Disclaimer: I am not a lawyer, just a layperson
Why not just call the Washington State’s Attorney General’s Office and ask for a clarification? That would be a better source for accurate information than a forum like this one.
Normally State's Attorney Generals do not give legal advice to private individuals.
CA state Attorney General's website is VERY CLEAR about firearm and magazine laws -
https://oag.ca.gov/firearms
And answer to concealed carry permit reciprocity is a CLEAR "No" -
https://oag.ca.gov/firearms/pubfaqs#12
I live in another state and have a permit to carry a concealed handgun that was issued in my home state. Does my permit allow me to carry a concealed handgun while in California?
No
Same seems to be the case for WA and these are straight from WA state's Attorney General's website -
https://www.atg.wa.gov/firearms
High-Capacity Magazine Restrictions - On July 1, 2022, a law prohibiting the sale, attempted sale, manufacture and distribution of high-capacity magazines that hold more than 10 rounds went into effect in Washington. The law does not prohibit the possession of high-capacity magazines.
I live in Idaho and have an enhanced CCW license, which is recognized by the state of Washington. With the new ban on importing "high capacity" magazines, I presume that it's illegal for me to carry a handgun with a 12 round mag, even though I am not a resident, when I travel into the state? I assume that I have to have 10 round magazines?
Best option may be to contact the local enforcement agencies of region you plan on visiting and ask them directly. I am quite certain local law enforcement agencies will give you CLEAR answers to what they WILL ENFORCE, particularly for out-of-state visitors.
From Attorney General's "Firearms FAQ" page, here are some information that may answer your questions/concerns regarding conceal carrying in WA with larger than 10 round capacity magazines as out-of-state visitor -
https://www.atg.wa.gov/ConcealedWeapons/FAQ.aspx
I will be visiting Washington and want to continue carrying a concealed pistol. What does Washington law require I do?
Except in your home or fixed place of business, and subject to the exceptions listed in
RCW 9.41.060, under
RCW 9.41.050 you cannot carry a pistol concealed on your person in Washington without a license or permit to carry a concealed pistol. Additional information about carrying a pistol in Washington can be found in
RCW 9.41.050. Please visit our concealed pistol license reciprocity page for detailed information about whether Washington will recognize a concealed pistol license or permit issued to you by another state.
And "concealed pistol license reciprocity" page says only "Enhanced" Idaho CCW permit is recognized but you must carry "in accordance" with WA law.
Concealed Pistol License Reciprocity -
https://www.atg.wa.gov/concealed-pistol-license-reciprocity
With certain qualifications as indicated, the following table lists the states ... from which a concealed pistol license or permit issued by those states will be recognized in Washington so long as the pistol is carried in accordance with Washington law
Idaho - Enhanced Permit only
What does Washington’s law related to high-capacity magazines prohibit?
So if you have "Enhanced Permit" from Idaho, it is recognized in the state of Washington but you must carry in accordance to WA law. WA law prohibits the sale, attempted sale, [import], manufacture and distribution of high-capacity magazines.
So the question comes down to whether 12 round magazine you own is legal to be brought into WA under your conceal carry reciprocity from Idaho and the answer may lie with the words "...
so long as the pistol is carried in accordance with Washington law ...
The law prohibits the sale, attempted sale, [import], manufacture and distribution of magazines with a capacity of more than 10 rounds" and
"Washington’s law does not ban possession of high-capacity magazines."
Does conceal carrying under reciprocity 12 round magazine the act of
import and/or
distribution of magazines? If it was me, I would want to be sure.
Section (38) speaks to large capacity magazines that were in WA before law went into effect in July 2022 and there is no provision for bringing in larger than 10 round capacity magazine into the state under conceal carry reciprocity.