Grendel ballistics overstated?

[Tony Williams]

In a debate on another forum, I pointed out that the claimed MV for the Grendel loaded with a 123 grain Lapua Scenar is 2,620 fps from a 20 inch barrel (8.0 grams at 800 m/s). This was challenged as follows:

The ballistics you quote for the Grendel are over-hyped. Either that, or they are from hand loads loaded to dangerous pressures and/or longer COAL's than 2.26". I've never seen a reloading manual that shows 8g at 800m/s from a 20" bbl for 6.5mm Grendel.

On page 13 of the Accurate reloading catalog edition 3.5, one finds 6.5mm Grendel with 20" bbl:

A maximum load for a 120gr Sierra HPBT loaded to a COAL of 2.260" is 26.3grains of 2230 propellant. This gives a muzzle velocity of 2,395 fps at a chamber pressure of 51,900psi (which is the max for 6.5mm Grendel in an AR15).

So who's right? What is the measured MV for factory-loaded 123 grain Scenar or 120 grain Sierra bullets from a 20 inch barrel?

[Bwild97]

So what was the quoted velocities? IIRC ALI. 2230 is not an optimal powder for the Grendel.

[Tony Williams]

[COTNTOP]

My average chrono for my reloads are 2652 fps/24 in. I know that does not answer your question but I can imagine the forum you got blasted on. I see it happening too frequently. That is why I really enjoy the Grendel forum.

[wiuprof]

My rifle with 20" barrel yielded the following results last month. 28.1 gr. AA-2520 with 123 gr. A-max averaged 2532 f.p.s. and the Hornady factory ammo with the same bullet averaged 2563 f.p.s. on the same day under the same conditions.

[LR1955]

In a debate on another forum, I pointed out that the claimed MV for the Grendel loaded with a 123 grain Lapua Scenar is 2,620 fps from a 20 inch barrel (8.0 grams at 800 m/s). This was challenged as follows:



So who's right? What is the measured MV for factory-loaded 123 grain Scenar or 120 grain Sierra bullets from a 20 inch barrel?

Tony:

Just my experiences using 120 and 123 grain bullets -- Sierra and Lapua -- with 20 - 28 inch barrel Grendels. Getting 2600 or more with a 120 or 123 is really pushing it. You will shear a bolt lug in short order.

With a 20" barrel, you are looking at about 2550 and that would be pushing it, too. You will shear a bolt lug if you shoot a diet of 120's out of a 20" barrel at 2550.

LR1955

[rasp65]

Tony All i can tell you is like what bwild said the published loads are not optimal. Powder companies do not like to publish compressed loads with ball powders. Yet all the top loads for the Grendel are compressed. AA uses a canister powder that is optimized for the Grendel and is not available to the public. I have no experience with the AA 123 Scenar loads at all. In my 18" Grendel I got 2520 fps with 30 gr. of AA2520. Reading this forum you will see a lot of chrono data and it will vary quite a bit and that is dependent on the barrel, chrono screen placement, temperature of the cartridges, and others.

[txgunner00]

I have not shot any factory ammo through my 20", but my experience is in line with what LR1955 said. I initially had my 123 SMK loads at 2550 and had a few cases try to pull apart. 2500 fps has been working well for a while now.

As rasp65 said, commercial loaders use powders not available to the public. A friend of mine here locally is a small re-manufacturer and he has shown me some of his data. I don't know why there is such a difference but there definitely is. AA's numbers are probably not overstated.

[JASmith]

Tony,

My sense is that someone gave you velocities for 24-inch barrels and mis-labeled them as 20-inch.

This seems to happen perhaps too often, and getting the bad information corrected seems to be a daunting task. For example over at least the past three years, Midway has been reporting velocities for the 14.5 inch barrel for Alexander Arms Grendel ammunition but neglect to mention the barrel length. This might be part of the reason for the vehemence of responses since a lot of folks seem to go there for quick looks at muzzle velocities.

The 16" data is very fast too, wich suggeests the possibility that the person doing the tests was using loads that are too hot for bolt longevity per other poster's comments.

[Drifter]

At the risk of repeating what has surely already been said at one time or another...

For many cartridges, the handloader can often safely exceed the velocity of factory ammo. However, with the Grendel, it seems that it can sometimes be challenging to safely meet or exceed the velocities of factory ammo. (On the other hand, amazing accuracy can be achieved by the handloader.)

As new powders continue to become available to handloaders, the game seems to be changing to some degree.

In the grand scheme, 50 fps doesn't seem like a game-changer anyway, as an extra click or two for distance shooting isn't significant. I don't think the Grendel was ever intended to be a barn burner. With high BC bullets, and despite modest muzzle velocities, the Grendel's ballistics are impressive at longer yardages.

