How important is it to use an OAL gauge and seat your rifle bullets just off the lands? I hear this is important because if the bullet has to "jump" to the rifle lands unsupported, it can affect accuracy. Are we sure about this? How, exactly, does what happens in the first few 1/100ths of a bullet's travel affect its accuracy, seeing as it spends all that time in the barrel? Shouldn't the barrel straighten out the bullet's path?
How important is OAL for accuracy?
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notaglockfanboy
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It can affect accuracy, but note that when you start seating close to the lands you may get some pressure spikes because the bullet doesn't have a "running start". Some say that it is real important to seat close to the lands, but cannot explain why ammo like Federal Gold Medal match ammo shoots so well in many different firearms when it is seated to a SAMMI OAL. When I am working up loads I usually start at SAMMI OAL, find my max powder charge, then start working closer to the lands if the groups need tightening. YMMV If you are using the rifle for hunting, when you get out to the lands most of the time you will not be able to load and feed from the mag, so keep that in mind as well. This is my experience, others have their way, hope this helps. As far as what is happening during the "jump", I cannot answer that with any certainty because in reality only speculation exists on this subject IMO.
Every gun is different. With some it doesn't matter, others have a sweet spot. You just have to test to see what she likes.
A long range shooting buddy told me he adjusts powder charge to find the smallest vertical dispersion, than tries different lengths with that charge to find the smallest horizontal group. He swears by that method. I've never tried that but it sounds logical.
Laphroaig
A long range shooting buddy told me he adjusts powder charge to find the smallest vertical dispersion, than tries different lengths with that charge to find the smallest horizontal group. He swears by that method. I've never tried that but it sounds logical.
Laphroaig
Otto
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All barrels vibrate when shot. The goal is to get the bullet to exit consistently within those vibration cycles. Fine tuning the COL is just one step of many that accomplish that.
A true statement, but I think the individual bullet is just as big of a factor. Some bullets matter more than others. And for most hunting applications there isn't enough difference to really matter most of the time. Benchrest shooters can win or lose by the tiniest fraction of an inch. It matters to them.
witchhunter
Member
Otto hit on it. When a round is fired it causes a vibration down the tube. By altering the jump, you alter the time when the bullet leaves the barrel. You want the bullet to leave at a different time than when the vibration is at the muzzle. All rifles are different, you must experiment.
nastynatesfish
Member
Barrel harmonics. That's why if you have contact between you stock and barrel it will throw rounds as it heats up compared to floating also. Jump or jam. You just need to work a load. I have two loads with same bullet in same rifle that shoot almost identical and are .130" different and still not jammed
nastynatesfish
Member
Propped neck tension and having enough bullet in the case is more important to me. With light bullets I always start with a bullet diameter in the case, if I'm touching back in. Most times it's not
Not sure if my findings will be helpful but in my Savage 30-06 using the OAL given in the load data my groupings at 100 yards would be consistently around inch and a half using the Hornady GMX in 150 grain. I did a check on the amount of movement before engaging the lands and came up with a longer overall length, I am now seating about 25 thousands longer than in the load data and using the factory crimp die as now the cannelure is totally exposed. My groups now are sub 1 inch shooting off the bench and that is using all the same components just the change in OAL. I find OAL to be critical in some rifles, finding the sweet spot is a bit of trial and error, but always err on the side of caution.
30Cal
Member
IME, with a tight match rifle, and a good match bullet, it's a 2nd order variable. Measurable, but not all that much. When you stray from those 2 assumptions though, it can sometimes make a real difference.
climbnjump
Member
How important? Well it depends on many factors from the particular load and rifle you are using to the profile of your chosen bullet to what accuracy you are trying to achieve at what range. In other words, it may be very important or not important at all.
Many people have produced very accurate loads without ever worrying about bullet jump. However, in one of my rifles, I had a bullet go from producing 3 inch groups at 50 yards to producing 1/2 inch groups at the same distance simply by varying the seating depth. This is an extreme example, but it is a real one.
Here are a couple of articles that might be worth reading:
http://www.bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-1/
http://www.bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-2/
BADUNAME71
Member
I learned a lot from this thread
I am fairly new to reloading and have been having some problem with my bullets tumbling and key holing. I finally got the problem solved or stopped by using a slightly larger dia. bullet and a different charge powder. But I always questioned what difference the OAL made as I am using resized 30-30 brass to build 32-40 cartridges. This leaves the brass somewhere around .006 to.010 short. My max OAL is supposed to be 2.500 for the win 94 lever gun. I have been crimping the bullet at the cannelure which put the OAL at 2.434. After reading this thread started a bullet into a case to about 2.700 then chambered it to the lands to see what the length would be. It came to 2.600. I am fairly sure this won't load through the magazine via lever after reading the Berger pages above. Here is a pic of the 3 cartridges. The one on the left is the longer 2.600 which touched the lands. The one on the right is the 2.500 that Lymans and Lee says is the max OAL. My load that I have been shooting is the middle one at 2.434. This and the Berger article tells me that I have a little leeway to experiment with on length. I had been just pressing the bullet til it reached the cannelure and crimped it.
