Seating Depth/Pressures?

[Siggy Stardust]

Hey All!

Had a couple questions to throw out there regarding seating depth and pressures. I've been reloading for some time but couldn't really seem to find any hard answers on these issues...

#1) Seating Depth - I remember hearing long ago that in many cases the closer you could reasonably get a bullet to the lands without contacting it, the better for accuracy. It's been so long, I can't even remember where it came from, but it seemed the concensus on a good distance off the lands was about 0.020".

I was just wondering what you fellow reloaders out there had in mind for a starting point to seat a bullet off the lands. Is 0.020" too close/too far? What has generally worked for you? This leads me to:

#2) Pressure - I always assumed that seating a bullet further out for a longer C.O.L. would result is slightly lower pressures since there is more room in the case for gases to expand. I then got to wondering if, on the flip side, that having a bullet closer (too close?) to the lands could result in higher pressures since said bullet hasn't built up as much momentum before jamming into the rifling as it would if it was seated further back, resulting in a pressure spike?

...or maybe I'm just splitting hairs here...

I remember loading for a Browning A-Bolt Stalker my wife had years ago in 7mm-08. I was seating 0.020" back and a few grains below max load. Velocities were in the ball park but man - was that thing punishing. Got the 7mm since it's renowned for being easy on kids and women in the recoil dept., but it was more than I would've expected - more kick than my .270. Wife decided she didn't like it and we traded it away on a .243.

Anyway, just looking to see if I'm on the right track or way out in left field on these couple points.

Any feedback would be much appreciated!

Cheers!

 

[savage.3006]

For accuracy I am 5 thou off the lands in my target rifle but 20 thou in my hunting rifle. There is more pressure the closer you get to the lands ( so I have been told) .

 

[Johnny_Zanni]

You are correct about the pressure. A bullet drove into the lands will develop a higher peak pressure. Some bullets like to be close to the rifling, some don't and others don't care much. 0.010-0.020" off seems the be the norm people suggest.

 

[bigedp51]

Many competitive shooters jam their bullets hard into the rifling without any pressure problems, you just need to use workup loads starting at the recommended start load. At http://www.accurateshooter.com/ you can read about it and its done all the time.

When thinking about pressures and seating off the lands as normally done, the bullet starts to move forward without any resistance. The pressure is building and suddenly the bullet hits the rifling and the pressure spikes. When the bullet is jammed into the rifling the pressure builds and because there is no bullet jump there is no rapid pressure spike. This might sound a bit odd but after reading about it I tried it using a workup load to near max without any pressure signs. The actual pressure problems occurs when you make larger bullet seating adjustments without backing off your powder charge and working up again.

Using the software Quickload your pressures are higher by seating the bullets deeper into the case than seating the bullets long. Also case capacity effects you pressures more than seating depth, below is an example of the pressure curve with case have 2 grains less internal capacity and have higher pressure.

Below both cases have the same exact powder charge and seating depth, but the higher pressure curve has less case capacity.





Below is an article from AccurateShooter, the bullets are "jammed" into the rifling with NO bullet jump. These bullets are seated .005 to .010 into the rifling from the point where the bullet first made contact with the rifling and were stopped.


The F-Class Winning Formula

Reloading and Load Testing

"My loading procedure is pretty simple. I use a Lee auto prime to seat primers and I weigh all my powder charges on an RCBS 502 scale. I use Redding ‘S’ FL-sizing dies and try to keep neck tension to about .001″ to .0015″. If possible I want light enough tension that I can soft-seat the bullets but heavy enough so as not to pull the bullets when unloading a live round. This can be difficult to achieve. I seat the bullets about .005″ to .010″ over the ‘touch’ length when using the split-case method. Brass prep consists of chamfering and running them through a sizing die to straighten the necks. On my 6.5-284, I turn the necks to .003″ clearance. The 6BR is a .271 no-turn neck. I don’t do many of the things that other shooters do. I don’t debur flash holes or recut primer pockets. I don’t weigh or sort bullets and cases. And I don’t clean primer pockets. I’ve tried all those procedures at one time or another but never saw any gain in accuracy."

http://www.accurateshooter.com/guns-of-week/gunweek063/

 

[H4831]

My experience has been that no noticeable difference in pressure occurrs in rifles, whether the bullet is seated real deep, or whether it is jammed into the lands when the bolt is closed.
I just started reloading for a Marlin in 35 Remington. First thing I wanted to know was whether or not I had to crimp the brass.
So, after shooting a couple that were a grain under Hodgdon's full charge, from memory I think it was 39.5 of Varget, with 200 grain bullet, I put five loaded full charge, according to Hodgdon, into the magazine. The first one took a little extra on the lever to fully seat it, thus it was hitting the lands. I fired four, then checked the last one, to see if the bullet had moved in the case. It had moved, tight back on the powder and was obviously seated much deeper than normal. I then fired it and examined all the spent brass. With pressures of a lever action, abut the only pressure signs one can look for is the unreliable indicator of how flat are the primers. The CCI primers had absolutely no excess flattening, but there was no noticeable difference between any of them, even when examined with a magnifying glass. And remember, those five went from the first one hitting the lands, to he last one with a very large jump.
Also, all five made a group of what one would expect from a a 1950's Marlin with a vintage Weaver K3 scope at 100 yards, an inch and a half, five shot group.
It was obvious that I will have to crimp the brass. It also reinforced my firm belief that with a sporting/hunting type rifle, it doesn't matter, as far as acurracy and/or pressure is concerned, two hoots in high hell, whether the bullets are seated deep, whether they hit the lands, or are seated somewhere in between.

