Lots of questions come up around here on this subject, so I thought I'd post about my method for figuring this problem out.

First of all, many who ask seem to be under the impression that seating a bullet too long will create an unsafe condition. Generally, this is not so. There are two main considerations for a maximum overall length: one is whether the finished cartridge will fit the magazine and feed properly, and the other is that you do NOT want to be jamming a bullet into the lands when you close your bolt. If you're not jamming the bullet into the lands and the cartridge will feed, it does not matter whether you're a little longer than the length specified in the manual. Seating to jam into the lands certainly can raise pressures and it probably is not a recipe for accuracy anyway in the typical sporting rifle anyway.

How to go about it?

A useful tool can be made with a fired and resized case. Split the neck with a hacksaw or a Dremel cutoff wheel so that it looks like this:



Take one of the bullets you plan to use and insert it into the neck of the split-neck case. The case should hold the bullet firmly, but not too firmly. Carefully chamber this test round, closing the bolt on it. Open the bolt and withdraw the test cartridge just a bit and then close the bolt on it again. Repeat this three or four times.

Next, VERY carefully extract the test round and don't let the bullet it anything on the way out of the action. Don't let anything disturb the position of the bullet.

The next step is to measure the lengthy of this test round. It is best to use a comparator. I like the one that Stoney Point used to make, but is now marketed by Hornady. You can get by just measuring the OAL and using that measurement as a reference, but a comparator works much better...I can't explain why, but it does. It is a good idea to repeat this process a couple of times with that same bullet to make sure you're getting a consistent length. So, once you're satisfied with your measurements record the length you got as a reference, and remove THAT VERY BULLET and don't toss it back in the box with the others!

When you're ready to seat bullets, set up your seating die and turn the seater plug out a few turns so that it will seat THAT bullet only a smidgeon. Use the same method of measurement you used to measure the test cartridge. By adjusting the seater plug inward a little at a time and measuring the result, you should be able to seat the bullet to within .001" of the lands if you like...not recommending it though! If you want to seat .030" off the lands, then keep adjusting the seater stem inward until the result is .030" shorter than the test cartridge was. Works like a charm, but there are a few things to consider:

1. That first bullet you seated while adjusting your die---it may have taken a bit of engraving from the seater plug which might cause it to have not seated quite as deep as the next fresh bullet will. So, measure your second cartridge to see if this is the case and then continue fine tuning. You should be able to get it just right on the second or third one.

2. You'll see some variance from cartridge to cartridge. The bullets are not perfectly shaped and identical to each other, but they should be pretty close.

3. If you're hard-headed like I was about this, and insist on measuring raw OAL with your caliper, you're liable to see what appear to be significant inconsistencies that will undermine your confidence in the system when you measure each round as it comes off the press. Get a comparator! You'll have a much better idea what's going on.

4. Different folks have different things to say about seating depth, but with most bullets I seem to find a sweet spot anywhere from .015" to .040" off the lands. I sometimes test seating depth in .010" increments or decrements to see if I can find the neighborhood where I get best accuracy, and then I'll zoom in and try .003" changes all around that "neighborhood" until I find my sweet spot. I think there are many different answers to this question and I am not sold on the idea that my answer is the one and only. In fact, I have seen evidence that there can be numerous sweet spots in terms of distance from the lands. I probably ought to play some more with seating depth on some of my loads. You never know until you know!

5. A word of caution: if you have a max load you've worked up, don't just arbitrarily decide to seat the bullet .150" deeper to see what happens. Seating .030" deeper won't change thing much, but it WILL change things in terms of pressure. Seating .150" or .200 deeper will raise pressures significantly. This is not something I have tried to do just for the sake of experimemntation, but I use QuickLOAD software and can vary parameters such as cartridge OAL to see what effect it has on pressure. I was surprised to see how much difference it made while running the software. Don't surprise yourself with that concept with a real rifle with real ammo in the real world.

I think you have it backwards on seating into the lands. Jumping to the lands increases chamber pressure, and two of my rifles are loaded with ammo that is jammed and they are sub MOA.

Thanks for sharing your technique.

Good post.

Yup..good post, well done!

Great job on the thread and KISS RiverRider.

Could go either way IMO
Obduration of bullet into lands or changes in case volume

Thanks.

I know that jamming the lands is or has been a technique used in benchrest, but most *authorities* (aaa-hem) advocate not doing so for the typical handloader. I would think that the way the rifle's chamber is cut and the bullets used probably have a pretty fair amount of influence as to what works and what doesn't.

Not sure I know what you mean by "jumping to the lands," I would assume you mean jamming into them. I agree that jamming into the lands could cause a higher pressure than seating, say, .030" (just picking a number here) off the lands. In fact, QuickLOAD indicates you can expect to increase peak pressure by 7200 psi if you jam into the lands. Because you posed this comment, I got off my dead arse and looked more closely at the Start Pressure parameter in QuickLOAD. Lotsa little numbers and stuff here and there to play with in there, and I haven't fiddled with half of it yet!