I'm not making excuses for the Grendel. It's a wonderful cartridge that doesn't need to be hot-rodded to achieve precision accuracy at surprising distances, especially considering the limitations of the AR-15 platform. There's been a few analogies and themes applied to the Grendel, some of which seem rather fitting (such as "start slow, finish fast", "tortoise and the hare", etc). Recoil is mild, and barrel life is reportedly quite good.

Internet debates regarding AR-15 cartridges seem to rarely sway opinions. But let a Grendel shooter take along a guest for a shoot, and I'll wager that the guest will soon own their own Grendel. When someone joins me, I usually warn them up front that it will co$t them. They might not understand initially, but eventually they do. Long range shooting is addicting, and the Grendel is currently the best choice for factory-loaded AR-15 cartridges.

[Bwild97]

Well said Drifter!!!

[bwaites]

At the risk of repeating what has surely already been said at one time or another...

For many cartridges, the handloader can often safely exceed the velocity of factory ammo. However, with the Grendel, it seems that it can sometimes be challenging to safely meet or exceed the velocities of factory ammo. (On the other hand, amazing accuracy can be achieved by the handloader.)

As new powders continue to become available to handloaders, the game seems to be changing to some degree.

In the grand scheme, 50 fps doesn't seem like a game-changer anyway, as an extra click or two for distance shooting isn't significant. I don't think the Grendel was ever intended to be a barn burner. With high BC bullets, and despite modest muzzle velocities, the Grendel's ballistics are impressive at longer yardages.

I'm not making excuses for the Grendel. It's a wonderful cartridge that doesn't need to be hot-rodded to achieve precision accuracy at surprising distances, especially considering the limitations of the AR-15 platform. There's been a few analogies and themes applied to the Grendel, some of which seem rather fitting (such as "start slow, finish fast", "tortoise and the hare", etc). Recoil is mild, and barrel life is reportedly quite good.

Internet debates regarding AR-15 cartridges seem to rarely sway opinions. But let a Grendel shooter take along a guest for a shoot, and I'll wager that the guest will soon own their own Grendel. When someone joins me, I usually warn them up front that it will co$t them. They might not understand initially, but eventually they do. Long range shooting is addicting, and the Grendel is currently the best choice for factory-loaded AR-15 cartridges.

Well said! In fact, I have yet to take anyone along to shoot the Grendel who has not either bought their own, or is saving for their own. The low recoil and long range performance of the Grendel, in an AR15 platform, is the deciding factor for most. It really is the king of the hill for long range shooting in an AR platform when the availability of factory ammo is considered.

[LRRPF52]

If people are only looking at internal ballistics and muzzle velocity, they are not focused on downrange performance. I just ran the numbers comparing 2550fps & 2600fps with a 123gr VLD type bullet with a G1 BC of .510, and there is .3 Mils of difference at 700yds in trajectory, and .1 Mil of wind deflection difference. In MOA, it is a difference of 20 MOA vs. 21 MOA.

[Bill Alexander]

The velocities in the first instance look like they are from a 24" barrel rather than a 20" barrel. Typically we see 2600 +/- 20 fps for the 123 Lapua scenar round in production ammunition across multiple batches. I usually use a figure of 2610 fps for range calculations if I am shooting in mild weather here in Virginia. For a 20" barrel the muzzle velocity will drop by typically 50 fps so 2550 fps for an average is not unreasonable. Operating pressures are held to 50,000 psi and below.

With deference to LR1955 he is correct that trying to duplicate this type of performance with hand loads will reduce durability considerably. In factory production we typically utilize a very carefully matched ball propellent with a high energy density. Hornady actually have a better powder but they load faster so demand a lower loading density to prevent spillage on the machines. Bullet construction with this small case must be considered in combination with weight. The 123 SMK will run faster than the 123 Scenar which is in turn faster than the 120 Berger all at near identical pressures. Although only a lab result, the variation across the three may be as much as 50 fps. I have not verified this yet but the 123 Hornady may be yet the fastest.

[LR1955]

If people are only looking at internal ballistics and muzzle velocity, they are not focused on downrange performance. I just ran the numbers comparing 2550fps & 2600fps with a 123gr VLD type bullet with a G1 BC of .510, and there is .3 Mils of difference at 700yds in trajectory, and .1 Mil of wind deflection difference. In MOA, it is a difference of 20 MOA vs. 21 MOA.

LR52:

That is true but he was talking about 2650, not 2550. If there is no difference between 2550 and 2600, there should be no difference between 2600 and 2650. Therefore, there is no difference between 2550 and 2650. The fallacy of extension.

Eventually you come to a point where there is a difference. Where is that point?

LR1955