Thanks to all who posted here on this subject and to climbnjump for the Berger links.
I am fairly new to reloading and have been having some problem with my bullets tumbling and key holing. I finally got the problem solved or stopped by using a slightly larger dia. bullet and a different charge powder. But I always questioned what difference the OAL made as I am using resized 30-30 brass to build 32-40 cartridges. This leaves the brass somewhere around .006 to.010 short. My max OAL is supposed to be 2.500 for the win 94 lever gun. I have been crimping the bullet at the cannelure which put the OAL at 2.434. After reading this thread started a bullet into a case to about 2.700 then chambered it to the lands to see what the length would be. It came to 2.600. I am fairly sure this won't load through the magazine via lever after reading the Berger pages above. Here is a pic of the 3 cartridges. The one on the left is the longer 2.600 which touched the lands. The one on the right is the 2.500 that Lymans and Lee says is the max OAL. My load that I have been shooting is the middle one at 2.434. This and the Berger article tells me that I have a little leeway to experiment with on length. I had been just pressing the bullet til it reached the cannelure and crimped it.
Thanks to all who posted here on this subject and to climbnjump for the Berger links.
Ron,
Don't overthink this
For a M94's tubular mag, you need to crimp into the cannelure. I don't think you'd notice much accuracy differences with different COAL's in that rifle anyway.
This topic is for bolt rifles (mainly) who are trying to squeeze out the last drop of accuracy in their rifles.
Laphroaig
Don't overthink this
For a M94's tubular mag, you need to crimp into the cannelure. I don't think you'd notice much accuracy differences with different COAL's in that rifle anyway.This topic is for bolt rifles (mainly) who are trying to squeeze out the last drop of accuracy in their rifles.
Laphroaig
BADUNAME71
Member
Laphroaig, I appreciate that information too. I suppose that is because the bullet could move in in the tube magazine under spring pressure?
With my old eyes that accuracy change wouldn't help me much :^)
I was more concerned with anything that might help me understand and solve the tumbling issue. I have that worked out I believe. Being new to reloading I appreciate these threads because I learn not just things that work, but WHY they work the way they do.
With my old eyes that accuracy change wouldn't help me much :^)
I was more concerned with anything that might help me understand and solve the tumbling issue. I have that worked out I believe. Being new to reloading I appreciate these threads because I learn not just things that work, but WHY they work the way they do.
Tcruse
Member
The OAL also affects the pressure and thus the velocity. When bullets are seated deeper they will travel faster with the same amount of power. Seating depth also effects the crimp performance. For lead or plated bullets over crimping can cause "key hole" problems. The fun is to vary the parameters and experiment with what you get.
Now, if you just want practice ammo, the advantages of reloading may be questionable. With Walmart now selling Federal 9mm ($9.75) and .45ACP ($14.50) it may be better to just purchase practice ammo. BTW CCI aluminum cases reload just fine.
Now, if you just want practice ammo, the advantages of reloading may be questionable. With Walmart now selling Federal 9mm ($9.75) and .45ACP ($14.50) it may be better to just purchase practice ammo. BTW CCI aluminum cases reload just fine.
ElevenBravo
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In my experience, proper OAL is absolutely vital after finding a stable powder charge. Barrel whip requires that the bullet is leaving the muzzle when it is in the same place in order to achieve consistency.
After finding a consistent charge weight using OCW, I load up a new set of rounds starting at SAAMI max cartridge length and ending 1/100 of an inch short of the lands. I just did loads for my 300 WSM and the wife's 223 Remington this weekend. Wife is shooting sub-MOA groups, almost keyholing with the loads I've developed for her, although the COAL is too long to fit in the magazine.
Here is the results of my bullet seating depth tests for my 300 WSM:
Add 2/100" of OAL to that and you'd see a 2" group at the same distance. So yes, COAL matters. Even more so if you're using all copper bullets like Barnes as they need a bit more pressure due to their hardness.
After finding a consistent charge weight using OCW, I load up a new set of rounds starting at SAAMI max cartridge length and ending 1/100 of an inch short of the lands. I just did loads for my 300 WSM and the wife's 223 Remington this weekend. Wife is shooting sub-MOA groups, almost keyholing with the loads I've developed for her, although the COAL is too long to fit in the magazine.
