223 Seating Depth

[rg1]

Hornady 55 gr Spire Points the recommended oal is 2.200”. I load them from 2.218” to 2.230”. Or seat them to mid cannelures and you will be fine. Sharp pointed 55gr FMJ’s at 2.250” and 77gr bthp match get loaded to 2.255” all for multiple guns. 2.260” is a maximum magazine length and my loads are a tiny bit more reliable in some AR’S. I crimp if the bullet has a crimp groove and don’t for non cannelures. On my one .223 bolt rifle 2.246” is the max oal for the bolt to close With Hornady 55 SP’s.

 

[HiBC]

A general rule that may not always apply:

If your barrel is marked .223, it will have a 1 in 10 or slower twist tailored to light varmint bullets generally up to 55 gr. The accuracy/ benchrest crowd can make gains measuring/testing /obsessing over seating depth/jump.etc. These are typically loaded shorter than 2,260. Maybe 2.2. Cannelure length
would be typical. Cannelures and crimps have advantages for battle ammo.
Lets not forget there are .223 bolt varmint /target guns that may not use military magazines.

The .223 Wylde chamber is designed for match shooting. The barrel typically has tighter twist for long range heavy bullets. These may be 80 + grains and some loads for 600 yds ,etc don't get magazine loaded. They are(can be) single loaded. Typically 75-77 gr bullets get loaded to mag length,near 2,260

The Wylde chamber is toleranced for accuracy on the case body but it has a longer throat to accomodate the long,heavy bullets. You are unlikely to contact rifling with 55 gr bullets. Or even get close. With the long throat,some say the primer can unseat the bullet before good ignition. Some say a light Lee Factory Crimp into a cannelure can provide more consistent ignition and better accuracy when using 55 gr bullets in a Wylde chamber. Kind of like why we crimp in a revolver. Some say. I generally don't load 55's and I don't crimp. But they may have something,

The military 5,56 chamber /barrel may allow a bit more "looseness" for reliability. Bullets are 68 gr +. SDMR s and SOCOM,etc may get 77 gr loads .

Military 5,56 chambers will be throated to handle heavy bullets.

If you are inclined to find the lands and load to a specific "jump" you may find accuracy gains but more likely we load to the magazine, At least I do.

 

[Unclenick]

I once bought a box of HSM 223 loaded with 80-grain SMKs that were seated with the shoulder of the ogive below flush with the case mouth so they would still fit in an AR magazine. Shot just fine. The small annular gap at the case mouth didn't make any difference.

 

[stagpanther]

I once bought a box of HSM 223 loaded with 80-grain SMKs that were seated with the shoulder of the ogive below flush with the case mouth so they would still fit in an AR magazine. Shot just fine. The small annular gap at the case mouth didn't make any difference.

I've often wondered about that. I built a 284 win AR and end up doing the same thing with longer high BC bullets, but found evidence of bullet creep in the dynamic environment of AR cycling. I suspect that having a full or compressed charge might alleviate that but that too carries its own risk I would think if the bullet somehow ends up further compressing the charge.

 

[tangolima]

High BC is for longer range. It requires BC and MV to work. Sticking the bullet lower into the brass lessens the case capacity, which lessens MV. That probably washes out the benefits of high BC bullet.

For medium range, less than 300yd for instance, I'd rather use lower-BC, but shorter, bullet to maintain higher MV. It may work out better. I have found flat-base bullets doing better than boat-tail. They have more straight shank for bearing surface and bullet hold. Accuracy is better. Just something I have learned.

-TL

Sent from my SM-N960U using Tapatalk

 

[MarkCO]

High BC is for longer range. It requires BC and MV to work. Sticking the bullet lower into the brass lessens the case capacity, which lessens MV. That probably washes out the benefits of high BC bullet.

Yep. And having the base of a flat-base, or the shoulder of the boat tail below the neck- shoulder junction of the case also degrades accuracy. Why length, BC, shape and magazine length all have to be considered for best accuracy.

 

[Unclenick]

It all can be so but never say never. Too much depends on the gun and chamber and bullet shape. At the time the 223 Rem was introduced, the ability of a long neck to best support and align a bullet was taken as evidence the 223 Rem could never be made shoot up to the 222 Rem, but subsequent experience has pretty much shown it can hold its own. The same reasoning was given to predict the 308 Winchester would never equal the 30-06 for match accuracy back when the 308 was new. The neck was considered too short, not to mention too little powder capacity for adequate velocity.

I have found flat-base bullets doing better than boat-tail. They have more straight shank for bearing surface and bullet hold. Accuracy is better. Just something I have learned.

Bryan Litz gives a reason for flat bases being more accurate than boattails. It's a geometry matter. It is simply more difficult to manufacture a boat tail perfectly concentric with the rest of the bullet than it is to manufacture a perfectly square flat base. If the boat tail axis is even slightly off-axis with the rest of the bullet, there is uneven muzzle blast influence as it exits the muzzle, and this imparts lateral drift that opens the groups up.

