Reloading accuracy-bullet seating depth

[Morrey]

I have a question regarding seating depth, accuracy and how velocity data interacts together.

I had developed a very accurate hunting load with Hornady's new ELD-X 178 grain bullet in .30-06. My rifle is a Cooper bolt action with a 24" 1:10 twist match barrel.

My load development was IMR 4350 56 grains at 2800 fps. The accuracy was great in my opinion for a hunting bullet at .350 MOA avg for two 5 shot groups.

So I get smart and purchase a Hornady OAL guage, Hornady bullet comparator and a Hornady modified 30-06 case. Testing went well and my ELD-X ogive touched the lands at 2.730". I figured my ideal depth would be backed off the lands by .020, so my optimum seating depth on the ogive would be 2.710. I go back and check a box of bullets I had loaded w/o the comparator to find the ogive was at 2.650, considerably deeper than my new data indicates. (But remember this bullet seating depth had previously given me .350 MOA)

I pull the bullets (collet puller) and reseat them at 2.710. On the range I have conflicting data. With a 10 shot test, two groups of 5 shots each, my accuracy with the new 2.710 depth actually was LESS accurate by .250 MOA. My new seating depth accuracy was .600 MOA...not bad for a hunting gun with a hunting bullet, but I went the wrong way accuracy-wise.

Here is my conflict....on my chrony, the new seating depth gave MUCH better ES and SD than with the previous load. With new depth I was getting several shots that were DUP velocity, and my ES/SD numbers were both single digits.

The chrony was telling me it likes this new depth, but the POI said not as good. There was no vertical stringing on the paper, only horizontal point of impact movement.

Any ideas on this data...this conflict is confusing to me. Or maybe MY BAD as the shooter pulling the shots? Not like me but what else can we figure? Did pulling the bullets gently with the collet puller scar the bullet enough to make a difference? But why is the stringing all horizontal and none vertical?

 

[GooseGestapo]

A single 5-shot group of .350" means little, other than an accurate rifle.. Five, 5-shot groups with an average of.350", I'd say you should be shooting that rifle in br competition. Consistently shooting in the "3's" is remarkable for any rifle. Especially so for an '06.

I'd say you are just actually seeing the repeatable accuracy level of your rifle.
Seating the bullets to touch the lands, though often improving accuracy, also increases pressures. I normally have to back off 1-2gr with loads seated to touch vs .02-.035" off the lands.
I normally use 55.0gr IMR4350 with 180gr bullets and bullets seated to feed from the magazine. If accurate and you're happy, sounds like a good load.

 

[Morrey]

A single 5-shot group of .350" means little, other than an accurate rifle.. Five, 5-shot groups with an average of.350", I'd say you should be shooting that rifle in br competition. Consistently shooting in the "3's" is remarkable for any rifle. Especially so for an '06.

I'd say you are just actually seeing the repeatable accuracy level of your rifle.
Seating the bullets to touch the lands, though often improving accuracy, also increases pressures. I normally have to back off 1-2gr with loads seated to touch vs .02-.035" off the lands.
I normally use 55.0gr IMR4350 with 180gr bullets and bullets seated to feed from the magazine. If accurate and you're happy, sounds like a good load.

I'll be happy with this load in most any hunting situation I'll personally face here in SC. I plan to repeat my tests with this load and seating depth and do several more 5 shot test group evaluations before we call it a day.

 

[Newtosavage]

If it's a hunting rifle, I would not worry about how close to the lands my bullets are seated. Instead, I want repeatable one-shot accuracy.

After running various tests in the three rifles I load for, I am no longer convinced of the ".020 from the lands" logic - not for a hunting rifle anyway. None of my most repeatably accurate loads are anywhere near the lands.

That's my experience anyway, which admittedly, is very little.

