Hi, I'm new here, but looks like a good place to get info. I'm shooting a Rem 700 with a Shilen 6mm AI barrel. My question is, I see a lot of pet loads mentioning seating .010 into the lands, how is this done? Mine is a coyote rig, I'm playing with two loads: a 70gr. Ballistic Tip with 52.0 gr of RL 19, and a 75 gr. V-max with 49.O gr. of H414. With these loads, will seating into the lands create too much pressure? Any info appreciated.
into the lands?
- Thread starter gwomack
- Start date
gwo
Most precision shooters will determine, by careful measurements, the OAL of a loaded round when the bullet ogive is in contact with the lands,throat). That gives a starting point for adjusting bullet seating "off the lands". Some bullets/rifles/chambers/cartridges shoot best when the bullet is backed off a certain distance, usually no more than .020" or so. By experiment the shooter finds the best amount of jump to the lands.
Likewise, a shooter may find that seating the bullet long, or "jammed" into the lands may be more accurate. "Seating into the lands" does not mean that the bullet is literally engraved by the rifleing. This is impossible given the force necessary to seat a bullet that far forward. When the bolt is closed the bullet is actually pushed back into the case neck to the point where it is no more than a thousandth or two forward of where it is when just touching. This results in every bullet being in the same position relative to the beginning of the rifleing. Doing this also helps to keep the bullet aligned with the bore. So whether the bullet is seated .010" or .020" or any other distance into the lands the end result is the same. Many shooters, me included, will simply seat the bullets '010" long and let the closing of the bolt complete the seating. This also means that you have a certain amount of shots before you will have to seat even longer to accomodate throat wear.
What's best for your rifle can only be determined by loading and shooting groups.
Many feel that jamming or seating into the lands raises pressures beyond safe limits. I personally think this is an urban myth. I have never observed any difference in pressure signs regardless of bullet seating depth, within certain narrow limits, of course.
It's a lot simpler than this long explanation and maybe someone with a better gift for words can describe it better.
Ray
Most precision shooters will determine, by careful measurements, the OAL of a loaded round when the bullet ogive is in contact with the lands,throat). That gives a starting point for adjusting bullet seating "off the lands". Some bullets/rifles/chambers/cartridges shoot best when the bullet is backed off a certain distance, usually no more than .020" or so. By experiment the shooter finds the best amount of jump to the lands.
Likewise, a shooter may find that seating the bullet long, or "jammed" into the lands may be more accurate. "Seating into the lands" does not mean that the bullet is literally engraved by the rifleing. This is impossible given the force necessary to seat a bullet that far forward. When the bolt is closed the bullet is actually pushed back into the case neck to the point where it is no more than a thousandth or two forward of where it is when just touching. This results in every bullet being in the same position relative to the beginning of the rifleing. Doing this also helps to keep the bullet aligned with the bore. So whether the bullet is seated .010" or .020" or any other distance into the lands the end result is the same. Many shooters, me included, will simply seat the bullets '010" long and let the closing of the bolt complete the seating. This also means that you have a certain amount of shots before you will have to seat even longer to accomodate throat wear.
What's best for your rifle can only be determined by loading and shooting groups.
Many feel that jamming or seating into the lands raises pressures beyond safe limits. I personally think this is an urban myth. I have never observed any difference in pressure signs regardless of bullet seating depth, within certain narrow limits, of course.
It's a lot simpler than this long explanation and maybe someone with a better gift for words can describe it better.
Ray
Hey Donovan
Interesting stuff.
Do you consider 1708 psi increase with .020" seating depth change to be significant enough to worry about? It would seem that individual rounds may have psi differences of that much?
We know that velocity differences of 18 fps occur all the time.
So what conclusions, if any, have you drawn? Have you done similar tests where you also varied the neck tension AND seating depth? It would seem to me that very light neck tension such as many BR shooters use would lessen the extremes.
But I'm only speculating and have nothing to back up my speculations.
Regards
Ray
Interesting stuff.
