the case heads are very close, .223 being slightly smaller than 5.45 case head. .223 brass will fit and function in a 5.45 bolt head.

 

extraction may not be 100%

 

Is there a specific 5.56 bolt then?

Mark

 

yes
small stem and large stem IIRC too

 

the Kvar bulgy 223 bolt is large stem for the record.

also many 5.45 bolts dont have spring loaded firing pins, I would highly advise having a spring loaded firing pin on a 223 so you can safely shoot commercial ammo with the softer primer. especialy inlight of the atf recently prosicuting when guns that accidently double. not to mention the saftey factor.

Im not sure if any 5.45 bolts do have the spring loaded pin. Im not an expert there. my tantal dosent it also small stem.

if you use a 7.62x39 carrer you will need to narrow it were it runs through the mag as well.

 

The Bulgarian 5.56 bolt is large stem but the bolt carrier is cut to clear the narrower opening in the 5.56 magazine. The Bulgarian 5.56 barrels are designed for a small lug bolt. Using a 5.45 Bulgarian bolt will force the barrel farther forward in the trunnion that designed. This moves the rear sight block farther back and then the gas tube and then the gas block. The gas port is already in the Bulgarian barrel. The other option is a Romanian 5.45 bolt with the small lugs. The 223 Saiga bolt has large lugs similar to the Bulgarian 5.45 bolt.

I use 222 Remington (not 223) brass to handload 5.45 so the 5.45 bolt face will work with 223 cases but it is looser than the Bolgarian 5.56 bolt face and the 223 Saiga bolt face. The 223 Saiga ejector is about .010" longer than the 5.45 Romanian ejector. tHis shouldn't make much difference. The 7.62x39 Saiga ejector is .010" longer than 7.62 Romanian ejector. K-var used to sell the same Romanian rails as "5.45/5.56" and they semm to work alright.

 

i used a 545 bolt and carrier in my 556 build and it works great, its a small stem