Seating Depth

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Wm Cook posted this 3 weeks ago

This is a pretty broad topic but I assume that most people, including myself have biases we bring into the initial bullet seating depth on all “new” or “new to us” rifle/barrel. What’s your starting point before you start to go further in or further out and how is it impacted by bullet design?

I guess this is more directed to long guns and shooters looking for small groups but any opinion is valuable. Thanks, Bill.

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RicinYakima posted this 3 weeks ago

Using conventional cast bullets and lube, I start with the top driving band touching the lead/origin of the rifling. The only time it is not used is with a bullet with a bore riding nose. Then I start with the nose definately engraved checked with black marker. 

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Little Debbie posted this 3 weeks ago

I use the Stoney Point (now Hornady) seating depth tool. It allows you to find where any bullet touches the lands. I adjust from there depending on what I’m trying to do. I generally like ammunition to fit in and feed from magazines, so seating depth some time becomes moot as an accuracy variable.

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John Carlson posted this 3 weeks ago

I use a cleaning rod with a flat jag.  Measure the distance from the bolt face to the muzzle.  Insert the bullet and measure from the tip of the bullet to the muzzle.  This gives me the minimum OAL.  Same as Ric for bore riders.  For tapered bullets I'll try seating longer until there is light resistance when closing the bolt.  I haven't found a sweet spot or a sour spot within those parameters.

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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Wm Cook posted this 3 weeks ago

Rick for the top driving band to touch the lead/origin of the rifling the free-bore would have to be large enough in diameter for the driving band to pass through in order to reach the leade/lands wouldn’t it?

I’v had two new Savage .308’s in the past year and both free-bore’s measured .308. The length of the free-bore is .120 on the one I’m working with now. At .120 the leade begins to form the lands.

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RicinYakima posted this 3 weeks ago

I have never had that issue, as the Savage FP rifle I have has a free bore of .310" I size to the next larger 1/2 thousandth larger. I use SAECO dies that come in 1/2 thousandths. 

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Wm Cook posted this 3 weeks ago

My FP has a free-bore of ~.3085 measured with both a pound cast and a chamber side tamped seating of an unsized bullet.

So the front band of my 311299 is seating against the wall at the end of the chamber. The seating depth variable I have with this chamber/mold combination (bore-rider) is how much crush I put on the driving band as it hits the end of the chamber before the free-bore.

The crush can be see with damage to the driving band on dummy rounds as well as with felt bolt resistance as John described.

I can jump it, kiss it or crush it into the free-bore. Or at least crush it until the neck tension allows the bullet to slip back into the case.

To be honest I’m a little bit squishy about seating out to where “light resistance is felt when closing the bolt” or “into the lands until you see engravings “. The person doing the hand-loading, the bullet taper (non-bore-rider) and/or the hardness of the alloy used makes this seem awfully subjective.

I’m crossing over from jacketed benchrest and in that discipline we know exactly where “jam” or “push back” is and best accuracy is found within .009” of “jam” position on barrels with less than 600-700 rounds through them.

I’ve talked to a couple guys who shot at the Nationals and they described the neck tension they used as light. Light to the point that it almost sounds like each round seats itself as the bolt closes.

I got a lot to learn.

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RicinYakima posted this 3 weeks ago

Cast bullet shooting is an art, not a science. Your cast bullet will become a wad of bubble gum upon ignition. 

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Wm Cook posted this 3 weeks ago

Probably a lot of truth to that but I nearly busted a gut laughing when I read your response. I just gotta laugh at myself once in a while. Thanks, Bill.

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4and1 posted this 3 weeks ago

Aint touching any of this............

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Geargnasher posted this 3 weeks ago

Cast bullet shooting is an art, not a science. Your cast bullet will become a wad of bubble gum upon ignition. 

 

Actually, the bubblegum phase happens much farther up the bore, likely an inch or more depending on the load.  Once the bullet moves and encounters enough resistance from engraving to increase the powder gas pressure beyond the ultimate strength of the alloy, the bullet base can begin to rivet and/or bend in the throat.  

