Is the Mossberg 100 ATR built on the Howa 1500 action like the Howa Lightning and Weatherby Vanguard? They're so cheap I was originally afraid of them being crap like the Remington 710, but the Howa action would make a nice "utility" gun, not the ultimate, but it'd work just fine in a pinch. Float the barrel, work over the trigger, and glass bed in a B&C Carbelite and it should be as good as any factory rifle.

Someone has got to have an answer to this question? Is it the same action?

I have owned several and still own one HOWA 1500 rifle. They are the very same as the Mossberg 1500, Weatherby Vanguard and Smith & Wesson 1500 rifles. Except for the trigger, they are primarily a Japanese copy of the older SAKO, very nice, smooth action. I have heard complaints about their barrels and have to admit, none of mine are outstanding shooters. I have one in .300 WSM and would like to know how they got the test group sent with the rifle at 1/2". I read in the American Rifleman of several months ago that they test fire these without the stocks in a machine rest and then stock them. That might be the reason I'm not getting any better than 1 1/2" groups. My son has one that started life as a 7 m/m RemMag and is now a 7 m/m Weatherby and it shoots about the same. I am changing the plastic stock on my for a laminated wood and hope that I will be able to shrink those groups. The factory stock is one of the "cheesiest" I've ever seen. Weatherby does, however, take selected Vanguards that shoot very well and puts them in an HS Precision stock and charges about twice as much for them.
I guess I didn't answer your question and, truth be known, I've never seen a Mossberg 100 ATR. Given there previous relationship with HOWA, I suppose that it could be. Having taken a look at the 100 ATR on their website didn't give me any better a chance at defining it's origins.
If your a mind to buying a HOWA/Weatherby Vanguard rifle, go to your nearest Wally World (WALMART), they sell them for under $400. I walked out the door for $396 and I had to special order the .300WSM.

No, it is not the same action.

James is right, they are not the same actions. The Mossberg is a redesign of the old Raptor rifles. The Raptor was not on the market long. I would think the Mossberg is a major upgrade of the old design.

Aaron