Antoniniano¹, zecca di Roma², 249-51 d. C., RIC IV/III  29(c), indice di rarità "c".
D. IMP C M Q TRAIANVS DECIVS AVG³. Traiano Decio, busto radiato, drappeggiato, corazzato a destra.
R. VICTORIA AVG⁴. La Vittoria corre a sinistra sorreggendo una corona e una palma.

A titolo di confronto e per le indicazioni di valore riporto i link relativi a monete di tipologia simile reperiti nel WEB:

1. http://www.wildwinds.com/coins/sear/s2702.html Trajan Decius, 249-251, AR Antoninianus (20-21mm), aEF. RSC 113a, RIC 29(c). Obv. IMP C M Q TRAIANVS DECIVS AVG, radiate, draped and cuirassed bust right. Rev. VICTORIA AVG, Victoria running left. The portrait and reverse image show very good detail, including what could be balding on the harilin, or perhaps some of the hair was simply not struck. Legends are full. After successfully fulfilling an appointment from Philip I to restore order on the Danube frontier, Trajan Decius was declared emperor by his troops, and he gained the throne by defeating Philip in battle. Trajan Decius was later killed fighting against the Goths. Item price US $36.00 Ends May-24-02 
2. http://www.wildwinds.com/coins/sear/s2702.1.jpg Lot: 33   Trajan Decius. 249-251 AD. Silver Antoninianus, 3.2 grams. (Sear2702) Grade:VFRx: VICTORIA AVGG, Victory advancing leftholding wreath and palm. [L448515]Next Bid: $22.00
3. http://www.wildwinds.com/coins/sear/s2702.2.jpg TRAJAN DECIUS (Caius Messius Quintus Decius) Emperor, AD 249-251 Silver Antoninianus Obverse: IMP.C.M.Q.TRAIANVS DECIVS AVG, His radiated and cuirassed bust right. Reverse: VICTORIA AVG, Victory advancing left holding wreath and palm-branch. Currently $47.12 Ends 11/11/99
4. http://www.wildwinds.com/coins/sear/s2702.3.jpg Date: A.D. 249-251  Reference: Sear 2702, RIC 29c, RSC 112a, Cohen 112  Obverse: IMP C M Q TRAIANVS DECIVS AVG, draped radiate bust right   Reverse: VICTORIA AVG, Victoria running left, holding wreath and  palm  Condition: aXF, slightly weak obverse strike but unusually sharp  reverse Currently $24.00 Started 12/14/99
5. http://www.wildwinds.com/coins/sear/s2702.4.jpg This is a nice grade, good silver antoninianus of Trajan Decius (249-251). It is attributed as Sear 2702 (C113var, RIC29c). The obverse shows his radiate bust right with the legend: IMP C M Q TRAIANUS DECIUS AUG The reverse depicts Victory advancing left with the legend: VICTORIA AUG Currently $18.50 Started 12/20/99
6. http://www.wildwinds.com/coins/sear/s2702.5.jpg Lot: 51  Rome. Ancient. Trajan Decius. Antoninianus. (SR 2702) Silver. Grade:XF 249-251AD, Rad., dr. and cuir. bust r./Rev. Victory advancing l., holding wreath and palm, Est. 125 [L660731] Next Bid: $31.00
7. http://www.wildwinds.com/coins/sear/s2702.6.jpg Trajan Decius silver antoninianus, 249-251 AD. Reverse features Victory advancing left. S#22702. 4.31g. Horn silver in dark areas and slightly porous. Currently $12.71 Started Mar-05-01 
8. http://www.wildwinds.com/coins/sear/s2702-o.7.jpg
http://www.wildwinds.com/coins/sear/s2702-r.7.jpg ORC2333 T. Decius ant, lustrous EF  Trajan Decius, AR antoninianus, (4.43g) IMP C M Q TRAIANVS DECIVS AVG Radiate, draped and cuirassed bust right. / VICT OR IA AVG Victory advancing left, bearing wreath and palm. Lustrous EF, nice metal. Currently First $1.00  $24.60 Started Oct-19-01
9. http://www.wildwinds.com/coins/sear/s2702.8.jpg TRAJAN DECIUS, 249-251 AD. AR Antoninianus. FDC OBV: Radiate bust; REV: Victory advancing. RARE! RSC 113. High relief. Artistic portrait. All detailes, excellent silver. Trajan Decius -- General under Philip, then usurper, he was quite unequal to the task of stopping Gothic invasions and died in battle against them. $26.01 (reserve Currently First bid $20.00 not yet met) Started 07/09/99
10. http://www.wildwinds.com/coins/sear/s2702.9.jpg Roman Empire. Trajan Decius. A.D. 249-251. AR Antoninianus. 4.396  grams. Obverse: IMP. C. M. Q. TRAIANVS DECIVS AVG. Bust, radiate,  draped and cuirassed r. Reverse: VICTORIA AVG. Victory running  l., holding wreath and palm. RIC 123, 29c. Good Very Fine. Currently $26.00 Started Dec-19-00
11. http://www.ancientcoins.ca/19299.jpg Superb EF silver antoninianus of Trajan Decius (249-251 AD). IMP C Q TRAIANVS DECIVS AVG, Trajan Decius facing right. VICTORIA AVG reverse, with winged Victory advancing left, holding wreath. Beautiful EF, attractive. RIC 7c, Cohen 111. Stock #19299. US$ 48.00
