Actually I had read an aticle or this question in a Magazine a few years back. I would imagine that in todays political and legal climate any modification may be viewed detrimentally in court. The article had to do with handloading, and from the expert (If I remember properly is was Massad Ayoob) he said use factory loads only for self defense. In court the claim could be that “normal factory rounds were not deadly enough so the defendant needed to make his own deadlier rounds.” The same could be made about the pistol, rifle or shotgun. One might think that Cosmetic mods could be viewed poorly as well, for example if a “no knock warrant” was issued and police showed up at your residence by accident and your Pistol said “Molon Labe” it could be viewed that you had anti gov’t sentiments. A homemade firearm again may be stigmatised by an over opportuinistic DA as “not deadly enough” from he factory. Maybe I am off base, but I would say factory firearms with normal mods like a red dot sight, tritium nightsights or mild changes to a factory AR that the average shooter would do would be be the best way to go. Keep the really cool stuff in your safe or at the range.
@Christopher_S1 Massad Ayoob wrote a series of articles on TTAG. Here is the one your probably talking about:
About half-way through the article he talks about modified firearms. Interesting read.
Enjoyable read. 5 stars would read again. 
Recent video from Massad Ayoob on ASP Extra, talking specifically about modified triggers. It appears he is speaking about pistol triggers (looks at Geisselle SSA 2-stage 4.5lb trigger in safe)
That is a very good video. I am a huge fan of Ayoob and have all of his books and watched a lot of his information. This video is regarding your carry handgun, and the information is solid gold. But it also focuses my question a bit more. Again, for the sake of argument, if I were to use one of my “custom” AR’s or say a sporting shotgun I modified for home defense, what is my liability? Take a look at the AR for instance. How many aftermarket triggers are there out there? If I look at the trigger on my High Power match rifle, it is a GI standard two stage style that is “modified” from the original design to be adjustable to allow me to adjust it to the minimum allowed by the rules of competition. Compare that with my blackout that has a POF-USA single stage trigger. By this logic, I would contact Colt, since they were the original producer (yes, I know the history of the AR, and that they did not design it and all that) and would set the standard spec. Or the comment on keeping with the appearances theme such as the attacks against the AR/MSR but not say the Ruger mini 14 due to appearances, what can be argued when you take that used Remington 870 with a 28" barrel and wood furniture, put “tactical” magpul furniture on it, and a 18" barrel with extended magazine?
I agree 100%. Maybe @MikeBKY can offer a little more general guidance?
It seems like for handguns 4lb seems to be the lower limit. I think Glocks are around 5-6lbs factory depending on the model (as a factory example).
But what about for an AR? My 1st AR has a DD stock single stage trigger which I think is around 7-8lbs. I put a Geisselle SSA two-stage 4.5lb trigger in my HD rifle, and i loved it so much it will find its way to all my ARs (the ones that I didnt lose in a boating accident). Is that a bad idea? I think 4.5lbs is good and the two-stage gives you a little buffer (if you want it). As @Brian139 points out there is an untold number of aftermarket triggers and (based on my limited experience researching) most of the nicer ones are 5-6lbs for single-stage and 3-5lbs for two-stage.
I agree that the video says, especially the part about zombie killers and the like. I would limit modifications on your EDC and would recommend that modifications be done by a certified gunsmith.
For any weapon, you the key is keeping it safe. both too light and too heavy trigger pulls can be the cause of negligent discharges. But not everyone can handle a 12-15 pound pull on a DA.
If I’m fighting for my life I want every advantage. Overthinking and hesitation may mean you don’t need to worry about being taken to court. How about a fancy holster and gun belt that allows you to draw quicker? Also, I’ll bet the prosecution will bring up the fact I have USCCA insurance.
Is there some guidelines about what constitutes “too light” or “too heavy”? Or is it just one of those things that fall into the “it depends” category?
That was one of the good points made in the video. The “too light” and “too heavy” really depend and the real answer is to contact the manufacturer and have them send you their “spec” for trigger weight and to stay within that guideline.
According to Mr. Ayoob, anything less than 4 pounds is problematic.
I’ve never actually built my own firearm, but I did stay in a Holiday Inn Express last night.
Why did all musicians (in our time) always stay at Holiday Inns? We always did unless we were some place special.
@MikeBKY, how about my barrel change from .40 S&W to .357 Sig? Drop in change.
@Harvey
Colt 1911s I have owned have had very light triggers. Many clones also have triggers under that limit. Many stock revolver triggers are very light in SA operation.
Also, how about the trigger travel adjustment on many 1911s? It’s a simple no take down adjustment that requires no special skills. Just adding to the question pile.
We’re going to need a bigger boat lol.
@Bugleboy, you are right, some firearms have lighter triggers. For instance, my Springfield 1911’s are probably safe, but my Dan Wessons arent by that standard. That is why you get and archive an email from the manufacturer with what they consider their spec. That way you have that letter to state that your firearm is “in spec” if it ever becomes an issue.
I have seen those drop in barrels, mostly from .40 to 9mm and .45 to .22 so practice is cheaper.
I don’t know how a jury would feel about that.
From that source, he states: “Generally, as a rule of thumb, anything that will make the gun shoot better for the shooter under extreme stress and poor light is absolutely defensible. And the reason is, if it makes you more likely to hit under those adverse conditions, it concomitantly reduces the danger of a wild shot that might hit a bystander.”
“If you read the fine print, you’ll find all those laws are worded so they do not cover negligence . So all the other side has to come up with is say “Yeah, well, but he killed him by accident, and that’s not what this law is about. Our theory is, he accidentally shot him.” The light trigger lends itself to that. And you’ve basically just given them an argument they can use against you.”
As he has been an expert witness in many court cases, I will not offer my uninformed opinion on this.
@Dave17 No argument from me. Been following Massad Ayoob for years. I carry a bone stock Sig-Sauer Scorpion Fastback 1911 with factory .45 ammo for EDC. My primary back up is a Gen5 Glock 17 with Trijicon sights and a Zev barrel. Pretty innocuous stuff. I assembled everyone of my AR platforms, mostly AP, myself.