I have a leupold 2 piece scope base on almost all my rifles the other has the 1 piece base.... I never see target rifles with 2 piece bases, am I missing something?

More pieces = more potential movement

More misalignment.

Only advantages I can think of for the 2s is less weight and more thumb room if loading topside.

There are pros and cons.

One piece bases can, when properly mounted, add a small degree of stiffness to the receiver of a traditional bolt action design.  

A one piece base will make any misalignment of the holes drilled and tapped into the receiver instantly obvious - not that it will actually solve the problem however.  

A one piece base makes it seem to be easier to mounting a one piece base on a receiver where the tops of the bases would not be in the same plane with two pieces bases.  However, mounting a one piece base on said receiver will still result in vertical stringing, so it's not a good solution.

It's easier to bed a one piece mount for full contact with the receiver than it is to bed a set of two piece mounts (which is the correct solution to the above problem).

A one piece base, if attached fore and aft with four screws rather than three, can be cantilevered out in front of the receiver ring, giving the shooter some additional options for mounting larger optics.


On the other hand many one piece bases, particularly on short action receivers, only use three screws rather than four, so they have less shear strength than the 4 screws used on two piece bases.

A two piece base will be lighter than a one piece base.

A two piece base will allow more room for loading.

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In either case, if you are using quality bases and mount them properly, either  design will get the job done.

I would say lapping rings is almost mandatory with 2 piece bases.

But few people understand that ring mounting surfaces of factory rifles are seldom even so I am sure many will disagree

Personally, I think lapping the rings is a bandaid approach to the problem.

Ideally, what you are looking for is a perfectly aligned set of rings that won't stress the optical tube, but just as importantly, won't be stressing the receiver either.

If you are using a one piece base on a crooked receiver, the base will be taking the stress off the optical tube and you'll be tempted to declare victory and call it good.   However the one piece base will still be placing stress on the receiver, which is not conducive to accuracy.  

Similarly if your two piece bases are not in the same plane they will stress the optical tube and the receiver - it's just a lot more obvious that this is happening.

If you have a one pice base, you install the screws and snug them up on one end and then see if you have any space on the other end.  If so, you now know you need to bend that end.  If there is no space, then you re-install the base from that end and see if you have any space under the other end.  If so, then you've now identified it as the end that needs to be bedded.  If you fond no space under ether end, when the other end is screwed down, then you don't need to bed the mount at all.

You can do basically the same thing with a set off two piece bases - you just have to install the bases and rings on an optical tube (or a straight piece of 1" bar or tubing) first to be able to check each base for excess clearance.  And once again, if you find clearance under one base, then that's the base you bed.

That will accomplish the same thing as lapping (aligning both rights so that there is no stress on the optical tube), without encountering all the downsides of lapping the rings.  Plus you are actually resolving the underlying alignment problem by bedding the base, rather than just accommodating the alignment problem by creating a set of mis-aligned rings to match the mis-aligned base(s).

The only reason to lap a ring is to allow for full contract between the rings and the optical tube, but even then it's imprecise given variation between the optical tube and the tube you are using to lap the rings.

Lapping rings however has a long history and is something many shooters seem to regard as the holy grail in scope mounting, so many of those same shooters will choose to ignore any suggestion that it's not a great idea, rather than sit back and think about what it is they think they are accomplishing versus what they are actually accomplishing.

It is a myth that one piece mounts or bases are inherently more accurate than two piece designs.  Each has advantages and disadvantages.  Quality two piece bases do regularly appear on world class competition rifles. Below is Jim Carmichael's recent world record holding light varmint class bench rest rifle with separate front and rear bases.  The five five shot aggregate at 100 yards was .1332"

That's a custom action, the front and rear bridges are more than likely on the same plane. On the Remington action where the rear bridge is lower than the front and it's all different rifle to rifle.

Without bedding the base and lapping  the rings will ruin those rings for any other rifle.

Always  use quality  components  and bed your base, one piece or two.

The ease of loading rounds into the rifle is a moot point if you use a detachable  magazine  ;)

I bed my quality one piece bases, my thought process is bedding would be more difficult with a 2piece base

dt.

It isn't - you just have to connect the two via rings and a tube. Then you effectively have a (large) one piece base.  In both cases you're going to tighten down the end with the least amount of clearance first.

I would use the lapping bar a fixture to connect  the rings with base.

I'd recommend one piece base on the mags. Had a 300wm Remington Sendro. My scope(8.25x25) and two piece bases were Leopold.  My issues was the scope kept moving in the rings and no matter what I did they moved. Switched to a one piece base and everything was good. Someone said it was receiver flex and the one piece bases helped with this?? Funny my problem went away once I switched.

Bingo

The exception only proves the rule.  I'm sure Jim put in a ton of timing making sure those bases and rings were perfectly aligned.   I'm sure the very vast majority of people that will use a two piece base will not put in that amount of time and effort. Do you think they will have equally good results?  I'm thinking no

That rifle has rings mounted directly to the action. There is NO base--in essence it is a zero base mount, not a one or two base mount.

I have used Burris Zee rings and inserts to avoid lapping. This has worked well for me in compensation of misalignments. And it negates scope tube torque but does require additional shots for verification.

Aren't those Burris Zee rings Chinese crap? Inserts seem like a real cheesy set up.

I've never seen any negative comments form the people who have used them.

I've used them on some .22LR rifles where 20 MOA bases are not available and they work well to put up to 40 MOA of angle on the scope.

I also used them on an M77 VT, where I didn't want to spend huge bucks on the limited rail options, and they stood up very well to recoil even with a large scope.

The rings are well made, and the system works quite well.  Although exactly how much angle you get with the inserts depends on the spacing between rings (less space = more angle).

The inserts prevent ring marks on the optical tube and they actually hold the scope very securely - more so than most single screw rings.

One advantage of the rings is if you happen to have mis aligned holes in the receiver. Rotating one of the insert sets slightly will compensate for the hole misalignment without stressing the scope, without the need for lapping.

I'm curious about the ring marks. Which rings were you using that left ring marks? I've never had any ring marks on my scopes, and I have never lapped the rings.