With DRO.
Couldn’t be happier for the money.
A friend who is a retired machinist has a big, realllly nice Grizzly lathe.  
The guy is rich and sold a multi million dollar machine/fab shop.  He has a Grizzly.

What size through bore did you end up with?  The 4003 series has a bit bigger than average...

Well,it took a while but I finally found what I wanted.A south Bend 10 inch heavy.4 foot bed,2.25 inch X 8 Spindle. It came with a fair amount of tooling but Im going to get more.