I think it can best be done in step-by-step pictography.
Some have taught putting the gun between the knees.
The top of the slide being supported by the vehicle seat made this method quite viable.
If possible, take cover. Use your thumb to eject the spare magazine as demonstrated by the author here.
Rogers teaches his students to perform this technique effectively in his Advanced course.
With the proper mindset and training, you might overcome this situation and survive.
Go to forum thread
EchelonTMSeries
Leave the slide locked back and insert the pistol into that handy gun-holder, your holster, so you can use your hand.
Grab your spare mag andbeginto insert it as shown. Don’t do it too hard. Your holster wasn’t designed to hold a pistol at slide-lock and you don’t want to knock your gun out of the front of the holster. Consider expert Bill Rogers’s advice to keep a spare magazine accessible to both hands.
Complete the magazine insertion as shown. Once you know the magazine is in the mag well, do a “got your nose” like playing with a little kid, with your thumb between middle finger and index finger. The index and middle fingers act as pincers stabilizing the pistol grip while your thumb pushes the magazine the rest of the way in, until you feel it lock into place.
With the magazine now in place, draw the pistol and bring it out in front of you.
Use your thumb to press the slide release lever downward to chamber a round. Pointing the tip of your thumb straight downward will give you more leverage to do this.
Alternatively, you can catch the rear sight on your belt or holster and with the muzzle approximately 45 degrees away from you. Push downward and then pull the gun out away from belt or holster. This is also the plan if your slide has closed on an empty chamber. You now have a round chambered.
The magazine release button is usually on the left side of the pistol frame. Running the gun southpaw, the easiest and fastest release is using the trigger finger to drop the empty magazine, as shown here.
If you are left-handed, simply insert pistol at slide-lock into the scabbard as you would normally holster. If right-handed, insert into holster cross-draw as shown. WARNING: This is unlikely to work if your pistol has a weapon light attached. For that, inserting into a side pocket may be the best fallback.
Grab a spare magazine and insert it as shown. Don’t try to slam it all the way in: the holster was not designed to hold a pistol backwards and the gun could pivot out. Just get the magazine started.
Perform what author calls “the crush.” As shown, the thumb of the reloading hand goes laterally across the back of the grip frame to stabilize the pistol in the holster, while the palm crushes the floorplate of the magazine all the way into the pistol until you can feel it positively seat.
Once the magazine is seated, grasp the pistol in a firing hold for a cross-draw.
As you bring the gun to bear on the threat, bring your left index finger to the slide stop/slide release lever.
Press the slide stop lever downward to chamber a round. The more your fingertip can be pointed straight down, the more leverage you’ll have.
Alternatively, you can catch the rear sight against your belt and, with the muzzle pointed away from you, push down and then let go to release the slide and chamber a round.
If your pistol has a red dot sight, it is an ideal “catch point” to use against your belt to operate the slide and chamber a round. You are now ready to re-enter the “fight for your life.”
Here the author demonstrates a between the knees reload. While this method has definite drawbacks, modifications of it worked well under fire during the Battle of Mogadishu.