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  #21  
Old 02-27-2012, 07:08 AM
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That method of gauge construction sounds very interesting and effective. Cost is right up my ally too, I think I am going to have to give this one a shot. I have a spent case with a slotted neck that I was trying to use but that just resulted in a jam into the lands and pulled the bullet back out when I turned the bolt out so not very effective. Thanks for your post!
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  #22  
Old 02-29-2012, 12:14 PM
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Try pushing the case into place just using a finger or a piece of dowel rod. Then use a cleaning rod to gently push the bullet and case out from the bullet nose. The idea is that the rod will overcome the jamming grip and that the friction between the case and the chamber will not be so great that the bullet is pushed into the case in order to back it out.
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  #23  
Old 10-14-2013, 07:07 AM
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If a reloader could drill the flash hole/primer pocket to a diameter of a cleaning rod and had a short cleaning rod they would not need the Hornady/Sinclair comparator. There would be no need for modified cases with necks that had reduced bullet hold.

I want my case necks to have all the bullet hold I can get, by drilling out the flash hole I can seat a bullet in the case, chamber the case and push the bullet out until it contact the lands. By pushing the bullet out of the case I have made a transfer for transferring the dimensions of the chamber to the sizing die. To seat ‘off the lands’ I simply zero the seating stem height above the die when adjusting the die to the transfer.

Why all the bullet hold? Bullet hold makes it possible to save the modified/drilled out case, there is no reason for waking up everyday and starting over. Then there is the length of the case, the modified cases that screw onto you’re gage, modified cases come in one model, they do not offer go, no and or beyond length, what length? Who knows? No one measures.

F. Guffey
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  #24  
Old 10-14-2013, 07:10 AM
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Quote:
Originally Posted by westcoaster222 View Post
That method of gauge construction sounds very interesting and effective. Cost is right up my ally too, I think I am going to have to give this one a shot. I have a spent case with a slotted neck that I was trying to use but that just resulted in a jam into the lands and pulled the bullet back out when I turned the bolt out so not very effective. Thanks for your post!
Squid necks, slotting the neck reduces bullet hold, I want all the bullet hold I can get.

F. Guffey
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  #25  
Old 11-27-2013, 01:37 PM
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Very slightly off topic, Personally I use the Hornady OAL tool and also the Hornady bullet comparator (with all the different inserts), the Hornady tools work well as they should and any tool which does similar is showing that the shooter cares about achieving best accuracy.
The questions I have are what desired measurement (if any) is best for each rifle brand / calibre, surely there are countless users who have experimented and come upon a set measurement of what the actual best distance is to seat whatever bullet type off the lands in their particular rifles, if so lets hear them, and share the knowledge with us all.
Comparing some factory rounds will show some factory offerings are set well back off the rifling, some at .250" or more, so I have started investigating this magic seating depth for at least my rifles (222, 22:250, 7-08, 308 7RM and even the 30:30 which can be the least accurate and have set all my first serious reloads at .020" back off the lands which is documented to be at least a good starting point.
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  #26  
Old 11-27-2013, 01:50 PM
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Are you saying you only back off the 30-30 bullet .020?

Thats one that I would simply use the max recommended OAL.

On spitisers depending on the type of barrel (factory or custom) you can back them off from .010 to .030

Hunting bullets ars best left at typical recommended length for safety and sure chambering and extraction, other wise may not be able to chamber it remove it safely.

As far as bench shot target bullets you have to test each bullet and rifle barrel for best accuracy.

Last edited by JimboLLN; 11-27-2013 at 01:56 PM.
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  #27  
Old 11-27-2013, 02:43 PM
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Well yes, some of the JHP bullets made for the 30:30 with cannelures the measurement is close to that when crimped into the centre of the groove, obviously the bullet makers have some idea of the desired jump, I simply tested the COAL for my information to find they were near spot on at .020".
That's for a Marlin 30:30 lever action in my case.

Winchester 150g PPFN
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  #28  
Old 11-28-2013, 07:26 AM
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Digisol,

You're chasing a phantom. There is no fixed best seating depth. It varies with the normal tolerances in chambers and bores. Manufacturers follow the SAAMI standard which is there to ensure fit in and feed from a magazine, not for best target precision.

