From what I've gathered, if you simply mean a one piece base vs a two piece, a one piece bridges the recievers port adding ridgidity, if you believe this even matters, if the action and bolt are trued, I think it's pointless myself. It could aid in repeatability, especially if swapping scopes between rifles etc. Ring alinement should be better too.
Downside is weight, more port obstruction and some may say looks.
A rail mount elliminates concern about the fact that factories frequently cannot drill and tap four holes in a straight line. This may be from sloppy workmanship and I have been told that it can also result from manufacturing stresses induced when major cutouts are made in the reciever. This results in rings not being true, they do not line up with the centerline of the bore or they are wonky and torque hell out of the scope body. That is why we sometimes get nasty ringmarks on the scope body when we take the scope out of a set of rings. Solution can be shimmable rings (Burris) and lapping.
The mounting holes in rails are somewhat oblong to accomodate the sloppily located holes, and the top deck is usually machined to very tight tolerances - good enough that the scope will return to zero if it is removed and properly re-installed.
Besides the above the rail can provide varying degrees of elevation, 20moa is usually the average - can go to 60moa or so. This is a real asset for long range shooting.
Main suppliers of rails are Richard Near and Badger Ordnance - both make very nice products. Leupold also makes one-piece MK4 rails, without the Picatinny spec slots.
Rails also enable the user to switch pre-zeroed scopes, install tactical gear such as night vision and as mention, to remove and replace scopes with great precision.
Like a lot of things, they are very expensive but very nice to have.
Thank you for the comments, gentlemen. Most informative.
The rifle is a budget conscious project; M700 in 25/06, trued/bedded, 27" Lilja, McMillan HTG, Rifle Basix trigger, and Weaver T-16, freshly blueprinted.
I originally intended to use Lightforce 2-piece bases as I wanted the additional 20 MOA but preferred the looks of the separate bases.
After reading these posts, I think I'll spring the extra $40 for the one piece Picatinny spec style. I had not considered the possibility of misaligned receiver holes.
As I am rapidly depleting my bank account, I am considering using the Burris Signature rings with inserts even though I have always lapped my own rings. I have heard good things about the Burris rings, but would certainly be interested in your comments.
BTW, Ian, is "wonky" an official technical term used by the Long Range shooting crowd?! [img]images/icons/grin.gif[/img]
"wonky" pretty much describes lots of my best efforts also - particularly trying to mount a frigging scope with the reticle perfectly up and down. Did you know that some people are born 20 degrees out of plumb...
My shooting partner is the opposite, anything he does is "bang-on" so he fixes a lot of my disasters - used to be when he looked through one of my scopes he had to lean so far over his left foot came off the ground! That is wonky.
There are several sources of good rails, here are a few to check out:
and of course Leupold's site for the MK4's but they don't have all the neat cross-slots that the other guys do, neither do some ggg's.
None of these rails are wonky, I assure you that.
Brownells has a few more. I would also consider the Warne non-detachable Maximas as a reasonable priced alternative to big dollar tactical rings. Sounds like a very nice rig you are putting together, that is my favorite McMillan stock.
I'll second the motion of Ian M. I really like the Warne Premier ND rings. I have them on my two walking rifles, a .243 AI and a.280 AI, both with the NF two piece bases and both with #5 taper fluted Pac-nor barrels. Both rifles are wearing Lupy 4.5-14x50 LR tacticals. Be careful about going to a base set-up with more than 20 MOA, you could tilt yourself out of a 100 yd zero if you're not careful. Both of my LRT's are in the botton revolution on the elevation knob--I got lucky, they both worked out perfectly. My .300 Tommy has a 30MOA one piece Piccaretta base, and it is also in the bottom revolution on the 8.5-25x50 LRT. I have approx. 70 MOA of internal UP adjustment in that scope. If you want a one piece base, Rick Piccaretta will build you whatever you want for $75. Just call him and discuss the amount of forward cant(MOA) and how many slots you want. He will also drill the base for 8-40 screws if you're interested. Have your 'smith redrill and tap your holes true to the bore center and open them up to 8-40. Rick's phone # is RDP Rifles (570)864-0989. Here is a photo of the base he made for my .300 Tomahawk...