Home Forums Hunting & Shooting Ask The Gunwriters AUGUST column--Cartridge Overall Length

CARTRIDGE OVERALL LENGTH

Handloaders often have interesting ideas about cartridge overall length (COAL), the distance from the rear of the case to the tip of the bullet. Apparently quite a few think the COAL listed in reloading manuals was used when the company worked up loads in their ballistic lab, like the one in the photo below. But usually it's simply the maximum overall length set by the Sporting Arms and Ammunition Manufacturers Institute (SAAMI) to insure all factory ammo for the round will fit in the magazines, and function through the actions, of factory rifles.



Sometimes there are other, not-so-obvious considerations. The SAAMI maximum length of the 7mm Remington Magnum, for instance, is 3.29 inches. Exactly why is another question, because many American big game rounds designed for "standard length" bolt actions have a COAL similar to the .30-06's, 3.34 inches. So why is the 7mm Remington Magnum's COAL only 3.29, since it was introduced in 1962 in the brand-new Remington 700 rifle?

The 700 came in two action lengths, the same as the Model 721/722 rifles it was based on. The short action 700 had a magazine about 2.85 inches long, the same as the 722, introduced soon after World War II. The longer 700 action, however, did not have a .30-06-length magazine, but one long enough for the .375 H&H, and its descendant the .300 H&H. The H&H rounds have a maximum SAAMI COAL of 3.60 inches, and the "long" 700's magazine was long enough to accommodate both rounds, along with other "full length" magnums (as they were called back then) such as the .300 Weatherby, an improved .300 H&H.

As a result of the short COAL, heavier 7mm bullets had to be seated pretty deeply, using up potential powder space, back then (and sometimes even today) considered a ballistic misdemeanor. So why 3.29 inches?

The 7mm Remington Magnum appeared in 1962, during the peak of post-WWII conversion of "war surplus" military rifles into sporting rifles. Among the most-abundant and desirable rifles were various 1898 Mausers, often available for around $20. This was cheap enough to modify the action for easy scope-mounting, fit a new barrel and stock, and still spend less than the price of a new "pre-'64" Model 70 Winchester. (In case you're wondering, the list price of the standard-grade M70 in the 1963 GUN DIGEST, the issue that first listed the Remington 700, was $139. This may seem like an incredible bargain to the many shooters who apparently don't get the concept of monetary inflation, but the average American worker made around $4300 a year back then, so a new Model 70 cost about a half a month's take-home pay.)

War-surplus military 98s had magazines 3.315 inches long, to accommodate such cartridges as the 8x57 used by the German army, and the 7.65x53 used by the armies of several South American and European countries. The 3.29 inch COAL of the 7mm Remington Magnum was devised to fit inside the magazine of a typical war-surplus 98, with a little room to spare--a major market consideration back then.

So why did Winchester's four "short" belted magnums, introduced between 1958 and 1963, have a COAL of 3.34 inches? Because of the pre-'64 Model 70 Winchester. When the M70 first appeared in 1936, the basic model had a magazine designed for the .30-06 and its step-child, the .270 Winchester. As a result, the .264, .300, .338 and .458 Winchester Magnums were all given a SAAMI COAL of 3.34 inches, so they'd fit in the standard magazine, instead of having to be made with the H&H-length magazine. (It's also why so many war-surplus 1903 Springfields were rechambered to .300 Winchester Magnum. The .300 fit in the 1903's .30-06-length magazine--but not a standard 98 Mauser's magazine.)

Even many 21st-century cartridges have SAAMI COAL's due to magazine lengths established long ago. The 6.5 Creedmoor's is 2.825 inches, just enough to fit in the short action magazine-length established by the Remington 722 in 1948 and, 14 years later, the short-action 700. While quite a few new short actions have magazines around three inches long, 2.85 inches remains far more common--as are new cartridges designed to fit 2.85 inch magazines.