This write-up from Berger on how to select a best seating depth explains that their standard recommendation to work loads up with the bullet jammed into the lands worked well for some, but failed to group well in other rifles, leaving the owners of those rifles with the impression the Berger VLD's just wouldn't shoot in their rifles. But eventually it was figured out those same rifles would often shoot well only with the bullet backed up as much as about an eighth of an inch off the lands. They test in steps of about 0.030" for target work until the best spot is found.

Item 3. in the first half of this old page explains that the powder maker Somchem in South Africa used to do the same thing with hunting rifles as a shooter service, backing the bullet up a little at a time until the best seating depth for precision on the target was found, rather than merely what's best for feed and function from the magazine.

In the Precision Shooting Reloading Guide in 1995, Dan Hackett, a benchrest shooter, describes how, in changing to loading a Nosler 50 grain bullet from loading another bullet for his 220 Swift, he accidentally turned the micrometer adjustment on his seating die down 0.015" instead of backing it out 0.015", so he wound up seating twenty rounds with the bullet 0.050" off the lands instead of the target 0.020" off the lands. He intended 0.020" because "everyone knew" that was the best number (at least, everyone in his crowd did; other crowds like 0.015" and others like 0.025" and others like 0.030").

Once he noticed the error, Hackett stopped loading and corrected the adjustment. But he decided to use the 20 rounds in practice rather than pulling them down and re-seating. Good thing. At 0.020" off the lands the gun had never shot 5 rounds into less than 3/8" at 100 yards, despite his various efforts at charge adjustments and tweaking the rifle. But the rounds that were 0.050" off the lands gave him two 1/4" 5-shot groups, and two bughole groups in the 1's (groups between 0.100" and 0.199"). So on that day, with that bullet, Mr. Hackett learned his rifle likes them 0.050" off the lands.

So, why didn't 0.020" (or 0.015", or 0.025", or 0.030") work equally well. I don't think anyone knows for sure. Dr. Lloyd Brownell's theory that pressure change with seating depth is affected by the amount of gas that bypasses the bullet base after the neck lets go of it and before the bullet gets to the throat and obturates the bore, cutting that gas off, may be a factor. As that gas bypasses the bullet it can form an air cushion around the bullet rather like an air hockey table, and that cushion may help center the bullet in the freebore if the gas flow is not too slow to make the cushion and not so fast it tilts the back of the bullet up. This means it has to be in the right pressure range and have enough clearance to flow, but not too much clearance. Obviously all that will change with how fast the powder builds pressure, and what the exact diameter of the chamber neck and freebore are and with what ogive radius the bullet design has. So, for any combination of a particular bullet nose profile and a particular chamber, you will have to find the seating depth that minimizes the group size, then further adjust the powder charge for minimum group size at that seating depth.

All that said, it is, in a good rifle, usually possible to tune loads down to 1/2 moa range with a standard seating depth where the bearing surface of the bullet is about 1 caliber into the case neck, where that's practical. So we are talking about very fine tuning here in most cases, and only a few where a gun just won't shoot anything well without tuning seating depth.
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Last edited by unclenick; 11-28-2013 at 12:20 PM.
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  #29  
Old 11-28-2013, 07:43 AM
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I too got in the habit long ago of starting jacketed bullets 0.020" from the lands, under the mistaken impression it was always "best." The eye-opening for me was getting a couple of rifles (one a tang-safety Ruger 77 in .338 Win Mag and the other a Vanguard .257 Weatherby) that had throats too long to do that. Both rifles group extremely well, the .338 amazingly so considering the recoil, with bullets a long ways from the lands.

Actually, years before that, I had experimented with 40 grain Ballistic Tips in a .22-250 where the throat was too long for that bullet, but never fired many of them and failed to quite grasp they were also quite accurate even though that bullet weight had to be seated a fair amount from the lands. The gun has a heavy barrel and is quite accurate with practically anything. But I had just started serious handloading and that, too, didn't sink in till many years later. The .338 was really the kicker (pun intended) for me to figure all this out.

