How exactly is seating depth changes causing the tightening of group size?

[jlow]

Sorry, I had hoped by this point it would have been understood that seating does little to case volume,,
Changing case dimensions is a different issue as it applies to reactions in the chamber.

Tilting the gun to position the cartridge either against the breech or shoulder prior to ignition will do nothing when the nano second of the firing sequence is dissected.
Newtons 3rd Law of physics still applies with little regard to how quickly it happens.

Over thinking can lead to lead to a bit of confusion, while to some degree it is Rocket Science, alot of the application of that said science can be learned with Estes Rockets in the back yard.

It’s OK, not a big deal, just wish folks would read the post before jumping in but that is life on the boards.

 

[bozo699]

When charge weight is found, I seat the bullet deeper by .005" fire 3 round groups.

"deeper" into the case... I assume.

Bradley,
You are probably correct but the terminology is incorrect, thanks for clarifying for me I am old school and need things black and white I guess ??
Wayne.

 

[22XC Guy]

I would think any changes to the seating depth would increase or decrease the case internal volume of pressure with a known charge of powder..

We do narrow test loads in increments of powder charges, then work around seating depths, or a slight powder adjustment with seating, this includes looking for the optimum pressure..

If we knew the optimum pressure, seating could be placed accordingly or anywhere.

Steve

 

[BoydAllen]

With a given powder, bullet and barrel, one would think that there would be a pretty good correlation between pressure and velocity.

 

[Steve Blair]

With a given powder, bullet and barrel, one would think that there would be a pretty good correlation between pressure and velocity.

[br]
lex parsimoniae

 

[mikecr]

Well, since there is no 'given', all remains unpredictable until validated.

I can't think of any load component more fine(and isolated) than kernels of powder.
It very finely affects pressure, timing, and usually velocity though non-linear.

Seating can pure mangle groups -without affecting velocity at all. That is, until seating step changes into or out of the lands. Barring this, I doubt seating changes pressure at all.
IMO, this leaves only timing, and a huge affect on it at that.

 

[LongRanger]

I've gotten lost in the clutter of a handful of other good sub topics in this thread and wonder: has anyone partially answered the original question by noting that if the bullet is seated deeper/shallower into the case there will be more/less friction between bullet and neck possibly causing more/less pressure upon ignition....followed by all kinds of unexplainable and unexpected good/bad/zilch results on group size?

Frank B.

 

[BoydAllen]

Correlation is not causation. We are into the region of "I think that it works like this." We can guess, but we really don't know. The best we can do is to make a change and record what happens, building our stock of data to the point where useful predictions are possible. My suggestion to any one that wants to know more about what happens when seating depth changes are made is to go to the range with all your loading gear, and a chronograph. If you are looking for a way to sit at your desk and reliably calculate your outcomes, good luck with that.

 

[Steve Blair]

What is possible to reasonably predict is velocity, provided you have gathered some preliminary data as Boyd suggested. What I have not found possible to predict are: [br]
1. The point at which velocity variation is at minimum
2. The effect of seating depth changes [br]
As far as I know, physical testing is the only way to know 1 & 2.

 

[Bradley Walker]

Correlation is not causation. We are into the region of "I think that it works like this." We can guess, but we really don't know.

Thank you!!! I think I have been saying that repeatedly.

In fact, I will go so far as to say that no one can really say if ANY of this stuff has a SIGNIFICANT effect. Most people don't understand what it takes in terms of data sets to say that they have an ACTUAL statistically significant effect. They shoot a few group or even ten, and say it's significant at 1000 yards... when there are a 100 other factors that are more significant than a few thousandths of seating depth...

It's like talking about Global Warming... and I feel like I am some kind of denier...

 

[BoydAllen]

A friend who has a tunnel, has let a friend of his work up loads for his 600 yard shooting that has resulted in some matches won and at least a couple of records. He tells me that the 100 yard accuracy in the tunnel has correlated well with the results at the full distance, outdoors. Recently, I spoke with a fellow who was able to shoot 1,000 yards at night, in very still conditions, his results were very exciting to say the least. I think in those cases where it can be done, that shooting at night to reduce the influence of wind, should be considered, at least for testing. One thing that should be considered is that, roughly speaking, if the distance to target is halved, the deflection caused by a given amount of wind is quartered. From this we might conclude that, assuming that a distance is chosen at which the bullet has "gone to sleep" (ceased its coning motion) that long range shooters might profit from shorter range tuning sessions, for all purposes except tuner adjustment, which may be distance specific.

 

[Heavies]

When charge weight is found, I seat the bullet deeper by .005" fire 3 round groups.

"deeper" into the case... I assume.

Bradley,
You are probably correct but the terminology is incorrect, thanks for clarifying for me I am old school and need things black and white I guess ??
Wayne.

Yes, deeper in the case. Sorry for the confusion.

for all purposes except tuner adjustment, which may be distance specific.

I've thought that too, about tuners and specific distance.

 

[Steve Blair]

One thing that should be considered is that, roughly speaking, if the distance to target is halved, the deflection caused by a given amount of wind is quartered.

[br]
Boyd, you should also note that you refer to displacement on the target in linear units, like inches. Given a mythical steady state wind, the angular deviation (MOA or MIL) is close to linear, although it increases with distance.

 

[Bradley Walker]

A friend who has a tunnel, has let a friend of his work up loads for his 600 yard shooting that has resulted in some matches won and at least a couple of records. He tells me that the 100 yard accuracy in the tunnel has correlated well with the results at the full distance, outdoors.

Tunnel... Yes... I need a tunnel... and a vise...

 

[Bradley Walker]

http://www.angelfire.com/ma3/max357/houston.html

 

[Cigarcop]

http://www.angelfire.com/ma3/max357/houston.html

Old News................

After reading all 9 pages I'm doing everything wrong yet having great results

 

[Bradley Walker]

It's an interesting read, although not new . There are some interesting statements about bullet seating.

 

[bozo699]

I have forgotten what this thread is even about, but the bottom line is seating depth changes is a PROVEN way to shrink groups, the guy's I shoot with at 1k fine tune there loads in this manner, I have seen it time and time again, it isn't a myth it isn't a maybe, it is a fact!!! that your groups WILL shrink once you find your ocw, primer selection, then fine tune with seating depth. You can discuss it on here tell the cows come home, break it down, analyze it to death, it works period the end, how do you unsubscribe from a thread, other forums give that option, this one has become ridiculous .
Wayne.

 

[Bradley Walker]

Well there it is...

Someone turn off the Internet on the way out... Hahaha!!!

 

[jlow]

I have forgotten what this thread is even about, but the bottom line is seating depth changes is a PROVEN way to shrink groups, the guy's I shoot with at 1k fine tune there loads in this manner, I have seen it time and time again, it isn't a myth it isn't a maybe, it is a fact!!! that your groups WILL shrink once you find your ocw, primer selection, then fine tune with seating depth. You can discuss it on here tell the cows come home, break it down, analyze it to death, it works period the end, how do you unsubscribe from a thread, other forums give that option, this one has become ridiculous .
Wayne.

You are not the only one, even the OP.... : Use the "unnotify" buttom on the bottom.