(.25-caliber rounds such as the .25-35 WCF, .250 Savage, .257 Roberts, .25-06 Remington and .257 Weatherby Magnum all have different SAAMI COALs, due to being designed specifically for different actions and magazines, even though some of the cartridges are of similar size.)

All of this is why the COAL listed by most loading manuals is NOT the "seating depth" they used when developing loads. Instead it's the SAAMI maximum, which involves mechanical function rather than accuracy. Of course, it makes sense for chamber throat-length to "match" COAL, so bullets can be seated close to the lands, which according to conventional handloading theory, results in finer accuracy.

However, some loading manuals do list the exact COAL used for specific bullets when working up data. Hodgdon's Annual Manual, the yearly magazine they started publishing over a decade ago instead of producing an expensive book every few years, lists COALs for every load listed. A good example is the data published for the 6.5 PRC (Precision Rifle Cartridge) , which I used when working up loads for a 2019 Annual Manual article on handloading the new round.

For some reason, Hornady (and SAAMI) gave the 6.5 PRC a maximum COAL of 2.95 inches, but Hodgdon seated different bullets to various lengths short of 2.95. They seated the 120 TTSX, for example, to 2.875 inches, perhaps because TSXs have the reputation for shooting more accurately when seated farther from the lands than lead-cored bullets. In fact, Barnes advises starting .050 off the lands--and then seating TSXs a little deeper if they don't shoot as well as desired.

Deeper seating also often helps other monolithics shoot more accurately, but over the past several years many handloaders have also discovered that lead-core, high-BC bullets also respond to deeper seating. Contrary to another popular belief, seating bullets deeper does NOT necessarily increase pressures. Instead, when seated up to about 1/4 inch deeper pressures normally drop, because the bullet's farther from the beginning of the rifling, providing a little more "freebore." (You can generally tell when pressures start to rise with much deeper seating, because velocities start to increase when using the same powder charge. But it's rare to observe this in modern rifle rounds.)

Other COAL's listed for Hodgdon's 6.5 PRC data are 2.930 for the 130-grain Swift Scirocco II, 2.880 for the 140-grain Nosler Ballistic Tip, and 2.945 for the 143-grain Hornady ELD-X and 147-grain ELD-M. I seated all those bullets to Hodgdon's COAL for my range-tests, and also used the Hornady brass and Federal 210M primers Hodgdon used.

Essentially my velocity results duplicated Hodgdon's, but after the initial duplication of their loads I experimented some more, not only with other bullets but COAL. Two bullets I really wanted to try were the 127-grain Barnes LRX and 129-grain Nosler AccuBond Long Range. When seated close to the lands, they both resulted in 5-shot groups well under an inch--but when seated considerably deeper, to a 2.860 COAL, both grouped even better:



Tweaking COAL can also allow handloads to function more reliably in rifle actions other than the ubiquitous bolt. Traditional lever-actions, with outside hammers and tube magazines, can be particularly picky about COAL. Most of the time they work fine with the blunt-nosed bullets designed for them, seated with the cannelure at the case mouth, but once in a while I've found a slight adjustment of COAL allows them to feed a little more reliably.

Often this depends on the shape of the nose, with flat-nose bullets occasionally hanging up sometimes when seated with the case-mouth around the cannelure. Seating flat-noses a little deeper often solves this problem--though of course that means the crimping cannelure's inside the case neck.

However, I've also found crimping bullets for tube-magazine lever-actions often isn't necessary. Elmer Keith pointed out decades ago that most of a case's grip on a bullet comes from a tight neck, not the relatively small crimp applied after seating the bullet, in both handguns and rifles. Consequently it's been many years since I crimped any .30-30 handloads.

