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Really short throat

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Skunk View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Skunk Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 14:09
[QUOTE=trigger29] I am assuming my throat is just that short? I don't know what's causing it, but it's irritating. QUOTE]
 
You and I couldn't go on a date then!!!!!
 
Let me give you my two scents worth
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ckk1106 Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 14:16
Originally posted by rifle looney rifle looney wrote:

I think Sako is saying to seat deep meaning into the case not the lands.this in return gives less volume for powder.ie less velocity.

Yes I think he is saying that, but also that it produces less pressure.  Geezer says the opposite.  I'm just curious as to which is right or even if it matters.Big Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rifle looney Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 14:42
Less powder less pressure?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ckk1106 Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 14:54
Originally posted by rifle looney rifle looney wrote:

Less powder less pressure?

That's true.  I just didn't see where he was suggesting less powder.  Powder can be compressed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rifle looney Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 15:04
yes this is true...compressed loads can cause high pressure too I believe .we need to find out the truth its buggin me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ckk1106 Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 15:15
Originally posted by rifle looney rifle looney wrote:

yes this is true...compressed loads can cause high pressure too I believe .we need to find out the truth its buggin me.

It seems the more I read about reloading the less I know.  It's definately a fun hobby, though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rifle looney Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 15:25
Originally posted by ckk1106 ckk1106 wrote:

Originally posted by rifle looney rifle looney wrote:

yes this is true...compressed loads can cause high pressure too I believe .we need to find out the truth its buggin me.

It seems the more I read about reloading the less I know.  It's definately a fun hobby, though.


you are a POET and don't even know it!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote geezer Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 16:10
This is what one of the powder mfgs says about COL -

It is important to note that the SAAMI “COL” values are for the firearms and ammunition manufacturers industry and must be seen as a guideline only.The individual reloader is free to adjust this dimension to suit their particular firearm-component-weapon combination.This parameter is determined by various dimensions such as

1) magazine length (space),
2) freebore-lead dimensions of the barrel,
3) ogive or profile of the projectile and
4) position of cannelure or crimp groove.
 
This is another note:

"CAUTION!

Reducing the seating depth may dramatically increase pressure in some handgun cartridges. Always use caution when changing seating."

 This is what I was referring to when I made the statement about increasing seating depth.  It doesn't affect the internal volume nearly as much in cases with larger capacities.  Sorry if I caused any confusion.
I would give you my two cents worth, but then you would probably have to give half to the gov't and what good is one penny
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rifle looney Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 16:17
Thanks !.....we are not confused....well maybe? we are curious to learn more than we think we know. all input helps, 

Edited by rifle looney - February/04/2009 at 16:18
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dale Clifford Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 16:50

the amt. of pressure needed to get the bullet into the lands is nill, usually a primer with no powder will accomplish this, its the time delay that causes the pressure, the bullet is acutually stopped  until the pressure overcomes inertia which has a time frame much larger than the progressive burn rate of any powder used. Usually log type powders can be compressed easily while ball powders cause more problems, and slow powders can be compressed more because there is less density per unit volume. (larger kernels).

pistol cases are somewhat different in dynamics, if the bullet has set back usually due to a feeding problem in autos. , ( called compressed load here) and depending on severity will usually blow the primer  before anything, but more from the way they headspace, usually the hammer blow pushes the load completely forward and the primer is blown out of the pocket and against the recoil shield, then the case is pushed back and it is reseated, the time frame is shorter than than the return spring on the firing pin and the primer is moulded around the firing pin with a hole in it.

pressure from seating depth can be effected more by headspacing on the shoulder (necksizing) or FL resizing. a fireformed case with the bullet on lands with less powder will often show the same pressure as fl resized case with more powder.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote rifle looney Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 16:57
Originally posted by Skunk Skunk wrote:

[QUOTE=trigger29] I am assuming my throat is just that short? I don't know what's causing it, but it's irritating. QUOTE]
 
You and I couldn't go on a date then!!!!!
 


This .^^^.....and shoot something else for a while .


Edited by rifle looney - February/04/2009 at 18:33
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trigger29 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote trigger29 Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 21:42
OK! well I'm glad I have a short throat then. Well, if somebody could explain the fliers to me, I'd be in good shape. It seems as though every time I think I have a load figured out, there has to be a flier in the group. Here are some examples.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote sakomato Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 21:45
What I meant was that when you seat the bullet a little deeper, you are not changing the size of the combustion chamber.  The combustion chamber is not the inside of the case (which would be reduced by seating deeper) but the size of the space from the bolt face to the lands. 
 