The less "jump" or "run at the throat" that the bullet has, the higher the initial pressure and more steep the pressure curve.  An analogy is an air or refrigerant compressor starting against a full load versus against no load due to a check valve and relief valve.  More inertia from the bullet accelerating prior to taking the rifling form and less engraving resistance reduces bullet distortion, which is why relatively soft powder coated bullets with a tapered, self-aligning nose shape sized smaller than throat entrance diameter can be fired with full charges of rifle powder at maximum loads with decent accuracy and no riveting of the bullet base.  Pressure may reach 55K psi but the bullet is 3" down the bore and running away from the gas at many hundreds of feet per second squared before that pressure level is achieved, so the bullet is fully-contained in the bore and has nowhere to go but straight ahead.

The same principles of jump, self-alignment, sizing, and ductile alloy can be applied to ordinary, lubricated cast bullets, but it is trickier and has lower limits than the powder coat allows.  Still, if the bullet is raking off a bunch of metal on the abrupt throat entrance angle because it is too big, or is cast of a very hard alloy and jammed hard against the ball seat, the base will rivet and then draw down through the funnel of the throat, often not in any semblance of concentricity, balance, or squareness. 

I say all that to recommend never sizing larger than throat entrance diameter, never jamming a cast bullet hard into the ball seat, never use hard, brittle alloys, and avoiding perfectly-matching bullet/throat angles which bring a sudden increase to engraving resistance and spike the powder pressure against the bullet's base.  I know this is contrary to everything ever done in cast benchrest shooting, but it works very well in conventional, production rifles. 

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freebullet posted this 3 weeks ago

Err..uh... sometimes a little jump aint bad thing.

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Larry Gibson posted this 3 weeks ago

"The less "jump" or "run at the throat" that the bullet has, the higher the initial pressure and more steep the pressure curve."

That is the theory that has been around for as long as I remember.  The analogies supporting it, for the most part, all sound reasonable.  However, I have not been able to verify higher pressure occurs and/or a steeper pressure curve in actual pressure tests with cast bullets seated firmly into the leade or seated off the leade any reasonable distance.

A cast bullet, even a "hard" cast bullet, is much softer than a jacketed bullet.  The pressure needed to swage down and engrave the lands into the bullet is much less.  That swaging down and land engraving happens very early, at the beginning actually, of the pressure rise.  It seemingly, so far at least, has little if any measurable effect in the pressure or pressure curve with normally sized cast bullets that are not larger than the chambers throat.

LMG

Concealment is not cover.........

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45 2.1 posted this 3 weeks ago

Not everything (common knowledge or otherwise) one sees , reads and hears will get you what you want. Let the target decide.

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Wm Cook posted this 3 weeks ago

Not everything (common knowledge or otherwise) one sees , reads and hears will get you what you want. Let the target decide.

Agreed that you need a number of groups shot consecutively under real or simulated match conditions to see the effects of COAL changes.  My initial post was to see if there were any prejudices that you bring to the loading bench on the first attempt at developing an accurate load.

Cast bullet shooting is an art, not a science. Your cast bullet will become a wad of bubble gum upon ignition.

Maybe sometimes we mix the definitions of learned skills and art.  To a newbie, laying bricks may look like an art, but for most, not all maybe, but for most people if they put in the time and effort they can become average or maybe even good at laying bricks.  Some may think that casting quality competition bullets is an art.  But maybe we aren't giving enough credit to the individual that worked in the field long enough that skills were gained (trained or self taught) that enabled them to exceed. Just look at the results of the Nationals this year the the number of sub 1" group aggregates that were shot.  Look at all the .5's that were shot in the unlimited class.