Even some bolt-actions feed better with certain bullets when COAL is adjusted a little from "standard." My Mannlicher-Schoenauer 6.5x54, a custom rifle built on the 1930 Greek military action, feeds the 156-grain Norma Oryx better when it's seated to a little under three inches COAL, somewhat shorter than the standard 3.063 inches. This isn't entirely surprising, since the M-S action was designed around the original military load, a 160-grain roundnose. The Oryx is a flat-tipped spitzer, like some other bullets including the Trophy Bonded Bear Claw, Federal Fusion, and Speer Grand Slam. When the Oryx does hang up, it's usually the flat tip at the rear edge of the chamber, so I also help the bullet a little by gently rounding the "corners" of the flat tip with a fine file.

At the opposite end of the spectrum, single-shot rifles don't have any cartridge-feeding problems, so one of their advantages is being able to seat the bullet wherever we want. In particular I've handloaded for a bunch of Ruger No. 1's, in the process noting that chamber throat length has varied considerably in some cartridges over the years.

My first No. 1 was a "red pad" 1A in 7x57, acquired in a trade over 30 years ago. It had a throat so long that no lead-cored spitzer weighing less than 160 grains could be seated near the lands--and in that rifle, bullets needed to be near the lands to shoot well. Eventually I ended up using the 160 Nosler Partition with enough Reloder 22 to get around 2700 fps, and the bullet was barely seated deep enough to stay firmly in the neck.

Years later I bought a new, black pad No. 1A 7x57, and found the throat a lot shorter. As a result it was much friendlier to a wider range of bullet weights. My No. 1B .22 Hornet, on the other hand, likes bullets seated well beyond SAAMI COAL, which would be a no-no in bolt-action Hornets, especially with longer plastic-tipped spitzers like the 40-grain Hornady V-Max, Nosler Ballistic Tip and Sierra BlitzKing. It shoots all three into tiny groups, seated more than .1 inch longer than the SAAMI length of 1.723.

My custom 6mm PPC bench rest rifle, like most a single-shot bolt rifle, also shoots best with bullets seated longer than the SAAMI standard. Like many short-range bench rifles, it shoots best with bullets jammed lightly into the rifling--something not advised for a hunting rifle, but perfectly okay when killing paper.

So no, COAL is not written in SAAMI stone. There are several reasons to vary cartridge length, one of the advantages of being a handloader.


Obviously, this .375 H&H handload is longer than the SAAMI maximum COAL of 3.60 inches. That's because it was loaded for a Ruger No. 1, where there's no magazine to constrict overall length.

Interesting, thanks MD

Regarding the 6.5 PRC, I suspect there’s an interesting back story about how chamber dimensions were finalized. While a 2.95” magazine length and preferred seating depths were certainly considerations, so was the long bearing surface of Hornady’s 143 ELDX and 147 ELDM bullets.

Should that be 0.050?

Great article. I always appreciate your point of view.

Thanks.

Thanks!

And good catch on the typo. I changed it, one of the advantages of writing columns for the Campfire: You have a day to correct such stuff, and something always slips through.

Great read MD,
had not considered the 30_30 w out a crimp. My Late 40's Marlin may get a little testing before the leaves fall this September.
Thanks again for the informative take on the reloading side of rifle work.

Kingston et al : As I recall, the SA Ruger has a smidge longer IL magazine . Interesting that MDs testing with the 6.5 PRC showed better results at SAAMI length.

Room to chase the lands ?

What intrigues me is the various idimensional nteractions between leade, throat length, freebore and COAL
33 Nosler in a 3.33 mag box comes to mind.

I think if I had that long throat “red pad” #1 in 7x57, I would be sorely tempted to run it out to .280 Rem.
I have heard that this conversion doesn’t always fully clean-up the neck without some set-back.

But hey, it’s all about the twist anyways.

338Rules,

Guess I'm a little puzzled. Where did I say the 6.5 PRC "showed better results at SAAMI length"? The the SAAMI max length for the round is 2.95 inches. SOME ammo/bullets did best close to that, but others shot the tightest groups with bullets seated almost an inch shorter.

As an aside: The one "black pad" Ruger No. 1 in 7x57 (which had a MUCH shorter throat than the red pad 1A) I've owned was rechambered to .280 AI, and it still didn't totally clean up the old chamber neck--which could easily be seen in a bore-scope. But it shot great....

