From: bbx!bbxrbk!russ@unmvax.cs.unm.edu (Russ Kepler)
Newsgroups: rec.guns
Subject: Re: Trajectory question
Date: 8 Nov 92 23:05:35 GMT
Organization: /etc/organization

In article <1992Nov7.011048.29459@bbxrbk> bbx!bbxrbk!russ@unmvax.cs.unm.edu (Russ Kepler) writes:
#Hatcher's conclusions (found in _Hatcher's Notebook_, page 259) would
#indicate that John is correct.  The *energy* in a recoiling semi-auto
#will be higher than that of a similarly weighted revolver, due to the
#fact that there are 2 systems involved: the slide and the frame.  The
#slide essentially recoils alone until encountering the frame.  After
#hitting the frame in a highly elastic collision (as one would expect
#from a steel on steel collision).  Hatcher confirmed this
#experimentally using a recoil dynamometer, first firing in a semi-auto
#mode then after locking the bolt in place.

OK, the above partial post demonstrates the inadvisability of posting
on serious loads of pain killers.  Sentence fragments, incomplete
concepts, abrupt endings...  my standard writing style, granted, but
this time I have an *excuse*.

The original post was asking about the reasons why a lighter and
faster bullet would have an impact point *lower* on a target that a
slower and heavier bullet.  The answer (not well received) was that in
a revolver the recoil starts bringing up the muzzle the moment the
bullet starts movement in the barrel, and the faster&lighter bullet
exits before this upward motion affects it as much as the
slower&heavier bullet.  There are folks who have experimentally
"proven" this, and others that have written on it extensively (try
_Hatcher's Notebook_, page 296 "Effect of Recoil on the Jump of
Revolvers").

Alongside this series of post and counterposts was the assertion of a
general lack of recoil in a firearm before the bullet exits the
barrel.  Again, lots of folks believe this, but the evidence is
against them: _Hatcher's Notebook_, page 293: "Motion of Gun Prior to
Bullet Exit".  In this short section Hatcher makes note of an
experiment he performed to prove the calculations of gun travel that
actually measured the real motion of a rifle being fired.  It moved in
accordance with the calculations.

Somehow the subject of semi-auto firing came up - perhaps in the point
of the faster vs. slower bullet and how a semi-auto pistol such as the
GM 1911 doesn't seem to be affected by load changes.  If this was the
case then it's a trivial observation that the recoil of the slide and
barrel is inline with the barrel until the barrel unlocks, and the
barrel doesn't unlock until the bullet is well out of the barrel.  The
point I was answering in the post above was that of the recoil energy
in a semi-auto being higher than that of a similar weighted firearm
firing with a locked action.  In the semi-auto the part that slides
(be it a bolt, a slide, etc.) has an elastic collision with the part
of the (receiver, frame, etc.) that isn't moving, transferring all of
it's energy (minus the amount stored by the return spring) to the part
that hits you.  Since only 1/2 to 3/4 of the mass of the firearm is
adsorbing the recoil moment, it'll have a higher than predicted 
velocity and thus hit you harder (don't forget old mv^2).

Well, in rereading the above I think I sum up my thoughts.  I'm sure
that they're still a bit confused (trust me when I suggest never
mixing a sinus infection and painkillers...) but this should summarize
the various posts on firearm recoil.

I'd suggest to anyone interested in firearms design, powder making,
machinegun design, recoil, ballistics, etc. that they get a copy of
_Hatcher's Notebook_ from Stackpole Books.  It's 600 pages of
fascinating reading all written by one of the top gun techs in the US
in the years from WWI to 1960.  It's even good reading when you have a
horribly infected sinus...

-- 
Russ Kepler, posting from home   bbxrbk!russ@bbx.basis.com
Will hack unix for food