12. http://www.ancientcoins.ca/19291.jpg EF silver antoninianus of Trajan Decius (249-251 AD). IMP C Q TRAIANVS DECIVS AVG, Trajan Decius facing right. VICTORIA AVG reverse, with winged Victory advancing left, holding wreath. Good Fine, attractive. RIC 7c, Cohen 111. Stock #19291. US$ 25.00
13. http://www.ancientcoins.ca/15819.jpg aEF silver antoninianus of Trajan Decius (249-251 AD). IMP C Q TRAIANVS DECIVS AVG, Trajan Decius facing right. VICTORIA AVG reverse, with winged Victory advancing left, holding wreath. aEF, reverse softly struck. Scarce. RIC 7c, Cohen 111. Stock #15819. US$ 30.00 SOLD
14. http://www.ancientcoins.ca/16997.jpg EF silver antoninianus of Trajan Decius (249-251 AD). IMP C Q TRAIANVS DECIVS AVG, Trajan Decius facing right. VICTORIA AVG reverse, with winged Victory advancing left, holding wreath. EF. RIC 7c, Cohen 111. Stock #16997. US$ 40.00
15. http://www.cgb.fr/monnaies/vso/v19/gb/monnaiesgb1999.html?depart=283&nbfic=2014 Antoninien - 249-250 Mint name : Rome Issue : 2e-3e Officina : 5e Diameter in mm : 21 mm Die axis : 6 h. Metal : Billon Actual weight : 4,65 g. Legal weight : 3,87 g. Pieces to the mark : 1/84 L., 3,5 scrupules Fineness per thousand : + 400°/oo Current for : 2 deniers Condition : TTB+ Starting price 75.00 € Unsold lot (around 90.00 USD) OBVERSE Legend : IMP C M Q TRAIANVS DECIVS AVG Translation : "Imperator Cæsar Messius Quintus Traianus Decius Augustus", (L'Empereur César Messius Quintus Trajan Dèce Auguste). Description : Buste radié de Trajan Dèce à droite, avec cuirasse et pan de paludamentum, vu de trois quarts en arrière (B). REVERSE Legend : VICTORIA AVG. Translation : "Victoria Augusti", (La Victoire de l'Auguste). Description : (La Victoire) allant à gauche et tenant une couronne dans la main droite et une palme dans la gauche. Reference number in specialised litterature : C.111 - RIC.4 29c - HCC.13 Description of the condition of the coin: Beau portrait sur un flan large. Frappe molle au revers. About this type: Le type Victoria est apparu dès la première émission. Il fut ensuite réutilisé avec la titulature de droit IMP C M Q TRAIANVS DECIVS AVG lors des deux émissions suivantes. Comme l'exemple suivant, la Victoire de l'empereur désigne ici l'accession de Trajan Dèce au pouvoir. History : Dèce est né en 201 en Pannonie inférieure. Après une brillante carrière qui lui ouvrit les portes du Sénat, il fut gouverneur de Mésie inférieure sous le règne d'Alexandre Sévère. À la fin du règne de Philippe, vainqueur sur le Danube de hordes barbares, il est proclamé auguste malgré son refus. Il l'écrit à Philippe qui ne le croit pas et marche contre lui. Philippe et son fils trouvent la mort dans la bataille qui a lieu près de Vérone. Dèce joint à son nom celui, prestigieux, de Trajan. Après un passage à Rome, Dèce se rend sur le limes danubien qui, déserté, a laissé filtrer des Goths qui ravagent les provinces danubiennes dont l'empereur est originaire. Il ne parvient pas à endiguer l'invasion. À partir de 250, un nouveau fléau ravage l'Empire, la peste qui décime population et troupeaux et faiblit encore le limes. Il entame une persécution contre les chrétiens en 250 (Polyeucte, Corneille). L'année suivante, il se porte sur le limes, bat les Goths, mais son fils est tué. Il trouve lui-même la mort en voulant le venger. Il est le premier empereur à tomber au combat contre les Barbares.
16. http://www.coins.msk.ru/mk/ch2/2_80.jpg 80. Trajan Decius, AD 249-251. Double denarius, AD 249-251, AR 3,90g. IMP C M Q TRAIANVS DECIVS AVG Radiate bust right. Rev. VICTORIA AVG Victory advancing left, holding laurel-wreath and palm-branch. RSC 113a. Good Very Fine.
17. http://www.buchplus.de/gordiii.htm Silber ANTONIAN Traianus Decius (249 - 251 n. Chr.).  Kankelfitz 1996 Nr. 12  AV.: IMP C M Q TRAIANVS DECIVS AVG  RV: VICTORIA AVG  Erhaltung: "AV f vz - RV f vz". Preis: 27.00 Euro
18. http://www.ancientromancoins.biz/civil.html TD01 Trajan Decius 249-251 AD AR Ant  O:Decius Bust IMP C M Q TRAIANVS DECIVS AVG R:Victory Running Holding Wreath VICTORIA AVG RIC 7c RSC 111 F $30
19. http://www.vcoins.com/calgarycoin/store/viewItem.asp?idProduct=353&large=0 CC -Trajan Decius, AD 249-251. Silver Antoninianus  Trajan Decius, AD 249 to 251 Denomination : Silver Antoninianus. Mint : Rome. Reference : Sear-2702 Size : 20.7 x 22.0  Weight : 4.38 grams. Grade :  XF Obverse : Head of Trajan Decius right, with IMP C M Q TRAIANVS DECIVS AVG around. Reverse : Victory advancing left, holding a wreath, with VICTORIA AVG around. Price US $ 55€ 43,97   £ 30,53 Rates for 10/19/2004.