Do you consider 1708 psi increase with .020" seating depth change to be significant enough to worry about? It would seem that individual rounds may have psi differences of that much?
We know that velocity differences of 18 fps occur all the time.
So what conclusions, if any, have you drawn? Have you done similar tests where you also varied the neck tension AND seating depth? It would seem to me that very light neck tension such as many BR shooters use would lessen the extremes.
But I'm only speculating and have nothing to back up my speculations.
Regards
Ray
Ray and Donovan, thanks for the help! Looks like I picked the right site to ask questions on! Ray, you mentioned throat erosion: will jamming into the lands significantly increase erosion? If so, I'd probably be better off staying where I am,.020 off) to prolong barrel life. I do not shoot competetively, just varmint hunt, but at the same time want to shoot the best I can. Thanks again, guys. Gary
Gary
I didn't mean to imply that jamming will increase throat erosion. The throat will wear regardless of how you seat your bullets and you have to periodically check the amount of wear so that you can keep the bullet ogive in contact with the lands or maintain a constant amount of jump. By seating .010" or .020" long and letting the lands finish the seating, you give yourself that much leeway before having to make an adjustment in seating depth. Sounds kinda confusing but it really isn't.
There are some shooters who believe that seating away from the lands,jump) will actually increase erosion because hot gasses will squirt past the bullet into the throat before the bullet has chance to seal the bore. I can't say if that is true or not but I don't think it is. Those hot gasses are going to erode the throat sooner or later and .020" of jump isn't going to make any difference. But, that's just my ignorant farm-boy opinion.
In the end Gary, you need to experiment with your particular rifle and use what works best. It may mean jumping the bullets, seating them hard in the lands, or somewhere in between. It only takes a few groups to find out. The best procedure is to start by hard jamming and then backing out .005" at a time. That way you are only changing one thing and you'll be able to see the changes, if any.
Ray
I didn't mean to imply that jamming will increase throat erosion. The throat will wear regardless of how you seat your bullets and you have to periodically check the amount of wear so that you can keep the bullet ogive in contact with the lands or maintain a constant amount of jump. By seating .010" or .020" long and letting the lands finish the seating, you give yourself that much leeway before having to make an adjustment in seating depth. Sounds kinda confusing but it really isn't.
There are some shooters who believe that seating away from the lands,jump) will actually increase erosion because hot gasses will squirt past the bullet into the throat before the bullet has chance to seal the bore. I can't say if that is true or not but I don't think it is. Those hot gasses are going to erode the throat sooner or later and .020" of jump isn't going to make any difference. But, that's just my ignorant farm-boy opinion.
In the end Gary, you need to experiment with your particular rifle and use what works best. It may mean jumping the bullets, seating them hard in the lands, or somewhere in between. It only takes a few groups to find out. The best procedure is to start by hard jamming and then backing out .005" at a time. That way you are only changing one thing and you'll be able to see the changes, if any.
Ray
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Administrator
NOTE: Cheechako is describing one method of seating into the lands--which is done with relatively light neck tension.
I can assure you that, with even moderate neck tension, the bullet jacket WILL engrave, and the amount of marks will roughly correspond to how far into the lands you are seating.
In fact, many Benchresters check their seating depth by visually inspecting the marks made by the rifling on the jackets.
While it is true that, as some point, you can't shove the bullet any farther into the rifling, in my experience, with VLD bullets, this is somewhere around .025" plus. There is definitely a difference between a bullet seated .010" longer than "touching" and .020" longer than touching. You will see the difference in velocity, in pressure, and, more often than not, in group size. In my 6BR a load that had a very low ES at .010" into the lands ran about 15 FPS faster, but with much higher ES, at about .020" into lands.
As a test to determine if I was getting bullet setback, I've loaded rounds .005, .010, .015, and .020" into the lands. I measured OAL before placing the rounds into the rifle and closing the bolt. AFTER closing the bolt I re-measured the round. There was no difference in OAL with the .005, .010, and .015". A few of the .020s showed barely measureable reduction in OAL at most, but usually the bullet was in the same place, just more heavily engraved. This was with relatively light neck tension,.0015" after springback), in no-turn brass.