 

[22to45]

Thanks for this, I have been loading for various hunting rifles for about 35 years, and while I have had a couple rifles that were not accurate, for the most part I seat bullets to the cannalure, and if I happen to have a Lee crimper for the cartridge I crimp them. I have had lots of rifles that would shoot 2 inches this way and a few that would shoot under 1. I have not spent a lot of time looking for the sweet spot in the overall length department.

My experience has been that no noticeable difference in pressure occurrs in rifles, whether the bullet is seated real deep, or whether it is jammed into the lands when the bolt is closed.
I just started reloading for a Marlin in 35 Remington. First thing I wanted to know was whether or not I had to crimp the brass.
So, after shooting a couple that were a grain under Hodgdon's full charge, from memory I think it was 39.5 of Varget, with 200 grain bullet, I put five loaded full charge, according to Hodgdon, into the magazine. The first one took a little extra on the lever to fully seat it, thus it was hitting the lands. I fired four, then checked the last one, to see if the bullet had moved in the case. It had moved, tight back on the powder and was obviously seated much deeper than normal. I then fired it and examined all the spent brass. With pressures of a lever action, abut the only pressure signs one can look for is the unreliable indicator of how flat are the primers. The CCI primers had absolutely no excess flattening, but there was no noticeable difference between any of them, even when examined with a magnifying glass. And remember, those five went from the first one hitting the lands, to he last one with a very large jump.
Also, all five made a group of what one would expect from a a 1950's Marlin with a vintage Weaver K3 scope at 100 yards, an inch and a half, five shot group.
It was obvious that I will have to crimp the brass. It also reinforced my firm belief that with a sporting/hunting type rifle, it doesn't matter, as far as acurracy and/or pressure is concerned, two hoots in high hell, whether the bullets are seated deep, whether they hit the lands, or are seated somewhere in between.

 

[Siggy Stardust]

Many competitive shooters jam their bullets hard into the rifling without any pressure problems, you just need to use workup loads starting at the recommended start load. At http://www.accurateshooter.com/ you can read about it and its done all the time.

When thinking about pressures and seating off the lands as normally done, the bullet starts to move forward without any resistance. The pressure is building and suddenly the bullet hits the rifling and the pressure spikes. When the bullet is jammed into the rifling the pressure builds and because there is no bullet jump there is no rapid pressure spike. This might sound a bit odd but after reading about it I tried it using a workup load to near max without any pressure signs. The actual pressure problems occurs when you make larger bullet seating adjustments without backing off your powder charge and working up again.

Using the software Quickload your pressures are higher by seating the bullets deeper into the case than seating the bullets long. Also case capacity effects you pressures more than seating depth, below is an example of the pressure curve with case have 2 grains less internal capacity and have higher pressure.

Below both cases have the same exact powder charge and seating depth, but the higher pressure curve has less case capacity.





Below is an article from AccurateShooter, the bullets are "jammed" into the rifling with NO bullet jump. These bullets are seated .005 to .010 into the rifling from the point where the bullet first made contact with the rifling and were stopped.


The F-Class Winning Formula

Reloading and Load Testing

"My loading procedure is pretty simple. I use a Lee auto prime to seat primers and I weigh all my powder charges on an RCBS 502 scale. I use Redding ‘S’ FL-sizing dies and try to keep neck tension to about .001″ to .0015″. If possible I want light enough tension that I can soft-seat the bullets but heavy enough so as not to pull the bullets when unloading a live round. This can be difficult to achieve. I seat the bullets about .005″ to .010″ over the ‘touch’ length when using the split-case method. Brass prep consists of chamfering and running them through a sizing die to straighten the necks. On my 6.5-284, I turn the necks to .003″ clearance. The 6BR is a .271 no-turn neck. I don’t do many of the things that other shooters do. I don’t debur flash holes or recut primer pockets. I don’t weigh or sort bullets and cases. And I don’t clean primer pockets. I’ve tried all those procedures at one time or another but never saw any gain in accuracy."

http://www.accurateshooter.com/guns-of-week/gunweek063/

I know what I'm seeing here and it all make sense, except for one thing:

As it shows, the two loads are identical in every way, except case capacity. What exactly is it that has to change in order to change the case capacity itself? Bullet, powder charge, C.O.L. are all identical. Is it perhaps the brand-name/manufacture of the case that has changed? Do the case capacities vary that much for the same calibre from manufacturer to manufacturer?

