I've begun load development with a Sako A1 6 PPC and the bullets seated to just kiss the rifling (I think; I used the Hornady OAL gauge). There was no mark on bullets seated this way when a loaded round was extracted. I'd like to try the same loads with the bullets seated to engage the rifling by, say, .01". My question is whether, with the same powder charges as before (which exhibited no pressure signs), these loads are likely to be safe with the bullets seated .01" into the lands. I'm hoping for an accuracy improvement with the bullets seated into the lands.
Bullet Seating Depth and Pressure
- Thread starter South Pender
- Start date
CaptainMal
Silver $$ Contributor
"Likely so" is my opinion.
Another opinion is you will have major difficulty to measure contact with any Hornady or Sinclair tool. You can play and play to get a fair idea, maybe with an accuracy level of +- .010" Doubt you can do .001"
To do that level of detection you would have to remove the firing pin apparatus in the bolt and play with bullet-seated cases while feeling for a "free-fall" of that bolt as the cartridge is chambered. Look for Alex Wheeler's video on that subject on this forum. That could work if your bolt can be used like that. Remember also you would have to remove any spring ejector to do that or that pressure would mess with the bolt fall.
First sentence is my opinion. The rest is related but not exactly your question.
Another opinion is you will have major difficulty to measure contact with any Hornady or Sinclair tool. You can play and play to get a fair idea, maybe with an accuracy level of +- .010" Doubt you can do .001"
To do that level of detection you would have to remove the firing pin apparatus in the bolt and play with bullet-seated cases while feeling for a "free-fall" of that bolt as the cartridge is chambered. Look for Alex Wheeler's video on that subject on this forum. That could work if your bolt can be used like that. Remember also you would have to remove any spring ejector to do that or that pressure would mess with the bolt fall.
First sentence is my opinion. The rest is related but not exactly your question.
Just another opinion.
I get repeatable measurements within 2 or 3 thousands with my stoney point. I want to know where the lands are not the begining of the throat. I push the bullet in till i feel resistance. That is the begining of the throat. Then with another little push and a few taps on the rod i feel the bullet stop. That is hard into the lands and that measurement is very repeatable. Now you have to be very careful about how you extract the gauge. Best way i have found is to make sure the set screw on the rod is tight and extract the gauge leaving the bullet in the barrel. Then use a dowel rod.or your cleaning rod to push the bullet out. Put the bullet back in the gauge and measure.
The wheeler method will find that first resistance point, the begining of the throat, but it will never find the.lands.
There is a good chance you are already in the lands. It takes almost zero pressure to push the bullet into the lands with the Hornady OAL tool. ALEX Wheelers video is a better way. If you have zero pressure (No measured case expansion) I don't think another .001 is going to raise it to a danger level. Matt
Northridge
Gold $$ Contributor
Richard all methods of finding seating zero can and are flawed not just the "wheeler method as it has been dubbed, this method has been used for years long before wheeler made time to video the procedure. but I disagree with your statement partially. on a fresh or less used throat the wheeler method is quite precise given a round is used with little to no run out, but as a throat advances you will loose actual contact of land face and will be measuring front of lead erosion not land erosion. land erosion will be advanced and forward of the lead diameter contact. as this developed all methods of finding zero become less repeatable.
Shawn Williams
Mulligan
Silver $$ Contributor
^^^^^what he said^^^^
CW
A soft jam is another technique i use. Then you really don't have to worry with chasing the lands.
I really don't worry too much about the pressure rise from jamming bullets but then again with my bench guns i usually do my load development jammed. Start about .010 into the lands and work out from there.
I really don't worry too much about the pressure rise from jamming bullets but then again with my bench guns i usually do my load development jammed. Start about .010 into the lands and work out from there.
With all due respect, seating a bullet to “kiss the rifling” is a fool’s errand. No one can do this with that degree of accuracy. Remember, even if you can seat a bullet to that degree of accuracy, there are still other variables such as headspace, bullet variation in BTO measurements, just to name a few. Most people for safety sake and consistency are either OFF or JAMMED especially if you are loading to the edge of pressure.
Bullets seated near or in build excessive pressure on ignition. So if pressure is a issue jump them . Larry
Why "Excessive Pressure"?
dmoran
Donovan Moran
Benchrester's for one, will knock holes in those statements.
Myself over many years, barrels, and bullets its typical for my optimal seating to be in the .003 to .010-ITL neighborhood to my match petloads. From qualified bullets, it is relatively easy to hold 0.001" max seating comparator measurements. In fact, if getting more then 0.001" variation in seating depths, need to step back and find/fix the issue. Hardly know anyone who is not similar to this in the benchrest crowd.