Going into the lands WILL, normally raise start pressures,with a CAVEAT). If you are comparing, a load that is, say, .010" into the lands vs. .050" short of touching, the case capacity will be significantly smaller with the shorter OAL. The reduced case capacity means that there CAN be higher pressures at the shorter OAL,off the lands). [In a small case such as the 6BR I can almost guarantee that, with a heavy bullet, you'll get more pressure .030" short of the lands than when seating .010" into the lands.] However, I've generally found that, with a smaller delta in load length, say .010" off vs. .005" into lands, the load in the lands will have a higher start pressure, as indicated by casehead growth and higher recorded velocities. Using QuickLOAD, I've found that adding 5500-6000 psi to a "non-jammed" load will usually give you a good prediction of observed velocity changes as you go up to about .015" into the lands.
I think it is important to give this cautionary warning, and I think ALL the powder makers agree. Going from an OAL just short of land contact to .010" or more into the lands WILL raise your start pressures and you have to modify your loads accordingly.
And getting back to the first point. Yes there IS a difference between .010" into the lands and .020" into the lands.
One other thing to keep in mind is that there is some confusion of terminology. Some people, when referring to "jamming" the bullet mean seating it at any point past initial touching, as measured by a Stoney Point or similar guage. Other people mean jamming as seating VERY long, where the HARD JAM POINT is the farthest distance you can seat the bullet before it starts being pushed back in the case. You seat past the hard jam point and let the rifling push the bullet back.
But this is very different than talking about seating past the point of "first contact" between bullet jacket and the barrel's rifling.
I think it is much more useful to talk about a point of initial jacket to barrel contact, and then talk about how far the bullet is seated past that point. This is more useful because the distance can be measured easily with a comparator.
Here on this site when, in an article, we talk about ".015" in the lands", for example, we mean the cartridge OAL,measured on the ogive) is .015" longer than it would be if it were loaded to just contact the rifling.
FYI, with a 6mm bullet, .015" into the lands, as defined above, will make a mark on the jacket that is about 60% as high as it is wide. Short-range benchresters often talk about seating so they see a "square mark", meaning the rifling mark,on the jacket) is as high as it is wide.
Keeping in mind that jackets and land shapes/sizes will make a difference, the "square mark" typically means these short range guys are going .025" or more past initial contact. This may or may not,depends on barrel and jacket hardness), push the bullet to the point of HARD JAM or beyond.
And yes, some shooters do follow the practice Cheechako describes, namely seating the bullets extremely long and letting the rifling set them back to the same point. But normally, that would be an OAL quite a bit longer than that which would have the bullet .010-.015" from the point of initial contact,unless you're running very light neck tension).
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DMoran,
You raise a good point. My numbers are based on a "just touching" ZERO position determined by a Stoney Point,now Hornady) OAL gauge. Over the years I've developed a particular touch for this, and can get a very repeatable number. But I just use a series of light taps and I don't press the bullet hard enough that it sticks in the lands,usually). And the bullets, at my zero position, will show no marks on the case--or maybe just the start of one.
I will say, I'm surprised you're starting to see bullet set-back at .015" or so "into the lands". I consider .010-.015 a "normal" amount of bullet seating, not a lot of crunch. But I also shoot with relatively fresh, no-turn Lapua brass and this stuff is strong. Even with only .0015" or so tension, you can literally bang on the bullet tips and the bullet won't move.
But, as I mentioned in my post, bore dimensions and land configuration DO make a difference. I have 3- and 4-groove buttoned barrels. Conceivably a 6-groove cut-rifled barrel could have it's "NO MAS" point not so far in. Bullet shape/diameter and jacket hardness also make a difference. Obviously, a skinny Scenar can be seated further than a fat Berger. AND I should say that jacket hardness makes a BIG difference.,As an extreme example, German Salazar tells me that rimfire shooters, pushing lead bullets, are seating their bullets .050-.060 past the point of first contact with the lands. The bullets are not moving they are actually being swaged into the rifling BEFORE the shot).
