Seating Depth Work up Q

[daveyboy]

I've worked up an optimal charge. Now it is time for seating depth.

I am loading 50 rounds. Should I load 5 groups of 10 rounds each at 0.010" differences or 10 groups of 5 rounds each at 0.005" differences?

I am leaning towards the 5 groups of 0.010" and extrapolating info from it since 5 round groups can give a bit of a false impression.

What would you do?

Edit to add: This will be for a precision rifle. Groups will be tested on a 300 yard range.

 

[someguy2800]

Many will tell you differently but it has been my experience in 7 years of loading precision rifle ammo that seating depth usually makes little to no difference in practical accuracy. In many production rifle barrels it is impossible to seat the bullet out far enough to "touch the lands" and still fit in the magazine. If this is just hunting ammo, my recommendation is to try .040", .060", and .080" off the lands. If none of these make a noticeable improvement in accuracy, pick the one that fits in the magazine the best.

My personal deer rifle a Tikka 25-06 started loaded .060 off the lands. No noticeable improvement was found with a bullet jump of .120" to .000". The rifle shoots about a 5/8 group consistantly. Over the last 1500 rounds or so shot in the gun, the start of the rifling has worn away to the point that it is now a .120 jump with the same seated depth. Accuracy has not changed.

I have a H&R that has such a long throat that if you were to load my favorite 40 grain varmint bullets out to the rifling, only .030" of the bullet would be in the case!

If you are benchrest shooting a PPC, mabey it can start to mean something.

 

[daveyboy]

Thanks. Editted to add that it is for a precision rifle and the groupings will be tested at 200 or 300 yards. Depends how wind looks that day.

 

[someguy2800]

In that case start on the lands and work out in .010" increments, 10 shot groups. If there is a sweat spot it will usually be fairly close to the rifling.

As another real world example, my 223 with a CBI barrel likes a .020" jump, but the range of group size from a .050" jump up to touching the rifling is at best a change of .100" in the group at 100 yards. Gun shoots about a 3/8" group at best. You need a fairly large sample size to really make sure you have a trend and not a lucky group or good wind at this level of accuracy.

 

[gamestalker]

Why is it that so many reloaders think that a production rifle won't allow you to seat all the way to the lands. that is just plain bologna. I think about the only rifle I've come across that would accommodate seating to the lands, was a Weatherby. Plenty of bullet in the neck, a caliber worth or close, no magazine issues or feeding issues, so why is this so often presented as being almost impossible?

Over the last year or so I started loading for various Ruger Americans, 22-250, .243, and .270, in all probably 7 or 8 different Americans, and all have been just fine with them touching or slightly jammed. Even the short neck 300 WM has been just fine with them touching, and that's a pretty short necked cartridge by bottle neck standards.

GS

 

[Grumulkin]

Why is it that so many reloaders think that a production rifle won't allow you to seat all the way to the lands. that is just plain bologna. I think about the only rifle I've come across that would accommodate seating to the lands, was a Weatherby. Plenty of bullet in the neck, a caliber worth or close, no magazine issues or feeding issues, so why is this so often presented as being almost impossible?

Over the last year or so I started loading for various Ruger Americans, 22-250, .243, and .270, in all probably 7 or 8 different Americans, and all have been just fine with them touching or slightly jammed. Even the short neck 300 WM has been just fine with them touching, and that's a pretty short necked cartridge by bottle neck standards.

GS

I have a number of production rifles (none of them Ruger) and none of the ones with magazines permit bullets touching the lands if I wish to run the cartridges through the magazine.

The main thing touching the lands gets you is better alignment of the bullet with the bore. If the chamber, throat, bore are in good alignment and to reasonably close tolerances, getting the bullet near the lands will make much less of a difference.

 

[gamestalker]

I have to ask Grumalkin, do you actually ever attempt to seat them up to the lands?

