The homebrew gunsmith saga continues, and it's just as bad as I thought it'd be! There's a little more leeway when you're crafting your own ammo, but messing with the wrong kind of powder is a dangerous way to go. Either those sinkers end up too small and you get blowby, or they're too large and you get a squib. The failure to cycle (called it, by the way...) is a symptom of significantly worse issues.
I mean, you say it in a good way to caution people, but I don't think what you say is always true. I have seen a video of people in Asia (Pakistan something) loading ammo at home, where they fill the powder to the top. People were concerned if that will explode the gun, but there are also people who say that there are different kind of powder. A weaker one and you can fill it to the top with no problem.
That is, if it's weaker than normal. If it's stronger, P+ load exists, but you would have to watch your chamber thickness. Actually, you also have to be careful even if it's normal ammo, but what I think is pipe gun exists, .45 acp pressure is also not as high as other type of ammo (although it's like double the 12 gauge pressure), so you can make it possible. I'm not sure his 1911 is 9 or 45 though.
If you read it again, when he fires, the gun has a suppressor on it, and I think you know that adding weight on a short recoil gun like Browning tilting barrel action significantly hinder the gun action.
His solution in changing recoil spring also can be okay. For the gun to work properly, I bet he did bring normal spring and other type of spring for the gun.
Nevertheless, if he can comes up with this, I think he has done at least sometime before, as getting gun and ammo is hard in this manga.
What I think about more is, where did he gets primer and ammo case? Of course you can makes some, but about the primer part, it's a hard and dangerous thing to make.
Also, people have asked about this in the last chapter, but how did he makes the barrel rifling? Some type of rifling like hexagon rifling exists, but it's not something you normally see to be something he would tries.
Edit: I shouldn't talk like this, since, you know, even 5.56 and 9mm can be rare sometime, but primer is something reloader would definitely want, as they're getting more expensive.