----
RE pressure, yes I am going on the basis of what QuickLOAD tells me is the pressure change. FYI, QuickLOAD actually says to increase start pressure by 7200 psi if you are seating "into the lands". I've found this a little excessive, and 5000-6000 seems to work much better.
Moly changes the equation significantly, both in terms of the ease with which the bullet is moved back, and the increase in start pressure.
But considering a naked bullet, is there really a 5000+ increase in start pressure say, going from .010" off lands to .010" into the lands? In smaller cartridges, I think there is. I have done a LOT of predictions for people, giving them a predicted max pressure. For the 6BR and 6-6.5x47, I normally set the max at 63,000 psi in QuickLOAD after using a 5000-5500 psi "add-on" for being "in the lands". So long as the people give me the correct H20 capacity, and good ambient temp information, we have generally found that I can predict max pressure within about plus/minus 0.2 grains, and usually very close to the predicted velocity where PSI exceeds 63,500 psi or so.
So, either the cases are pressuring out,showing ejector wipe and excess web expansion) at lower than rated pressures, or indeed we are getting to that 63000 psi number, and the 5000-6000 psi "add-on" is correctly predicting the effect on start pressure of jamming the bullets.
I've talked with the powder-makers,Hodgdon, Alliant) about this and they all agree the jam seating will raise pressure in significant ways. It's somewhat hard to predict the effect universally over all cartridges. If you are shooting a low-pressure cartridge in a big bore, such as a 45/70, the effects aren't so dramatic. If you are shooting a 22BR that is running a "true max" charge already when seated, say, .005" out, I can almost guarantee you'll have a pressure problem moving .010" into the lands.
I do want to reiterate, however, that the reverse phenomenon can occur. Namely that if you shorten case OAL enough, you'll start to see pressure rise. From .025" jump to .015" in the lands is a difference of .040" in seating depth. This significantly reduces effective case capacity, which, in turn can give you MORE pressure at the shorter length, when not touching the lands.
The bottom line in all of this is: WHEN APPROACHING MAXIMUM LOADS ALWAYS EXERCISE CAUTION.
One reason I felt compelled to respond to Cheechako's previous post is that I believe people WILL get themselves in trouble if they are at or near MAX pressure just outside of touching and they then extend their OAL well into the lands. There is absolutely no question in my mind this will change the start pressure and may lead to things like excessive casehead stretch, pierced primers or worse.
One last anecdotal note. When fire-forming new 6BR brass I seat .022 longer than my Stoney Point "just touching" measurement. This gives me nearly a square engraving mark. But I can extract the round and the OAL will be the same. This is in the 3-groove with 6mm Scenar, known to be on the skinny side. YMMV with a different barrel and fatter bullets.
You raise a good point. My numbers are based on a "just touching" ZERO position determined by a Stoney Point,now Hornady) OAL gauge. Over the years I've developed a particular touch for this, and can get a very repeatable number. But I just use a series of light taps and I don't press the bullet hard enough that it sticks in the lands,usually). And the bullets, at my zero position, will show no marks on the case--or maybe just the start of one.
I will say, I'm surprised you're starting to see bullet set-back at .015" or so "into the lands". I consider .010-.015 a "normal" amount of bullet seating, not a lot of crunch. But I also shoot with relatively fresh, no-turn Lapua brass and this stuff is strong. Even with only .0015" or so tension, you can literally bang on the bullet tips and the bullet won't move.
But, as I mentioned in my post, bore dimensions and land configuration DO make a difference. I have 3- and 4-groove buttoned barrels. Conceivably a 6-groove cut-rifled barrel could have it's "NO MAS" point not so far in. Bullet shape/diameter and jacket hardness also make a difference. Obviously, a skinny Scenar can be seated further than a fat Berger. AND I should say that jacket hardness makes a BIG difference.,As an extreme example, German Salazar tells me that rimfire shooters, pushing lead bullets, are seating their bullets .050-.060 past the point of first contact with the lands. The bullets are not moving they are actually being swaged into the rifling BEFORE the shot).