 

[Metal God]

What type of rest and or how did you hold the rifle in each of your test . I have ran some limited test the show how you hold the rifle or how consistently you hold the rifle will impact muzzle velocity , specifically ES/SD

I dont have my notes in front of me but I did a 10 shot test using the exact same ammo . 5 shots holding the rifle very tight and hard against my shoulder and 5 shots barely touching the rifle , pretty much just letting it freely recoil .

The tight hold had a ES of thirty something and an SD of 18

The light hold and free recoil had a ES of 15 and SD of 5

 

[Morrey]

If it's a hunting rifle, I would not worry about how close to the lands my bullets are seated. Instead, I want repeatable one-shot accuracy.

After running various tests in the three rifles I load for, I am no longer convinced of the ".020 from the lands" logic - not for a hunting rifle anyway. None of my most repeatably accurate loads are anywhere near the lands.

That's my experience anyway, which admittedly, is very little.

I too, am not convinced of the .020 off the lands theory. Especially now that I have kinda proved this to be un untruth at least in this particular gun. Possibly other guns will react differently. I was MORE accurate at .065 off the lands as opposed to .020 off the lands. I follow your thinking, I need one shot exacting reliability.

 

[Morrey]

What type of rest and or how did you hold the rifle in each of your test . I have ran some limited test the show how you hold the rifle or how consistently you hold the rifle will impact muzzle velocity , specifically ES/SD

I dont have my notes in front of me but I did a 10 shot test using the exact same ammo . 5 shots holding the rifle very tight and hard against my shoulder and 5 shots barely touching the rifle , pretty much just letting it freely recoil .

The tight hold had a ES of thirty something and an SD of 18

The light hold and free recoil had a ES of 15 and SD of 5

I use a custom front rest by Dan Greenlaw and a rear bumble bee bag from Protektor.

I very much understand your topic of how shoulder weld and gun hold can impact chrony information. I mentally attempt to use the same reliable hold and trigger squeeze with each shot and each group. I totally agree that consistency in my hold can make or break velocity information.

 

[jmr40]

I load the rounds as long as possible and still fit and feed from the magazine. If they are long enough to hit the lands then I seat them deeper until they don't. I have no idea how far off the lands or what the OAL is. I've always been able to consistently put 3 rounds under 1" and quite often get groups under .5"

On a hunting rifle 3 rounds is plenty. The key is will you do it with 3 rounds on a consistent basis on multiple range trips. Stressing about anything smaller than 1" groups with a hunting rifle is a waste of effort and is just for bragging rights. Fired from field positions while hunting you can't take advantage of any more accuracy.

 

[Toprudder]

I'm a relative newbie to rifle reloading, but you did not say what the velocity was, or if it changed, with the new seating depth. Seating depth can change pressure, and if it changed the velocity much, this would change the barrel time, right? Bullet arrives at the end of the barrel at a different time relative to the barrel harmonics.

I may very well be barking up the wrong tree here, but I'm just curious as I am learning.

 

[Morrey]

I'm a relative newbie to rifle reloading, but you did not say what the velocity was, or if it changed, with the new seating depth. Seating depth can change pressure, and if it changed the velocity much, this would change the barrel time, right? Bullet arrives at the end of the barrel at a different time relative to the barrel harmonics.

I may very well be barking up the wrong tree here, but I'm just curious as I am learning.

No, you're not barking up the wrong tree at all. Every small component and every tiny aspect of reloading has an impact on the end result.

In a nutshell: Load one seated at 2.650" same powder grains, same bullet, all same as load two except seating on two was 2.710".

Average mean velocities were identical. No pressure issues since both loads were off the lands. Again the average velocity was the same EXCEPT load one at 2.650" had more of a spread in velocity than 2.710 load two. Despite a wider velocity spread, accuracy of load one was slightly better than load two, hence scratching my head.

I'm basing my results on two separate 5 shot groups of load one and two separate 5 shot groups of load two. I had a 10 shot string of one, and a 10 shot string on two. I then averaged the group sizes of two groups together for my POI measurement on paper.

