Gunsmithing Primary Extraction in AR-15 bolt...

[GasLight]

Hello all,

I saw a bolt rifle built using a bolt head from an AR-15. Seemed to me it had like a 30° bolt throw. What I am wondering is how you could deal with primary extraction on a bolt head like this in a bolt action?

 

[Massoud]

Re: Primary Extraction in AR-15 bolt...

The short answer is that you don't. Primary extraction is less important in a bolt gun than a machine gun or semi. The time between the firing of the round and the extraction of the round is orders of magnitude greater in a bolt gun, which gives the case time to both cool and to shrink back close to normal size. For this reason the case is easier to extract.

Now if you are using hot loads, or cause major deformation of the case in some way (i.e. oversize chamber, etc) then you can get a "sticky" bolt and you would have a difficult time extracting the case without primary extraction.

Years ago I built a straight pull bolt action that had a cam, bolt, and bolt carrier similar to a semi. By using mild loads, I never had an extraction problem. I never tested it with anything other than mild loads.

Also to add, not all semi-autos have primary extraction, the AR does not (556 or 308), the SCAR doesn't as far as I can tell, the ACR does not. The Sig 556 does, as does the AK, etc.
Justin