Seating Deapth Tuning

C

C.L. Peterson

Active member
Has anyone done any experminting in tuning by seating deapth.
When on has their pet load and its out of tune rather than adjust powder is it possible to recapture the tune by seating deapth change only? If possible does one increase or decrease seating seating deapth as the conditions of the day (match) change?
Any tunnel experminting done on effects of seating deapth changes?
CLP
 
Cl

The long range shooters vary seating depth to improve SD's and other velocity variables.

Many 100-200 yard shooters will find a seating depth that a particular combo likes, and leave it there, varying the charge to keep the Rifle in tune.

I think there has always been a debate about this. A shooter will say, "I changed my seating depth .005, and the thing really started shooting". My first reaction is, "if the barrel is that finiky, it probably will not stay there".

Of the three common ways to tune, seating depth, neck tension, and powder charge, I would say that seating depth and neck tension are the least important. The main thing is to be sure that they are consistant.

It is a known fact that my dies do not even have bushings, so I keep the same neck tension all of the time. I also never change the seating depth, I maintain it at a constant, because I know thw bullet-barrel combo I shoot likes it. So, that leaves me with the powder charge, and the tuner.

I will get the barrel shooting as well as I can with the tuner, and keep, (ie, TRY to keep), the Rifle agging with subtle powder changes.

I will turn the tuner if things just go haywire, but many times I resist, because if you start messing with too many things during a match, you can make a mess real quick.........jackie
 
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Jackie is a supreme competitor. He is in a different place with his practices than the average competitor because of his means, circumstances, and desire. I don't disagree with anything Jackie said but some people do things differently than he and view these subjects through a different lens so to speak. If I remember correctly Jackie posted earlier in his career the fact that he constantly set his barrels back refreshing the throat area after every 200-300 rounds (if my memory serves correctly; I apologize Jackie if I am misrepresenting you; not my intention), which precludes the necessity of changing a seating depth once established. I am not aware of many in ME that do that, so we chase the lands. I believe Jackie also uses new brass for every match? If so, that solves any neck tension issues when compared to some others that use the same brass all year (can't imagine doing that but I suppose some do).

Some people FINE tune using neck tension and seating depth but the tune has to be found first. I believe that if you have found the seating depth that the combination likes best, changing it during a match will not bring you back in tune if the gun is now out of tune. I don't think seating depth and neck tension change the bullet's barrel time enough and you have to go to changing powder charge. Of course, testing is the only way to tell for sure. Talking is cheap, especially mine! :) Randy J.
 
Seating depth is a varrible to be concerned with to all reloaders

Most Bench rest shooters set back barrels to bring barrels with erroded throats back to their original state (throat depth).

Most Long range prone shooters find a sweet spot seating depth. Many move their bullets forward during the life of the barrel. Some do what is called soft seating IE: little neck tension and the bullet after engaging the rifling pushes back in the neck until it either stops or is stopped by the powder resistence.

Different bullets with different ogives like different seating depths/engagement or jump.

Factory guns are made with a SAAMI spec chamber and the troat is cut to accept a particular range of bullet lengths and still fit in a magazine. One complaint that has been common of factory guns is that the throats are cut to long.

In my experimentation I have found generally Bergers for example like being into the rifling .010-.025 and Sierra like a slight jump .003- .006. Hunting bullets such as Barnes and Swift Scirrocos tend to like a jump to prevent presure issues.

There is much been said and written about Tangent vs Secant ogive bullets.

This is a topic that the individualshooter needs to explore with his or her rifle and ammunition.

Nat Lambeth
 
Yes, there are benchrest shooters who strictly tune with seating depth. Ed Watson's powder measure was welded to one setting and he HAD to be making adjustments some way... more than likely seating depth. It's been my experience that cut rifled 4-groove barrels seem to respond a lil more to seating depth changes than the "conventional" 6-groove. Seating depth is obviously important, but if you have a superior barrel, you will more than likely almost never touch the seating depth. Just a thought

Matthew S Keller
 
Jackie,

"I will get the barrel shooting as well as I can with the tuner, and keep, (ie, TRY to keep), the Rifle agging with subtle powder changes."

What do you consider subtle? When things begin to show a need for a change, how much of a change with powder, leaving the tuner alone, do you make? Thanks, Bro.D
 
Easy enough

Start with the bullet well into the lands but not so that it is perceptible when closing the bolt. Find the best powder charge for that seating depth and then screw around with the seating depth until you find the better spot. Then, lock it all down and have fun. Try to resist changing because you don't understand the condition. I can't resist, but changing seldom constrains a bad day.
 