----
RE pressure, yes I am going on the basis of what QuickLOAD tells me is the pressure change. FYI, QuickLOAD actually says to increase start pressure by 7200 psi if you are seating "into the lands". I've found this a little excessive, and 5000-6000 seems to work much better.
Moly changes the equation significantly, both in terms of the ease with which the bullet is moved back, and the increase in start pressure.
But considering a naked bullet, is there really a 5000+ increase in start pressure say, going from .010" off lands to .010" into the lands? In smaller cartridges, I think there is. I have done a LOT of predictions for people, giving them a predicted max pressure. For the 6BR and 6-6.5x47, I normally set the max at 63,000 psi in QuickLOAD after using a 5000-5500 psi "add-on" for being "in the lands". So long as the people give me the correct H20 capacity, and good ambient temp information, we have generally found that I can predict max pressure within about plus/minus 0.2 grains, and usually very close to the predicted velocity where PSI exceeds 63,500 psi or so.
So, either the cases are pressuring out,showing ejector wipe and excess web expansion) at lower than rated pressures, or indeed we are getting to that 63000 psi number, and the 5000-6000 psi "add-on" is correctly predicting the effect on start pressure of jamming the bullets.
I've talked with the powder-makers,Hodgdon, Alliant) about this and they all agree the jam seating will raise pressure in significant ways. It's somewhat hard to predict the effect universally over all cartridges. If you are shooting a low-pressure cartridge in a big bore, such as a 45/70, the effects aren't so dramatic. If you are shooting a 22BR that is running a "true max" charge already when seated, say, .005" out, I can almost guarantee you'll have a pressure problem moving .010" into the lands.
I do want to reiterate, however, that the reverse phenomenon can occur. Namely that if you shorten case OAL enough, you'll start to see pressure rise. From .025" jump to .015" in the lands is a difference of .040" in seating depth. This significantly reduces effective case capacity, which, in turn can give you MORE pressure at the shorter length, when not touching the lands.
The bottom line in all of this is: WHEN APPROACHING MAXIMUM LOADS ALWAYS EXERCISE CAUTION.
One reason I felt compelled to respond to Cheechako's previous post is that I believe people WILL get themselves in trouble if they are at or near MAX pressure just outside of touching and they then extend their OAL well into the lands. There is absolutely no question in my mind this will change the start pressure and may lead to things like excessive casehead stretch, pierced primers or worse.
One last anecdotal note. When fire-forming new 6BR brass I seat .022 longer than my Stoney Point "just touching" measurement. This gives me nearly a square engraving mark. But I can extract the round and the OAL will be the same. This is in the 3-groove with 6mm Scenar, known to be on the skinny side. YMMV with a different barrel and fatter bullets.
I really hope that we haven't lost gwomack. He's the guy who started this thread, remember?
As I recall, he asked a simple question about a Rem M700 varmint rifle in 244 Ackley. I admit that I myself may have gone a little overboard in answering, but I really don't think that most of the subsequent discussions added much to answering his question. It IS interesting reading and maybe he learned a little in the process. I hope so.
Are you still there Gary?
Ray
As I recall, he asked a simple question about a Rem M700 varmint rifle in 244 Ackley. I admit that I myself may have gone a little overboard in answering, but I really don't think that most of the subsequent discussions added much to answering his question. It IS interesting reading and maybe he learned a little in the process. I hope so.
Are you still there Gary?
Ray
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Administrator
One thing to keep in mind is that we are not comparing apples to oranges. When I say 5000 psi, I am simply talking about changing the "start pressure" data entry value in QuickLOAD to modify the algorhythms to conform to observed increases in velocity. Keep in mind that this is also only a "start pressure" value change. In QuickLOAD, Maximum chamber pressure is a different thing. Going to 5500 psi start pressure does not, even in QuickLOAD, translate to a 5000 psi overall load pressure increase.
