GECO 5.56x45mm 55 Grain FMJ







This ammunition appears to be loaded with the same 55 grain FMJ projectile that is found in the GECO 223 Remington 55 Grain FMJ Target ammunition.  









The 55 grain FMJ projectile loaded in this ammunition has a groove cannelure, instead of a rolled cannelure that is typically found on 55 grain FMJ bullets. The boat-tail on the GECO bullet is longer than that found on typical 55 grain FMJ bullets and the GECO bullets have some of the most uniform bases I’ve ever seen on bullets in this category.









This ammunition is loaded in brass cases that have the annealing iris still visible. The cases have sealed primer pockets. The primer pockets are crimped with three “stab” crimps. The head-stamp reads:

T   5.56 x 45  

The case-mouths are also crimped and sealed. The ammunition is charged with a ball powder.
















(The individual squares in the red grid pictured below are one-tenth of an inch.)








Velocity




I chronographed the GECO 5.56x45mm 55 grain FMJ  ammunition from a semi-automatic AR-15 with a chrome-lined, NATO chambered, 20” Colt M16A2 barrel.









Chronographing was conducted using an Oehler 35-P chronograph with “proof screen” technology. The Oehler 35P chronograph is actually two chronographs in one package that takes two separate chronograph readings for each shot and then has its onboard computer analyze the data to determine if there is any statistically significant difference between the two readings.  If there is a difference, the chronograph “flags” the shot to let you know that the data is invalid.  There was no invalid data flagged during this testing.

The velocity stated below is the muzzle velocity as calculated from the instrumental velocity using Oehler’s Ballistic Explorer software program. The string of fire consisted of 10 rounds over the chronograph.














Each round was single-loaded and cycled into the chamber from a magazine fitted with a single-load follower. The bolt locked-back after each shot allowing the chamber to cool in between each shot. This technique was used to mitigate the possible influence of “chamber-soak” on velocity data. Each new shot was fired in a consistent manner after hitting the bolt release.  Atmospheric conditions were monitored and recorded using a Kestrel 4000 Pocket Weather Tracker.









Atmospheric conditions

Temperature:  78 degrees F
Humidity:  33%
Barometric pressure:  30.05 inches of Hg
Elevation:  950 feet above sea level


The muzzle velocity for the 10-shot string of the GECO 5.56x45m 55 grain FMJ ammunition fired from the 20” Colt barrel was 3276 FPS with a standard deviation of 22 FPS and a coefficient of variation of 0.67%.  




For those of you who might not be familiar with the coefficient of variation (CV), it is the standard deviation, divided by the mean (average) muzzle velocity and then multiplied by 100 and expressed as a percentage. It allows for the comparison of the uniformity of velocity between loads in different velocity spectrums; e.g. 77 grain loads running around 2,650 fps compared to 55 grain loads running around 3,250 fps.

For comparison, the mil-spec for M193 allows for a coefficient of variation of approximately 1.2%, while one of my best 77 grain OTM hand-loads, with a muzzle velocity of 2639 PFS and a standard deviation of 4 FPS, has a coefficient of variation of 0.15%.











Accuracy


I conducted an accuracy (technically, precision) evaluation of the GECO 5.56x45mm 55 grain FMJ ammunition following my usual protocol. This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group-reduction techniques (e.g. fliers, target movement, butterfly shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. Also, a control group was fired from the test-rifle used in the evaluation using match-grade, hand-loaded ammunition; in order to demonstrate the capability of the barrel. Pictures of shot-groups are posted for documentation.

All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrel used in the evaluation was free-floated. The free-float handguards of the rifle rested in a Sinclair Windage Benchrest, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VAR-X III set at a magnification of 25X and adjusted to be parallax-free at 100 yards. A mirage shield was attached to the objective-bell of the scope. Wind conditions on the shooting range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.








 
The Wind Probe.







The test vehicle for this evaluation was one of my semi-automatic precision AR-15s with a 20” stainless-steel Lothar Walther barrel.  The barrel has a 223 Wylde chamber with a 1:8” twist.









Prior to firing the GECO 5.56x45m 55 grain FMJ ammunition, I fired a 10-shot control group using a hand-load topped with the Sierra 77 grain MatchKing.  That group had an extreme spread of 0.71”.









Three 10-shot groups of the GECO 5.56x45mm 55 grain FMJ ammunition were fired in a row with the resulting extreme spreads:

2.55”
2.09”
2.19”

for a 10-shot group average extreme spread of 2.28”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the 30-shot composite group was 0.79”.




The smallest 10-shot group . . .







The 30-shot composite group . . .







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Lastly, for any Internet Commandos in our viewing audience tonight, here’s a pic of a sub-half-MOA group of the GECO ammunition fired from 100 yards.  The group has an extreme spread of 0.46”.








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For comparison, here's a link to my accuracy evaluation of the GECO 223 Remington 55 grain FMJ Target ammunition . . .



Range Report:  GECO 223 Remington 55 grain FMJ Target





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Great report as always! I have been very pleased with the .223 pressure version. Shoots very well for the price.

I would love to try that bullet out with some hand loads.

Thanks for the write up.  

....Off to buy some .223!

I don't think I've ever seen a case of faster = better accuracy.

Almost every 5.56mm load that I've tested, I've been able to make more accurate by loading it to a lower velocity.


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I've had the same experience.  It doesn't have to be a big reduction.

Glad I bought the .223 version, based off of your last review.

Local Rural King had both in stock for the same price.


I'll take the added precision, over the added velocity in this case.


Nice work, as usual sir.

Thank you for the test.

I'd like to see how that projectile performs at 5.56 pressure in gel.

GECO would be smart to release the bullet as a reloading component.


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Aside from showing once at TargetSport, has anyone seen it in stock anywhere?

Another excellent review!!

The accuracy would not be bad for a typical XM193 load. Maybe even better than IMI. But, I doubt that GECO bullet has much frag potential.

I will continue to seek out the 223 version.

I bought a bunch of the Geco .223 55gr FMJ target ammo awhile ago from SGammo

I only started to really use it recently since I bought my new Daniel Defense V7 (16" barrel).

I am getting CRAZY accurate results with it. This is even using a pretty low end Simmons Aetec scope.

Here was my last range results at 200 yards. This was only my third time shooting the new gun.



I can consistently shooting 1/2 moa or less at 100 yards with the DD and this ammo. I am VERY impressed with this stuff....I think the gun has a lot to do with it also though.

3rd groups

I'll do 5 shot groups next but I'm willing to bet the groups stay somewhat consistent. In the end, this Geco stuff is still extremely accurate...

Muchas gracia.  


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Thanks for the info Molon!

Looks like the GECO 5.56 has the smallest extreme spread and mean radius of the M193's

By chance are you going to test the MEN M193?

Thanks

Da nada.


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Interesting - and thank you very much for another excellent review.  I had sort of figured this was GECO's 223 ammo, with a larger powder charge, and that would be that.  Not so!  they are using a different powder in the 5.56 than in the .223 (ball vs extruded).   I also figured accuracy would be about the same.  Again, not so, with the 223 loading notably more accurate.

Good to know, because I was considering getting some of the GECO 5.56 ammo, with some good sales out there.  I don't think I will now, instead looking closer at the .223 variants.  The .223 variant is more accurate (by enough to actually start to matter).  And since it's lower pressure, it's probably milder on the brass for longer life to the reloader.   This is very good information to have, so thank you again.

De rien.


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SGAmmo has the 556 for .34 a round..

Average case capacities in grain of H2O



GECO 223 Remington:  29.75

GECO 5.56x45mm:  29.60









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