Zeroing the scope on my PTR-91

[Father Knows Best]

I have a new Hensoldt Fero Z 24 scope mounted in an HK claw mount on my PTR-91 (HK91 clone). I'll be heading to the range Saturday to zero it. Anyone here have any experience in zeroing this set-up? Want to check my figures and give some helpful advice?

The info I've found is that 7.62x51 NATO milsurp ammo should have a muzzle velocity around 2,500 fps in my rifle (18" barrel). The bullet is a 150 gr spitzer with a BC of approximately 0.37. If I measured correctly, the scope centerline is approx 3.5" inches above the bore centerline. Using those figures, it looks like a 200 yard zero would be a good one for me.

With a 200 yard zero, the scope should also be zeroed or extremely close to it (less than .20" off) at 50 yards. POI will be +/- 2.0" from POA all the way from 20 yards to 230 yards. POI will be -9.8" at 300 yards, which is the longest range I shoot at (I don't have a longer range available, and if I did, I wouldn't use this rifle/ammo combination).

My ammo supply for this rifle right now is a mix of Argentine, Belgian and Korean milsurp. Any reason to think any of this ammo will significant vary from the specs listed above (MV 2,500 fps, 150 gr bullet, BC .37)?

Any reason I should zero at 100 or 300 instead of 200?

 

[Onmilo]

If you zero at 25 meters your rifle will shoot about 1 inch high at fifty meters,
2 inches high at 100 meters
4 inches high at 200 meters, 1 inch low at 300 meters and 6 inches low at 400 meters.
Placing the center post at center neck of a human target with this zero will insure hits at all ranges from point blank to 400 meters using standard NATO ball cartridges.HTH

 

[waterhouse]

Please post a review of the scope after you take it to the range. I've never really thought about scoping mine, but someday I might decide to.

 

[Father Knows Best]

Onmilo, do you have ballistics info for standard NATO ball 7.62x51? I've got good calculators, but I'm estimating the MV and BC. Is your data based on calculations or actual measurements? If the latter, did the data come from an HK91 or PTR-91 with an 18" barrel?

 

[Ghost Walker]

Well, that seems to be some pretty complete flight path information you have there! Certainly better than page #692 of my Speer #13 reloading manual.

You're right; a 200 yard zero is the most functional. It's obvious you didn't start shooting yesterday; so I'm hesitant to add: It's just easier to bring a new rifle/scope combo on target by starting in close.

The usual procedure is to get on paper at 25 yards (shooting level, not downward). Then, for this particular load look for it to start printing 2.6" high at 100 yards. After that you should be able to easily reach out and touch someone at 200 - dead on! The information I have shows -11" at 300.

Once you've got the 100 yard POI correct, everything should nicely fall in place for ya. (That's, 'Why' starting in closer is just easier to do!)







Of course, you know that the different ammo you have is going to move the POI around on you; but, hopefully, not by much.

 

[Father Knows Best]

If you zero at 25 meters your rifle will shoot about 1 inch high at fifty meters,
2 inches high at 100 meters
4 inches high at 200 meters, 1 inch low at 300 meters and 6 inches low at 400 meters.

Hmmm ... I don't get those results using my ballistics calculator. Here's what I show with a 25 meter zero:

Range Velocity Impact Drop
0 2500 -3.5 0
25 2437 0 0.24
50 2380 3.14 0.84
75 2324 5.89 1.83
100 2268 8.23 3.23
125 2213 10.17 5.04
150 2159 11.64 7.31
175 2106 12.65 10.04
200 2053 13.17 13.26
225 2001 13.17 17
250 1950 12.63 21.28
275 1900 11.51 26.14
300 1850 9.79 31.6
325 1802 7.43 37.7
350 1755 4.42 44.46
375 1708 0.68 51.94
400 1663 -3.8 60.16

According to my calculator, zeroing at 25 meters results in a bullet path that is 10+ inches above POA from 125 to 325 meters, with the second zero occurring at 375 meters.

I've tried recreating your figures using different sight heights to see if your results were based on irons, but it doesn't work. It's clear to me that your figures assume a significantly higher muzzle velocity and BC, as your figures suggest a drop of only 5 inches between 300 and 400 meters. And that's what concerns me. I don't have good data on the actual MV and BC of the 7.62x51 NATO round. If my assumptions about MV and BC are seriously off, then everything else falls to pieces.

 

[Father Knows Best]

The usual procedure is to get on paper at 25 yards (shooting level, not downward). Then, for this particular load look for it to start printing 2.6" high at 100 yards. After that you should be able to easily reach out and touch someone at 200 - dead on!

Yeah, that will be my procedure, but since I'm bore-sighted I will start out at 50 instead of 25. With luck, I'll be on paper, and a zero at 50 should put me very close to zero at 200. If all goes well at 50, though, I'll move to 100, and I should see the shots printing a few inches high.

 

[Andrewsky]

I don't mean to threadjack, but...

I have an M1A with a 16" barrel. I fire 150 gr commercial ammo out of it. I have it zeroed at 1.5" high at 25 yards. I believe this will put me dead on at 200. I'm using iron sights though.

