Hey,
I'm pretty new to make guides but I thought ill give it a shot:
well too many people do drop 10,000ammo in there house thinking it cannot be stacked. well in fact, myself, I stacked about 850k ammo (no, not selling) using a simple trick:
Essentials:
http://s15.postimage.org/wlhpb5h9n/IMG_0087.png (Unsupported image host)
You will need 1. stock which provides the ammo that needs to be added
2.Main which is the amount which will be added to (PS: main would be the biggest amount for more time)
http://s13.postimage.org/z5ifpwnmf/IMG_0088.png (Unsupported image host)
3. Trash if you are using more than 9999 ammo on each stock.
Step 1:
Drop on Stock 9999 of each ammo, or get it as 9999.
http://s7.postimage.org/clhc1sj4b/IMG_0089.png (Unsupported image host)
Step 2:
After you dropped all you'r stock, pick up one of them (MUST have you're inventory ammo empty)
http://s17.postimage.org/eprmw7n9b/IMG_0090.png (Unsupported image host)
Step 3:
Then grab the Main amount of ammo
http://s15.postimage.org/opfllvzcb/IMG_0091.png (Unsupported image host)
Step 4:
Then Drop all your ammo and start over =D
http://s13.postimage.org/8h0c2p0ur/IMG_0092.png (Unsupported image host)
Grabing 10,000 ammo (for people who already made it, please next time keep them 9999)
Step 1:
empty you'r inv ammo and grab 10,000.
http://s14.postimage.org/5jvum9c9d/IMG_0093.png (Unsupported image host)
Step 2:
drop 1 ammo on your trash area
http://s18.postimage.org/rzb2cx1vd/IMG_0094.png (Unsupported image host)

Step 3:
Grab back the Main and Drop it!
http://s14.postimage.org/wff2sn80d/IMG_0095.png (Unsupported image host)
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This is as far as I can go, even something small can help someone... Well hope it helped you, I suck at that but might do better next time