(BRP) RuneQuest, Stormbringer and BRP seem to user roughly the same weapon and armor rules, which is weird because Stormbringer had about 3k-5k years better technology. This might be fine as realistic combat isn't exactly the goal of either, but I'd really like to make the alloys behave properly, even if they're not found together.
Here are some ideas on how to think about and adjust equipment and armor to reflect that quality steel is found only in the last thousand to half thousand years or so, and that other types of alloy have very different properties.
Bronze is far more frangible than iron or steel. Though most bronze is harder than most iron, and the absolute limits of bronze hardness are twice or more that of iron, bronze is more likely to shatter and crumple under stress. Bronze armor works primarily by deflecting points. Unlike steel plate or mail, which is almost physically impossible to cut through, it is quite possible for a for man to drive a spear right through a bronze breastplate and the man inside. In fact, bronze's properties make it better as a sharp weapon than as armor, meaning a bronze age warrior faces a double inequality: absolutely inferior armor and relatively superior arms. In some cases bronze weapons perform better than iron weapons, add they're stiffer and can be sharpened more.
In order to be viably strong bronze armor is also quite a bit heavier than steel or iron, a bronze greave well weigh as much as three times that of a steel counterpart one reason we don't have Attic full plate. This is an important feature, because between the weight, lower relative benefit, increased absolute scarcity of bronze and absolute poverty of the pre-classical world you well see VERY FEW people in full 'hoplite' armor, and essentially no one in more. This means lots of bare flesh in every battle; flesh which is no match for even bronze edges.
My suggestion is that weight be tripled for armor, DR reduced by 1/3 and HP reduced by half. For weapons, double weight for small blades and bludgeoning weapons, and triple the weight for Longsword and full sized axes. For all weapons reduce damage slightly (perhaps -1) but reduce HP by half.
As I'm primarily talking the near prehistoric and very early historic periods, shields will be even crappier; basically wicker or leather of limited use except as a disposable arrow catcher. Even bronze and wood shields as were used much later will be penetrated by a solid blow, so we're taking 1/5th to 1/2 DR and HP, and that's being generous.
Copper is much like bronze, but inferior in all respects. Stone would also be common in maces, axes, arrowheads, knives and tools in general. Many people outside the small cores of civilization and urbanity will still be living in primitive hunter-gatherer and partial conditions. They will have essentially nothing but the simplest handicrafts, and metal will beer outside their income and possibly outside their experience altogether. Some will be in a more mixed state, especially if they have organized war bands or valuable resources to barter with. Stone weapons would be terrible, incredibly fragile, very heavy, virtually impossible to repair and very tedious to produce.
This was probably the biggest deficiency I found I the BRP family, there seems to be acknowledgement of this fundamental issue; and considering it's original setting was Bronze Age it's even more glaring an omission. I'd course we can't for everything in a book but I've seen only one fan book that even acknowledges that bronze and steel are different, and it's far too conservative/favorable to bronze IMO. GURPS handled this issue in their core rules, and I might use them as a rough guideline to audit/edit BRP and RuneQuest weapons/armor top confirm properly to the relatively junky and bulky ancient equipment.
The further back in time you go, before the renaissance anyway, the more of an edge weapons have on armor (somewhat balanced by greater effectiveness of static fortifications on the large scale), and bronze age warriors face the same sort of situation as modern soldiers; their armor is really only there to stop glancing blows and stray projectiles; against a direct hit it's of very limited utility and against a well aimed hit it's useless because overt half the body is effectively naked/unarmored.
Skills will also be far more limited, both in terms of what skills one can acquire, how intensively one can train it and how crude the available tools are. It's not likely people with high skill ratings, other than some communication skills, would really exist. Wealth and accumulated techniques make a huge difference, the more talented the warrior or scholar in the first place the greater the benefit from advances in technique and tools. It's simply not possible to train warriors to Immortal standards, much less chivalric or Ottoman standards, without this vast accumulation of knowledge, wealth, stuff and free time; it doesn't matter if you have a 19 intelligence or a 20 dexterity, you will not have the opportunity to exercise your talents to that limit.
Other than survival and communication skills the limits would be much lower, and even these benefit immensely. The smartest Babylonian priest may write a brilliant epic, but it's going to be limited and formulaic compared to Homer, much less Dante (or Robert Howard). These people are basically cavemen and 80 word vocabulary starving farmers with bricks and asphalt, and their greatest aren't as well off as poor people in Mexico in terms of access to accurate information, food and time to develop specialized skills.