Simple, yes. But that doesn't necessarily mean it's right. Your final sentence is just a false appeal to authority, no better than the Southpark cliche lampooning exactly that tactic - "VOTE PROP 10 OR YOU HATE CHILDREN!"
I will ignore it. It's a rather unpleasant thing for you (or anyone) to do.
You're making at least two different definitions and an extremely unclear definition in the opening sentence, which is an extremely bad basis for law.
Is murder any crime involving a weapon (your first definition) or an attempt to kill (your second definition)? They're very different things. For example, many people have one or more knives with a blade more than 7.62cm long and/or with a fixed blade in their kitchen. Taking that knife out of their home is a crime involving a weapon. Under your first definition, that would make them guilty of attempted murder solely for carrying it. If they're taking it to a friend's house to carve a joint of roast beef, your first definition makes them guilty of attempted murder and they must serve at least 35 years in jail. Another example - it's legal to own a gun with the appropriate firearm licence, but there are numerous restrictions. Person A has a licence for a .22 rifle they use at a registered sports shooting club for target shooting. They have 2 safes in their house. Both safes conform to regulations. Both safes are in places in their home that conform to regulations. They scrupulously keep only the unloaded rifle in one safe and only the ammunition in the other safe. Their licence allows them to own 100 bullets. They buy 100 bullets. Legally, from a licenced source. But they had forgotten that they had 20 bullets in their ammunution safe at home. So they now own 120 bullets, which is more than their licence allows. Under your first definition, they are now guilty of attempted murder and they must serve at least 35 years in jail.
And yes, you did explicitly specify that attempted murder would have a minimum 35 year sentence under your regime. Note that your statement "For good behaviour you get out in 35 years" comes after your sentencing for attempted murder and thus applies to it. "66% of life" is meaningless because it's impossible to know in advance how long a person would live. Under your regime, time travel would be required in order to release people you convicted of attempted murder at what you regard as being the right time, if they were to live long enough for 66% of their remaining life to be more than 35 years.
Your second definition is better as it at least requires intent, but all you're doing is removing the manslaughter categories (which exist for good reasons) and the ability of a judge to set a minimum amount of time before parole can be even considered (which exists for good reasons).
Regardless of which of your two completely different definitions of murder you actually meant, there's the issue of the weapon used. You specified "a weapon such as a knife or gun". So it wouldn't apply to a weapon not like a knife or a gun. Which leads to another problem - how alike does the weapon have to be. A sword? Is that enough like a knife? How about a spear? That's not really like a knife at all. Or a club? That's not at all like a knife or gun.
On to your allowed defence against a murder conviction, in which the defendent is only allowed to use a weapon which happened to be nearby. How near is near? A metre? Two metres? You need to specify things if you're writing laws.
You've also explicitly forbidden defence of others, since you've explicitly stated that only a person being attacked would be allowed to pick up a nearby weapon or disarm the attacker. Say, for example, you were being attacked by someone with a knife and I was nearby. Under your regime, I wouldn't be allowed to intervene because I'm not being attacked. I'm not in fear of my life. I could run away while they killed you. Under your regime, that would be the best course of action.
Here's a real example from UK law:
Person A was known to be a very dangerous person. B and C were in a house when A turned up with the intention of killing them both, an intention which A repeatedly made extremely clear. B and C knew A to be very dangerous and had every reason to believe that A would indeed kill them if A got in, as A was repeatedly and explicitly stating they were going to do. B shot A through a window as A was in the process of breaking into the house to kill B and C. The gun B used was licenced. This, of course, meant that B had to open two seperate safes, load the weapon and then go to within line of sight of the window to fire. It was not a weapon they picked up while being attacked.
Under your regime, B is guilty of murder and must spend at least 35 years in jail. Under UK law, B was tried and acquitted on the grounds of reasonable force in defence. It went to trial because the authorities deemed it to be a grey area without legal precedent and therefore needing a trial by jury.
