The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: General

Reply
 
Thread Tools Search this Thread
Old July 14, 2019, 08:16 PM   #76
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,089
thanks!
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old July 14, 2019, 08:23 PM   #77
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,089
I have a pressure trace and have seen some interesting behavior in pressure plots as the bullet goes down the bore. There's even a theoretical pulse that goes down the barrel and "rebounds" back to the projectile before it even exists the muzzle that I've heard about.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old July 14, 2019, 08:42 PM   #78
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 6,648
Quote:
Originally Posted by stagpanther View Post
I have a pressure trace and have seen some interesting behavior in pressure plots as the bullet goes down the bore. There's even a theoretical pulse that goes down the barrel and "rebounds" back to the projectile before it even exists the muzzle that I've heard about.
Yes, that shock wave goes back and forth in the barrel. When it is at the barrel muzzle, the claim is it enlarges the bore a few millionths inch and that degrades accuracy. Modes 4 and 8 in that link shows the muzzle diameter changing but no back and forth shock wave claimed in this web site:

http://www.the-long-family.com/OBT_paper.htm

I and others have had Garand match barrels whose bore at the muzzle enlarged well over a thousandth inch from steel cleaning rod wear that had no accuracy loss. They still tested sub MOA at 600 yards.

Last edited by Bart B.; July 14, 2019 at 10:50 PM.
Bart B. is online now  
Old July 15, 2019, 02:45 AM   #79
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,089
My tests have been on AR's--which are difficult because most of the chamber is usually covered by the barrel nut--and many of the barrels are made of SS416 which supposedly has an "erratic" molecular expansion and contraction behavior compared to say conventional 4150 CM.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old July 15, 2019, 12:08 PM   #80
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 16,224
I've done hoop stress analysis suggesting upwards of a quarter of a thousandth deformation can occur. The impulse seems to be initiated when the bullet hits the throat on its way out of the case. At that one moment, it pushes forward on the barrel and the reaction force applied to the breech end causes the chamber to stretch a little. As the bullet eases into the throat and gets to build up speed again, the chamber snaps back into position and those seem to be the pressure wave initiating forces.

Interestingly, those waves were first described (AFAIK) by Dr. Lloyd Brownell in his 1965 study of absolute pressure at the U of Michigan with funding from DuPont. You can seem them as small wiggles superimposed on the pressure curve where they occur. They don't seem to have equal magnitude in different loads and I have not done Pressure Trace readings to see if starting with the bullet in contact with the lands, which eliminates the bullet bumping into the throat, also mitigates the waves.

__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member and Golden Eagle
Unclenick is online now  
Old July 15, 2019, 12:50 PM   #81
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 6,648
Unclenick, what are your thoughts on this Optimum Barrel Time theory:

http://www.the-long-family.com/OBT_paper.htm
Bart B. is online now  
Old Yesterday, 12:19 PM   #82
Cosine26
Junior Member
 
Join Date: July 7, 2019
Posts: 2
Exterior Ballistics

Exterior Ballistics is a very complex subject. There is a very interesting, detailed and complex discussion and explanation of projectile stability in the July 1962 issue of the American Rifleman by E. H Harrison entitled Projectile Stability. It gives a very detailed description of a projectile in flight and the forces acting on it.
In general, group size does not expand in a linear fashion with range because of changing forces acting on the projectile at various velocities and at various ranges.
The article just too long and too complex to copy and put on this forum.
The use of Doppler radar to measure inflight characteristics of projectiles available today gives much greater insight into exterior ballistics than existed in 1962.
FWIW

Last edited by Cosine26; Yesterday at 12:23 PM. Reason: Added content
Cosine26 is offline  
Old Yesterday, 01:03 PM   #83
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 6,648
One can use one of the exterior ballistic software sites (JBM?) to see the bullet drop spread at different ranges with a 15 fps or 60 fps spread in muzzle velocity (or horizontal shot spread in a 1.5 to 6.0 mph spread in crosswind).

Change the bullet rated BC 1 to 2 percent lower to see cross wind drift changes as well as bullet drop variables.

Last edited by Bart B.; Yesterday at 01:28 PM.
Bart B. is online now  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 09:34 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2018 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.05246 seconds with 10 queries