Air whip leaks toward end of fill?

So my hand pump came with a fill whip and so did my SCBA tank from AoA. Both whips do like what just happened as I was trying to fill my Marauder pistol just now. 

1. Seem to be attached securely to the pistol, as in I cannot readily pull them off.

2. Let air through to the tank to and beyond the point I hear the "click" that I understand means the pressure in the hose is strong enough to open the valve to the pistol's air chamber and start filling it.

3. At some point fairly soon thereafter, air starts leaking out of the hose and the gun can fill up no further.

P.S.: My rifle's bolt is pulled back.

So ... I'm figuring it must be me ... but it seems such a simple thing I don't know how I'm screwing it up. If the fitting was flying off, or if the gun was not taking air at all, obviously I didn't attach the hose properly. But those two things aren't happening.

And this didn't always happen either. I have successfully pumped and tank-filled the pistol to its normal 3k limit before.

Ideas on what I might be doing wrong?
 
First off are you sure it's leaking between the female Foster and male nipple on the gun and not the female quick connect and the hose? If so be sure it's screwed tight and if still leaks then use couple wraps of Teflon tape on the threads.

If not...

You need to do attach fill connector to gun and a hard deliberate @NIPPLE @TWISTER when attaching it to leaky guns and if it still persists lube the female with non petroleum based silicone oil.

If it still happens after doing the regular routine @NIPPLE@TWISTER on problem guns and even after lubing it then you need to replace the female foster quick connectors at the end of your hoses with better ones.
 
Quick connects have an A009 size o-ring inside. Yours may have a slight cut or defect that isn't sealing properly and doesn't leak until pressure gets high enough. If its a leak from the fitting, replace that o-ring inside the quick connect. Have you used soapy water to check for leaks?

And some imported fosters have a double stack of o'rings rather than a single o'ring typical in an American made foster.
 
Thanks guys. I didn't trust my old eyes with the soapy water test, so I put a Huma Air Quick Connect Test Plug HE0006 I got from Trenier on, then submerged the end of the hose in water to check for the leak. Turned on the air and saw the bubbles come right away. It was where the hose met its fitting. Twisting the fitting on tighter fixed it.