When it comes to the performance of a mechanical object (mold, chamber, leade) science may have its part to play.  Larry is the only person I know that has can measure chamber pressure.  If jumping to jamming shows no significant effect on pressure some would have to give credit to that.  Maybe n my old age I'm getting more cynical about the use of the word "art" as if there are some things that only some can achieve.  If I think the numbers are gathered correctly I take that as a solid foot hold that I can build on.  And absolutely no offense to Geargnasher.  I've been reading you post for years and you have helped me an others more than you could possibly understand.

My motive is cast accuracy.  I believe it was Ken (if I am wrong and it wasn't Ken I apologize) who said that accuracy is defined in the first inch of travel.  If I remember correctly, and I'm paraphrasing, if the necks are turned, the case is neck sized the anchor points of the tension of the bullet in the case and the tension of the grip in the leade/lands will at least start the bullet in the right direction. 

My personal opinion is whether you call it art or learned behavior that's were the proper bullet seating depth comes into play.  I was just wondering if there was a tendency to self seat the bullet or were you just short of sticking in the lands.  Sorry for being lengthy.  And I apologize if I offended anyone. That was not my intentions. Thanks, Bill.

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RicinYakima posted this 3 weeks ago

Bill,

 "Some may think that casting quality competition bullets is an art.  But maybe we aren't giving enough credit to the individual that worked in the field long enough that skills were gained (trained or self taught) that enabled them to exceed."

That is the definition of a manual art. 

Science is "knowledge about the natural world that is based on facts learned through experiments and observation." It has to be 100% repeatable by anyone doing the same experiments without regard to place or time. Cast bullet shooting isn't there yet.  

IMHO, Ric 

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John Alexander posted this 3 weeks ago

I agree with both Bill and Ric in the two posts today. I also agree that that there is little scientific method applied to improving cast bullet shooting.  But that isn't because shooting cast bullets is  somehow different from other areas where applying the scientific approach to figuring out truth from myth has allowed great strides and great improvement.

The reason that there few instances of scientific methods being used to improve results is that cast bullet shooter, in general, aren't interested in doing experiments and repeating other shooters experimental results to sort out what thing might improve performance.

Larry's post above, by using a scientific approach to find the truth about an aspect of CB shooting, discredits a perfectly reasonable sounding theory about pressure rise. These things can be done -- we just don't generally do them, and when they are done we tend to disregard the results and go back to our previous belief.

Instead of experimenting with enough shots fired to have repeatable results most CB shooters would rather rely on three other approaches to try to improve.

1. Seek perfection with absolutely perfect bullets carefully sorted by weight, careful powder weighing, elaborate case prep, indexing bullets, cases and even primers, etc.

2. Depend on old rules handed down as the conventional wisdom. A perfectly perfect base is needed with sharp edges even when covered with a gas check. Don't let the base of the CB hang below the neck in the case.  Make sure your rounds are concentric. Make sure your crown is perfect. The way to improve your groups is to eliminate fliers -- believe that small groups don't have fliers without ever looking at them. Find the sweet spot for your rifle by ladder testing with a series of single five shot groups. Tune your load to your rifle by depending on single three shot groups being a valid measure for what the load will actually do in a match.  

3. Use logic without checking your assumptions. Think real hard and reason out what happens to a cast bullet from case to target. Reasoning that since the muzzle is the last thing the bullet touches, a less than perfect crown will cause inaccuracy. Reason that variations in bullet weight or variations in case weight (thus volume) obviously will affect accuracy.  Reasoning (without considering the numbers involved) that variations in neck tension affect accuracy.

None of these three approaches will help us improve what we know about CB shooting, nor shrink our groups.  Many of the above have been shown to be worthless more than once starting with Dr. Mann 120 years ago and by others since then using a scientific approach. However, the typical CB shooter disregards information that shows that what he had been told by good shooters and believed up until now is false. Worse than disregarding experimental information he is often hostile to it. We don't like to change our beliefs. This is just human nature and people in science or engineering research have to guard against it to make progress.

Until we change our approach there will be little improvement in cast bullet performance.

