Re: US Optics 30mm vs 34/35mm tubes
The 34mm and 35mm tube options for U.S. Optics scopes offer more elevation and windage adjustment than the 30mm tubes. The larger tube diameter gives the erector inside the scope(which houses the reticle and makes contact with the elevation and windage knobs) more room to move up/down and left/right. There is no difference in travel between the 34mm and 35mm tube, though. We offer 34mm for shooters who already own or prefer a certain 34mm mount. The amount of elevation/windage travel gained varies from model to model as scopes with lower magnification tend to have more travel than higher magnification scopes.
Contrary to what some people think, the larger tube diameters on U.S. Optics scopes do <span style="font-weight: bold">not</span> allow more light transmission. The lenses in a 34/35mm tube are the same size as in the 30mm tube, which is why the larger tubes get more travel.
Hope this helps.