DPMS AP4 BSZ question

[barrysuperhawk]

I have me a brandy new DPMS AP4 .308 rifle and I am thinking of trying it out in Heavy Metal. My question involves zeroing.

With a 5.56 and a 16" bbl, I know 50M gets me out to 250m, and with 5.56 and a 20" bbl 25M gets me 300M.

Currently I have either 25M or 50M available to zero at [or pretty much any range under 50M, I guess] and I am using SA 147FMJ 7.62. I do not have access to a chrono, so I can't give y'all velocity, but I figure I cannot be the first guy to shoot SA through a 16" bbl gun.

So, what range should I zero at for a BSZ, and where does the buller re-cross my LOS?

Edited August 26, 2010 by barrysuperhawk

[warpspeed]

If you have the "published" velocity, you can use This Ballistics Calcto figure out zeros an such.

It will give you drop out to 1000 yds. Then verify @ range and make corrections as needed.

[barrysuperhawk]

If you have the "published" velocity, you can use This Ballistics Calcto figure out zeros an such.

It will give you drop out to 1000 yds. Then verify @ range and make corrections as needed.

That's part of the problem, I have no idea what South African 7.62 does out of a 16" barrel. That is part of what I am asking.

[mpeltier]

You need to chrono and verify that load with the tables at those distances in your rifle. All else is nothing but guess work.

[benny hill]

You are getting about 2575 .

[Bryan 45]

To the best of my memory, SA 7.62x51 out of my 22" M1A only yields around 2600 fps. It's on the light side of 7.62.

[benny hill]

Out of my 21" it was getting 2742. Dpms barrel.

[Bryan 45]

I've always found the SA that I have to be of acceptable accuracy, but there must be some inconsistancy from lot to lot, or year to year. I used it a Benning last year and only needed 14 rounds to hit all 9 of the targets on the long range stage. Actually, I guess I only needed 9 rounds to do it, the 5 I fired that did not hit I did not need.

As has been suggested, it's best to chrono.

[barrysuperhawk]

I've always found the SA that I have to be of acceptable accuracy, but there must be some inconsistancy from lot to lot, or year to year. I used it a Benning last year and only needed 14 rounds to hit all 9 of the targets on the long range stage. Actually, I guess I only needed 9 rounds to do it, the 5 I fired that did not hit I did not need.

As has been suggested, it's best to chrono.

Ok, I get I need a chrono, but I can't afford one before I go to the next match, and I also don't have the time or availability to shoot it at range to see where it hits. My options are simply this: zero somewhere between 0 and 50m [the longest range I have available, right now] and then have some type of guess how far my BSZ is good for, and at what point I need to mess with my sights. I know it's not optimal, but it's as good as I can do with what I have, so it will be good enough.

So, a little more research on my paet yielded 2 separate places that placed the SA BC at around .350 and the SWAG of 2500fps velocity. A quick trip to Hornady's ballistic calc tells me:

Input Variables Firearm type Rifle Sight Height 1.5

Bullet Weight (grains) 147 Ballistic Coefficient .350

Muzzle Velocity (fps) 2500

Range (yards) Muzzle 50 100 200 300 400 500

Velocity (fps) 2500 2378 2259 2032 1819 1622 1444

Trajectory (25 yd. zero) -1.5 1.1 2.2 -0.9 -12.4 -34.5 -69.9

Trajectory (50 yd. zero) -1.5 0.0 -0.0 -5.4 -19.2 -43.6 -81.3

This tells me a 25 yard zero will stand me in good stead out to 300, and at 400 I am still aiming at the top of the plate. 3 gun isn't benchrest and my relative shooting skill [or lack thereof] will have more of an effect than any slight miscalculation here... Tahnks for y'all's help./

[mpeltier]

I've always found the SA that I have to be of acceptable accuracy, but there must be some inconsistancy from lot to lot, or year to year. I used it a Benning last year and only needed 14 rounds to hit all 9 of the targets on the long range stage. Actually, I guess I only needed 9 rounds to do it, the 5 I fired that did not hit I did not need.

As has been suggested, it's best to chrono.

Ok, I get I need a chrono, but I can't afford one before I go to the next match, and I also don't have the time or availability to shoot it at range to see where it hits. My options are simply this: zero somewhere between 0 and 50m [the longest range I have available, right now] and then have some type of guess how far my BSZ is good for, and at what point I need to mess with my sights. I know it's not optimal, but it's as good as I can do with what I have, so it will be good enough.

So, a little more research on my paet yielded 2 separate places that placed the SA BC at around .350 and the SWAG of 2500fps velocity. A quick trip to Hornady's ballistic calc tells me:

Input Variables Firearm type Rifle Sight Height 1.5

Bullet Weight (grains) 147 Ballistic Coefficient .350

Muzzle Velocity (fps) 2500

Range (yards) Muzzle 50 100 200 300 400 500

Velocity (fps) 2500 2378 2259 2032 1819 1622 1444

Trajectory (25 yd. zero) -1.5 1.1 2.2 -0.9 -12.4 -34.5 -69.9

Trajectory (50 yd. zero) -1.5 0.0 -0.0 -5.4 -19.2 -43.6 -81.3

This tells me a 25 yard zero will stand me in good stead out to 300, and at 400 I am still aiming at the top of the plate. 3 gun isn't benchrest and my relative shooting skill [or lack thereof] will have more of an effect than any slight miscalculation here... Tahnks for y'all's help./

Only if the plate is 36". If you are talking a typical 10-12 inch plate you will need to aim about 24" high with that 25yd zero. If you plan to do a lot of your shooting at that distance I would suggest something like a 300yd zero. This would allow you to hold about 12" over the top of the plate at 400. A 300 zero would be a zero of 1" high at the 25 yd target for the load you posted. Verify that at 50 by a group 3.2 inches above point of aim. The thing to remember is mid range trajectory would be a bit higher than line of sight so on targets of 75-250 your hits would average about 5 inches high, so just hold a tiny bit low. I do this all the time and it works very very well.

[Jefe73]

I, for one, get kind of frustrated that there seems to be a lack of understanding by manufacturers of the need for "battlesight" zero information for different weapons/calibers.

The military- US or European understand what a 25m or 30m battlesight zero is.

Its not hard to find data for a 25m zero for the M-4 or M-16; or data for the FAL or G-3 or AK-47.

Perhaps its me, but to believe that many (most?) can accurately "zero" a weapon w/ iron sights at 100yd is ludicrous.

The US military puts a battlesight zero on their weapons at 25m. We do it w/ the M-4 and M-16. I cant remmember if we did it at 25m or 25yd w/ the M-14. I think that we did a 25yd (1000 in) w/ the M-1.

In this case, why cant DPMS come up w/ something like "To zero your weapon at 25m using standard 147gr NATO ball ammunition, use the small apeture sight and adjust your sights so that POI is 4cm lower then POA. This will give you a 200m battlesight zero" or whatever the correct data is...