It is commonly stated that King Saul reigned in ancient Israel for forty Years. However the 20 years the Holy Ark spent at Kirjath-Jearim shows Saul's kingship only lasted 10 to 12 years.

1. Sauls Time as King dated by the years of Holy Ark at Kirjath-Jearim OP Armstrong Dec/2016
Years of Eli, Samuel, Saul, Eshbaal Saul Son, David & Holy Ark
Tag => A B C D E F
Event Ark David I'baal Saul Sam Eli
Ark Move to Jerusalem 20 38 48 68 83 118
Esh-baal /Ishbosheth/ die 14 32 42 62 77 112
Saul Die 12 30 40 60 75 110
Samuel Die 10 28 38 58 73 108
David kill Goliath w/Kg Saul 2 20 30 50 65 100
Eli Die & Ark to Kirjath-jearim 0 18 28 48 63 98
Esh-baal born, Saul's son -28 -10 0 20 35 70
Eli retired, sons next Priests -48 -30 -20 0 15 50
Samuel weaned &to Tabernacle -58 -40 -30 -10 5 40
Samuel Conception -64 -46 -36 -16 -1 34
Eli appointed as High Priest -68 -50 -40 -20 -5 30
Years. to Ark of God A 18+A 28+A 48+A 63+A 98+A
Years to primary variable 18+A 10+B 20+C F-35 98+A
This table shows the years of
Eli, Samuel, Saul, Esh-baal
(Saul Son), David, & Moses-
Ark. The time runs from Eli
appointment as Tabernacle priest until the
Ark was moved to Jerusalem in Y38 of
David. David’s Y30 was 435.9Y after Exodus
& 1052.6Y before Jesus Baptism by John.
Only the year of a key event is given in this
table. Also, Samuel-1&2 does not specify
time of some events. The ‘sequence-tie-
object’ is the 20 years Moses Ark stayed at
Kirjath-Jearim in the house of Abinadab.
There were 20 years from its return, after
capture in Eli 98 year, until moved by King
David, in his 38 year, to city Jerusalem.
If A denotes the Ark years, then 18+A will be
the years of David, B.
Esh-baal, (aka: Eshbaal, Ishbosheth, Ishui, denoted by C) was
Saul’s last living son. He was 40 years old when David
became King at age 30. So C=10+B = 28+A.
Next an age of Saul, 20Y, is assumed for the birth year of
Eshbaal. This could also have been 25 or 30. This only affects
the age of Saul at various events. Within reason, these ages
are unspecified by scripture. So Saul’s age, D=20+C=48+A.
The age of Eli, called F, is specified as 98. This was when the
Ark was captured. Seven months later, the Ark is returned to
the house of Abinadab, in Eli’s 98 year. So F=98+A. No
attempt is made to work in partial years.
Lastly, find age of Samuel in terms of Eli years. Here guidance
is given by two facts. A priest’s allowed years of service is set
by Moses Law to be not less than 30 and not more than 50.
Samuel mother Hannah came to the Tabernacle in Eli time as
she prayed to God for a son. She vowed he would be given in
service to God. Next see that when the child was weaned
she presented Samuel to Eli at the Tabernacle. The
conception year of Samuel is taken to be Eli 34Y. Five years
of age in Hebrew tradition is the age of weaning by which
time Eli was 40. Variable E, Samuel’s age, is F-35 = 98+A-35
or 63+A.
Considerations on the Results
The years of any event for any listed single age can be found
by adjusting the single variable, A, ark years from capture
return, until the specified event age is achieved.
Saul died when Esh-baal was 40; this is at age 60 or ark year
12. Samuel died 2 years prior at age 73. As Sam entered
priestly service at age 30, then yes 43 years of service was a
goodly term of service and he was ‘old and full of years. Saul
became king about 2 years after Eli died. This was in Samuel
63 year and Saul 50th
.
This same year, a young David is 20 and kills Goliath. By
Moses law youths could enter military service from 20Y
upwards. So David’s service conforms to Moses
requirement, as expected. Neither the age of Saul nor
Samuel is given when Saul is appointed king. One or 2Y
after Eli death is reasonable. Thus Sam’s age at that time is
64 or 65 years. As said Samuel, he was old. Anything over
50 in the priest system would be ‘old’. By this table, Saul’s
time, as king, was only 11-9 years. During that time he
fought 6 or 7 wars. During most that time, David lived on
the land as a fugitive. Thus the translation of Acts 13:21-22
must be either that the time of Saul and Samuel were
about 40 years or that the 40 refers to the years of David
reign as King of Israel.
v21: ...the Saul son Kis out of tribe Benjamin. v22: Years
forty, and deposing him; He lifted to them the David into
king to whom also he witnesses... (From Greek interlinear
and Strong's Greek words & my punctuation and verse#)
Some incorrectly argue the ark was moved during Saul’s
days. A close reading of 1Sam14:3,18-19 shows Saul asked
moving the ark but midsentence withdrew the order.
Nowhere in the days of Saul is it stated the ark moved. This
concur 1Chr13:3 ... Bring again the ark… for we inquired
not at it in the days of Saul. Also it specified where the ark
stayed since return from capture. That was the very same
place David fetched Moses Ark unto Jerusalem.
Please download the PDF, if interested in reading more on
this topic. Within the PDF are hyperlinks to over 50 bible
reference verses and others writings. Inclusion of those
references would have made the length of this writing to
exceed 7 pages.