 

[Das Capitolin]

I have a question regarding seating depth, accuracy and how velocity data interacts together.

I had developed a very accurate hunting load with Hornady's new ELD-X 178 grain bullet in .30-06. My rifle is a Cooper bolt action with a 24" 1:10 twist match barrel.

My load development was IMR 4350 56 grains at 2800 fps. The accuracy was great in my opinion for a hunting bullet at .350 MOA for a 5 shot group.

So I get smart and purchase a Hornady OAL guage, Hornady bullet comparator and a Hornady modified 30-06 case. Testing went well and my ELD-X ogive touched the lands at 2.730". I figured my ideal depth would be backed off the lands by .020, so my optimum seating depth on the ogive would be 2.710. I go back and check a box of bullets I had loaded w/o the comparator to find the ogive was at 2.650, considerably deeper than my new data indicates. (But remember this bullet seating depth had previously given me .350 MOA)

I pull the bullets (collet puller) and reseat them at 2.710. On the range I have conflicting data. With a 10 shot test, two groups of 5 shots each, my accuracy with the new 2.710 depth actually was LESS accurate by .250 MOA. My new seating depth accuracy was .600 MOA...not bad for a hunting gun with a hunting bullet, but I went the wrong way accuracy-wise.

Here is my conflict....on my chrony, the new seating depth gave MUCH better ES and SD than with the previous load. With new depth I was getting several shots that were DUP velocity, and my ES/SD numbers were both single digits.

The chrony was telling me it likes this new depth, but the POI said not as good. There was no vertical stringing on the paper, only horizontal point of impact movement.

Any ideas on this data...this conflict is confusing to me. Or maybe MY BAD as the shooter pulling the shots? Not like me but what else can we figure? Did pulling the bullets gently with the collet puller scar the bullet enough to make a difference? But why is the stringing all horizontal and none vertical?

I'm reading this, and then you say it:

There was no vertical stringing on the paper, only horizontal point of impact movement.

If that's the case, it's not the bullet! Shooters and environment typically introduce horizontal dispersion, but vertical dispersion is usually the result of cartridge or hardware (all presuming secure rest and proper technique). A consistent velocity with low SD is better than the opposite for accuracy, but in your case the results are influenced by something else.

 

[Morrey]

I'm reading this, and then you say it: If that's the case, it's not the bullet! Shooters and environment typically introduce horizontal dispersion, but vertical dispersion is usually the result of cartridge or hardware (all presuming secure rest and proper technique). A consistent velocity with low SD is better than the opposite for accuracy, but in your case the results are influenced by something else.

I am buying into the above scenario as MY BAD. Correct me if I am wrong, but variations in velocities would typically mean my bullet would impact with a higher velocity round shooting higher (less drop) and a lower velocity round shooting lower (more drop). Not always, but typically with all other factors removed. Example: horizontal stringing is horrendous in cheap .22 LR ammo with velocities all over the place.

Slight and erratic winds swirling E-W could make horizontal stringing a problem as could the shooter (me) pulling the trigger or flinching slightly. I didn't notice winds any more than normal, nor did I notice flinching...but that is a factor really hard to always determine.

I plan to do this entire scenario all again and all on one day so the winds will not have changed much from test one to test two. If I can narrow down the error to ME as the shooter, that alone is a much easier factor to correct than many other issues.

