I am in the middle of developing a load for my 243. I have found two loads that shoot sub-moa...both are the max book loads with RL 19 and IMR 4350, and both were seated at 2.68 OAL. I have determined that the rifle throat is ~2.80 and would like to reduce the jump. If I back off the lands and seat at 2.76, will the pressure increase such that I need to back off a grain or two with the powders? Obviously, that would be the safe way to approach it, but was wondering what ya'lls experience has shown. Thanks.

Going by your ~loose numbers, you will still be about .040" off the lands. By increasing the COAL by .080" and still .040" off the lands, you will be REDUCING your pressure. When you seat the bullet out further, you are increasing the internal case volume, which will reduce your overall pressure.

Thanks, Chad. I figured as much, but have heard of pressure spikes when seating into the lands. Since I am just off, your explanation makes perfect sense. Just wanted to make sure.

There are two different things at work here.

Without regard to the lands, the deeper you seat the bullet, the higher your pressure will go. This is true of rifle cartridges as well as handgun cartridges, but it's much more apparent in cartridges like 9mm and other cartridges with relatively low case volume, to the point of becoming hazardous if one is not very careful.

The leade does come into play in raising pressures when you start getting "close" to them. The QuickLOAD program indicates that seating into the lands will raise start pressure by some 7000 psi. This does not simply add 7000 psi to the net peak chamber pressure, but rather alters the pressure curve somewhat immediately following ignition and DOES ultimately raise the peak pressure overall.

I've never seen a detailed analysis of just exactly how the pressure increase responds to incremental charges in the distance from the lands, but because of what I've generally seen by observing muzzle velocities leads me to think that you'll see pressure increases as you decrease distance from the lands starting about ten thousandths off.

If you want to seat with zero clearance from the lands, then develop your loads that way. If you find a max charge while seating 0.050" off the lands, don't just change up and seat into lands without dropping the charge back also and looking for the new max charge. That should keep you out of trouble.

Like RR said, there are two things going on here. Moving the bullet in and out of the cases changes pressure, and moving into and away from the lands also changes pressure. If you worked up your load .040 out, and you want to shoot with the bullets into the lands I'd recommend lowering the charge, moving the bullet out, and working back up again. Example... you want the bullet into the lands, let's call it .000 for the sake of this discussion, yes you're increasing case volume. However it has been my experience that the increase in case volume, and resulting drop in pressure from that, isn't nearly as much as your offset increase in pressure by having the bullets into the lands.

Hopefully that makes sense. It's going to depend on how close to the lands you are etc. as to whether or not the increase in pressure will be a problem. Considering you're still going to be .040 out, you shouldn't have any issues.

Good info, guys...I appreciate it. Probably shouldn't mess with an accurate load (.66"@100 yds), but I guess I just want to learn what will happen. Should've started my load development with a longer OAL to start with! Oh well, there are plenty more rifles to tinker with.

I always typically start pretty close to the lands but it usually gets set back fast due to the limits of the magazine.

Be careful on seating the bullet touching the lands, depending on the rifle the lands can be sharp enough to grip the bullet to where it will detach when unloading and you'll have a mess of powder in your chamber.

I typically use a dummy cartridge without a primer and seat it where I know it will touch the lands then try to load it in the gun if touches make small adjustments on your die and re-press until its almost bolting then a I make a 1/4 turn on my die and thats my starting point. You may have to push the bullet out when going through the first few steps.

I've been fortunate lately and my .308 loads fit all three and work well, but usually if one has several firearms same caliber I always kept a dummy round for ea to set my dies to. If you are loading Barnes, they seem to like being off the throat a little.

That would be called jamming the bullet into the lands. Seating touching should not cause this.

I call it "kissing" the lands. Most Nosler Partitions like such a cousins' relationship, a peck on the cheek if you will.

Most Barnes bullets dislike the lands with high disdain....as if they've just endured an acrimonious divorce. Set these bullets way back.

Reason I said that Chad was a guy brought me his gun to take a look at it and said some of the rounds were sticking in his barrel, long story short his buddy reloaded some rounds for him (berger VLD's) and must have moved the die off the proper setting while loading his rounds, some would fit others were to long. Your correct that would be jamming.

I seldom load barnes bullets because of the price, usually if I use them their for my sons 260rem. My 300 mag likes the swift scirroco but its not cheap either, I usually load hornady interbonds, there cheap, pretty accurate, and never had one fail to kill any animal.