Reference this by Hornady (I will try to include the illustrations but if they don't come up just go to the link)  http://www.hornady.com/ballistics/internal.php :
 

variations of bullet travelTo illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.

In a "normal" load with the bullet seated to allow about one 32nd of an inch gap (A) between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period (B), and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.

Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D).

bullet seated to touch the riflingWhen the bullet is seated to touch the rifling, as in the accompanying illustrations, it does not move when the pressure is low (E); and not having a good run at the rifling as did the other bullets, it takes greatly increased pressure to force it into the rifling. As the rapidly expanding gases now find less room than they should have at this time in their burning, the pressure rise under these conditions is both rapid and excessive (F). Velocity is high at 3650 fps - but at the expense of rather dangerous pressure.
Many rifles deliver their best groups when bullets are seated just touching the rifling. Seating bullets thus can be done quite safely if the reloader will reduce his charge by a few grains. The lighter load will still produce the "normal" velocity without excessive pressure.

 
 
 
 
This clearly states that pressure decreases when the bullet is seated deeper the pressure decreases.  I have noticed the same thing with reduced velocity in cases where the bullet needed to be seated deep in order to fit the mag.  Now if you added more powder such as Weatherby does in their cases with large jumps, then you would increase pressure and velocity because of the larger amount of powder to burn.
 
Now if you have a rifle with a "short throat" then you have to be careful and work up because your combustion chamber is small.  Like in the 338RUM that I recently had rebarreled.  It was a conversion from 338 win mag and in order to fit the mag with the longer 338RUM case, I had to have the gunsmith ream the chamber with a "short throat".  I can not load to manual max or the primer pockets go bad quick.  The reason is that my combustion chamber is smaller than normal.
 
Weatherby is the opposite.  Most of them have .275" or so jump to the lands and Weatherby uses this additional jump as part of the combustion chamber and load more powder.  Do not chamber a round for a Weatherby cartridge with the lands set to where you can reach the lands and shoot a factory load!  You would have reduced the size of the combustion chamber and the pressure would blow your primers out or worse.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sakomato Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:01
BTW, Tip, the general consensus of the best method for reducing flyers is to seat deeper.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Wilson Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:15
it's not the size of the combustion chamber, but the fact that the bullet is against the lands. the farther the bullet starts from the lands the easier it is for it to engrave into them. it takes in the neiborhood of 15k psi to start the bullet into the rifling. peak pressure occures when the bullet is at the point of complete engagement into the rifling. pressure then drops as the bullet goes down the barrel.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Wilson Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:21
as far as the groups, have you bedded this thing? trued the action? you've got stuff stringing vertically, horizonal, and on an angle. no rhyme or reason. you've got stress on the action/bedding somehow.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Roy Finn Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:29
Originally posted by sakomato sakomato wrote:

BTW, Tip, the general consensus of the best method for reducing flyers is to seat deeper.


Why is that?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote trigger29 Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:29
This rifle came pillar bedded, but I don't know how good of a job they do at the factory. It shoots Winchester Power Points to 1/2" -3/4" consistantly. I just can't seem to figure out what it needs. I guess I went the wrong way. I just seated some closer to the lands today. Maybe I'll go the other way instead.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote sakomato Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:36
Dave is right.  I kinda got off on a tangent with that combustion chamber stuff.  I was just trying to illustrate that a lot of reloaders think that because you seat your bullet deeper then you are reducing the size of the volume for the powder gases to expand into and therefore you will increase pressure.  Not so.  You can't think about the volume inside the case but the volume inside the chamber, then seating deeper will make it easier for the bullet to enter the bore and reduce the pressure. 
 
Roy, I have read repeatedly on threads that if you are having flyers seat deeper and if you have large but concentric groups seat closer.  Can't verify that by personal experience but worth a try.


Edited by sakomato - February/04/2009 at 22:40
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rifle looney Quote  Post ReplyReply Direct Link To This Post Posted: February/04/2009 at 22:43
Also check those action screws don't crank on them just snug and a 1/8 turn.
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