I was just curious… I was thinking about trying MagGuts to add one more round to my CM9 magazines (as well as to add one round to my slightly larger spares). I was just wondering if modifications like this had any negative inferences from a legal perspective.
In case it is important, the MagGuts kits do not add any length to the stock magazine (as in it does not aid in the grip of the firearm).
Depends on if you are trying to get around 10 rounds or less laws. If you have an issue and they take your weapon and mags from you. Be sure they will check the capacity of those mags.
It’s my understanding that in my state CCW permit holders are not limited to 10 round magazines for carry. However, in this case I’m talking about increasing from 6-7 rounds, and from 7-8 rounds.
Any modifications can be touted by a prosecutor or plaintiff’s attorney in a negative fashion. But, as long as the modification does not break a law, they are ok from a legal standpoint.
I always love @MikeBKY’s responses! 
Can you articulate why you are adding one more round to your carry? That is a good starter question to get you thinking in the legal manner.
For your example, we know that statistically speaking self-defense shooting situations average 3-5 rounds of ammunition. What happens if there’s a misfire or a jam? Tap and rack and get back to defending yourself. That extra round could save your life.
EDITED: I had the wrong numbers - it’s 3-5 rounds, not 5-7. Sorry for any confusion!
My EDC is a Glock 26. It came with (3) 10 round magazines. When I picked it up, I added +2 extensions to each factory mag. I also have a a KelTek sub2K that can shoot 15+ round Glock magazines. It came with a Magul 17 round mag. I made a trip to CA in May of 2017 to drive home with my son from Twentynine Palms via San Diego and Route 66 to Louisville. I took my +2s off of the factory mags and brought them back down to 10 rounds for the trip. I thought about bringing a 380 with 6 round mags but 10 or more is always a better starting point. After that trip, The 10 round mags became range magazines and were replaced with (3) 12 round promags. In addition I have accumulated a couple 15 round Glock factory mags and more than a few 17 round Promags and maybe a 33 round mag or 2.
I don’t plan on being in a gun fight but I prepare as if I will. What I know is that an active aggressor (shooter or other other method of attack) is out to kill me or those near me, I want to be prepared to respond accordingly. If the aggressor is using a truck, or if there are more than one, more than just a couple magazines may be required.
Thank you, all, for your responses. Please understand that my lack of response is because I am really thinking about your suggestions and how they might be related to me and my current carry system.
Dawn (or whoever might have access to the statistic), would you be so kind as to link the reference to your 5-7 round statistic?
@MikeBKY dontcha just love the CA sun? But not the political antics. Grew up there last century and left when I went into the service.
I have a FMK made in CA but for export to other states has 2 14 round mags. Have a P89 that came with 2 10 round mags that I never used, switched for 15 round mags as I worked security for HUD, and then County here in TX. Still have those 2. I bought mine when the federal ban was in effect. I can purchase 10 round mags for the FMK.
@Scotty, Ii put the wrong numbers in initially, sorry about that. It’s 3-5 rounds not 5-7 as I initially stated. We teach 3-5 shots in our Defensive Shooting Fundamentals class.
It is based on a number of different studies. Here’s a blog that goes into it a bit:
https://www.usconcealedcarry.com/blog/the-statistically-perfect-gunfight/
Although the average is 3-5, you shoot until the threat stops. That could mean one shot or 15.
I still remember two very high profile police shooting cases in Louisville. One in Sept. 2000, 6 Louisville police officers were involved in the shooting death of Rodney Abernathy. Police were called to an incident where a man was beating himself with a car jack. He charged the officers several times which resulted in all the officers shooting him each time. The last time he rushed the police, he was shot in the head. Police had tried to wrestle him but could not get hold because he was soaked in blood even before they arrived. If my memory is correct, he was shot more than 40 times and an autopsy showed that even in combination, the only fatal wound was the head shot.
The other happened in 1995 in Jeffersontown, a small city in Jefferson County. FBI chased a man accused of shooting an Ohio police officer 70 miles into J-Town. A gunfight ensued and the suspect Roger Fein was killed y police. Dozens of rounds were fire and many hit Fein. Is was later determined that he was high on PCP which kept him in the fight. Soon after, most police agencies in Louisville, including Louisville Police Department, Jefferson County PD and Jefferson County SO and J-Town PD, switched from 9 mm to .40 cal as service weapons.
While 3-5 shots is the average, average depends on a lot of factors.