Recoil versus blowback action

>>29735250
locking the bolt gives the gases time to reach safe levels before extraction happens.

recoil operation relies only on the inertia of the bolt to delay the action, which would require fuckhueg and heavy bolts with larger calibers

You just answered your own question. Blowback doesn't have any sort of locking surface, while recoil operated guns do. Any caliber could function in a blowback gun, it just becomes unwieldy pretty quickly.

>>29735250
when the bolt and barrel are locked together it extends the time in which gas pressure is contained so that it can drop to safe levels and not make your face do the hurty hurty

Or i could be completely wrong because I didnt bother to look this up before i typed

>>29735250
Weren't there some blowback rifles in the competitions that lead to the Garand?

>>29735313
>>29735304
https://www.youtube.com/watch?v=YKRMcTlbWTs#t=13
From my understanding the bolt and the barrel both seem to be able to move in recoil action (they're just locked together). What prevents the bolt+barrel from moving before the bullet has left the barrel? Is it the intertia due to the combined weight of the bolt and barel?

>>29735355

In a recoil operated gun, yeah. Both the barrel and breech face start moving before the bullet exits the barrel. The important part with a short-recoil system is the timing.

Let's say you're shooting a .45 ACP going 1000 fps and the bullet needs to travel 4" to exit the barrel.

It'll travel that 4" in 4/12000th's of a second (0.0003333... seconds)

So, calculate the time it'll take for the pressure to drop down to safe levels after the bullet leaves the barrel, add that to the travel time through the barrel and add a safety factor to it (just in case the pressure is higher than normal for some reason). Then you need to figure out how fast the moving components travel rearwards based on their mass and the spring tension (and remember: springs increase in strength per distance traveled... They're kinda fucky to work with like that) and then you make sure that the breech only unlocks after it has traveled the appropriate distance.

And that has to sync up properly with stuff like the magazine spring. If the firearm cycles too fast, then it won't have time to push a new round into position and you'll get a failure to feed.

>>29735525

The easiest method of preventing the firearm from cycling too fast is to have the breech travel past the point it needs to go to pick up the next round. The greater this buffer is, the more reliable it'll be with underpowered ammo, but it'll also significantly decrease RoF if it's an automatic.

>>29735355
It's called "static friction".

>>29735332
The Thompson rifle basically was. It was supposedly Blish locked, but seeing as their Blish principle isn't real it ended up being blowback. It had a fuckhuge receiver and had extremely violent extraction and ejection.

gas delayed blowback.

>>29735250
>>29735355

okay OP, Others have given you good answers but to summarizer:
1) You do not want the the action to open too early. This will cause a split case at best, kaboom at worst depending on the cartridge.

2) Blowback has no positive love between bolt and barrel/chamber. It relies on the inertia of the bolt alone to ensure action does not open too soon.

3)Recoil operation HAS a positive lock between bolt/slide and barrel/chamber and both move TOGETHER at first.

4) Because of the POSITIVE lock recoil operated firearms can handle larger cartridges then blowback while still keeping the weight of the firearm within reasonable levels (via not needing fuckhuge bolt).

5) Generally Blowback firearms are more accurate then recoil as the barrel does NOT move in a blowback. Less of an issue in modern times but still true.

6) Blowbacks are incredible simple and some would argue more reliable... If the ammo is decent.