6.5 GAP 4S a.k.a. 6.5 SAUM, what is it?

by AJ | Last Updated: November 6, 2020

What is a 6.5 GAP 4S

The the same cartridge as the 6.5 SAUM, the GAP stands for GA Precision, who originally made the cartridge famous during owner of GA Precision, George Gardner’s use of the caliber during professional competition rifle shooting in 2012. The 6.5 denotes the diameter of the bullet used in the cartridge being referred to as a 6.5mm bullet, but in fact it is actually a 6.72mm (.264 inch) diameter bullet. The 6.5 GAP 4S is exactly the same as a 6.5 SAUM or 6.5mm RSAUM, just by a different name.

6.5 GAP 4S Drawing Cartridge Dimensions
6.5 GAP 4S / 6.5 SAUM Cartridge Dimensions

What is a 6.5 SAUM?

Also often called the 6.5mm SAUM or 6.5 GAP 4S, the SAUM stands for Short Action Ultra Magnum, and the case is similar to a 7mm SAUM which has been necked down to accept a 6.5mm (.264) bullet. This cartridge is often refered to as the 6.5 GAP 4S, which is what is was coined by George Gardner from GA Precision who made the cartridge famous. The RSAUM often used stands for Remington Short Action Ultra Magnum.

The Creation

The 6.5 GAP 4S or 6.5 SAUM as some call it, was bound to happen at some point as almost every new caliber or cartridge created, gets necked down to a wildcat with a lighter bullet for more speed at some point in time. With the 6.5mm bullets offer some of the best Ballistic Coefficients available, most larger caliber cartridges get necked down to 6.5mm to test the effectiveness of the superior BC bullets in the larger cases, and in this fashion, a 300 SAUM or 7mm SAUM cartridge was necked down to create the 6.5 SAUM or 6.5 GAP 4S. The exact person to first do is unknown, but George Gardner from GA Precision made it famous during his competition use of the cartridge as far back as 2012, and then subsequently building many rifles chambered for this cartridge.

Regardless of who the actual pioneer was, the caliber was created, and with it, an excellent (if not arguably the best) long range 6.5mm cartridge, even outperforming the now popular 6.5 PRC in velocity.

There are not yet 6.5 GAP 4S SAAMI specifications, however with the excellent performance of the cartridge leading to a gain in popularity and how it’s use is becoming more widespread, we should soon see SAAMI release drawings a specifications for it.

George Gardner 6.5GAP 4S 1157yds
George Gardner shooting 3.89″ Group at 1157 yds with his 6.5 GAP 4S. Source: Facebook


22 Creedmoor brass

Initially to create brass for 6.5 GAP 4S cartridges, one would simply neck down high quality 7mm SAUM brass with a good full length sizing die and enough case lube. Thankfully though, there are many companies now including Hornady, ADG and a few more, making 6.5 GAP 4S brass cases. The 6.5 SAUM trim length for brass is 2.020″.

6.5 GAP 4S vs 6.5 PRC

Shooters Decide

With the 6.5 PRC and many other more popular 6.5mm cartridges to decide from, many question the future of newer or unique wildcat cartridges like the 6.5 GAP 4S. There aren’t currently any factory rifles chambered in 6.5 GAP 4S that we know of, whereas the closest competitor the 6.5 PRC already has factory rifles from a number of manufacturers including Sauer with their new Sauer Fieldshoot and Sauer Pantera rifles.

The 6.5 PRC holds around 60-61 grains of powder, whereas the 6.5 GAP 4S holds 64-65 grains of powder, which is where the velocity advantage of the 6.5 GAP 4S over the 6.5 PRC comes in.

Looking at the competitive scene however, which is a good predictor of what cartridges become popular in future as many novice and intermediate shooters follow the pros, the future looks good for the 6.5 GAP 4S with it being the second most popular cartridge choice for the top 10 shooters in the extended long range competition in 2020. As more of the pros compete and do well with it, the demand for rifles, ammo and brass for it also increases, and eventually major manufacturers start producing rifles chambered for those cartridges in order to capitalize on the trends.

Create Your Own

Creating a 6.5 GAP 4S chambered rifle is also fairly simple, you simply use the action of a rifle, or a rifle with a compatible bolt face and action length as can be seen on our bolt face database, and then have a gunsmith chamber and fit a .265 barrel to it. The gunsmith would need to preferably have a 6.5 GAP 4S reamer or 6.5 SAUM reamer to create a chamber in the barrel for it, however some advanced gunsmiths can turn a chamber based on a fired brass case. We used a Savage Model 12 LRP Stainless Action from a rifle originally chambered in 260 Remington, fitted a .264 Broughton barrel on it with the chamber cut for a 6.5 SAUM, and then changed the bolt face out to a magnum bolt face (which the savage bolt allows you to easily do yourself at home), and now we have a custom long range Savage 6.5 GAP 4S.