Using .270 win as an example, SAAMI max cartridge over all length has been established at 3.340" so as to assure factory ammunition will fit all modern production magazines and chambers. This standard is consistent with all the publishers I've consulted, and is SAAMI standardized specification. So with that having been established, why is it that when I seat at or into the lands, the oal always falls well below that of industry standard, usually by at least .080" to as much as .100" of the established 3.340" maximum established by SAAMI? I can't even force a 3.340" oal into any of the rifle's chambers I load for. They fit the magazines though.

My current loads for a Ruger American are seated at 3.232" with Hot Cores and as short as 3.220", the .012" variance is due in part to a combination of olgive inconsistencies, and soft point bullet deformations. Jammed OAL's for other chambers I load for are all pretty consistent with those results, in that they fall significantly below SAAMI max., and fit the magazines with ample room to spare, as indicated above. Now some of the super tapered bullets, such as Nosler ballistic tip BT's have a longer oal when seated to the lands, but even so, they still meet SAAMI max standards, and they still fit the magazines. This has been the norm for over 30 years of experience, and not ever the exception.

I think there is some misconception or confusion of sorts. I just can't imagine, nor have I experienced a manufacturer producing a magazine that won't accommodate SAAMI specification, which is the standard by which factory ammunition is manufactured, and has been established to ensure that factory ammo will fit nearly every modern production rifle made.

GS

 

[someguy2800]

Your ruger rifles and the bullet you are working with seam to be an exception. The majority of factory production hunting rifles have throats that are very long. The reason is that they must work with all factory loaded ammo and it would be unacceptable to have a bullet jam into the rifling and get pulled out of the case on extraction. I have seen this happen on a friends 22-250 with uncrimped handloads. I believe he made a reloading mistake and didn't fully seat that bullet. He pulled the round out after noticing higher than usual pressure to close the bullet and pulled the case out leaving the bullet. Factory ammo is also held to a tolerance on the ogive length which is why factory ammo is usually not at max OAL.

 

[Grumulkin]

I have to ask Grumalkin, do you actually ever attempt to seat them up to the lands?

I always do except with copper or bronze monometal bullets. I've only been successful with my single shot firearms.

 

[Blue68f100]

All depends on when the gun was made. Guns manufactured in the 60's-70's or even earlier seam to have SAAMI specs chambers, with short leads.

 

[someguy2800]

GS[/QUOTE]

Over the last year or so I started loading for various Ruger Americans, 22-250, .243, and .270, in all probably 7 or 8 different Americans, and all have been just fine with them touching or slightly jammed. Even the short neck 300 WM has been just fine with them touching, and that's a pretty short necked cartridge by bottle neck standards.

By the way, what kind of accuracy are you getting from the American rifles? I have 3 family members with ruger m77's and all three are turds in the accuracy department. I've been curious if Ruger finally worked out how to make a barrel.

 

[Andrew Leigh]

Altering seating depth has a couple of outcomes from my experience. There are two forces at play, the first is the mechanical force called inertia and the second the pressure from the internal ballistics. They are not mutually exclusive and work together.

Pressure, for same given load data and discounting the effect of the proximity of the bullet to the lands then as you seat further out the pressure drops as you seat shorter the pressure increases.

Inertia. Now there is a point at which the pressure drop in the cartridge is negated by the effect of inertia as the bullet tries to overcome the lands. In tests I have done on a .308 (165gr. SGK's) for me it is clear that from 0.040" (1.00mm) the gradual decrease in pressure is arrested and the effect of inertia comes into play. Also what is evident is the exponential nature of the rise in pressure. The blue curve illustrates no effect of the lands until one is seated directly in the lands. The red curve is a bit of reverse engineering, I loaded the same load with ever increasing COL. The speed was recorded and then using QL I arrived at a corresponding pressure for the speed and did the plot.



So the effect of seating depth is not linear and this must be seriously considered as one approach the lands.

Now getting to the accuracy part of it. I think that unless you are seating into the lands with the appropriate load then proximity to the lands has no bearing on accuracy.

