Is this a mistake in The Book of Mormon?

"weapons of peace" was clearly not a MISTAKE, but just a bad way of saying what he wanted to say. He wanted to say in as few words as possible that they had buried their weapons for the purposes of peace, then read it and saw how it made no sense, and clarified what he meant. Something I find interesting is the 'Los Lunas inscription' found in America, which contains the Ten Commandments in Hebrew. This may possibly be a hoax, but the WAY it is written is interesting. A portion of it was COMPLETELY MISSED OUT, and then added underneath, with an arrow pointing to where it belonged. Also there may POSSIBLY be a spelling mistake in it, but it may be acceptable spelling. Apparently when the Jews were copying the scriptures, if they found a tiny error in it, the whole thing was destroyed and started again. But the Nephites clearly did not follow this practice!

Perhaps he said exactly what he meant in the way that he intended to. To bury your weapons of peace is a commitment to die before you will take up arms against another. It comes from a total revulsion of, or distaste for, bloodshed of any kind, ever. To bury your weapons of war, for peace, is commendable if not a little less righteous in that you have given up on the principle of waging war in deference to and for the sake of peace. We see a lot of wars; maybe Alma is trying to teach us something about war.

It's all about intention. Weapons for peace are defensive weapons intended to prevent annihilation from a possible war being inflicted upon your nation by an aggressor nation; while weapons for war are offensive weapons intended to wage and prosecute a war against another nation.

One possibility is that it was indeed a typo.

And whoso receiveth this record, and shall not condemn it because of the imperfections which are in it, the same shall know of greater things than these. Behold, I am Moroni; and were it possible, I would make all things known unto you. ...

And if there be faults they be the faults of a man.

Mormon 8:12,17

If this is the case, the (amended) mistake was likely kept because the translation of the Book of Mormon was meant to be a literal translation of the original record, even to the point where the Book of Mormon often uses grammatically incorrect English.

The other possibility is that the author really wanted to say "weapons of peace" (poetic, no?), and then explained what he meant by that.

That kind of explanation happen frequently the Bible and Book of Mormon: use a word or phrase and then explain its interpretation.

This might not be the best example, but it is the one that come to mind:

And I went unto the prophetess; and she conceived, and bare a son. Then said the Lord to me, Call his name Maher-shalal-hash-baz.

For before the child shall have knowledge to cry, My father, and my mother, the riches of Damascus and the spoil of Samaria shall be taken away before the king of Assyria.

Isaiah 8:3-4

By itself, "Mahershalalhashbaz", meaning "Hurry to the spoils!" might be confusing (in fact, it sounds favorable for Israel). Fortunately, Isaiah then clarifies its meaning.

The book seems to support the stance that the author meant exactly what was said, and then clarified the meaning. For example, the text in question reads:

And thus we see that, when these Lamanites were brought to believe and to know the truth, they were firm, and would suffer even unto death rather than commit sin; and thus we see that they buried their weapons of peace, or they buried the weapons of war, for peace.

Alma 24:19 (emphasis added)

Later, in Alma 44, covenants were made related to weapons and peace. For example,

Even as this scalp has fallen to the earth, which is the scalp of your chief, so shall ye fall to the earth except ye will deliver up your weapons of war and depart with a covenant of peace.

Alma 44:14 (emphasis added)

Having retained their weapons while entering into a covenant of peace, it seems reasonable to name the weapons based on the covenant taken most recently, and not for their origional purpose. The is inline with the ceremonial nature of the burial of the weapons, which was being discussed during the verse in question.

It is also equally possible that the original statement "weapons of peace" was given by Alma in his record and then the text was clarified by Mormon while he was abridging the records he was in possession of. (cf. Who wrote this book)

The question seems to be about potential errors made in the recording & translation process.

First, there is an important point I think I should mention:

• We do not believe that imperfect record keeping of men, & potential errors made by translators, discounts the principles of the God's original message (i.e. The Bible is not discredited because Matthew & Luke weren't consistent on the genealogies of Joseph, Matthew 1:2-17 and Luke 3:23-38)

Recording Process

• The "Abridgers," or "Compilers," of the Book of Mormon (Mormon & his son Moroni) were working with records that were considered archaic even for their time. (Mormon : ~380 A.D., Alma ~80B.C.). LDS Scholars have demonstrated that their ways of writing & speaking were different (Keller 1988, Welch 1986). Exposure to minor errors like that is not surprising.
• The Book of Mormon text informs us they made records, some of which would become our current Book of Mormon on a metallic, durable, substance. Any errors made would be difficult to correct.
• The authors & compilers of the record themselves admit that they are not able to make a perfect record

Translation Process

• During the translation process with the original manuscript, there were indeed small grammatical errors that were later corrected. There were ~1,500 minor changes during the translation process & shortly after. Most having to do with phraseology (Skousen 2002). It is possible that not all the grammatical errors were corrected by the time it got to our current edition.
• There are two main schools of thought within LDS scholars (with shades of grey in-between), as far as I know. The first is that the current Record we have is a literal, word-for-word translation of the original metallic records, the other camp is that our current Record is a "functional" not word for word translation, translated as accurately as possible from Mormon's times, to mid-1800's English (in a Scriptural style). If it's the first extreme, than all errors would derive from the Recorders / Abridgers, if the latter (which there is more evidence for), than there could be minor errors deriving from both.

I hope this was at least a little helpful as to why you may see errors in phraseology &/or grammar you may find in The Book of Mormon.

Please also see : Changes to the Book of Mormon