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MP1886 posted this 3 weeks ago

John I understand what you are saying. When you mentioned the crown of the muzzle it made me think of something not talked about much here. It's barrel turners.  I have a Mechanical Engineering friend who has a good friend that is a machinist and gunsmith. They came up with a barrel tuner/muzzle break. He was interested in how their tuner would work with my cast bullet shooting.  I done a lot of testing. This started when I bought a Browning A-Bolt Varminter with the BOSS tuner on it.  Now as compared to my engineer friend's tuner the BOSS is crude in only it's adjustments.  Well let me tell you that tuner sure shrunk my groups.  If you were adjusting it in the right direction you could actually see your group get smaller like you were dialing it in. Now on the my cast rifle with the tuner I came to the conclusion that the muzzle break portion of the tuner was doing something to the bullet so that it wouldn't group well.  Now let me stop there and tell this story.  I'm talking about an AR10 with a heavy barrel in 7.62 NATO.  When I built it I didn't put a flashhider on it at first. I made a thread protector.  I started developing cast loads and  had it shooting very well.  Then my flashhider came in the mail. I installed it and immediately my under moa groups went to 3 moa.  Just to make sure the hider done that I removed it and the groups went back to the tight ones.  Back on again they openned up. So that was it, no hider on that rifle. Back to the tuner/muzlle break.  We couldn't figure out why the break portion disturbed the bullet.  So my friend tells me to machine it off which I did.  Then it started working.  Tuners aren't going to make a miracle benchrest rifle out of your cast bullet shooting, but they do help and I believe more so then all the benchrest tricks with the case and such. Like I said tuners aren't talked much about here. 

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RicinYakima posted this 3 weeks ago

I did the tuner thing back in the '80's and '90's shooting BR 50 22's. Yes they work but only with a setting for one lot of ammo without changes. Some ammo was so inconsistent that the tuner never helped. Those pesky barrel vibrations keep rearing their ugly heads. 

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RicinYakima posted this 3 weeks ago

John, I was disappointed when no one expressed any interest on my work a couple of years ago on bad bullet groups. Five shot groups will be OK with some pretty ugly bullets. BUT using the old "tricks" more X's and ten's are scored if shooting for precision of each shot. Ric

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MP1886 posted this 3 weeks ago

I did the tuner thing back in the '80's and '90's shooting BR 50 22's. Yes they work but only with a setting for one lot of ammo without changes. Some ammo was so inconsistent that the tuner never helped. Those pesky barrel vibrations keep rearing their ugly heads. 

Rick listen to this story. There's this benchrest shooter gunsmith. He got to thinking one day about the forward action screw in the front receiver ring and also a gas escape hole if it had one.  He build a test 222 Rem, nothign fancy.  First he got an average group with the rifle untouched. Then he drilled a hole direct opposite of the forward action screw. I can't remember if he treaded it or not and of course the hole he drill was on top of the receiver ring. Back to testing and the average group got a little smaller. He done the same with the gas port hole and again the average group got smaller.  This all started when he was thinking about barrel vibration and how the holes in the receiver might affect them. There's many vibrations going on when we fire a gun. 

That Mechanical Engineer friend of mine was very interested in my cast shooting.  That is something he had never done. He asked me one day if I could take a picture of me firing that AR10 at night so he could see how much flash came out of the muzzle break portion of the tuner and also the muzzle. It happened to be a very dark night. I'm not kidding you there wasn't even very much of a glow at the muzzle!  He inquired about the load. At that time I was using a very slow surplus ball powder with a booster.  His exact words were when he saw my video "The Military would be interested in that"!!  It wasn't any reduced load either, it was a factory equivalent jacketed load. The total powder charge was 44.5 grains. The barrel length was 20 inches and plus the tuner/muzzle break which wasn't very much longer then a flashhider if that.  No I never shot the rifle without the tuner minus the muzzle breaker portion. I also don't have the video anymore. Maybe some night I'll do it again. I have no explanation for it and agreed with my friend that the powder charge definitely was totally consumed in the barrel, but yet why no flash?

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