Here are the thoughts of Erik Cortina… Someone that can offer you very sage advice!
SEAT DEPTH ???
- Thread starter Bill Norris
- Start date
I've found with almost all the 30 Cal rifles I've used in Score Benchrest, .006" into the lands give me consistency. One can open their bolt and extract a case with a dud primer without dumping powder @ .006". I then try to find a flat node and hopefully groups under .100", three at least. I'm satisfied then. I'm only interested in small round holes in the paper and don't care about anything else. I pick the one in the middle and go with it. Gave up on tuners too. I just go with the middle of the node and hope I can read the flags.
Pete
Pete
Erik and I live in different worlds.
Sadly true for most of us… But HEY, I keep trying and do the best I can..
I believe the saying, The Target Tells… Listen, learn then test, test, test…
I'd like to get to the point where I didn't need to test after the first Satisfactory results are obtained. Why waste the components and barrel? I'll be doing a lot less in the future.
Erik makes a very good point that bullet Jam is completely dependent upon your neck tension
with relation to seating depth and how far it actually jams into the rifling
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which I was not understanding why so many people Jam but always play with neck tension
I was thinking they were playing with neck tension to adjust initial ignition burn.
which I think more now what they actually adjust with neck tension, is their seating depth if they Jam
Yes, sorry to imply that I need to continually test, once I have things dialled in for seating depth and powder that’s it for the life of the barrel. My new lot of Varget is running slower than the last lot but 12 rds to get back to the velocity that was producing the best accuracy with the same lot of bullets was all it took… Needed to go up half a grain…I'd like to get to the point where I didn't need to test after the first Satisfactory results are obtained. Why waste the components and barrel? I'll be doing a lot less in the future.
Then results were back where it had been previously. Only when something changes with powder, primers or bullets in a new lot if the barrel is still good.
Barrel timing seems to be a “thing” over lots of other issues and perhaps secondarily neck tension…
No question, tuners are a big aid in tune if one wants to try to stay in tune
I've almost always found that >006" in was magic and remained so. I have had one barrel that liked .009" better but only that one.I've seen jumping .009" in a friends rifle worked the very best also. He got there by mistake but it worked so well, he stayed there. Why Not, eh?
From a short range benchrest perspective, one of the simplest things I ever did when I started this endeavor was take the tuning information in the Tony Boyer book and apply it. A simple powder charge and seating depth matrix as outlined in his book is about all it took to see real differences on target that were repeatable. I started off that way and still do it that way, albeit it in an abbreviated fashion now since I have more experience and can apply what I have learned over time.
The science of it does not interest me even though I am a big tester. I don't need to know why the powder charge and seating depth are playing nice with the barrel. It is cool that guys get wrapped up in that, but I have very little interest myself. I am strictly a results oriented guy. A simple matrix is about all it takes to get me where I want to be. I highly recommend going about it this way for anyone with equipment good enough to show you the difference, especially for the new guy. Easy peasy lemon squeezy.
The science of it does not interest me even though I am a big tester. I don't need to know why the powder charge and seating depth are playing nice with the barrel. It is cool that guys get wrapped up in that, but I have very little interest myself. I am strictly a results oriented guy. A simple matrix is about all it takes to get me where I want to be. I highly recommend going about it this way for anyone with equipment good enough to show you the difference, especially for the new guy. Easy peasy lemon squeezy.
Alex Wheeler
Site $$ Sponsor
Its definitely a relationship to the lands. If I chamber myself a barrel with my reamer and dont change components every single barrel will shoot at the same seating depth and they will want to be chased at a 1 to 1 ratio. Even at different barrel lengths. I dont know exactly what is happening, but I kind of think pressure curve. We know a tuner is altering harmonics to line up with exit time. Im not sure I would use a tuner as a replacement to chasing the lands. Im sure it will make things better, but your tuning 2 different things. Keep in mind some cartridges are easy on throats and some are not. I think our ppc is close to 700 rounds and the lands have not moved. If that was my only cartridge I would think chasing the lands is a waste. But in something like a dasher your going to need to make an adjustment almost every match.
Yes sir. That is a lot of good information you put out for those who want to learn Alex.
I can't speak to the Dasher, but this has pretty much been my experience as well with a PPC and a 30BR in short range games. Seating depth does not move much if at all over the useful life of my barrels. I don't formally check for erosion anymore on the PPC or 30BR. I just evaluate the targets. If I see the groups opening up as the barrel wears and if I can't fix it with a simple powder adjustment, lengthening the CBTO by another .003 give or take can make a big difference. I have also found barrel length has not mattered. My seating depth from barrel to barrel have all been close to one another. Not always the same, but close. Two different contours hasn't seemed to matter either. Agree about the tuner assessment. If I am using a tuner, I make sure my seating depth is right on the screws before I ever mess around turning that thing. IMO, the tuner is clearly not a replacement for nailing down proper seating depth.
The key to the above is dependent on a few things. Having your own reamer and a good gunsmith who can provide barrel to barrel consistency is a must. Also, laying in a good supply of same lot number powder and as many quality bullets as budget allows is critical. There are no absolutes and I clearly am not at the top of the game like many here are, but I do know this. My shooting life got simpler and better when I finally figured some of this stuff out.
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Alex Wheeler
Site $$ Sponsor
Coming from long range Im super anal about seating depth, checking my touch point every time I load. A window is usually about .003" wide. Outside of that groups can go to hell bad. When I started playing with a ppc I understood why a lot of short range shooters dont worry about it as much. It just doesnt move much. So I stopped checking it and apply the same method as you, if the groups open up I will then look at seating depth. We are burning about the same amount of powder so I guess the N133 is just nicer to throats than H4895 or Varget.