What I did find that helped more than anything else was to check the concentricity of loaded rounds. I had a .257 Roberts die with a cracked seating stem and the gun would throw flyers even with rounds seated the "magic" 0.020" from the lands. About that time I got an RCBS Case Master and on further investigation, noticed that an occasional round was reading as much as 0.019" off center, when "good" rounds were generally well under 0.005" via the tool. Disassembling the seater die showed the problem. The seating stem may well have been cracked from day one - who ever takes those things apart? I put a seater stem from a 6.5x55 set in the die and presto, the problem went away.

RCBS, to their credit, sent me a new seater stem for free.

Anyway, long story - I still do start load development for jacketed bullets at 0.020" from the lands, out of habit, if the gun will take that length through the magazine. And, honestly, for hunting guns, once the powder charge is worked up to best accuracy, never have had a reason to change that. But that's for big game hunting guns not target guns or small varmit guns.

There is no doubt that some of the groups could be improved by messing with seating depths further, but generally I can hit MOA or close to it with the 0.020" seating depth, seating bullets straight, glass bedding the actions and free floating the barrels as needed, and working up the powder charge carefully. That's good enough for what I do and saves further trips to the range.

You can hit a pig farther out than you want to walk to retrieve it with a 1.5 MOA load....
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  #30  
Old 11-28-2013, 04:05 PM
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Interesting topic indeed, I guess that I'm no different to any shooter who is chasing that perfect group or at a minimum a reliable 1 MOA load given that after the basics have been done and all measurements are as close to the same in each round made.

A tech from Sierra bullets had said recently "Overall I've probably seen more rifles give their best accuracy between .010" and .025" off the lands. There will always be exceptions but if I had to use something for a "gauge" it would be that measurement".

Given that I keep seeing similar starting points, it will be at least just a safe starting point and nothing more until time and the right rifle may show outstanding accuracy promise where fiddling with that jump distance might be at least a good idea at the time to investigate.

Thanks Fellas.
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  #31  
Old 11-29-2013, 07:27 AM
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It depends who you talk to.

Mid Tompkins, who has more long range gold medals than anybody else alive, AFAIK, uses soft seating. The necks are sized so the bullet can still be moved by finger pressure. They are seated long and closing the bolt on the rifle finishes seating the round against the throat. He's always loaded for himself, his wife, Nancy Gallagher-Tompkins and her daughters Sherri and Michelle Gallagher, all of whom are national and international champions.

Bart Bobbit, a two time Palma team member who's had some records in the past (his picture and a tiny 600 yard group used to be featured in one of the Precision Shooting ads for a barrel maker; Hart, maybe) says all the testing he's done over the years, including for the development of the 1992 Palma match ammo, has shown him best accuracy with tangent ogive bullets (most common) comes from loading with throat contact. There was a time when all benchrest shooters did this. Humpy, on this board, has also shot on Palma teams under Tompkins coaching, and he may have some further information on this and some ideas of his own about it.

I'll also point out that in my experiments and with those reported by others here and at The Firing Line forum, that there is often more than one seating depth sweet spot. This does not fit will with the air cushion theory, but it occurs anyway. One tends to be closer to the lands and a second one often appears with the bullet bearing surface somewhere around 1 caliber into the neck. Chambers where both are true at once with standard ammunition, like the M852 Match chamber Clymer makes a reamer for, shoot quite well. To me this suggests more than one mechanism may be involved. I'm pretty sure all of it gets back to optimizing bullet alignment at entry to the throat, though.

So it also depends on chamber geometry. Bart, for example, would likely have been working almost exclusively with tight match chambers. These tend to help limit bullet misalignment. A loose chamber may have more or different constraints, as a bullet then has more rattle room on its way to the throat.

Below are two groups fired with around 0.004" of bullet tilt off the case axis. The first is from information in Harold Vaughn's book, Rifle Accuracy Facts, in which he fired 8 rounds of 6 mm PPC by indexing the high point of the measured tip tilt at 90° intervals for a 100 yard group fired from a benchrest type gun with integral linear ball bearing free recoiling rail type machine rest, shooting down a tunnel that shields from wind. Each leaf of the four leaf clover group that results is a double hole from one of the index positions, as this gun is a one-holer with this load and no tilt. It is a group not quite 0.4 moa C.T.C.

