Which .308 bullet weight for zeroing new ACOG? Does it matter?

[dodging230grainers]

So I picked up a Trijicon ACOG TA11-E (.308 BDC) for my PTR-91, and was wondering if there was a specific bullet weight I should use to zero in the ACOG at 100 meters, as its intended?

My main stockpile/plinking load is standard 147 grain NATO ball, so would it wiser to zero in using that?

Or should I sight in with 168 grain match ammo, as is apparently what Trijicon uses to calibrate the BDC, so I have precision shooting with 168 grain ammo (as that's all you really use it for, anyways), and with the 147 grain NATO spec I'll just be off a little bit?

What say you guys?

thanks.

 

[rangerruck]

I would zero it, with whatever ammo you will be most using.

 

[dodging230grainers]

that's what I was thinking too, I'm not sure if I zero it with 147 grain if the BDC will be off so much that I might as well zero it with what it was intended, 168 grain, and just make do with the 147...

 

[funfaler]

The BDC for 168 gr will be plenty close enough with the 147 gr, out to 500 yards. So, use your 147 gr.

 

[taliv]

i would use the 168 so you know you at least have one load that will work. then you can plink with your 147g and be just a little off.

 

[HorseSoldier]

I'd recommend zeroing with the intended 168 grain load, and then running the numbers through some sort of ballistic computer to see what the trajectory difference will be with you 147 grain surplus. I doubt it will make a whole lot of difference except at longer ranges than an ACOG is really intended for use at. Going the other direction with bullet weight, shooting Mk 262 with a 5.56mm ACOG reticle, holding shoulder height puts hits on a steel chest plate reliably out to 5-600 meters with no real drama.

 

[rcmodel]

Trajectory differance is the least of your problems.

If you zero with one load, and then change loads, you could be off several inches up, down, or sideways at 100 yards with another load.

The only way to find out is to test both loads and see where the POI turns out to be with each one.
Then decide which one you want a perfect zero with.

Very few rifles will shoot two different loads to the same vertical line.

rcmodel

 

[MTMilitiaman]

So does it say it was intended for the 168 gr load? Because I inquired here earlier and was told that as far as people knew, it was calibrated for the standard 147 gr M80 ball load.

I doubt it will make too much difference at moderate distances, but might be appreciable at the farther ones.

 

[HorseSoldier]

Trijicon's website says that the TA01B and TA11C were designed for a 168 grain round (I assume M852), fired from a 20" barrel.

 

[dodging230grainers]

As long as the 147 grain would hit minute-of-torso up to 600 yards, I wouldn't have a problem sighting it in with that. But I think it would do that anyways, even if I sighted with 168 grain.

 

[Tarvis]

Here's a thought:

If the reticle is designed for 168gr bullets in a 20" bbl, each tick mark will only be accurate (read really close) for the exact same setup. So, if you sight in for 147grs, your range marks will be off because they aren't calibrated right; and 168 gr projectiles will most likely be off at the zero as well as the range marks. If you sight in for 168gr bullets, you will be right on with all of the marks when shooting 168, but off when shooting 147gr.

So, you can either sight in for 168gr and be calibrated on all the marks, or sight in for 147gr and only have the zero calibrated.

 

[24kshooter]

+1 on the 168's - use a SMK or AMAX.

 

[dodging230grainers]

Yeah, I think 168 grain is the smartest choice.

BTW, what is SMK or AMAX?

 

[KBintheSLC]

I would zero it, with whatever ammo you will be most using.

Ditto.

Your zero will change when you change ammo, so I would take the advice above.

 

[dodging230grainers]

hmm...

Perhaps the deciding factor is, will I be more off with 147 grain if I zero in with 168 grain, or will I be off more with 168 grain if I zero in with 147?

 

[strambo]

I'd zero w/ 168 gr since that is what it is designed for. Then try out the 147s and get data (if they are close out to your intended shooting distance leave it there). It's not like changing a zero is a pain. It's quick and easy to change an zero or confirm it or record variance for a different round.

 

[MTMilitiaman]

Yeah, I think 168 grain is the smartest choice.

BTW, what is SMK or AMAX?

SMK = Sierra Matchking, a traditional HPBT Match projectile
AMAX= Hornady A-Max, a spitzer boat tailed match projectile with a polymer tip

 

[hiccups]

http://www.biggameinfo.com/index.aspx?page=/balcalc.ascx

Some random numbers.
Use a ballistic coefficient of .391 for a Winchester 147gr FMJ with a muzzle velocity of 2800fps
Use a ballistic coefficient of .495 for a Berger 168gr HPBT with a muzzle velocity of 2650fps

Zero'd at 200 yds there's 1.1 inch difference at 500yds.

 

[sinistr]

i would zero it with the ammo i was using.then practice with 19"
wide targets at uneven intervals (545,610,etc.)to get used to the reticle.