3 Gun Optic

[Onagoth]

FWIW, I'm not totally going nuts on this. I'm gonna work up an accurate load and go from there, just marking out my POIs at 200, 300, 400 and 500 (if I can find a range over 300).

Just trying to understand whats going on.

[Jadeslade]

Get a load and stick with it, learn the holds from the BDC. ie; I know my 400 + 500 yd holds are to put the correct line on the top edge of the target with my XTR.

jj

What about 600 yds?

[trevoro]

I looked but couldn't find what focal place the XTR uses. If it is a 2nd focal plane scope, which I think it is, being close to max power but not completely there would explain what you are running into with having to use the 400 yard hash mark for a 300 yard shot.

[co-exprs]

It might help to look at this from a different angle. Zeroing at 100yds only serves to give you a very precise hold for your easiest targets. As the distance gets further your error is compounded. When I zero my rifle, I zero using my 400yd mark at 400yds, on paper, with my long range match load. I do this because our most precise shots tend to be between 350 and 450yds. The targets used at 400 tend to be the same 12" targets found at 200 and 300. Beyond 450, the target sizes get big again, like a full size IPSC or a 20" gong. By zeroing your 300 or 400 mark at the appropriate distance it splits the error in half on the short side and half on the long side. Here are the benefits: 1. Your greatest hold error in your reticle is on close stuff where it doesn't really matter. So what if you are 2moa off at 100yds, when the target is usually 10". 2. Your holds at distance will actually mean something.

With your 1:8 twist, you should have a good 69gr load worked up. You don't need a ton of them, only enough each match for the long range stage. I bring 100 each month and shoot about half of them. Zero your scope with that load rather than your 55gr. You shouldn't have any trouble pushing a sierra 69gr or hornady 68gr match bullet at 2750 from your 18" barrel. That round will line up much closer to your BDC than the 55gr does. Also, You should be able to run an easy 3000fps from 55s in that 18. With your long range precision need covered, you don't need to worry about getting sub moa accuracy from the 55s, so load them for the trajectory you want. My LR match load is 69gr SMK over 23gr 8208, Remington benchrest primer, 2.235 OAL, no crimp. I get a little over 2800fps from my 20" and about 2750 from my 18" and it matches my Meopta BDC really well, providing me with a 260yd center dot zero, which is super easy to work with. My CQB load is 55gr Hornady FMJ over 24.4gr 8208, Remington benrest primer, 2.200 OAL. Gets me 3150 from my 20" and 3075 from my 18".

The Burris XTR is still one of the most popular and succesfull, 3gun optics. Tons of people have figured out how to make them work. No BDC is going to match up with any round all the time.

[carlosa]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Edited May 16, 2012 by carlosa

[outerlimits]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Actually, barrel length has nothing to do with BDC. You can get a load to match the BDC with bullet/muzzle velocity/zero distance/scope height over bore combinations. No black magic there.

[Onagoth]

Thanks all, but I have kind of given up on this.

I'm not necessarily willing to change my load to match my BDC, I'd rather let accuracy determine how fast or hot I make the rounds.

I've since shot a few different scopes and am finding the XTR, while great glass, isn't really for me. I've gone with a simple MOA reticle and will be doing a 50/200y zero. I will barely ever shoot beyond 300y so this makes the most sense, plus it is kind of a personal preference thing.

If I do shoot at 400 or 500y, it will probably be a crapshoot anyways since I have very restricted ability to practice at those ranges....(ie, in canada)

[carlosa]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Actually, barrel length has nothing to do with BDC. You can get a load to match the BDC with bullet/muzzle velocity/zero distance/scope height over bore combinations. No black magic there.

It does if your barrel is so short it can't push the projectile at the require speed to match the Bcd safely.

[Alaskapopo]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Like Outerlimits said that is not correct. BDC are not all based on a set load. The Swarovski BRT reticle is in mills and you figure out how your load fits in and you can tweak it by changing where you zero. The reason why most people run an 18 is because that is about the shortest barrel you can run with a rifle length gas system and that gives you softer recoil.

Pat

[Alaskapopo]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Actually, barrel length has nothing to do with BDC. You can get a load to match the BDC with bullet/muzzle velocity/zero distance/scope height over bore combinations. No black magic there.

It does if your barrel is so short it can't push the projectile at the require speed to match the Bcd safely.