Little hard to explain. But here's an example:
30.0 grains Varget with a 105gr Amax, 38.0 case capacity, 2.349 COAL, yields at estimate of 61235 psi maximum chamber pressure. If I reset the start pressure to 5500,up from 3626 default), the max chamber pressure changes to 63730 psi. That's a difference of 2495 in max chamber pressure.
I don't want to get too hung up on QuickLOAD variable tweaking. The important thing is that powder makers, and the QuickLOAD simulation both predict pressures will rise for seating into the rifling vs. seating out of the rifle. How much, as DMoran observes, is really something that can only be determined in your own rifle.
Little hard to explain. But here's an example:
30.0 grains Varget with a 105gr Amax, 38.0 case capacity, 2.349 COAL, yields at estimate of 61235 psi maximum chamber pressure. If I reset the start pressure to 5500,up from 3626 default), the max chamber pressure changes to 63730 psi. That's a difference of 2495 in max chamber pressure.
I don't want to get too hung up on QuickLOAD variable tweaking. The important thing is that powder makers, and the QuickLOAD simulation both predict pressures will rise for seating into the rifling vs. seating out of the rifle. How much, as DMoran observes, is really something that can only be determined in your own rifle.
Hey, guys, I'm still here! And I'm not totally lost. This is interesting reading. I do know that I'm close to max pressure, especially with the H414 load, as I've felt the bolt tighten a little on warmer days, therefore I will be careful when I start playing with this stuff. I'll be out of pocket for a couple of days, then I'll catch back up with you guys when I get back. Again, many thanks! Gary
Since I am just in the beginning stages of starting to learn,basic enough?)about LR benchrest this has been a most interesting thread. I have already found out that 0.005" into the lands with a VLD is no where the same start pressure effect as would be with s 0.005" ITL with our normal 7.5 nose bullets used in the 100/200 game.It seems so far that the VLD builds up the initial pressure spike much faster than the 7.5 does when both bullets go beyond the "square mark" seating depth.
It is seeming to me that deeper seating with a 7.5 nose is nearly a straight line initial pressure change where the VLD seems to logarithmically increase the start pressure as it is seated deeper. I am guessing this is because the 7.5 starts moving deeper into the case way before the VLD does.
For one thing I have found it takes considerably less seat-depth change with a VLD than it does with a 7.5 ogive when it comes to blanking primers.This is using a 40 degree PPC which is very small for a 105 VLD.
I'll look at changing my QL start pressure factor since the VLD is about 0.505" into the case at zero jam.
Keep up the discussion, you are writing a good book.
It is seeming to me that deeper seating with a 7.5 nose is nearly a straight line initial pressure change where the VLD seems to logarithmically increase the start pressure as it is seated deeper. I am guessing this is because the 7.5 starts moving deeper into the case way before the VLD does.
For one thing I have found it takes considerably less seat-depth change with a VLD than it does with a 7.5 ogive when it comes to blanking primers.This is using a 40 degree PPC which is very small for a 105 VLD.
I'll look at changing my QL start pressure factor since the VLD is about 0.505" into the case at zero jam.
Keep up the discussion, you are writing a good book.
Hey guys,
This is a great discussion.. I'm a long time gun enthusiasts but fairly new to making hand loads..
My question is how important is it to trim all your cases to the same length if you're seating your bullets based off the OAL measurements? I'm trimming. 308.. I have case variences of 2.35 to 2.65. I'm playing around with different setting depths of .020 -.005. So far .005 is the most accurate with 178 grain AMAX H4895.. Shooting a Savage 10 FCP, Shilen Match Barrel 26" 1/10 twist.
This is a great discussion.. I'm a long time gun enthusiasts but fairly new to making hand loads..
My question is how important is it to trim all your cases to the same length if you're seating your bullets based off the OAL measurements? I'm trimming. 308.. I have case variences of 2.35 to 2.65. I'm playing around with different setting depths of .020 -.005. So far .005 is the most accurate with 178 grain AMAX H4895.. Shooting a Savage 10 FCP, Shilen Match Barrel 26" 1/10 twist.
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