Last Season

Lowell Hotenstien and his son Ken attended one of our group matches at Harrison. Ken shot a .264" in match 1, a .280" in match 2. Lowell told Ken to remove the .005" shim from his seater die after match 2. Ken shot a .190" in match 3, .195" in match 4, and a .092" in match 5.
 
Yesterday I was testing some loads for a new Krieger barrel 13.5 twist. Typically I take a sized case, just start a bullet, then chamber it for the jam seating depth. This leave a mark on the bullet that is about twice as long as wide, on a 4 groove barrel. That was where I set my seater. Loaded some at my usual load and then loaded some with the seater turned in .020" more. These did not have a land mark on them, so they had a slight jump. Results were the jammed ones shot as I expected. Those that were seated .020 deeper all had verticle, a bunch of verticle. After the Saturday match at Luther I am going to do some testing on seating depth. I was told by a HOF shooter as little as .003" in seating depth will make a difference, sometimes a big difference. Looking forward to the testing..........Donald
 
Rustystud said:
Most Bench rest shooters set back barrels to bring barrels with erroded throats back to their original state (throat depth).
Click to expand...

I would take issue with this statement. I just don't know that many people that have the necessary equipment to do this regularly and it is cost and time prohibitive to have it done for you if you do not have access to the equipment. It may well be common amongst many top Group shooters, it is not (to my knowledge) common amongst Score shooters and I find it hard to believe it is common in Long range competition by people who do not do their own machine work.

Dick Grosbier
 
Dick

Dick, I agree. The reason I do it is it is so easy for me. I originally chamber my barrels with the expressed intent that I will be setting them back up to set back. Heck, I can do it in about an hour.

But then, all I have to do is walk over to my shop from my office and do it. No shipping, no cost,and no waiting.

If I did not have my facility, I doubt it would be practicle. But, quite a few Benchrest Shooters do have their own lathes, and I would highly recommend the practice to those that do.........jackie
 
Tune and tuning...

I like to generalize my tuning as something akin to a 60's vintage Zenith television when there was a channel knob and a "fine-tuning" knob to bring the channel in clearer.

For a particular barrel/chamber job/bullet combination, the powder charge is the channel knob -- it finds the light, medium, or hot load that works for the conditions of that day. Seating depth and the tuner (if you subscribe to that philosophy) are the fine-tuning knobs. Sometimes a particular charge hits a sweet spot and the whole mess just shoots at the standard .000 off the lands. And sometimes the conditions are just enough different that the system must be fine-tuned... for a given channel, tweak the seating depth a touch, or twist the tuner in or out a few thousandths to bring it in even clearer.

I do believe that the difference between top competitors and the rest of the pack is ability to anticipate, recognize, and correct tuning situations throughout the course of the day. The difference between 1st place and halfway down the page is often one out-of-tune target and that can often be attributed to chasing the tune, rather than anticipating it.

Rod
 
Wilbur said:
Start with the bullet well into the lands but not so that it is perceptible when closing the bolt. Find the best powder charge for that seating depth and then screw around with the seating depth until you find the better spot. Then, lock it all down and have fun. Try to resist changing because you don't understand the condition.
Click to expand...
Most shooters I talk with use the method Wilbur describes. A 4-groove cut-rifle barrel seems to shoot best with a heavy "whisker" of the marks showing.

An issue with seating depth tuning is that the proper depth for best groups keep changing as the barrel wears, usually about 0.001"-0.0015" per 100 rounds. But, the only option to get away from the seating depth/barrel wear effect is to jump the bullet. Every barrel I've ever shot would NEVER shoot better jumping the bullet than it would with an optimum seating depth.
 
As some have found out

It mattters a great deal what one is shooting. A 30 BR is a lot less demanding than a 6PPC from what one sees written here. Why there hasn't been a search for something that is less finicky that the 6 PPC is wonder to we who do not shoot them.

From my experience with the 30 cal rifles I shoot, I find accuracy usually at
.006 into the lands from where one can just barely see land marks. I like to find where the lands just barely touch so I know very closely where I am at. The last two barrels I have had installed give the best accuracy where the bullet just barely touches and comes into tune again .006 in. The best of the two holes is just kissing. I do think the brand of barrel makes a difference. The two barrels I just mentioned are Rock Creeks. The kreigers I used prior to them liked .006 in , pretty much.
 
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