For other SU-16 related articles, visit About the SU-16
The question of modifying the Kel-Tec SU-16 comes up mostly in California, where it was (until the advent of Off-List Lowers) the closest thing to a true detachable-magazine AR-15 that a post-2000 rifle buyer could get. Due to its budget-priced construction, a number of areas have been identified where the base model's performance can be improved.
A number of SU-16 owners have come up with their own solutions to reliability issues encountered with Kel-Tec's SU-16 rifle. This article attempts to create a list of the more common ones. Further submissions are welcome.
There is a bit of crossover between this page and the SU-16 Analysis page. In particular, the parts questions are addressed in great detail, particularly where the comparisons to the AR-15 are brought up.
There are presently (Nov 2008) no caliber conversions available for the SU-16. While it would theoretically be possible to put just about any AR-15 barrel info an SU-16 with extensive adaptation, it is unlikely that the SU-16 would hold up well, long term, to anything more powerful than 5.56mm NATO. I'm not 100% certain that the SU-16's gas port is located in the same position as the AR's, so it would be best to start of with a virgin barrel and drill the port apporopriately. The ejection port may also need to be expanded. As mentioned below, it'd also be necessary to cut down the bolt appropriately for the SU-16. A word of caution: I cannot possibly under-state how bad an idea it would be to attempt to adapt the SU-16 to use 50 Beowulf! The recoil of the Beowulf is far beyond anything the SU-16's frame was designed for. Last point - if anyone actually does try to convert an SU-16 to a different caliber, let me know how it turned out.
AR-15 Parts Compatibility Notes
Bolt: This part is NOT compatible with the AR-15 bolt. However, it is likely that an AR-15 bolt could actually be cut down to fit an SU-16. See AnalysisKelTecSU16 for side-by-side pictures in order to understand.
Extractor: The SU-16 extractor can be replaced with an AR-15 extractor. It is reported that this greatly decreases jamming.
Furniture: Kel-Tec now sells a replacement rear end which allows the SU-16 to accommodate any pistol grip and stock designed for an AR-15. This opens up a whole new world of furniture options for the SU-16.
Firing pin: The firing pin is not the same as that of an AR-15. AnalysisKelTecSU16 has close-up pictures of an AR-15 firing pin and an SU-16 firing pin - they are absolutely not the same!
Front sight: The front sight on the SU-16CA is a standard AR-15 front sight. This means that, if desired, one could install a Tritium or other fancy front sight on the SU-16.
Muzzle devices: The muzzle threads on the C/CA/D models, are the same pitch as used on the AR-15. Thus, it's possible to install an AR-15 muzzle brake or flash hider on the SU-16. In California, it's worth noting that the installation of a flash hider would make the SU-16 an illegal assault weapon unless other exotic/silly/pointless modifications were made.
Replacement stock pin: While the original pin has been known to fall out on its own, the diameter is actually the same as an AR-15 takedown pin. While a standard AR-15 pivot pin won't exactly work (the detent slots would carve up your SU-16's polymer eventually), there are a number of vendors which supply different takedown pins. .25" cotter pins from a hardware store will also work, however it's advisable to add grooves in them at the same location as the original pin. This will allow the retention mechanism to grip the pin on both sides and reduce the risk of it falling out. For details, consult AnalysisKelTecSU16. Information on the stock pin was kindly contributed by an anonymous source, then personally confirmed.
Railed handguards: Kel-Tec sells a 'compact foreend', which replaces the existing front end. It's also possible to use an AK accessory tri-rail handguard and clamp it onto the barrel, which does adversely affect accuracy. The one point to make on this is that if your goal with the Kel-Tec is an in-home short-range rifle, the change in accuracy won't be noticeable at those distances. Handguard information courtesy of Lectrikhed, from Calguns
Replacement charging handle: The slanted polymer charging handle on the SU-16CA is said to create jams, by kicking ejected shell casings back into the action of the weapon. Replacing the newer-style polymer charging handle with the old, round charging handle is said to correct this issue.
Replacement Magazines: Kel-Tec's original polymer magazines were absolutely horrible, and tended to vomit their contents into the magazine well with the slightest tap, if the action is open. They have since improved their designs, and offer a trade-in program for owners of the original magazines. All SU-16 rifles will also accept STANAG-spec AR-15 magazines.