Just remember when chambering a short action rifle in 6.5 GAP 4S, the COAL will most often be limited by the magazine length, so a good aftermarket magazine that can hold longer cartridges is recommended, to fully make use of the capability that the longer and higher BC 6.5 bullets offer. When using AICS pattern magazines, removing the front plate is all that is needed to fit those longer cartridges.

6.5 SAUM / 6.5 GAP 4s Reloading Dies

We have mentioned it a few times throughout this article so far, but really to reiterate, Lemi Shine works wonders for cleaning brass, removing the ugly green hue sometimes left after tumbling brass in a wet tumbler, and leaving the brass looking shinier than when it was new. You can also use Lemi Shine ultrasonic brass cleaners.

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6.5 GAP 4s Twist Rate

Heavier .264 bullets have become longer to offer better Ballistic Coefficients so a 1-8″ twist rate is recommended to be able to stabilize those long bullets. The longer higher BC bullets are also recommended for the 6.5 GAP 4S as they offer the ballistics needed for extended long range and ultra long range shooting, the main purpose this cartridge was developed for and excels at.

6.5 GAP 4S for Hunting

Deer, elk and even moose would not be a problem for 6.5 GAP 4S to take down with one shot placed in the vitals, provided a suitable expanding hunting bullet is used, our favorite hunting bullets for the 6.5 GAP 4S are the Nosler Accubond LR 142gr, and the Hornady ELD-X 142gr. Even a clean non-expanding competition bullet placed on the brain of heart will bring them down, but the risk becomes too big with those bullets so are not recommended for hunting at all.

The 6.5 GAP 4S can comfortably take down all CXP3 or larger size animals just as easily as any .300 caliber cartridge can, and often even better at longer ranges due to it’s increased velocities and higher carried energy at those longer distances.

6.5 GAP 4S for Competition

For gallery rifle, or medium range shooting competitions, the 6.5 RSAUM will easily be capable of offering winning precision and top of the bunch wind drift beating ballistics, however it may be overkill if just building a rifle for such shooting competitions, and there are many smaller, or slower shooting cartridges that offer less recoil, and will better serve you with longer barrel life for these dedicated competitions. If you do not have any 6.5mm caliber rifle and plan on building one, then you might as well get the 6.5 GAP 4S / 6.5 RSAUM and have the best from the start.

Where the 6.5 GAP 4S excels though, is in the extended long range and ultra long range competitions, where it outshoots almost all other cartridges with comparable recoil and bullet diameter. So if you only want to shoot in these competitions, or want one rifle to shoot all varying competitions from short to long range, and also hunt most of what you may want to hunt in your life, there is no better cartridge than the 6.5 GAP 4S to do it all. You must just make peace with the fact that you will be replacing barrels more often as a compromise for gains in velocity, however not as often as you may think if a slow burning powder is used.

Now let us compare the 6.5 GAP 4S against the other two top competition 6.5mm cartridges, the 6.5 PRC and the 6.5mm Creedmoor, all shooting the same Hornady 140gr ELD-Match, offering exceptional 0.646 (G1) BC and can be used for both competition and any hunting you may want to do. 6.5 SAUM Ballistics:

6.5 mm cartridge ballistic trajectories
6.5 GAP 4S trajectory compared to 6.5 PRC and 6.5mm Creedmoor
6.5mm Creedmoor ballistics table
6.5 PRC ballistics table
6.5 gap 4s ballistics table

Looking at the graph and tables above, you can see that the 6.5 GAP 4S has around 25 inches less bullet drop at 1000 yards than the 6.5 PRC, and astonishing 96 inches less bullet drop than the super famous 6.5mm Creedmoor at the same 1000 yard mark. Now if that alone does not convince you of the benefits of the 6.5 GAP 4S, I don’t know what will.

6.5 GAP 4S Barrel Life

This varies depending on your rifle, barrel, load, velocity and bullet. There are many factors that determine the number of shots a barrel can take before the lands and rifling become worn to a point where the accuracy suffers. For the 6.5 GAP 4S load of around 62 grains of Hodgdon H1000 powder, you can expect around 2000 shots from your barrel, although this is a very rough estimate, with a few shooters already getting over 3000 shots out of their barrels with proper maintenance and using other barrel protecting methods like hBN coating the bullets and barrels.

6.5 GAP 4S Load Data

Hodgdon H1000 powder works well with the 6.5 GAP 4S, and a good rule of thumb is to start at around 59 grains of powder for a 140gr bullet, and 61 grains of powder for a 130gr bullet, and work up in increments from there using one of the load development methods. The slow burning H1000 powder helps keep the pressures well below the maximum mark, keeping the recoil down and also extending the barrel life.

6.5 GAP 4S Velocity

In our own testing, the 6.5 GAP 4S has been shooting 140 grain bullets with a muzzle velocity at around 3180 fps and 130 grain bullets at around 3300 fps.

6.5 GAP 4S vs 6.5 SAUM

The 6.5 GAP 4S and the 6.5 SAUM are exactly the same cartridge, just a different name for the same, the 6.5 RSAUM is also the same thing.