Here is the results of my bullet seating depth tests for my 300 WSM:
Add 2/100" of OAL to that and you'd see a 2" group at the same distance. So yes, COAL matters. Even more so if you're using all copper bullets like Barnes as they need a bit more pressure due to their hardness.
spitballer
Member
Seems to me it's all about consistency, and I agree with the old-timers that a lot of us tend to overthink this stuff although it's good that we are concerned about it because at least we're thinking. I may be wrong here but it seems to me that in addition to seating off the lands, for rugged performance and consistency an autoloader is going to have to deal with a crimp whether they like it or not, so it might as well be a good one. As far as a bolt action is concerned, yes, a bolt action can butt the projectile up against the lands in lieu of a crimp, but they're not getting off scott free, either: neck tension has a profound effect on consistency when you're seated on (into) the lands, so you'll have to have to solve the problem of consistent neck tension. The best answer I've found for this is to make all the necks consistently loose (not finger loose!) and to tension the bullet against the rifling with a consistently measured, compressed load. Sounds easy enough, but take my word for it - arriving at the perfect combination when there are a zillion components and a zillion pieces of advice is a very time-consuming process. Hope this is constructive.
i don't get how some of you think OAL is related to barrel harmonics. that makes no sense to me.
i think there's a general consensus that some types of bullets (e.g. VLD) are jump sensitive, while others (e.g. the SMK 168 and 175 in Fed GMM) are not at all sensitive.
The berger hybrids seem not to care at all.
i don't attempt to seat at the lands at all because the lands keep moving on me! as i wear out the throat, it becomes difficult if not impossible
i also am not too keen on most of the measuring tools. with many of them, if you take 5 measurements in a row, you'll get 5 different answers. so most people may think they're seating at the lands, but i suspect their tools are lying to them and they have no idea where their lands are
it's helpful to keep a few things in mind.
1. depending on headspace and how you resize and your brass thickness, there's probably some wiggle room which means the case will probably be laying on the bottom of the chamber when you pull the trigger, which means the bullet won't be pointing straight down the barrel
2. the firing pin will hit the case in the butt, moving it forward
3. the primer explodes, and may send the bullet forward into the lands where it may even come to rest before the powder ignites
a cool experiment would be to use some laser measuring tool and aim it down the barrel (with a cheap mirror) to see how far away the bullet is and track its movement through the firing sequence
i think there's a general consensus that some types of bullets (e.g. VLD) are jump sensitive, while others (e.g. the SMK 168 and 175 in Fed GMM) are not at all sensitive.
The berger hybrids seem not to care at all.
i don't attempt to seat at the lands at all because the lands keep moving on me! as i wear out the throat, it becomes difficult if not impossible
i also am not too keen on most of the measuring tools. with many of them, if you take 5 measurements in a row, you'll get 5 different answers. so most people may think they're seating at the lands, but i suspect their tools are lying to them and they have no idea where their lands are
it's helpful to keep a few things in mind.
1. depending on headspace and how you resize and your brass thickness, there's probably some wiggle room which means the case will probably be laying on the bottom of the chamber when you pull the trigger, which means the bullet won't be pointing straight down the barrel
2. the firing pin will hit the case in the butt, moving it forward
3. the primer explodes, and may send the bullet forward into the lands where it may even come to rest before the powder ignites
a cool experiment would be to use some laser measuring tool and aim it down the barrel (with a cheap mirror) to see how far away the bullet is and track its movement through the firing sequence
carbine85
Member
Some guns won't feed properly if you go for the max length. A lot of times it's the max mag length that comes into play.
Excellent questions, this is exactly how I think. We can use something like the Hornady OAL gauge and think we know exactly where the bullet is, but if .002" makes a difference, our tools simply aren't accurate enough.
Those of you that have been rigorous with this and have shot better groups at one OAL than another, are you shooting from something like a Ransom rest? If you're simply shooting from a bench rest, how are you certain that you're seeing the effects of different OALs instead of normal variance in your shooting?
I have only be reloading for a few years, and depth when there is not cannelure has always been stumbling block for me.
I am now starting 30-06, previously only handgun. You look in the manuals and they give you OAL. I bought some Nosler Partions. The One Load book with Nosler loads just has OAL. But Nosler's site has a length that they tested with, shorter. But I went with that.
But I do get hung up, trying to figure out where to seat bullet. Then comes crimping or not.
I am now starting 30-06, previously only handgun. You look in the manuals and they give you OAL. I bought some Nosler Partions. The One Load book with Nosler loads just has OAL. But Nosler's site has a length that they tested with, shorter. But I went with that.
But I do get hung up, trying to figure out where to seat bullet. Then comes crimping or not.