 

[Das Capitolin]

Correct:

variations in velocities would typically mean my bullet would impact with a higher velocity round shooting higher (less drop) and a lower velocity round shooting lower (more drop)

 

[Wildfire]

Confused/

The faster a bullet is the lower it hits. With the velocity spread you say are in single digits I have never seen any sort of rise or fall to impact from a few fps difference even at long ranges.
My rifle was a Rem. 700 PSS with a very long throat. .250".
I could not load that way and get them in the magazine. My free bore was long and it still made near one hole groups. I have to disagree on how many rounds per group. 3 rounds proves any group for any hunting rifle.
I always let the rifle go cold and then fired the next round for the cold shot groups. If you need a second or 3rd shot hunting you are seldom concerned about small tiny groups at that point in that game.
Target or Competition would be a different game. Once powder and primer and bullet choice have been made it boils down to bullet seating depth and there are no rules. Every barrel is different. My long range varmint rifles have very close free bore of .012 and .010". But my .308 could not do that. Any bullet seated at the rifling will increase pressure. There is no advantage to ever doing that.
I was a tad confused or maybe did not understand the idea of a bullet hitting higher at lower speeds. It was never true in any of my years of doing this.

 

[Das Capitolin]

The faster a bullet is the lower it hits. With the velocity spread you say are in single digits I have never seen any sort of rise or fall to impact from a few fps difference even at long ranges.
My rifle was a Rem. 700 PSS with a very long throat. .250".
I could not load that way and get them in the magazine. My free bore was long and it still made near one hole groups. I have to disagree on how many rounds per group. 3 rounds proves any group for any hunting rifle.
I always let the rifle go cold and then fired the next round for the cold shot groups. If you need a second or 3rd shot hunting you are seldom concerned about small tiny groups at that point in that game.
Target or Competition would be a different game. Once powder and primer and bullet choice have been made it boils down to bullet seating depth and there are no rules. Every barrel is different. My long range varmint rifles have very close free bore of .012 and .010". But my .308 could not do that. Any bullet seated at the rifling will increase pressure. There is no advantage to ever doing that.
I was a tad confused or maybe did not understand the idea of a bullet hitting higher at lower speeds. It was never true in any of my years of doing this.

Yes, I would agree, you are confused.

Fast bullets don't strike low, they strike high. That's how ballistics work.

 

[Wildfire]

Yep. I read this wrong.

 

[Newtosavage]

My last experiment with seating depth showed a consistent incremental increase in velocity and corresponding increase in POI at 100 yards. It was scary how consistent it was. You could have drawn a line through 5 groups in a steady upward angle. The further out the bullet was seated, the faster and higher it went.

However, every group size was identical.

 

[Wildfire]

My group size always changed with different seating depths. But, as I said I had a very long throat.
Sorry about the last post. I was confused.
Loading for my hand guns and finding that a faster load shoots lower tossed me off on this.
My .45 Colt hits 2.5" high at 850 fps. Speed that up to 1000 fps and it hits lower.
Checking my old rifle targets showed you are correct that faster loads hit higher.
Oh well. That was my screw up for this year.

 

[Blue68f100]

If it was me I would go back to your original OAL. Then shoot 3 shoots with increasing OAL by 0.010". You may find that your gun shoots better some where in between or Not.

Don't get hung up in crony number, It's what on paper that counts. Some of my most accurate loads I have never crony. Then there are some that have not so great numbers but shoot good.

 

[Andrew Leigh]

I have modelled .30 calibre loads with regards to proximity to the lands.

Using the same known load I increased the COL by increments of 0.20mm (0.008"). Staring at 2.0mm (0.080") down to 0.20mm off the lands.

The method was to take the recorded velocity and to feed this into QuickLoad to get a corresponding pressure for each velocity (3 shot average) and then to plot this against the distance from the lands.

Many do not understand that merely seating the bullet longer does NOT result in an increase in pressure and will result in a decrease (case volume increasing) until the effect of inertia is felt. The increase in pressure in this case only started at 0.040" when the effect of overcoming the inertia of the lands started coming into play. The effect is rather exponential.

You will see the blue plot. This is QL theoretical pressure, QL is an internal ballistics program that does not factor in the proximity to the lands hence the linear decrease. The sudden increase when on the lands is the QL recommended added pressure for when shooting off the lands.

The red trace is the modelled pressures base on the velocities.