BUT---you'll also get some serious pressure increases if you seat a bullet significantly deeper with all else equal. As an example, I've run two theoretical loads for .25-06 on QuickLOAD. Here are the results in summary...

.25-06
120-grain Partition
60.0 grains H1000
OAL = 3.300"
peak pressure = 56000 psi

.25-06
120-grain Partition
60.0 grains H1000
OAL = 3.100"
peak pressure = 62600 psi

In this example, seating the bullet .200" deeper increases peak pressure by 6600 psi.

Here's another example:

6mm-284
95-grain Partition
52.0 grains H4831 SC
OAL = 2.575"
peak pressure = 50000psi

6mm-284
95-grain Partition
52.0 grains H4831 SC
OAL = 2.375"
peak pressure = 54000psi

An OAL decrease in this instance causes a 4000 psi increase in peak pressure.

Here's a good one:

.223 Remington
55-grain V-Max
24.0 grains H335
OAL = 2.260"
peak pressure = 46750 psi

Seat the same bullet to an OAL of 2.160" and pressure will increase to 51000 psi. Seat that bullet another .100" deeper and pressure will increase to 56000 psi. We gained 10000psi in the smaller .223 case by seating .200" deeper while the larger cases showed pressure increases about half that.

Anyway...there's more than one way to create an overload.

Nice write up. I'm a little confused as to why you say, "but a comparator works much better...I can't explain why, but it does."

I think you do know!!

Great job

Thanks guys...

Well Jeff, I think I have a little explaining to do...I hoped to avoid it. I suspect you are alluding to the variations in bullet point dimensions. In theory, if you do your chamber dimensioning with one individual, specific bullet and then use that very same individual bullet to set the seater die for depth, then you should be spot on. I think the real problem is just getting a good accurate measurement when measuring raw OAL from case head to the tip of the bullet, and I think this caused me to suffer the effects of inconsistency and a lack of repeatability. It's just a heck of a lot easier with a comparator.

I really didn't want to mention this in the first place. I've run into too many folks who can't understand how using the same individual bullet for getting the throat dimension and for making the seater adjustment on the first round loaded could possibly work. Their argument was always "bullet tip dimensions vary" and I KNOW that. That's why you use THE SAME BULLET for both steps! I've gone round and round and round with folks trying to get the point across...and it's too much work.

Me: You use the SAME bullet for both steps.

Other guy: But all bullets will have slightly different dimensions at the nose.

Me: Yes. I know. That's why I use the same bullet for both steps.

Other guy: But the next bullet will have a different dimension at the tip.

Me: Yes, that is correct but the seater does (should) not be touch the nose.

Other guy: If will be a different OAL.

Me: Yes, I know. The nose will be a bit different.

Other guy: So your method does not work.

Me: Good grief. Oh, someone's at the door.

River Rider,

You and I are arguing the same point brother!

.25-06
120-grain Partition
60.0 grains H1000
OAL = 3.300"
peak pressure = 56000 psi

.25-06
120-grain Partition
60.0 grains H1000
OAL = 3.100"
peak pressure = 62600 psi

This clearly shows what I meant in my first post to be true. I'll state it a different way. The longer you seat the bullet out of the case the less chamber pressure you incur. When you seat the bullet out of the case farther you are then closer to the lands of the rifling. Or what I'm saying IN the rifling, a.k.a. jammed.

Let's use a .308 Win for example.

When I was loading for the one I had, my O.A.L was 2.825" with a 175 gr. Sierra Match King. That O.A.L. was set with the bullet .0010" jammed into the lands. More importantly the bearing surface of the bullet was .0010" jammed into the lands.

Now, had I seated the bullet into the case .0030" deeper the bullet would've been jumping to the lands by .0020"

I'm really gonna muddy the waters here. I loaded the same recipe, everything the same, except that I loaded a 178gr. Horndady A-max and did not change the setting on the seating die. Since the A-Max is longer to the meplate than the Match King it produced an O.A.L. .0040" (if I remember correctly) longer than the Match King load but the bearing surface of the bullet was in the same position as the Match King which was .0010" jammed in the lands.

Oh, and I know scores of shooters that run their bullet jammed into the lands, and after X amount of firings on that particular barrel, they will use a technique almost identical to yours to learn where their new seat depth is due to throat erosion.

For instance, I used the technique you wrote about with my .22-250 (known barrel, or more importantly, chamber burner) 4 weeks ago. It was impossible to jam the bullet into the lands. Reason being, is that once I had .001" of the bullet jammed, I only had .130" of the bullet sitting in the case and that's a no-no. Once I set the die to get the .22 cal bullet .220" into the case the bullet was jumping .0080" to the rifling, which will increase chamber pressure. This means my barrel is on its last leg.

Again, we are on the same page here but you didn't read it that way.

