Can somebody explain to me the concern over a push feed instead of a controlled feed? What is the prevailing wisdom of concern, that push feeds do what?
Barkoff the mechanics go like this:
In a properly designed CRF, the cartridge is matched to the length of the magazine box,feed rails are set up for that cartridge,extraction is handled by a large,non rotating claw extractor.But there are subtle nuances to the system that work in sync with one anither, In a proper CRF system(Mauser 98) everything is there for a purpose and works in sync with everything else.
Feeding is accomplished as the bolt moves forward and the bolt face picks up the rim of the case and strips it forward.At the instant the cartridge pops up from the rails it slides under the claw extractor,which grabs or "controls it" on the balance of its trip into the chamber,the firing of the cartridge,and its trip out of the chamber as the bolt is turned up and drawn to the rear.These extractors generally grab a large chunk of the rimof the case,making it harder to "pull though" a soft brass rim.In a mauser 98 design,thereis a machined reces around the bolt behind the bolt head into which fits another claw on the extractor which supports the extractor's grip on the case, so that the harder you yank on the bolt, the tighter the grip on the case...helpful with a stuck or dirty case,and prevents the extractor from jumping the rim of the case and leaving a fired case into the chamber.
Extraction is accomplished by two functions in a proper design;the first is as you lift the bolt handle and the camming action draws the cartridge slightly to the rear,freeing its grips on the chamber walls(in a properly designed cartridge that is tapered.An improved case with parallel sides(AI)does not do this as well as a tapered case.)Again, helpful in extracing a dirty or stuck case. As the bolt is moved forcefully to the rear,the extractor holds the case until it encounters the standing ejector which slides into a slot in the bolt face(perfectly "timed") and kicks the fired case out the loading port.
It is important to note here,that in a proper CRF,the bolt cannot pick up the next cartridge until the one on the bolt face is kicked out the port(or it shouldn't and if it does, it is not a properly made CRF action).
In a PF action,the cartridge is loose once it clears the rails in feeding and does not get grabbed by the extractor until the cartridge is fully,or almost,chambered,when the extractor jumps over the rim and grabs it.
This is in part what distinguishes one system over the other....if in operating the PF, you short stroke the bolt for any reason(panic in wartime,a buff bearing down or plain old buck fever,or a cartridge reluctant to chamber)and withdraw the bolt, the cartridge is now sitting in the rails and loading port.If you pull the bolt back far enough,and then move it forward again, the bolt will pick up another cartridge and the result is two cartridges in the port and the rifle will jam.(In a properly built CRF,this should not happen provided the cartridge length is sync'd to the magazine box...if you chamber(say) a 7x57 in a 30/06 length actionso that the cartdige is not in sync with the nag box length,all bets could be off....it will likely work but you could double feed potentially with that set up).
Ejection with the PF is controlled by a plunger in the bolt face actuated by a small spring that exerts pressure on the cartridge as it is withdrawn from the chamber and kicks it out the loading port once the mouth of the case clears the receiver.
Extraction with the PF is accomplished(Rem700) with a small spring in the bolt face that jumps over the rim of the case as the bolt is turned down into battery;ditto a M70 PF where a small spring loaded extractor slides over the rim when the round is chambered.These are both small,don't grab as large a hunk of the rim as the more massive extractor of the Mauser 98 design.other designs use a different extractor,like the Sako,M16 type, etc.
Mighta left something out....my brain is fogged