Strelok Pro and ACOG 3.5x scopes; is this right?

[Amicus]

So, I set this up on Strelok with the following: M193 profile; changed MV to 3074 fps (which I believe is more accurate than the Strelok MV); 1/7" twist rate; 2.86" height above bore; sighted at 50 yards using an ACOG TA11-J (crosshair). The pic below shows the predicted points of aim/impact. Note that the BDC system appears to be very close to the drop rate of the bullet, but is off by 100 yards (e.g., the BDC mark for a 400 meter impact corresponds to a 501 yard range).

I have played around with this, and determined that the BDC was calculated for use with heavier bullets than M193 using slower velocities. I works for certain match cartridges (like Federal Gold Match, and heavier). Is this "off by one" correspondence correct? Is Strelok off, or does the software predict accurately what will happen?

[georgeib]

I've had very good results using Strelok, then Strelok Plus, and Pro. You didn't mention what BC you're using for the M193. Could that be where the issue lies? Also, isn't the 'Cog supposed to be zeroed at 100 meters?

[Amicus]

I've had very good results using Strelok, then Strelok Plus, and Pro. You didn't mention what BC you're using for the M193. Could that be where the issue lies? Also, isn't the 'Cog supposed to be zeroed at 100 meters?

I should have delineated those factors. They are one of the standards for the Strelok Pro database, and are: BC=0.243, bullet length=0.745, bullet diameter=0.224, bullet weight=55 grains. Yeah, the ACOG is supposed to be zeroed at 100 meters, but assumes you are using a much different cartridge than M193. I just decided to plug in values for a cartridge that I was using, and wanted to see what would happen if I zeroed at 50 yards instead of 100 meters. If this BDC data is correct, I only hope it could be of use to others who are using M193.

BTW, the little target is set to an impact point of 219 yards, which corresponds to a distance of 200 meters when using the 50 yard IBZ system. For those who do not know the Improved Battlesight Zero, a typical bullet (M193 or M855), with a zero at 50 yards, will rise above the PoA by about 1.37" at 100 yards, then fall to the same level as at 50 yards at 200 meters, or, 219 yards.

[jstone]

The information strelok gives you is only as good as the information you input. If your input information is good the results are solid. If you feel like all the information you entered matches up to your situation the posted picture is good to go. I have used strelok for BDC reticles and it was close enough for me.

[georgeib]

I should have delineated those factors. They are one of the standards for the Strelok Pro database, and are: BC=0.243, bullet length=0.745, bullet diameter=0.224, bullet weight=55 grains. Yeah, the ACOG is supposed to be zeroed at 100 meters, but assumes you are using a much different cartridge than M193. I just decided to plug in values for a cartridge that I was using, and wanted to see what would happen if I zeroed at 50 yards instead of 100 meters. If this BDC data is correct, I only hope it could be of use to others who are using M193.

I'm too lazy to do it myself, so I hope you don't mind me asking. But what happens if you input the zero at 100 meters?

[Amicus]

It looks like this (100 meter zero, 100 meter PoA):



That is more spot on than I remember.

[georgeib]

It looks like this (100 meter zero, 100 meter PoA):



That is more spot on than I remember.

Yeah, that's more like it. I bet if you tried it with M855 in 14.5" velocities, it would be pretty close too. The other factor is altitude. IIRC, the BDC is set for a 2000 ft elevation at 59 degrees, but I may be off on that.

[Amicus]

I had to extrapolate a bit, but here is the graph for XM855-ish (2885 fps, BC=0.304, 62 grain bullet) cartridges at 14.5". It's doable. My interest in this subject came from the idea that the best correlation for Strelok and the TA11J with my data came from a 50 yard zero setting. Or, to put it another way, an accurate 50 yard zero is available with the ACOG TA11J PROVIDED THAT you are using XM193 and are willing to add "1" to each listed range on the BDC (e.g., "4" becomes the range for 500 yards). Of course, the lines used for range estimation will remain the same, so if you are using the lines and determine that the target is 500 yards away, you will have to use the BDC line marked "4" for shooting.

This is probably not practical for shooting under pressure, unless you practice it a lot. I spend a lot of time dealing with pretty ridiculous minutiae.

BTW, I grab some of my data from TOS, which has a handy chart for historical military cartridges. If anyone knows of anything similar, please post the URL.

https://www.ar15.com/content/page.html?id=213

[georgeib]

Strelok Pro really is the best ballistic calculator available, IMO. Fun to play with, and after you've confirmed your drops at distance, you can either print it and affix to the rifle somewhere, or just memorize them. Good stuff.