Thanks for the excellent post.

Just to make sure...I'll say it this way:

1. The deeper you seat the bullet, the higher the pressure will be.

2. Conversely, the longer the OAL is, the lower the pressure will be, EXCEPT

3. Once you're jamming into the lands, there will be a steep rise in pressure.

The "jump" to the lands has nothing to do with pressure, but the lack of a "jump" most certainly does. It would not be the .080" "jump" per se that influences pressure, but rather the reduced volume in the case behind the bullet.

I think that once you get VERY close to the lands, like maybe just .002" as a guesstimate for example, you might begin to see the same kind of pressure rise that occurs when jamming the bullet into the lands.

Do you agree?

One thing I didn't see mentioned was it had to fit in the clip..
Unless you are loading a single shot...Especially freebored rifles like Weatherbys you could go a long way and never get close to the lands..but it must still fit in the magazine if you
want more than one shot..To make it simple..take a dry round w/a
spent primer, no powder..w/the projectile you will use..seat it out where it touches, then back it off until you are clear..see
if it fits in the magazine..if so..try loading a few and shoot them and check your group and pressure..Pay attention not to stick the bullet in the bbl. when you run the dry round..Don

River Rider,

I'm open minded. I'm not saying I agree or disagree. I've ran bullets jammed for a couple thousand rounds out of two rifles and have had very few signs of over-pressure. Maybe I just havn't loaded them hot enough to get there. Gotta be very close though.


"Reduced volume of the case behind the bullet" Does there need to be slack in the case to keep pressure down? Take a given load, do not change powder charge, load one .001" jammed, load one .002" jump, the one thats jumping will have more pressure because there's more bullet in the case, and therefore reduced, unused, volume in the case?

So if the bearing surface, of the bullet is at .000" in relation to the lands (not jumping, not jammed) is that as long as you dare go? Is that what you mean?

Yes, that was mentioned. And yes, you are right. If it's too long for the magazine you can operate in single-shot mode.

That's splitting hairs, really. IMO. I doubt there's really a whole heck of a lot of difference between .001" into the lands and .002" off the lands, but your guess is as good as mine. I think .002" off the lands is pretty insignificant because it would be difficult to be sure that's really where you are, and keeping everything within a tolerance of .003" is really a pretty tall order when it comes to mass-produced bullets in the first place.

I don't see that there has to be "slack" space in the case to keep pressures manageable, it depends on what powder you're using. Taking into account the increase in pressure you will see is a very good idea, that's all. And another thing to point out is that the extra duration in confinement that seating into the lands might contribute to good ignition is worth consideration. Seating into the lands can be good or bad...you just have to know what you're doing. I'll point out again, most authorities suggest that jamming the lands is not a good idea for the typical reloader. You don't have to jam the lands to get accuracy, and doing so can make the use of published data a little confusing. If you're into the long range stuff and using special VLD-type bullets, then different techniques might be justified. For the average guy shooting the average bullet in the average rifle, staying away from the lands is probably the way to keep it all as simple as possible. Simple is good.

very interesting reading., thanks to all for sharing your experience

I do not jam bullets into the lands on a hunting rifle because there is a, remote, possibility that a variation which might make one round slightly longer than the others could stick a bullet in the bore.

With some caliber/bullet combinations neck tension can suffer if you start loading them too long. Combine that with a bullet shoved into the lands, and it 'could' result in a pulled bullet upon extraction, dumping a charge of powder into the action.

It would suck to be in the woods, extract a live round for whatever reason, have the bullet hang up in the bore, and dump powder all into the action. Even if you can get the bullet unstuck, which would likely require a cleaning rod, you still have to get all the powder out of the gun. This means you are headed back to camp.

I usually don't have any problems finding very acceptable accuracy with a bullet .010" or so off the lands.

Here some good information about seating depth short or long.




Reduced Case Volume by seating deep will cause Higher Pressures.

And as seen above so can seating long (or into Rifling). We have to compromise and find a happy medimum for hunting loads or chance a extract and pulled bullet. Usually a good starting point for hunting loads is 0.030" off of lands . YMMV and each chamber /load is different.

Bench rest guys want the ultimate in performance and Flat shooting (fps and BC). They disregard max magazine lenght, and single load, and work up load while seating in the lands so they have can utilize maximum case volume.

Here's how I would sum it all up in regards to how seating depth affects pressure: seating for longer OAL will decrease pressures---until the bullet is seated shallow enough to contact the lands which causes pressure to rise again. That's it in a nutshell.

Bingo

Not THAT! makes sense to me.

I have viewed this thread as merely an informative discussion between educated men. And I learned something.

I START my loads with them jammed and work up powder charge from low to high all the while inspecting brass for overpressure signs. So in the end I'm being careful not to over pressure my hand loads anyway.

Thank you for taking the time to initiate and maintain this thread.

-JG

Sure thing. It's good when it all comes together and makes sense and thanks for your input.