 

[Siggy Stardust]

My experience has been that no noticeable difference in pressure occurrs in rifles, whether the bullet is seated real deep, or whether it is jammed into the lands when the bolt is closed.
I just started reloading for a Marlin in 35 Remington. First thing I wanted to know was whether or not I had to crimp the brass.
So, after shooting a couple that were a grain under Hodgdon's full charge, from memory I think it was 39.5 of Varget, with 200 grain bullet, I put five loaded full charge, according to Hodgdon, into the magazine. The first one took a little extra on the lever to fully seat it, thus it was hitting the lands. I fired four, then checked the last one, to see if the bullet had moved in the case. It had moved, tight back on the powder and was obviously seated much deeper than normal. I then fired it and examined all the spent brass. With pressures of a lever action, abut the only pressure signs one can look for is the unreliable indicator of how flat are the primers. The CCI primers had absolutely no excess flattening, but there was no noticeable difference between any of them, even when examined with a magnifying glass. And remember, those five went from the first one hitting the lands, to he last one with a very large jump.
Also, all five made a group of what one would expect from a a 1950's Marlin with a vintage Weaver K3 scope at 100 yards, an inch and a half, five shot group.
It was obvious that I will have to crimp the brass. It also reinforced my firm belief that with a sporting/hunting type rifle, it doesn't matter, as far as acurracy and/or pressure is concerned, two hoots in high hell, whether the bullets are seated deep, whether they hit the lands, or are seated somewhere in between.

Maybe it's not such a big deal in rifle cartidges with small seating-depth changes being, relatively speaking, a smaller percentage of the big picture. When loading smaller cartridges, however, it can make a huge difference.

The Speer #11 manual cautions when loading the 9mm Para that bullets need to be seated firmly enough to keep them seating deeper (than min. recommended) into the case due to recoil since pressures rose sharply from 28,000 CUP to 62,000 CUP by a mere 0.030" deeper seating. I guess it does make a difference, but we are talking rifle calibres here and granted it's the difference between a drop of water in a shotglass and one in a 5 gallon bucket.

Just sayin'.

 

[bigedp51]

I know what I'm seeing here and it all make sense, except for one thing:

As it shows, the two loads are identical in every way, except case capacity. What exactly is it that has to change in order to change the case capacity itself? Bullet, powder charge, C.O.L. are all identical. Is it perhaps the brand-name/manufacture of the case that has changed? Do the case capacities vary that much for the same calibre from manufacturer to manufacturer?

Competitive shooters buy Lapua brass for its quality and consistency, below the average weight of Lapua .223 cases were 93.35 grains and case weight only varied 1.2 grains out of 100 cases. At the bottom are Winchester cases that averaged 93.91 grains BUT the case weight varied 6.5 grains lightest to heaviest case.

The internal case capacity controls chamber pressure and wide variations cause inaccuracy due to wide variations in velocity.




Below shows the .223 internal case capacities going from 28 grains of water to 30.6 and working up a load in one brand of brass and switching to another could cause a serious over pressure condition.
1. 26.5 grains 748, cases capacity 28 grains of water, chamber pressure 57,281 psi (55,000 is .223 max)
2. 26.5 grains 748, cases capacity 30.6 grains of water, chamber pressure 46,174 psi
3. This internal case capacity variation of 2.6 grains of water caused the pressure to increase 11,107 psi and go over the max rated chamber pressure of the .223 by 2,281 psi.



This is why competitive shooters weight their brass and even sort their cases by internal volume to get more uniform velocities and better accuracy. (Extreme Spread & Standard Deviation)

Read the link below and look at the data.

"Precision Rifles & Handloading"
http://precisionrifle.wordpress.com/category/brass/

Once you digest all this you will understand the case has more to do with accuracy (SD & ES) Even when putting the most accurate weight powder charges in cases with wide variations in weight and volume your group sizes will still be larger. When you have cases very close in internal volume you will have smaller chamber pressure and velocity variations and thus better accuracy (smaller group sizes)

Below a custom tube gun and accurate uniform reloads at 200 yards. (this rifle isn't mine, I couldn't afford it)

 

[H4831]

Siggy Stardust, I am well aware of the importance of seating pistol/revolver bullets correctly.
Thus, I used this, "sporting/hunting type rifle," in stating my experience.
I thought that was pretty plain, that I was not referring to handguns.

 

[Siggy Stardust]

Siggy Stardust, I am well aware of the importance of seating pistol/revolver bullets correctly.
Thus, I used this, "sporting/hunting type rifle," in stating my experience.
I thought that was pretty plain, that I was not referring to handguns.

Roger, dodger - I'm picking up what you're throwing down. Just pointing out the huge difference that things which are almost insignificant on a large scale can make when scaled down - that's all. No offense intended.