My bad, and my apologies.

You said in your article in Wolfe, that the PRC shot better UNDER SAAMI length at ~2.8” , Not 2.95”
Ie SAAMI SA magazine length,

Age related memory, and lack of reading glasses handy when I posted.
Glad you cleared up the confusion I created
🤪

Good to know about the 7x57 to 280 conversion. Maybe it would’ve gone to 7mm-06 Improved Express easier. 😉

Thank you for an interesting read.
so, given that loading manuals generally simply list SAAMI specs what do you suggest as a method for, at least initially, selecting an COAL when working up a load?
presuming of course, that we are not relying on magazine length as the determining factor.

Sorry I didn't notice this post earlier!

Generally it's a good idea to seat bullets close to the lands to start with. I usually seat lead-cores .02 to .03 or so short of the lands, and monolithics like the Barnes TSX's, Hornady GMX's and Nosler E-Tips .05 short.

Then I try different powders until arriving at the most accurate load for that bullet. If the accuracy still doesn't satisfy me, then I started seating the bullets deeper, and sometimes find the finest accuracy up to.1 inch deeper. If so, I sometimes tweak the powder charge again.

much appreciated,
it's helpful to have an informed starting point

thank you

I’m have a 6BRA being built with a long throat. I intend to seat 105 Hybrids .075 off the lands. Mark Gordon of Short Action Customs has been compiling seating depth data on the 6BR, 6BRA, and 6 Dasher showing an extremely forgiving seating range between .070” and .085”. While there’s currently no dominant theory supporting Mark’s findings, a trend seems to be emerging in practice.

Although on an entirely different spectrum, whereas accuracy and expectations for consistent performance are concerned, factory “Match” loads for many of the newer standardized cartridges like the 6.5 Creedmoor and 6.5 PRC rely on lots of jump. Whether this is a coincidence, I can’t say.

In my case, I was quick to follow Mark’s lead after having seen similar results while developing 6.5 PRC and 6.5 CM loads for SAAMI spec chambers, both with the 147 ELDM and RL26. Last year, I started using ladder tests to identify seating depth nodes much in the same way they’re used to identify powder charge nodes. At extended ranges of 400+ yards (optimally closer to 1000), the vertical dispersion of impact groups on targets boards can identify seating depth nodes —if you’re lucky, really wide ones.

In the case of the 6.5 CM, I settled on .055”, but not really optimally. It probably would have responded even better to more jump, but I was up against case capacity. Reloder 26 charges became compressed and required vibrating or maybe a longer drop tube, neither of which were compatible with my criteria for a precision load expected to be produced by hand at a rate of 500 a month during match season.

To many, long throating a 6BRA to jump 105 Hybrids .075” will sound insane, we’ll see.

Interesting and informative OP, John. Thanks.

Am presently considering re-barreling a 1:10 twist 22" M700 BDL .270Win w/ a 1:8 twist 24" Bbl. for the same cartridge, except throated 0.250" forward w/ leade to the new 6.8 WESTERN specs., facilitating long-loading (3.550" COAL) for the 150/160 gr. Partition, as well as the burgeoning crop of long/heavy/ELD .277" bullet offerings.

Comments/Concerns/Suggestions appreciated.




GR

Good article! Growing up, I knew nothing about OAL other than "make sure it functions and isn't jamming the lands". I later found out about it being another component of building an accurate load.

With regards to thoughts on throat length for a project, having a handful of bullets you'd like to try, as well as some brass, a Sinclair nut, and some calipers will let a guy see what throating length is a smart and flexible choice.

Given either the 150 gr. Nosler Partition or Speer Gand Slam, an additional 0.250" free bore combined w/ the 3.600" capable M700 magazine, would provide a 1 dia. case neck seating depth, and still allow ~ 0.010" left for longer bullets (like the 160 gr. NP), or the heavy VLD's seated a little deeper.




GR