El Salvador 10 centavos KM#130a and 150a

What is the difference between these two KM types?

Of course, they were added here but seemingly they are the same types? Unless composition is slightly different in percentages, then it's another story. I did get both and realized the weight and every single detail are the same. Pity because both are really perfect.  Please note that the color is the same, too. On these photos here one might seem more yellow but it isn't.

Does anyone by any chance can find correct compositions so we solve this somehow

Same applies to 149b and 134a. Weight of 4g is incorrect for 1977 5 centavos, as discussed here: 
https://en.numista.com/forum/topic125508.html
(I will join that thread with my weights as well, especially if I find deviations)

Edit: Basically both of the new KM numbers were introduces when the denomination was modified. But the 1977 pieces have the old one and I guess the only reason they were assigned a new subletter was chronological.

For another cataloging take on the types, look at Schön.

1982: KM# 130a; Schön# 22a

1977: KM# 150a; Schön# 22b.1

1985: KM# 130a; Schon# 22b.2

(That's from my notes. I won't have access to my Schön book for the next week to find out the difference between 22a and 22b. I expect a metal change.)

natbaj

What is the difference between these two KM types?

Of course, they were added here but seemingly they are the same types? Unless composition is slightly different in percentages, then it's another story.
Does anyone by any chance can find correct compositions so we solve this somehow?

According to Schön there is indeed a slight difference in composition.

KM# 130a (Schön# 22a) is Copper (70 %) - Nickel (12 %) - Zink (18 %)

KM# 150a (Schön# 22b) is Copper (65 %) - Nickel (12 %) - Zink (23 %)

The same for the 5 Centavos KM# 134a and KM# 149b.

So now I'm interested in 1985, on SCWC as well as here it's listed with 1952, while Schon lists 1985 and 1977 as the same coins?

Several mails have been sent, including Mexico Mint and VDM. If we get any information, it's good. Unfortunately their legal archives do not specify and coin related laws or decrees. As rsirian said
 

rsirian1

 

We'd be making up an alloy composition without knowing if it was true.  Case in point: N#14260 contains only 12% nickel but is still called nickel silver by the mint.  We'd just be guessing how the remainder 88% was split between copper and zinc.

 

It would be a complete disservice to change a misunderstood composition to wrong composition.

I sincerely believe though Mr. Schön did this research before and got this correctly so we have two composition.

In the meantime, in local El Salvadorean catalog 10 centavos 1985 is listed as being 6g instead of 7g.
(No percentages of Cu-Ni-Zn specified there)

I have 1952 and 1977 only (luckily didn't swap for years so it's still in doubles). They are both 7g. Can someone weigh their 1985 please?

6.963 grams for my UNC 1985.

Thanks. Just as the 1977 ones they vary around 7-7.1 grams. 

Exactly copper, zinc and nickel composition needs to be determined yet. Only Schon lists them, presumably from an official sources. So its the catalog to be trusted. American mintages (130a) are clearly the most confusing as official listing says 12% nickel and nothing for the rest.

Essor Prof

natbaj

What is the difference between these two KM types?

Of course, they were added here but seemingly they are the same types? Unless composition is slightly different in percentages, then it's another story.
Does anyone by any chance can find correct compositions so we solve this somehow?

According to Schön there is indeed a slight difference in composition.

KM# 130a (Schön# 22a) is Copper (70 %) - Nickel (12 %) - Zink (18 %)

KM# 150a (Schön# 22b) is Copper (65 %) - Nickel (12 %) - Zink (23 %)

 

The same for the 5 Centavos KM# 134a and KM# 149b.

We have one confirmed by XRF thanks to @neotilva 

1985 - Indeed NickelSilver 12 :) 12% nickel, 67% copper, 21% Zinc. Closer to 1977 values of Schoen.

I think it's clear we can already assume 130a and 150a the same types? The difference if it even exists is so tiny and variable it makes no sense in numismatic context. In metal engineering maybe, but here?

And the same applies for 5 cents.

QED