By way of an analogy of machining principle, if you ever turned a muzzle crown on a lathe, you know you had to get out the 4-jaw chuck and put a mandrel in the muzzle of the barrel and indicate it as close to perfectly coaxial with the lathe spindle as you could get because otherwise the cone of the crown would be off-center and favor one side, which wreaks havoc with accuracy. The bore at the muzzle needs to be both perfectly centered and parallel with the spindle. But if you don't cut a taper but rather just part the old crown at 90°, you only need parallelism (provided by the chuck jaws) and don't have to center the barrel at all because there is no taper to go off-center. A boat tail vs. a flat base is like that. 90° flatness makes coaxiality irrelevant.

I once saw some really, really cheap "match" bullets for sale online. They were so bad you could actually see the unevenness of the boat tail centering in the photo of them. It looks sort of like the drawing below, but probably half as extreme. But do note only a 0.005" error is pretty blatant. O.001" would still be way too much. It needs to be pretty darn close to perfect.

 

[tangolima]

That makes sense. Imperfection in the base does more damage than the tip, because that's where the mass is.

I did some comparisons among external ballistics of different loads with different bullets, focusing mainly on flight time. There is little or no advantage using match (boat tail) bullets unless I go over 400yd. I have changed my procurement policy; buy flat base whenever available. I can save a little bit of money and increase MV. I will have less seating depth "to be or not to be". And I can load heavier bullet without barrel twist rate limitations, as they are shorter. Funny thing is they have become less available, probably due to the recent hype of long range shooting.

Long neck in brass is mostly unnecessary. It makes more sense to shorten it to have more capacity. Rule of thumb for seating bullet is to have more than 1 bullet diameter as seating depth. In practice we routinely go below that. It doesn't help to have neck much longer. Although I'm fond of .30-06, .308 is more efficient for their intended purposes. But it is different discussion.

-TL

Sent from my SM-N960U using Tapatalk

 

[Shadow9mm]

One advantage of boat tails is that they are easier to seat.

One other consideration is hunging vs target applications where bullet mass is needed to ensure proper penetration.

What of the dual taper bases, the ones that kind of have a ledge or step in them.

Lastly does the increased surface area of a boat tail give more area for the pressure to push on giving better velocities?

 

[tangolima]

One advantage of boat tails is that they are easier to seat.

One other consideration is hunging vs target applications where bullet mass is needed to ensure proper penetration.

What of the dual taper bases, the ones that kind of have a ledge or step in them.

Lastly does the increased surface area of a boat tail give more area for the pressure to push on giving better velocities?

The main, if not only, purpose of boat tail is to make the bullet shape more streamline so as to improve BC. Anything else is unintended side benefits. It really doesn't increase MV as the bear area perpendicular to the bore axis is unchanged.

-TL

Sent from my SM-N960U using Tapatalk

 

[Unclenick]

That step you see on the heels of some Lapua bullets was developed in the 1930s, I think. It may have been one way to mitigate some of the forming issues. Tooling was less precise back then.

The reason deformations in the nose are so much less significant than those on the base is that any nose influence that tries to push the bullet one way gets reversed when the bullet rotates 180°. Any influence on the nose due to epicyclic yawing gets reversed when it goes to the other side of the mean trajectory path. This won't be perfect neutralization because each epicyclic orbit of the trajectory is damped out a little from the previous one, but it keeps errors down to a minimum. This is why, when you look a the hollow points edges on a Sierra MatchKing and see a slight unevenness that slopes one way, it doesn't do much in flight. Some people bother with meplat uniforming just to be sure and use pointing dies to recover any loss of BC caused by the uniforming step, but these are guys talking about corrections of a few inches at 1000 yards, where wind variation is a bigger issue. Still, it will gain a point or two every once in a while.

Errors on the base, however, are influenced primarily by muzzle blasts blowing off one side of the bullet more than the other. This not only introduces additional initial yaw but introduces a lateral drift by pushing the bullet perpendicular to the bore line over the first few calibers of travel after exiting the muzzle. During that time, the muzzle blast from a gun without a muzzle brake will produce about 3% of the bullet's final forward velocity, so it is very strong briefly. Harold Vaughn measured that velocity gain by using a magnetometer to show the bullet spin was lower than its velocity suggested it should be if the bullet's acceleration had all been inside the rifling. He also showed a 2° slant filed onto a bullet base caused, IIRC, about two and half times more group dispersion than a 45° slant filed onto the bullet nose. Both kinds of filing unbalanced the bullet a bit, too, so the centrifugal effect also drifts the bullet to the side at the exit.

A rifle with an integral muzzle brake made by EDM'ing holes in the barrel should have enough lower muzzle blast pressure to reduce the effect of bullet base deformation or the influence of a crown that isn't perfectly symmetrical. But that's not something I expect, not something I've tested.

 

[44 AMP]

I remember an article where they tested it by drilling holes in the side of bullet noses and bullet bases.

Result, in simpler terms than Uncle Nick uses ,

unevenness in the heavy end (base) causes more and greater wobble than unevenness in the light end (nose) of a bullet....

I imagine that would hold true for any tapered cylinder spun around its long axis.

 

[Unclenick]

The greater the radius of a portion of a spinning bullet, the faster the surface speed and the greater the angular momentum each particle of its mass has. So it follows that if the same amount of material were removed from both the ogive and the bearing surface, the bearing surface removal would have the most effect on wobble.