Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!udel!haven.umd.edu!mimsy!bevsun.bev.lbl.gov
From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Newsgroups: rec.guns
Subject: blowback definition
Message-ID: <35179@mimsy.umd.edu>
Date: 3 Jun 91 19:41:16 GMT
Sender: magnum@mimsy.umd.edu
Lines: 26
Approved: gun-control@cs.umd.edu

I think a _blowback_ pistol is distinguished by the fact that its barrel
is not locked to its breechblock but is, rather, fixed to its frame.
A _delayed_blowback_ firearm has a delaying mechanism which delays
the breechblock's leaving the breech of the barrel.  In the Thompson
I think the delaying mechanism was some phony little brake which
was later deleted.  Some delaying mechanisms have worked fairly well but 
many haven't.  The purpose of them was to make a cheaper approximation of 
a short or long recoil _locked_ breech.  Then there are those firearms which
kind of fall in between the definitions, to my way of thinking.  Personally,
I think of the H&K roller lock as more of a delayed blowback but others
would say it's locked breech.  Then there was that pistol (who made it,
anyway?) that used gas bleed near the chamber to hold the breech shut.
I think of that as locked, but most would call it delayed blowback.
Part of the confusion lies in deciding whether or not all pistols with 
barrels locked into the frame are necessarily delayed blowback.  I would
say it's delayed blowback if a brake or inertia device (a' la roller lock 
et al) is used to keep breechblock and barrel breech more or less together.
In contrast a locked breech firearm would have _no_ relative motion of
breechblock and barrel breech during the high pressure part of the cycle.

Sometimes delayed blowback is confused with a retarder or an accelerator.
These are used to slow down full-auto rate and to speed up breechbolts, 
respectively, at least in the usual senses.

The above was off the top of my head, so I guess I'm fair game.  8-(
JHBercovitz@lbl.gov    (John Bercovitz)