I have a capacitor rated 15000 µF, 35V.

So, I charge my capacitor to 15V with no problems using a charging resistor.
Now while discharging, I am using thyristor (2N6509G) as my switching device and a coil as my discharge resistor. Coil resistance is about 2 Ω.

Using the discharge equation of capacitor, I calculated the discharge time in this setup, which comes out to be around 81 ms for (assumed) final voltage of 1 V.

In my application, I wish to discharge the capacitor only for 20 ms.
But when I do that, the capacitor voltage drops down to 0.9V in just this 20 ms duration instead of the calculated 7.7V (using discharge time calculators online).

If I am not doing anything wrong in the setup, what is it that I am not understanding conceptually? How do I go about discharging capacitors only to some fraction of the stored charge?

Edit: Thank you all for your comments, I am sorry for not being very clear with the details.

So, this is a coil gun model basically.
Coil :- Copper magnet wire: AWG 20; no of turns: 650; Coil resistance: 2ohms

I actually used an online calculator for capacitor. [Discharge Time Calculator](http://mustcalculate.com/electronics/capacitorchargeanddischarge.php) 

I used another calculator to get the inductance of this coil which came out to be 8.88mH. [Coil Calculator](http://production-solution.com/coil-calculator.htm)

[![Discharging side of the capacitor](https://i.stack.imgur.com/o85iR.png)](https://i.stack.imgur.com/o85iR.png)

\*Note: This circuit is not my original work.