So being 0.020" off the lands (0.50mm) you should not have seen too much pressure deviation but enough velocity change to take you off your accuracy node.

Hopes this makes sense.

 

[Das Capitolin]

I have modelled .30 calibre loads with regards to proximity to the lands.

Using the same known load I increased the COL by increments of 0.20mm (0.008"). Staring at 2.0mm (0.080") down to 0.20mm off the lands.

The method was to take the recorded velocity and to feed this into QuickLoad to get a corresponding pressure for each velocity (3 shot average) and then to plot this against the distance from the lands.

Many do not understand that merely seating the bullet longer does NOT result in an increase in pressure and will result in a decrease (case volume increasing) until the effect of inertia is felt. The increase in pressure in this case only started at 0.040" when the effect of overcoming the inertia of the lands started coming into play. The effect is rather exponential.

You will see the blue plot. This is QL theoretical pressure, QL is an internal ballistics program that does not factor in the proximity to the lands hence the linear decrease. The sudden increase when on the lands is the QL recommended added pressure for when shooting off the lands.

The red trace is the modelled pressures base on the velocities.



So being 0.020" off the lands (0.50mm) you should not have seen too much pressure deviation but enough velocity change to take you off your accuracy node.

Hopes this makes sense.

I am presently using QuickLOAD for this same chore, and it's turning into an interesting experiment. As you pointed out, seating shallow (longer COAL) produces lower pressure while seating deeper (shorter COAL) raises chamber pressure. All of this is true until, as you also point out, you reach the lands. I'm not sure I could quantify the results as it gets that close, since the program isn't 'aware' of lands. What I did notice however, was that as chamber pressure decreases (via deeper seating) the muzzle pressure increases (recoil).

 

[taliv]

Fast bullets don't strike low, they strike high. That's how ballistics work.

that is only true as a function of gravity assuming the muzzle is in a fixed location so that fast and slow bullets exit at the same spot
practically, the muzzle is vibrating up and down, and a faster bullet may exit while the barrel is at a lower point in its cycle. so at 100 yards, faster loads will often hit lower on paper.

 

[Das Capitolin]

I think you're referring to barrel harmonics, and although a thin barrel may whip low/high depending on where it's at when the bullet exits muzzle, most would agree that the typical result of velocity is that faster bullets strike higher than slower bullets when all other things are equal. Considering how little we know or can confirm about the shooter and his hardware, it seems safe to presume that it was not barrel whip causing issues because, as he stated

There was no vertical stringing on the paper, only horizontal point of impact movement.

 

[Morrey]

I think you're referring to barrel harmonics, and although a thin barrel may whip low/high depending on where it's at when the bullet exits muzzle, most would agree that the typical result of velocity is that faster bullets strike higher than slower bullets when all other things are equal. Considering how little we know or can confirm about the shooter and his hardware, it seems safe to presume that it was not barrel whip causing issues because, as he stated

Agreed. If all else remained constant, it seems to me that barrel harmonics were relatively close to the same evidenced by the fact that point of impact did not vertical string. Again, I am relatively sure by thinking this over, the horizontal stringing issue was due to factors other than the load and the gun....ie shooter and wind, temp, etc.

The impact of all bullets (closer to lands) was almost in a straight line L-R. Even though the groups spread out some with the bullet seated closer to the lands (.020 off the lands), average velocity stayed the same but ES and SD got much tighter and did not vary as much as did the loads that were .065 off the lands.

As we all discussed, with a tighter ES and tighter SD, this load has simply got to perform better in the long run. I need to reshoot a few more test groups to qualify this theory, so I'll post results in a few days.

BTW...these Hornady ELD-X bullets are shooting some impressive groups to be a hunting round.

 

[farmerboy78]

Your new seating depth simply made your burn rate very consistent. What I now would do is to keep that seating depth and go back to your charge weights. I would fine tune the powder charge to get the accuracy back.