Longest reasonable pistol

Hello all, new user here. I recently was given a crosman 2240 pistol that I’ve been shshooting and tinkering with. I’d like to put a longer barrel on it. The 14.5in seems popular but most folks seem to use shoulder stocks with them. What do you think is the longest barrel that is reasonable for use as a pistol?
 
I tried the longer barrel and then went the other way, shorter barrel.

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I put 14" barrels on all of my 2240's along with a BNM Breach and Moderator of 18". That makes for a long pistol that can still be manageable. I also keep a few crosman stocks that fit the 2240 on hand to switch the pistol to a small and light carbine and generally add a red dot scope because the BNM Conversion removes the original sights. Generally upgrade the triggers and valving along the way as well but keep most of them with the CO2 Powerlet or sometimes tether to a paint ball tank. These 2240's can teach you a lot about the workings of an air gun; most of the knowledge you gain during the mods is directly transferable to PCP's.
I also tend to add bright colors to the breach and moderators that make them appear to be paint ball guns and not much of a threat to the neighbors. Perception goes a long way in keeping peace in the neighborhood along with the quiet report after adding the moderator. Have Fun... 
 
"AirRanger"Gunnertones that is one sweet pistol. I’ve been contemplating a Ranchero for awhile and I really like the original synthetic stock like yours but in a perfect world I’d have your same stock but with a rifle butt to make it a small pistol/carbine similar to the Marauder pistol with the carbine stock.
Well, with a rifle butt it would be a small rifle, and then I rather would prefere a bullpup to be frank. Now it is 74 cm from butt to front of the silencer, and goes perfect in a backpack, or in the cocpit of my kayak. I consider a much smaller and lighter scope than this Athlon Midas. But it is very amusing, shooting beer cans at 120 meters with a pistol.
 
Well I finally settled on a 10in barrel afterall. I installed it last night and so far I’m pleased. I think 12in might be doable but any more than that I think would become unwieldy, just my preference. I could see a 14 to 16in barrel making a very handy carbine. The pistol has a little better balance for me, and between the longer barrel and clipping a couple of coils off the hammer spring, the pistol is noticeably quieter. Far from quiet but less harsh. Anyway just thought I would follow up.