 

[Lanyard]

Father Knows Best,
This may get to you a little late but here are some helpful sites for your sight in.

Here is a copy of the manual (notice it's not in order)

http://www.drzero.org/cetme/pdf/g3sm.pdf

Here is some info on your NATO ammo (sorry, no Korean)

http://www.cruffler.com/trivia-June01.html

Here is some info on general sight in. (ie: 30m equals 200m)

http://www.cruffler.com/trivia-June01.html

And a little off topic. It looks like Stubbicat has a PRS G3 from Magpul.

http://www.magpul.com/catalog/index.php?main_page=product_info&cPath=70_88_115&products_id=252

Hope this helps,
Lanyard

 

[salty]

You have a nice set up - designed for up to 600 m's but 400 is more practical. You are going ot be very pleased with how accurate the rifle shoots however you are going to be limited by your ammo selection. I would urge you to upgrade to a better ammo for your sight in session. You may have to file the feet of the mount a very small amount to get a good fit for mount. Scopes were custom fit to rifles when issued and PTR's receiver and paint can be a bit thicker than a stock G3. Go to Hornady . com and use the ballistic calcultor there and get your ballistics table. Use the 25 m range to get on paper and set windage. Go for about 1.5 in. above point of aim at 25 - then move to 100 and follow the Hornady tables to set the yardage zero you want. Remember to set scope bdc for 2 when shooting at 25 and then back to 1 for shooting at 100 yard.

 

[Father Knows Best]

I am very pleased with the accuracy of this rifle using the factory irons at 100 yards, so I expect good results with the scope, too.

I know that milsurp ammo isn't known for being highly accurate, but it's what I shoot most, so it's what I will use to zero the scope. I have shot Hornady TAP in three different bullet weights, Federal GMM, etc., and I have several boxes of each right now, so I could use one of those for the scope sight-in, but what would be the point? If I zero the scope using 168 or 175 grain match target ammo, I will get nice, tight groups, but the rifle won't shoot to point of aim when I go back to using what I shoot most (Argentine and Belgian surplus).

I don't intend to enter any high power competitions with this rifle, so it seems to me that I ought to zero it with the ammo I expect to be shooting most. Once I do, I'll also put some high quality match ammo through it just to see where that ammo shoots relative to point of aim (and perhaps note the number and direction of clicks to move the POA to that ammo's POI), but that's not where I want it zeroed.

Also, this is the second claw mount I've had on my PTR-91. The first one was a Tapco. This one is definitely a tighter fit, but that should be a good thing. With luck, I won't have to do any filing. If I run out of adjustment room before finding zero, of course, then I will need to break out the file.

 

[Nightcrawler]

The info I've found is that 7.62x51 NATO milsurp ammo should have a muzzle velocity around 2,500 fps in my rifle (18" barrel).

Really? South African ball averaged faster than that for me out of a 16.25" FAL barrel, and I'm fairly sure that SA ball is downloaded compared to NATO-spec stuff.

 

[Father Knows Best]

Yeah, I'm now questioning that number.

Further research suggests that the NATO spec for 7.62x51 ball is a 150 grain bullet at 2,750 fps. I know from other reports I've found that few people have actually observed velocities that high, but I haven't found good chrono data from a comparable rifle.

According to one of the links Lanyard posted, most NATO ball isn't actually certified to meet the NATO spec, and most also isn't loaded with 150 grain bullets (actually bullet weight on a lot milsurp appears to be closer to 140 than 150).

I do have a chrono I bought at a garage sale but have never used. I guess I'm going to have to figure out how it works, because I am curious as to what kind of velocities I am really getting.

What really matters, though, is what happens at the range. I'm going to zero it using actual ammo in my rifle in the real world. It will then be interesting to see how that real world data compares to the predictions made by the ballistics calculators.

 

[geekWithA.45]

I usually get 2600ish +/-

I'd zero with ONE ammo type (whichever you have most of, probably), and then learn how consistent the other ammo is to that.

 

[Father Knows Best]

I usually get 2600ish +/-

What ammo and rifle?

 

[salty]

FKB - The reason to use better ammo to sight in your rifle is to eliminate error from the ammo - use your milsurp for initial windage and elevation at 25 - then use match ammo for final sight in. You could end up chasing the target all day as you never really know if it was ammo, scope or you. After scope is sighted in then use what ever you want. I have generally got higher fps numbrs than 2500 for SA and Aussie ammo - more in the 2600 ish range.

 

[Onmilo]

FNB, sorry it took me a while to get back to this thread,,,,
My observations are personal and involve some experience with a G3 rifle and a Hendsoldt telescope.
Ballistic calculaters are great assuming you have the opportunity to shoot on a windless day at an ambient temperature of 72 degrees Farenheight using the exact same kind of ammunition in the exact same kind of barrel that was used to obtain the initial data,,,,,well you understand.

I own an JLD PTR-91 and I also have my rifle adjusted to a battle sight setting with the 300 meter apeture in eye position and the rifle zeroed from 25 meters.
It places bullets in roughly the same area I described with the scope in place and I normally shoot Portugese FMJ ammunition in my rifle.HTH