I believe 16 lbs. is standard.
14 or 15 is ok, if your loads are not too hot.
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This from one of the 1911 forums.
Recoil Spring
The correct recoil spring poundage is important to the reliability of your pistol. Too light a spring will batter the pistol and weaken the chambering process; too heavy a spring will result in failures to extract and eject, or in "stovepipe" stoppages. A too-heavy spring is also rough on the extractor. A too-quick closing of the slide will force the extractor over the rim of the cartridge, rather than allowing the cartridge to move up under the extractor in a controlled feed. It also has the effect of battering the slide stop unduly.
The stock recoil spring in a standard 1911 is rated at 16 pounds. Moving up one notch to 18 ½ pounds will be about right for most pistols shooting hardball and other full-power defense ammo. Anything heavier is too much. Be sure to test the new recoil spring by shooting the pistol one-handed and loosely. It should function positively. If not, go back to the 16-pound spring.
An extra-power recoil spring also aids in preventing the slide from opening too soon. You may have seen "skid marks" on primers, caused by the firing pin still being extended against the primer when the slide unlocks. Eventually, this could break the firing pin. The use of a heavier recoil spring often cures this problem.
Commander-size pistols do well with a 20-pound spring for full-power ammo, and Officer’s-size pistols utilize a 24-pound spring well for the same purpose. As long as it’s not overdone, a stiffer recoil spring will aid in positive chambering and lengthen the life of the pistol. If the slide becomes difficult to retract using a stiffer spring, consider using one of the progressive-rate springs which are easier to get started at the start of the slide’s recoil stroke.
The jury is out as far as the so-called "shock buffers" are concerned. These little polymer doughnuts slip over the recoil spring guide and cushion the shock of the slide banging against the end of the recoil spring guide. To this extent they are good, but they must be replaced regularly as they get chewed up. Having one disintegrate inside a defense pistol in a pucker situation is not something I would want to have happen, and for that reason I don’t use them.
Likewise, there is controversy over the use of a full-length recoil spring guide in a defense pistol. Theoretically, the full-length guide keeps the recoil spring from kinking in its channel, and assures uniformity in the recoil stroke. It has the disadvantage of preventing a "press check" of the pistol, and of preventing one-handed racking of the slide by pressing the recoil spring plug against a shelf, shoe or other solid object. It is doubtful if the full-length guide increases accuracy, but you may gain some life from the recoil spring. Recoil springs should be replaced about every 2-3 thousand rounds anyway, as they gradually lose their strength over time and usage.
