After a little research I found that OSHA rules are exactly 1/2 of actual needed concern; as in they think 25 is threshold while studies show it is 50.
I'm sorry but this statement is meaningless at best, and potentially harmful to those trying to understand and manage their lead exposure. First, measurements have no meaning without the units that those measurements are given in, and second, there has to be a clear understanding of what's being measured. In this case, there's the danger of confusing two very different types of measurements.
Up to now, most of the discussion in this thread has focused on serum (blood) lead concentrations, which are measured in micrograms per deciliter (mcg/dl). There are some differences of professional opinion among toxicologists and medical professionals regarding what concentration can be considered "safe" - not a word that any of them would use, BTW - for an adult in the US, but opinion is shifting to lower numbers, with an upper limit of 10 mcg/dl representing the current consensus. It is lower for children, who are more susceptible to harm from lead exposure.
A totally different measurement, and entirely different concept, is represented by the OSHA numbers. OSHA does not regulate blood levels, it regulates occupational exposures, i.e., the amount of lead that's allowable in the environment to which workers are exposed. That measurement is expressed in micrograms per cubic meter of air (mcg/m**3) and is called a PEL, which stands for Permissable Exposure Limit. The 50 mcg/m**3 number represents the maximum allowable lead concentration that can be in the air that workers are breathing. Now, there are some other things inherent in there that we don't necessarily need to get into, such as how the measurements are taken and averaged and how they can be adjusted if your workers aren't full time, etc., but that aside the 50 mcg/m**3 is the point at which the government says an employer has to fix the environment in his "shop."
There is also an OSHA Action Level for lead of 30 mcg/m**3 at which point an employer has to institute a monitoring program for the employees and take other steps, but not necessarily reduce the amount of lead in the air, that's only required for the 50 mcg/dl concentration. To the best of my knowledge (I'm not an Industrial Hygienist, but I do work in human health risk assessment), there is no OSHA-mandated action associated with an ambient concentration of 25 mcg/dl, but I don't have total familiarity with the regulations.
The important thing is that nobody reading this should get confused and think that because OSHA has "numbers" of 50 and 30 (or 25, or anything else) that they can have serum lead concentrations approaching those numbers and assume that they don't have a problem. They're two entirely different things, and nobody who has any knowledge of the issue would argue that a serum lead concentration of 25 mcg/dl or higher is OK.
If you shoot a lot indoors, think about getting tested for serum lead at your next physical. If you've got elevated (as in greater than 10 mcg/dl) blood lead, think about doing something differently to get it down. Or, if you like, just ignore it - it's your body and your life and if you want to smoke, get obese, not wear a seat belt, or whatever increases your chance of dying young it's your business and neither I nor the government have any right to tell you you can't. But if you're going to make that decision, at least have the facts to base it on.