The BaitShop Homepage
Forum Home Forum Home > FireArms, et cetera > Metallic Cartridge Handloading and Bullet Casting
  New Posts New Posts RSS Feed - Pressure Brain Teaser
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

This site is completely supported by donations; there are no corporate sponsors. We would be honoured if you would consider a small donation, to be used exclusively for forum expenses.



Thank you, from the BaitShop Boyz!

Topic ClosedPressure Brain Teaser

 Post Reply Post Reply
Author
Message
Moose6 View Drop Down
.416 Rigby
.416 Rigby
Avatar
AKA The Knoxville NASCAR Nut

Joined: 25 July 2003
Location: United States
Status: Offline
Points: 2191
Direct Link To This Post Topic: Pressure Brain Teaser
    Posted: 17 September 2003 at 02:14

Okay guys, here's a brain teaser for y'all.  Which situation creates more pressure?  (Assume equal powder charges)

1.  Bullet seated just off the lands (say .010")

2.  Bullet seated .050" off the lands

Before y'all yell out an answer, I want ya'll to stop and ponder this for a moment.  I would imagine that most people would respond by saying situation 2 since the bullet is taking up case volume.  Sounds good to me.

However... situation 1 has the bullet very close to the lands, which inceases the opportunity for pressures to build faster and higher.  As the bullet pushes into the lands, I would suggest that it stops moving slightly because the pressure is not enough to move it through the lands.  Pressure now builds VER RAPIDLY.  After this sudden increase (or spike) the burning powder can continue its normal progressive burn.  But, the pressure started off higher due to the closeness of the bullet to the lands, thus a higher overall pressure.  When a bullet is far from the lands, it has some distance to move first, allowing a steady build up of pressure.  By the time the bullet reaches the lands, there is enough pressure now to allow for a gentler shove into the lands.

Two things can come from this.  One, a slight increase in velocity can occure by seating the bullet farther out (and yes, my tests have shown this).  Two, and this is the dangerous one, when reloading, if the bullet is close to the lands, PLEASE BE CAREFUL WITH MAX CHARGES!

I had some .308s loaded with 48 gr of Varget.  The bolt was kind of sticky and accuracy was aweful.  I did not pull the bullets... I actually pushed them into the case another .020".  No sticky bolt, or pressure signs on cases, primers, etc. (accuracy was still aweful).

The point of all of this is, I've read posts where a guy is worried about pressure, so he moves the bullet farther OUT, to create more powder room.  That is the wrong thing to do.

Now, what do y'all think of my brain teaser?  Like I said, think through the scenareo first before y'all make a hasty reply.

 

Y'all shoot straight!!!

Moose - Knoxville, TN
Back to Top
The_Mountaineer View Drop Down
.416 Rigby
.416 Rigby
Avatar
** West BY-GOD Virginian! **

Joined: 02 July 2003
Location: United States
Status: Offline
Points: 2653
Direct Link To This Post Posted: 17 September 2003 at 02:33

Apples and oranges in my opinion,

You gotta ask "where the pressure is occurring".  More case pressure will be the case if loaded off the lands.  More pressure in the barrel if loaded into the lands.  Overall pressure both in the case and in the barrel would occur as you have described.  I would agree that there'd be more pressure overall when the bullets are loaded into the lands. 

Just my thoughts.

Back to Top
mr mom View Drop Down
.30/06 SpringField
.30/06 SpringField
Avatar

Joined: 10 June 2003
Location: United States
Status: Offline
Points: 342
Direct Link To This Post Posted: 17 September 2003 at 03:44
 could there be a problem with the case neck??? not trimed or out of round??crimpped?? these could all have a factor??????
mr mom
Back to Top
Guests View Drop Down
Guest
Guest
Direct Link To This Post Posted: 17 September 2003 at 05:18

I think you are neglecting the effect of the throat.  this area is over sized for the bullet diameter.  If you seat "on the Lands", all of the gas follows the bullet down the barrel.

If you seat "off the lands" some gas escapes around the bullet until the bullet seals the cchamber by engaging the lands.  Some loss of gas around the bullet will usually mean that  the pressure peak will be lower.  the further "off the lands" you seat the larger the gas loss and the lower the pressure will be.

This is the same effect seen in long throated chambers.

Actually if you are using the same identical charge, the friction hold by the case neck is an important friction resistance factor.  the longer it hold the higher the pressure builds prior to the bullet beginning to move.

 

BEAR

 

Back to Top
Moose6 View Drop Down
.416 Rigby
.416 Rigby
Avatar
AKA The Knoxville NASCAR Nut

Joined: 25 July 2003
Location: United States
Status: Offline
Points: 2191
Direct Link To This Post Posted: 17 September 2003 at 06:21

Oh yeah..... I like BEAR's thought.

By the way, I am in no way implying that I am right or wrong, just want to hear (read) y'alls thoughts.... and I like Bear's so far.

Y'all shoot straight!!!

Moose - Knoxville, TN
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 11.10
Copyright ©2001-2017 Web Wiz Ltd.

This page was generated in 0.109 seconds.