• Il peso da lei dichiarato è un po' altino, come desumerà dalla tabella in nota (1), tuttavia non mi sembra nemmeno inverosimile.
• Il diametro corrisponde allo standard d'epoca.
• L'asse di conio era indifferentemente ad ore 6 o ad ore 12 (tuttavia ho qualche dubbio che quello da lei osservato sia stato riportato correttamente).
• La leggenda del dritto appare un po'confusa in corrispondenza alla lettera "C" e, successivamente, nella parte relativa alla successione "..IAN.." ma altrettanto mi pare di rilevare in alcuni esemplari di antoniniano citati nei link.
• Anche lo stile in generale delle figure mi appare verosimile.

Un saluto cordiale. 
Giulio De Florio
www.monetaromana.it

-------------------------- 
Note: 
(1) L'antoniniano era una moneta d'argento battuta su un tondello contenente poco meno del 40% di fino, il cui peso progressivamente andò diminuendo sino a portarsi, ai tempi di Decio, ad una media di 3,7g, a fronte di un peso teorico di 3,87 g (1/84 di libbra). Da una ricerca sull'ANS (American Numismatic Society)  Database Search (http://data.numismatics.org/cgi-bin/objsearch), mediante la chiave "TRAIANVS DECIVS" per il dritto e "VICTORIA" per il rovescio, ho tratto alcuni dati significativi sulle caratteristiche fisiche di 11 antoniniani di Traiano Decio catalogati dall'ANS che di seguito trascrivo, unitamente ai dati rilevati dai link: