300 whisper Sig 556

[anubismp]

I'm new here and am looking at doing a bbl conversion on my sig 556 classic. I like the idea of the Whisper and I would like to try to do my own work but I'm unsure how feasible that will be. I saw the 552 conversion and I like the idea but I cant SBR in WA so I'll be trying for a 16". Please throw me ideas for bbl makers, gas plug ideas and the like. I'd be shooting suppressed when out of state so I'd like it to be mostly a suppressed sub load gun.

[amafrank]

as for the conversion it can be done but it is a pain. The 556 is not a real good candidate for the conversion and is a hell of a way to get into your first. The barrels have to be turned, threaded and chambered for the particular receiver you have. The guys in new hampshire have pretty low standards so nothing is interchangeable barrel wise....at least if you want the gasblock and port to line up. Your gas system will need to be modified rather substantially to be useable with and without suppressors and sub or supersonic ammo. The consequences of over-boosting are damage to the bolt and receiver. Under-boosting means your action won't cycle. I built the 552-300 and won't do another because its just not worth the trouble. Too much opportunity for problems and in a 556 you really aren't gaining anything worth those problems. There are a lot of parts and knowledge out there for the AR's and bolt guns that will help you end up with a good useable rifle and less trouble.

Good luck regardless of which way you choose to go.
Barrel blanks can be had from Pac-Nor and Lilja. I recommend you go with stainless and I like Lilja barrels the best.

Frank

[Buckshot]

Originally Posted by amafrank

as for the conversion it can be done but it is a pain. The 556 is not a real good candidate for the conversion and is a hell of a way to get into your first. The barrels have to be turned, threaded and chambered for the particular receiver you have. The guys in new hampshire have pretty low standards so nothing is interchangeable barrel wise....at least if you want the gasblock and port to line up. Your gas system will need to be modified rather substantially to be useable with and without suppressors and sub or supersonic ammo. The consequences of over-boosting are damage to the bolt and receiver. Under-boosting means your action won't cycle. I built the 552-300 and won't do another because its just not worth the trouble. Too much opportunity for problems and in a 556 you really aren't gaining anything worth those problems. There are a lot of parts and knowledge out there for the AR's and bolt guns that will help you end up with a good useable rifle and less trouble.

Good luck regardless of which way you choose to go.
Barrel blanks can be had from Pac-Nor and Lilja. I recommend you go with stainless and I like Lilja barrels the best.

Frank

If you would like to stay safe, you could also make TWO different sleeves.
This is what I am planning to do.
I recently continued with my project.
(SIG 551 SWAT with a Lother Walther barrel)


I tried to drill up the original sleeve for my 16" SWAT and currently have a 2.5 mm hole in the sleeve.
This won't make it cycle yet.
I am planning on drilling up to 3 mm max, before switching tot the longer gassleeve.
To make this sleeve fit, I will need to adapt the gastube as well.
This one is now the length of a .300 Whisper cartridge.
I will start with a minimum size of hole with a subsonic starting round.
After that, I will continue with a supersonic round and drill it up untill it works.
I will place masking tape (like painters use) on the sleeve of the cocking handle after loading a cartridge.
Than I will cut the tape with a razorblade.
This way, when I fire a round, I will be able to detect how far the cocking handle came to the rear.
This is a simple way to check your progress.