This is an illustration of cause and effect, let me explain;

Many people work up their load and then "tweak" the jump with good results believing that the distance from the lands is the "cause". However the "effect" is that the change in seating distance brings about a change in pressure which brings about a change muzzle velocity which alters the Optimum Barrel Time (OBT) bringing one onto the accuracy node (or for that matter taking one away from it).

So my advice to you would be to go both ways from the current COL as you don't know if you need to drop velocity slightly or increase it.

Hope this makes sense.

What is the calibre and how far are you off the lands?

 

[daveyboy]

Some interesting posts.

To the one above: then why would people claim a decent ogive is very jump dependent and a 175 SMK is jump tolerant?

Fwiw it will be for two 308s. A rem 700 with a deep throat 2.940" and a savage short throat 10fcp with lands at 2.807".

Bullets are 178amaxs. I can load mad mag length in the rem at 2.885"

 

[Andrew Leigh]

You get two primary ogive shapes, Secant and Tangent. Then the clever guys made bullets using the benefits of both and this ogive shape is called a Hybrid.



Now you can see why they are jump dependent, their shapes present profiles to the lands affecting the inertia and therefore pressure, then speed then OBT.

I cannot get closer than 0.28" from the lands with my .375 Sako. Does this mean the rifle will never be accurate? No I have shot a .26" group with her.

 

[daveyboy]

That's a good explaination. Auto correct on my phone took secant and made it "decent ogive" haha.

So I should mess with seating depth on the amaxs since they're more of a secant.

 

[Andrew Leigh]

You can if you want.

Load up and down by say .3mm (0.011") and see if the groups tighten either way. Load 2 groups of each, 2 shorter, two the same and two longer and have a go.

Cheers

 

[spitballer]

I have to use a slow powder in my .223 bolt rifle to get the most out of the longer barrel and can use all the breech-end pressure I can get, therefore I always seat into the lands and manipulate the charge instead. Makes it very simple, but this is for soft thin jacketed bullets. Hard, monolithic bullets and even FMJ's might be a different story.

 

[gamestalker]

Andrew puts it into very good perspective. It's all about timing, thus each barrel has an optimal velocity that it will shoot most accurately. Timing can be obtained through landing or jamming the bullets, or by increasing / decreasing the powder charge off the lands, or a combination of both.

GS

 

[Offfhand]

Quoted from an earlier post in this thread:

"Why is it that so many reloaders think that a production rifle won't allow you to seat all the way to the lands. that is just plain bologna."

I suspect that Mr. Gamestalker did not intend to seem as rude or insulting as it may appear. But rather only wishes to indicate that he, as yet, is insufficiently informed on the subject at hand. I'm confident that as he gains more reloading know-how, and more familiarity with a wider variety of firearms, he will discover that it is not at all unusual for it to be impossible to seat bullets to the lands with certain individual rifles of many makes, models and calibers.

 

[Bart B.]

I don't think it makes much difference in most rifles how far the bullet jumps to the lands. Many people shoot .308 Win ammo the same length over 3000 rounds in competition and the last bullet jumps .070" or more further to the rifling than the first one. Accuracy stays the same through 600 yards.

Especially when a .243 Win round erodes away the rifling at its origin about .001" for every dozen or two shots fired; twice that of the .308 Win as it wears out barrels twice as fast. Would you seat bullets a thousandth shallower every dozen or two loads you assemble?

Example for the .243 Win: Because the .243 case headspaces on its shoulder, the distance from case head to any point on the bullet is meaningless. Its the distance from the case shoulder to the diameter on the bullet that first touches the rifling that controls how far the bullet jumps. The case head will be off the bolt face by a few thousandths. On the .243 Win, that diameter is somewhere between that of the bullet down to about .236" which is the bore diameter.