Donovan
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The only way I've been able to get the Hornaday OAL gage to measure to touch, and do it repeatably is to run the Hornaday modified case through my sizing die, and seat the bullet long. Slide it into the chamber using the tool screwed into the cartridge, and give it firm push. Upon withdrawal you will feel it stick, and then break away. Continue reducing the seating depth until you feel no "stick". Helps to have cleaned the chamber/throat free of carbon first.
One caveat though, the Hornaday modified case will probably be shorter than your Fire Formed (FF) brass. Measure the difference and ADD that to your dimension to get what YOUR brass should measure with the bullet touching lands.
As a proof, take one of your FF brass and drill and tap the flash hole to 6/32 to fit a segmented cleaning rod. Perform the same test as above using YOUR FF brass to confirm your method and math.
One caveat though, the Hornaday modified case will probably be shorter than your Fire Formed (FF) brass. Measure the difference and ADD that to your dimension to get what YOUR brass should measure with the bullet touching lands.
As a proof, take one of your FF brass and drill and tap the flash hole to 6/32 to fit a segmented cleaning rod. Perform the same test as above using YOUR FF brass to confirm your method and math.
At least in my book, kissing implies touching, and 3 to 10 thousands off is not touching.
dmoran
Donovan Moran
@South Pender
In my experience and from collected pressure traces, pressure and velocity fallow suite dominantly. One can reference pressure by obtained velocity data and also by POI shifting on the targets. To experience pressure rises or falls, you can also expect to see the velocities rise or fall linearly, and also POI shift. Below is a target example of POI, and typical of the pressure variation I see from Off to In (normally minimal, 2% or less - IME):
Donovan
In my experience and from collected pressure traces, pressure and velocity fallow suite dominantly. One can reference pressure by obtained velocity data and also by POI shifting on the targets. To experience pressure rises or falls, you can also expect to see the velocities rise or fall linearly, and also POI shift. Below is a target example of POI, and typical of the pressure variation I see from Off to In (normally minimal, 2% or less - IME):
Donovan
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It really does not matter, my post was to the OP who was talking about touching and my comments relates to that. So with your technique can you honestly say that you can reproducibly do touch seating for every loaded round? Not 3 thousands jump or 10 thousands jam but exactly touching.
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Exactly, there are quite a few things that can foul that apparently perfect measurement. Unless you take all the precautions, and there are a lot, loading to touch length as I said previously is a fool's errand.
Hard to hit a moving target.
.001 neck tension or less, seat the bullet well past the lands and finish seating the bullet the rest of the way closing the bolt.
Solves a multitude of problems. Don't have to worry with seating depth. Don't have to chase the lands, Don't have to worry about how long the rounds have been loaded because you reseat them right before you fire them.
If you find a load and bullet that shoots well like that it simplifies everything.
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I am beginning to think along these lines too, seating long with low neck tension. Measurements I have taken since I started shooting my 6mmBR indicate that the throat is eroding at a rate of about .001" per 10 shots, or .042" over 454 rounds down the barrel, which seems excessive.
Maybe some of you more experienced hand loaders can write about your experiences with regard to throat erosion, how you cope, how often you measure. Inquiring minds would undoubtably like to know.
For my cartridges/bullets, luckily, best seating has been OTL. With this, I do not ever have to chase lands or change CBTO.
If my best seating was ITL, I would seek a soft seating load, and accept or not that I would have to replace barrels faster with that combo..
If best was TL, just touching, I would change everything needed to get away from that. Hell, within a few range sessions I would lose that condition with a given CBTO.
I agree also that depending on the ogives, what we refer to as land contact relationship, could actually be throat contact relationship.
Land marks are different than throat. And lands would erode away faster than throat, so I could picture combinations that are very short lived and leading to pure tail chasing.
So my preference will always be OTL to begin. It's better in the long term.
If my best seating was ITL, I would seek a soft seating load, and accept or not that I would have to replace barrels faster with that combo..
If best was TL, just touching, I would change everything needed to get away from that. Hell, within a few range sessions I would lose that condition with a given CBTO.
I agree also that depending on the ogives, what we refer to as land contact relationship, could actually be throat contact relationship.
Land marks are different than throat. And lands would erode away faster than throat, so I could picture combinations that are very short lived and leading to pure tail chasing.
So my preference will always be OTL to begin. It's better in the long term.
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