Found this on PS3Hax.
Everyone has been asking for this an it is really annoying, so here it is.

You need do need the usual jailbreak an regular ps3.


This has been confirmed by many members but a lot have also stated it does not work. as of right now INTERNAL DRIVE WILL GIVE INFINITE BOOT LOAD...


Delete ALL updates, if you want this to work.

You need these files
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Common.rpf (make a backup)
Located in \GAMEZ\Game_ID\PS3_GAME\USRDIR
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Now open up OpenIV.exe
open Common.rpf

You should now see three folders. click on the data folder and scroll all the way down to weaponinfo.xml.
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right click and extract.


Now open IV Needle.exe
and click on weapon editor.

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Now click on load and select weaponinfo.xml
click on the scroll down bar for weapon type and select DEAGLE.
we are now going to change the Fire type and the Damage Type.

change fire type to PROJECTILE
and change Damage type to EXPLOSIVE

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Now select the Projectile tab
Change Type to Create: to ROCKET

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you can save or make different changes.
Go back to OpenIV.exe and open common.rpf, and go back to weaponinfo.xml and right click and replace.
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Go back to where you see the three folders and this time select the folder TEXT.
Delete all the languages EXCEPT your own. I will delete all the ones except American.gxt. since my game is in American. apparently not English.
(we delete the unneeded languages because the file cannot be bigger than the original or the game will not work.)

Click on File then click Rebuild and hit yes
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Once it is done rebuilding you may now put the common.rpf file back into the game.
Now just start the game and checkout your new mods.

Heres a video of it