Again it depends on your BDC also if you have one setup for a certain load at a certain velocity (marks in yards or meters for hold overs) all you need to do is change your starting zero to get your hold overs to match better at the longer ranges. So if your loads a little slow zero at 235 yards instead of 200 etc.

Pat

[mikegot38]

the bullet drop marks are meaningless The XTR is zeroed for 62gr bullets pushing 3100 , but the bullet drop on a 55gr pushing 2900 isn't even close at 300y, nor would it be for a 69gr bullet.

I'm just getting into rifle shooting - silly question, but

how large are the 300, 400 & 500 yard targets? How close

do we have to be to hit them?

Are we talking about USPSA targets at those distances?

At FN 3 gun we shot at mini poppers (12 inch)and mini colt speed plates at anywhere from 75-275 yards. Rifle better be on at these targets and distances.

[bushmeat]

[

At FN 3 gun we shot at mini poppers (12 inch)and mini colt speed plates at anywhere from 75-275 yards. Rifle better be on at these targets and distances.

The Skinny Sammies were fun!

Suggest you chrono your loads and get your ballistic dope out to 500. Then find out what the subtentions are on your reticle and marry 'em up. That way you know whether to hold dead on, high, low or bracket at whatever distance. A little cheat sheet taped to stock or forend and good to go. Having a rangefinder is great too.

I use the XTR and love it.

[carlosa]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Actually, barrel length has nothing to do with BDC. You can get a load to match the BDC with bullet/muzzle velocity/zero distance/scope height over bore combinations. No black magic there.

It does if your barrel is so short it can't push the projectile at the require speed to match the Bcd safely.

Again it depends on your BDC also if you have one setup for a certain load at a certain velocity (marks in yards or meters for hold overs) all you need to do is change your starting zero to get your hold overs to match better at the longer ranges. So if your loads a little slow zero at 235 yards instead of 200 etc.

Pat

Ok.. maybe I'm failing to communicate here..

my point is..

if x optic has a reticule that per "manufacture instructions" is supposed have hold overs at 200y 300y 400y etc

based on a 100y zero using a 69gr projectile flying at 3200 fps.

if you can't get get your bullets to fly at that velocity your going to have a hard time using that reticule "exactly" as advertised by the manufacturer. which seems to me is the Op has given up on..

now yes..

i know you can "experiment" and zero at different distance to get better use of the those hold over marks (along with playing with the velocity of your load, and even height of your optic)..

I do that my self with my tac30.. seance the hold over marks that do not work as advertised with 69gr bullets (tac 30 bcd is designed for projectiles flying at 3200fps)..

and a bigger point is.. that if you're choosing an optic with a BCD reticule and you are expecting that BCD to work exactly as advertised by the maker, you first have to make sure that your rifle and load match the ballistic the BCD was designed around, or you might have to Seattle with close enough.

and yes this will vary by BCD... if but if your bcd is designed around a 62+ grain bullet going 3000+ fps, the shorter barrels are going to be much harder to tune at that range (unless your willing to go with much lighter bullets)..

Am i missing something here?

if I'm overlooking something please let me know..

cheers,

Los.

[carlosa]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Like Outerlimits said that is not correct. BDC are not all based on a set load. The Swarovski BRT reticle is in mills and you figure out how your load fits in and you can tweak it by changing where you zero. The reason why most people run an 18 is because that is about the shortest barrel you can run with a rifle length gas system and that gives you softer recoil.

Pat

it's my understanding most people ran 20" because of the extra fps you get out of it..

[Alaskapopo]

The problem with Bcd scopes that are tuned to a specific load is that must of them assume that the optic will be mounted on a 24" barrel.

Which would eazly achieve the velocities your looking for.

I think this alone is the reason why most people run at least a 18" barrel and in fact 20" is the standard..

With 18" I push 69gr at 2855, so 55gr at 3000 while on the hot side, is still possible..

What barrel length are you running?

Like Outerlimits said that is not correct. BDC are not all based on a set load. The Swarovski BRT reticle is in mills and you figure out how your load fits in and you can tweak it by changing where you zero. The reason why most people run an 18 is because that is about the shortest barrel you can run with a rifle length gas system and that gives you softer recoil.

Pat

it's my understanding most people ran 20" because of the extra fps you get out of it..

