XM556SBCT3 and 75gr GD Balisitic Data

J

jaschul

Newbie
I have a couple of hundred rounds of both XM556SBCT3 and 75gr GDs. I'm looking for external ballistic data for both of them from a 11.5" and a 16" barrel so I can know my drops.

I'm also wondering if a 50/200 yard zero is even a possibility with either of these two rounds from my 11.5" - Any thoughts from someone who has experience with these cartridges in a 11.5?

Does anyone have any Chrono data and ballistic coefficients I can plug into shooterscalculator?
 
You really need to Chrono it out of your guns. Even within the same manufacturer and length, you can get significant velocity differences from one barrel to the next, so unless the data is from your gun, it will be of very limited value. You almost certainly won't be able to get a true 50/200 with either gun/ammo, as that requires an incredibly specific combination of velocity, BC, and sight height, so I would recommend that you Chrono your ammo and then decide on your zero.
As to the BC, Speer advertises the 75 grain gold dot to have a BC of .411, and Federal advertises the 62 grain TBBC bullet as having a BC of .255.
 
You’ll end up with something like a 50/180 or something like that. Not exactly 50/200.
I have chrono’d the AE75gr out of both barrel lengths and that is the training round for the Speer 75gr Gold Dot.

2650 approx from the 16” and 2400 approx from an 11.5”.
 
Seeing 2975 to 3025 fps from XM556SBCT3 14.5" FN barrels and 16" DD barrels respectively. I've used 2995fps and that seems to work fine.

Second what @ggammell notes regarding the 50/200 zero...it won't be spot on at both.

In regards to the 75gr gold dot soft point BC... I'm extremely skeptical it will achieve a G1 BC that begins in a "4" at these velocities.
 
In my experience over the past 4 yrs the 75 GD out of a 11.5” barrel with a 50 yd zero is more like a 50/100 yd zero. You be about 2” low at 150 and 4” to 6” low at 200 yds. I’m getting about 2370 FPS from a 11.5 and 2340 with a 10.3. Haven’t done anything with 16” barrels with this load.
 
pointblank4445 said:
Seeing 2975 to 3025 fps from XM556SBCT3 14.5" FN barrels and 16" DD barrels respectively. I've used 2995fps and that seems to work fine.

Second what @ggammell notes regarding the 50/200 zero...it won't be spot on at both.

In regards to the 75gr gold dot soft point BC... I'm extremely skeptical it will achieve a G1 BC that begins in a "4" at these velocities.
Click to expand...

its got a bit of a sloped tail, wouldn't that lend toward g7?
 
ggammell said:
its got a bit of a sloped tail, wouldn't that lend toward g7?
Click to expand...

Based on the profile, yeah sure. Funny thing is, you can still get good data on boat tail bullets using G1. Had a few times that the data came out better than with G7 numbers.

Just think that .411 is a little....generous for that bullet. Probably a bit closer to 0.385 out of an AR15 of 16" or less.
 
Per the applied ballistics database

Speer Gold Dot 75grain:
G7 BC 0.148
G1 BC 0.289
Weight 75 grains
Diameter 0.224"
Length 0.933"

I can't find whatever bullet is loaded in the XM556SBCT3
 
Arrik1 said:
Per the applied ballistics database

Speer Gold Dot 75grain:
G7 BC 0.148
G1 BC 0.289
Weight 75 grains
Diameter 0.224"
Length 0.933"

I can't find whatever bullet is loaded in the XM556SBCT3
Click to expand...
Trophy Bonded Bear Claw. Same as the M556FBIT3
 
jaschul said:
I have a couple of hundred rounds of both XM556SBCT3 and 75gr GDs. I'm looking for external ballistic data for both of them from a 11.5" and a 16" barrel so I can know my drops.

I'm also wondering if a 50/200 yard zero is even a possibility with either of these two rounds from my 11.5" - Any thoughts from someone who has experience with these cartridges in a 11.5?

Does anyone have any Chrono data and ballistic coefficients I can plug into shooterscalculator?
Click to expand...
Here is my data from my 16” BCM mid CHF barrel. I grabbed data from multiple bullets on this day and the 75 GD’s were the most consistent shot to shot of them all. About 35FPS variable. 2735 was the avg.
 

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ggammell said:
Trophy Bonded Bear Claw. Same as the M556FBIT3
Click to expand...
I can't find that bullet by that name. The issue i've run into the past is that sometimes the bullets are actually made by someone else and then used in a particular loading. Also, it just might not be in the the AB database. I know the 62 grain gold dot bulletd isn't, for example.
 
Arrik1 said:
I can't find that bullet by that name. The issue i've run into the past is that sometimes the bullets are actually made by someone else and then used in a particular loading. Also, it just might not be in the the AB database. I know the 62 grain gold dot bulletd isn't, for example.
Click to expand...

it’s a flying bus so AB prolly laughed and said “Nah, we good.”
 
Two data points:

Centurion Arms 11.5" with a SOCOM556-RC2, Speer Gold Dot 24475, 10 round shot, 2471 FPS average, 2499 FPS max, 2436 FPS min, 19 FPS standard deviation.

Centurion Arms 16" cut down to 14.5" with a SOCOM556-RC, Speer Gold Dot 24475, 10 round shot, 2611 FPS average, 2631 FPS max, 2577 FPS min, 16.4 FPS standard deviation.
 
Default.mp3 said:
Two data points:

Centurion Arms 11.5" with a SOCOM556-RC2, Speer Gold Dot 24475, 10 round shot, 2471 FPS average, 2499 FPS max, 2436 FPS min, 19 FPS standard deviation.

Centurion Arms 16" cut down to 14.5" with a SOCOM556-RC, Speer Gold Dot 24475, 10 round shot, 2611 FPS average, 2631 FPS max, 2577 FPS min, 16.4 FPS standard deviation.
Click to expand...
I just clocked 5 rounds of the stuff from my kac 11.5 with qdc and it ran 2168-223X. Averaged 222X or so. This was a stoopid slow lot pulling under 2500 from a 14.5 gun as I recall. 75gr gold dot seems variable here. I have some more inbound to chrono.
 
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