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Andrew Leigh
Member
A widely used accuracy theory (Optimum Barrel Time OBT) has at it core harmonics of the barrel. Now to be clear, the barrel length determines the frequency of the shock wave that travels up and down the barrel. However the trick is to get the bullet exiting the muzzle at the point that their is the least change in muzzle diameter (where the harmonic peak is displaying the least amplitude spread). By altering the OAL you alter the pressure and in turn the speed. So according to the OBT theory a change in OAL can alter the elapsed barrel time enough to bring it onto an "accuracy node".
consequences of seating depth
Very good point. We usually kept our bullet seating about .01 from the lands as a minimum on all our hunting rounds as the general consensus was that was a safe place to be to prevent pressure spikes, unless you were a bench rest guy. On one rifle in particular with a short throat this is where we always left it. We would always cycle the rounds after loading and look for tick marks from the rifling since we figured our measuring technique probably left something to be desired.
Anyway several years back we were practicing a bit with some "new brass"
on an early fall day (40's) when there was a noticeable delay in the "striker "
spring. A weak spring being the culprit. Worked fine a few minutes before.
After waiting an appropriate length of time we extracted the "unfired round"
or most of it anyway as the bullet was stuck in the rifling. The weak striker spring, with the new brass and the likely error in our measurements
and no crimp all combined caused the issue ( loose powder seemed to be everywhere) . A freak thing no doubt.
Since we figured this would be undesirable in the field on a hunting trip, we changed the way we did things a bit. We moved the bullet back to .015 as a minimum on this particular rifle and employed a factory crimp. And we did change out all the striker springs on our various hunting rifles. This particular rifle actually liked the change.
Some rifles are more sensitive to seating depth than others with certain bullets. Long throat or short and throat diameter as well are all some of the variables. If someones having a problem with boat tail bullets in a rifle with a long throat, we often recommend trying a flat base bullet.
We never understood the harmonics thing that well except for the theory that is. Winchester came out with the BOSS system for a while many years ago to much fanfare. But it's not mentioned much these days. It was supposedly the "end all" solution to the barrel harmonics issue. OYE
Very good point. We usually kept our bullet seating about .01 from the lands as a minimum on all our hunting rounds as the general consensus was that was a safe place to be to prevent pressure spikes, unless you were a bench rest guy. On one rifle in particular with a short throat this is where we always left it. We would always cycle the rounds after loading and look for tick marks from the rifling since we figured our measuring technique probably left something to be desired.
Anyway several years back we were practicing a bit with some "new brass"
on an early fall day (40's) when there was a noticeable delay in the "striker "
spring. A weak spring being the culprit. Worked fine a few minutes before.
After waiting an appropriate length of time we extracted the "unfired round"
or most of it anyway as the bullet was stuck in the rifling. The weak striker spring, with the new brass and the likely error in our measurements
and no crimp all combined caused the issue ( loose powder seemed to be everywhere) . A freak thing no doubt.
Since we figured this would be undesirable in the field on a hunting trip, we changed the way we did things a bit. We moved the bullet back to .015 as a minimum on this particular rifle and employed a factory crimp. And we did change out all the striker springs on our various hunting rifles. This particular rifle actually liked the change.
Some rifles are more sensitive to seating depth than others with certain bullets. Long throat or short and throat diameter as well are all some of the variables. If someones having a problem with boat tail bullets in a rifle with a long throat, we often recommend trying a flat base bullet.
We never understood the harmonics thing that well except for the theory that is. Winchester came out with the BOSS system for a while many years ago to much fanfare. But it's not mentioned much these days. It was supposedly the "end all" solution to the barrel harmonics issue. OYE
sage5907
Member
If I were to rank the factors that contribute to accuracy related to cartridge assembly I would list them in this order:
Bullet selection, powder selection, consistency in reloading every round the same, case neck length and tension, primer, case manufacturer and case consistency, and lastly seating distance to lands. Following the point made by taliv about the case moving forward in the chamber when the firing pin strikes I have controlled feed rifles so the rear of the cartridge is held firmly by the extractor when the firing pin strikes which prevents that problem. I have found that if you use the most popular bullet weight for a particular cartridge (30-06 150, 270 Win 130, 25-06 100) and seat the rear of the bullet flush with the rear of the case neck you are in friendly territory.
Bullet selection, powder selection, consistency in reloading every round the same, case neck length and tension, primer, case manufacturer and case consistency, and lastly seating distance to lands. Following the point made by taliv about the case moving forward in the chamber when the firing pin strikes I have controlled feed rifles so the rear of the cartridge is held firmly by the extractor when the firing pin strikes which prevents that problem. I have found that if you use the most popular bullet weight for a particular cartridge (30-06 150, 270 Win 130, 25-06 100) and seat the rear of the bullet flush with the rear of the case neck you are in friendly territory.
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