In the best rifles, bullets seated gently into the lands will often give another 1/10th MOA of accuracy visible at the longer ranges. The bolt face has to be squared up and the case neck grip has to be minimum so the bullet will seat back about 1/100th inch when the round's chambered. Unless you can shoot your stuff into no worse than 1/3 MOA at 100 yards, you'll never see the change.

 

[243winxb]

Factory chamber OAL

http://www.bergerbullets.com/vld-making-shoot/ Find the maximum and minimum OAL, divide making 2 more in the middle of max and min. Makes for more testing/shooting. On factory guns, i start with the base of the bullet near the neck/shoulder junction, if possible, and try different powders. When the perfect powder if found, fine tune OAL. May or may not work for you. IMO

 

[fguffey]

I suspect that Mr. Gamestalker did not intend to seem as rude or insulting as it may appear. But rather only wishes to indicate that he, as yet, is insufficiently informed on the subject at hand. I'm confident that as he gains more reloading know-how, and more familiarity with a wider variety of firearms, he will discover that it is not at all unusual for it to be impossible to seat bullets to the lands with certain individual rifles of many makes, models and calibers.

Offhand, I do not know, I built a 270 Winchester, I did nothing to the trigger guard/magazine in the CZ24 meaning there was not a lot of room in front of the bullet or behind case head. I took the rifle to the range with 12 different loads of 10 rounds each with 12 different case head stamps. I did not have a group that was larger than a quarter and some groups shared the same hole.

I loaded another 12 loads of 10 cases each and delivered the rifle to the new owner. I asked him to find the load the rifle liked. later I asked, he said the rifle liked everything, he said he shot the first round of then adjusted the scope to zero on the hole in the target.

He then said he cleaned the rifle. I was surprised, he cleaned the rifle after 120 rounds? He then said he had never had that much trouble taking a rifle apart. I asked him if he got the rifle back together, I explained to him I did not build the rifle to be taken apart.

The ammo was delivered in ammo boxes made for 20 rounds, when I got the cases back all 120 cases were in a small box. Not a problem, after tumbling I sorted the cases by head stamp. I am the fan of sorting cases by head stamp. He did ask me to work on the trigger, I suggested as long as he hunted from a stand in a tree the trigger would seem stiff.

F. Guffey

 

[Bart B.]

GS,

Why does each barrel need bullets leaving at a given velocity for best accuracy?

I've read that bullets should exit when the shock wave from firing has to be at the breech end so the muzzle diameter is at its smallest. But that's false because there are two shock waves.

To everyone,

You shoot five 5-shot groups of a load at 100 yards measuring

1.0"
0.9"
1.2"
1.5"
0.7"

The 25-shot composite is 1.7".

What's the accuracy of that load?

 

[Andrew Leigh]

Quoted from an earlier post in this thread:

"Why is it that so many reloaders think that a production rifle won't allow you to seat all the way to the lands. that is just plain bologna."

I suspect that Mr. Gamestalker did not intend to seem as rude or insulting as it may appear. But rather only wishes to indicate that he, as yet, is insufficiently informed on the subject at hand. I'm confident that as he gains more reloading know-how, and more familiarity with a wider variety of firearms, he will discover that it is not at all unusual for it to be impossible to seat bullets to the lands with certain individual rifles of many makes, models and calibers.

Could you please quote examples of rifles and calibre's that you cannot get to the lands please, I am curious. There are always exceptions to the rule but always keen to learn.

I have personal experience of heavier calibres being far from the lands, probably a safety factor.

I have developed at least 60 loads for local forum members and the only calibres to date that remained far from the lands were 9.3mm and .375.

 

[Andrew Leigh]

GS,

Why does each barrel need bullets leaving at a given velocity for best accuracy?

I've read that bullets should exit when the shock wave from firing has to be at the breech end so the muzzle diameter is at its smallest. But that's false because there are two shock waves

The bullets should exit when the shock wave is at its minimum at the Muzzle. This is the term coined by Chris Long as the Node. When using the node calculator it is at the point of exit from that muzzle that the Node is given.

Google Chris Long's OBT Theory.