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I believe the issue is dependent upon the discipline that you are loading for. Since I am not a benchrest shooter or for that matter, a competitive rifle shooter, I can only address seating depth as a function of precision varmint / predator hunting reloads. These do require a fair amount of precision reloads so the issue is worthy of consideration since it may also affect these types of reloads.
Several years ago, Sierra published an article on seating depth noting some surprising results they obtained in their testing. Some bullets do better with a jump. The only way to know is to test it.
For precision hunting ammo, functionality becomes as important as precision. Therefore, I never seat bullets closer that 0.010" from the lands, and in many cases about 0.020" One of the last things you want to happen in the field is for the bullet to stick in the lands when you extract an unfired case. If that has ever happened to you, you know what I am talking about.
Furthermore, I found that the effect that seating depth has on a specific load combination can depend on the bullet just as Sierra noted in their article. Whether this has to do with the ogive, pressure effect of seating depth, or some reduction in run out with deeper seated bullets I do not know.
If you ever check premium factory ammo, most are seated well below SAMMI specs which makes sense since this ammo must accommodate a variety of rifle chambers. I've witnessed some amazing groups shot with Federal Premium ammo at the range so go figure.
Several years ago, Sierra published an article on seating depth noting some surprising results they obtained in their testing. Some bullets do better with a jump. The only way to know is to test it.
For precision hunting ammo, functionality becomes as important as precision. Therefore, I never seat bullets closer that 0.010" from the lands, and in many cases about 0.020" One of the last things you want to happen in the field is for the bullet to stick in the lands when you extract an unfired case. If that has ever happened to you, you know what I am talking about.
Furthermore, I found that the effect that seating depth has on a specific load combination can depend on the bullet just as Sierra noted in their article. Whether this has to do with the ogive, pressure effect of seating depth, or some reduction in run out with deeper seated bullets I do not know.
If you ever check premium factory ammo, most are seated well below SAMMI specs which makes sense since this ammo must accommodate a variety of rifle chambers. I've witnessed some amazing groups shot with Federal Premium ammo at the range so go figure.
Don’t know what You did or how You did it, but I can’t see how You didn’t see a curve or patterns that demonstrate the seating depth differences ?
Steve Donlon
Gold $$ Contributor
Doesn't the bullet have somehing to do with it? I know I had a bullet that would only shoot if it was .005 or closer, and others that had at least 3 different zones where everything was in tune. Of course if it's touching it takes a lot of variables away, I would think. So many things effect the harmonics. I think it's just blind luck with me sometimes.
Hi Alex,
What does 1 to 1 ratio mean regarding lands chasing?
Killing Time
Gold $$ Contributor
I have soaked up a lot of great information from this forum since joining a little over a year ago and seating depths is one topic at the upper portion of my lists of things that must be accounted for and tested. All of my 6mm cartridges are really happy and have a great accuracy node at around .015” jump. And those are the ones I shoot the most. But my 6.5 CM still needed more testing to find that node and I actually did that yesterday. I was blown away at how much difference just .010” made. I had loaded 3 groups of 10 identical rounds, and each group set at .010” increments … .010”, .020” and .030” off the lands. Where I was blown away was the accuracy and SD differences at .010” and .020” off the lands. The SD’s for .020” were 5.2 and were 8.6 for .030”, not to mention the groups for the .020” were tighter. Not by much, but still. This just proved even more to me how much this measurement has to do with performance and accuracy and I am nowhere near the conversation that most of you here are. But it is fun to me to figure these things out and this is just one of many aspects that I thoroughly enjoy about precision shooting!!!
Same question
How often do you chase the lands?
once the throat moves every .010"?
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I find the theory of chasing the lands interesting and contradictory at the same time
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Some guys do it with success
other don't chase lands and also have success
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it seems to contradict the whole theory of one optimal seating depth itself
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I've known of quality shooters who do not chase the lands, but who might, adjust seating depth after a long time of wear in the throat, but not chase continually as it wears.
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I recently measured throat wear in one of my ELR rifles, because while it is still 1/2MOA rifle
it used to be a 1/4 MOA rifle at 600.
Throat erosion is at .040" after approx 1300 rounds
I kept the same seat depth up until now for 1300 rounds and it was holding accuracy but starting to spit a flyer here and there maybe a few inches out
I did decide to adjust seat depth out that .040" of throat wear and saw accuracy return
SO I am not dissing the theory of adjusting seat depth for throat wear, just skeptical it needs to be done often.
(I figure if the throat has worn a considerable amount, the dia. has also enlarged in that area of the throat, now bleeding pressure around the bullet, so I adjusted depth out mainly to put the bullet out past that area of throat wear to hope to see velocity return,
it did go up a slight amount)
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Killing time, I have also had a lot of trouble with my 6.5CM finding a good seating depth, I got tired of that, so I loaded up a bunch of test ammo, my barrel likes the 147gn ELDM's an RL16 powder, I started off at 10k of the touch of the lands 15k and 20k, my chamber to touch is 3.001 with the 147's, it shot like a shot gun! started the test over, I went down in -3k increments for each load, from -17 to -29 still not good enough for me, then I tried -29 to -33, I ended up at 2.1655 from base to ogive measurement to get it to shoot a ragged hole at 100yds, about the size of a nickel, my 308win rifles were much easier to find the nodes, I think the long 6.5mm bullets just like a lot of jump, this is just my experience from a 24'' 1&8 HB Savage, I did find a few nodes on the way to this point but I'm going to keep it where it is for now,
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