In a different type of test in the early 60's, firing 829 rounds of National Match ammo that had been measured and sorted by runout in what would have been a tight headspace but otherwise military dimensioned chamber in a Springfield '03, A. A. Abbatiello got a larger spread of up to 2 moa from about the same amount of tilt. He also found that indexing the tilt high spot to one position in the chamber cut that group error in half and he found that tilt of more than 0.004"-0.0045" did not increase group size much further, as more tilt than that seems to straighten itself out in the bore. The second group is a calculation, therefore, using Vaughn's indexing result but applying Abbatiello's moa numbers to it. It's basically a 2.5:1 increase in effect in the sloppier chamber.



So, here's the thing: Whether you find your best seating depth or not, merely loading to maximize the straightness with which the bullet enters the throat will help a lot. At that point, finding the best seating depth mainly prevents or compensates for disturbance of that alignment during firing. It does help, as Dan Hackett's experience showed, but just by getting bullets seated straight does most of the work, you can load down to half moa groups in guns in good condition doing this and just using the bullet manufacturer recommended COL's for their bullets.
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  #32  
Old 05-07-2014, 09:17 AM
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A tech from Sierra bullets had said recently "Overall I've probably seen more rifles give their best accuracy between .010" and .025" off the lands
Could be Sierra has two shifts or more than one tech, I was told by someone that called Sierra and he said Sierra said cramming the bullets to or at the rifling in an effort to be kind to their bullets, seems they believe the bullet requires less pressure to move on down the like when it is setting at, or near or crammed into the rifling.

I make it clear I am the fan of the running start, I want my bullets to have 'the jump', if my rifle insist on seating the bullet into or near the rifling for accuracy it is not going to be accurate. Do not get me wrong, I want to know the length/distance/amount of free boar. I have rifles that are unaware they have a choice. I have pushed bullets out of cases before the bullet hit the rifling, that is FREEBORE!

I do not want my bullet to hesitate, when it gets to the rifling I want it to get on down the line, AND! I believe the bullet is upset less when it hits the rifling 'a running'. There is something about the bullet setting at the rifling at 0 miles an hour when the back of the bullet is hit with 40,000 psi +.

F. Guffey
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  #33  
Old 07-19-2015, 06:55 AM
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To resurrect and old and important subject.

The point at which the ogive hits the rifling depends on the leade angle and ogive contour of the bullet. There are two tapers coming together that are slightly different.

I've always measured where the bullet starts with a piece of straight drill rod about a foot long. Mine is something just over a 1/16" in diameter and fits through all CF firing pin holes. I made a 3/4x rod dia. collar that's a snug sliding fit on the ground drill rod.
Push the bullet into the throat firm enough to leave rifling marks and close a stripped bolt into the action. Run the spring wire through the bolt's firing pin hole and down to the bullet base and slide the collar on the drill rod to back of the bolt.
Measure the length of the spring wire, subtract the length of the bolt and add the length of the bullet base to rifling marks. That measurement is bolt face to throat leade.

When loading for one rifle, the seating dummy has been scribed at the rifling marks so I can compare a 'contact' seating with something else without using the rifle.

I find seating depth for one bullet and one load and it stays that way for the life of the barrel. Dangerous game rifles have bullets seated to feed the best.

Shortcut for a max COL seating dummy is to smear just a dab of five minute epoxy in a new, un-primed case. Barely start the bullet in the neck and carefully load in the rifle and let it set half hour or so. There is maximum COL with that bullet unless you want to add 'jamb' length to hard seat it.
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  #34  
Old 03-09-2016, 04:22 PM
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You have all the tools you need already! Your rifle's chamber and your seating die. Just remove your firing pin, ejector from your bolt, cocking pin/ ramp or anything that restricts your bolt from closing. You want the bolt to close just from the handle's weight. Seat a dummy round into a preped case slightly long. Chamber the round and GENTLY see if the bolt closes effortlessly. If it dosen't, seat the bullet a few more thou's and repeat. When the bolt almost closes by itself, seat the bullet another thousand more till the bolt closes with no effort. You are at the lands. Now set your die to your desired depth off the lands and you are good to go for the rest of your (same) bullets! No OAL, no tools to throw your measurements off, no variances in bullet tips since all measurements are taken off your gun and your die off your ogive. Even using bullet comparators throws you off because they can not and do not accurately reflect what your chamber looks like! This method limits almost all variables.

https://m.youtube.com/watch?v=Jv-D1mEI514
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