In the early days when people were concerned about making power factor with light bullets using an 18 inch barrel was a hedge against being under power factor. But with heavy bullets now its pretty much a non issue. Using a rifle length gas system however does have a softer recoil impulse and it seems to be the reason most prefer it.

Pat

[00bullitt]

Often times Ballistic Drop Compensated/Calibrated(BDC) reticles get the bad rap for not being dynamic in application. They can be if you apply some simple principles of ballistics. If it is second focal plane, the values change with magnification. If it is fron focal plane, the reticle remains in proportion to the target and values do not change.

If you have a BDC reticle with known subtensions(I've attached the subtensions of the Burris 5.56XTR reticle), you can assign your own drops to the subtended reticle.

Your reticle may be calibrated for "X" velocity with "X" zero, utilizing "X" sight height, at "X" atmospherics, but it can always be corrected for by utilizing a good ballistic program.

This means that you may no longer have to utilize the determined 100 or 200 yard zero. You pick the one that best aligns your drops to your ballistic program and the solutions it provides. Make it whatever you want.

If you were to utilize a 69gr. Sierra Match King travelling 2800fps at 2200'altitude with a sight height of 2.3" and a 100yd zero, you could assign drop values as follows:

Center dot zeroed at 100 yards

1st small dot below center dot(200yd)is 1.1moa - 195yds

2nd dot below center(300yd) is 3.3moa - 285yds

1st line below center dot(400yd) is 6.1moa - 380yds

2nd line below center dot(500yd) is 9.5moa - 470yds

3rd line below center dot(600yd) is 13.6moa - 565yds

4th line below center dot(700yd) is 18.4moa - 655yds

If I were to change my zero to 200 yards, the drops would be as follows:

Center dot zeroed at 200 yards

1st small dot below center dot(200yd)is 1.1moa - 250yds

2nd Dot below center(300yd) is 3.3moa - 325yds

1st line below center dot(400yd) is 6.1moa - 410yds

2nd line below center dot(500yd) is 9.5moa - 500yds

3rd line below center dot(600yd) is 13.6moa - 590yds

4th line below center dot(700yd) is 18.4moa - 680yds

The math is the math is the math. Its just all in how you work it. You can make any BDC reticle work for you with a good ballistic solver.

I utilize a ballistic program on my Android phone that was written by Bryan Litz of Applied Ballistics. It is the Applied Ballistics App in Google Play. Shooter is also great. Shooter is the lesser version of the slightly more advanced AB App. They are extremely accurate when you input accurate data. Just remember; any ballistic program is only as good as the data you feed it. GIGO(garbage in/garbage out) principle.

Provide me the data of your load and I will work your drops for you if you like.

You then print a small pic of the reticle, assign new drops to the reticle, and fasten it inside your scope cap or somewhere visible for reference on your rifle.

Does any of the above make sense?

[Onagoth]

Thank you for that write up. A lot of it I already knew and went through in my head and on paper, but I still cannot reconcile my results with what the calculators and reticle would suggest.

I still really love this scope though, great glass, good eye relief, Gen2 has good illumination...all that stuff.

IN reality, if I go with a 200 yard zero the reticle hash marks on this or the PSt probably don't matter much since 99% of my shooting is sub-300yards.

[00bullitt]

The subtensions in the reticle were designed using a sight height of 2.3". The majority of AR's use a 1.5" tall mount. That puts sight height at 2.75". A difference of almost a half inch in height. That will affect ballistics from your rifle matching more closely to the reticle if the exact designed load was utilized. Additional sight height needs to be accounted for.

[Onagoth]

The subtensions in the reticle were designed using a sight height of 2.3". The majority of AR's use a 1.5" tall mount. That puts sight height at 2.75". A difference of almost a half inch in height. That will affect ballistics from your rifle matching more closely to the reticle if the exact designed load was utilized. Additional sight height needs to be accounted for.

I factored that in as well....Also, I was shooting on a range denoted in meters, not yards but also accounted for that difference.

[Onagoth]

The is probably the reason for a majority of the variance I am seeing though. If the reticle subtensions are with a sight height of 2.3" and my optic is 2.75", then the MOA holds won't line up.

[00bullitt]

The is probably the reason for a majority of the variance I am seeing though. If the reticle subtensions are with a sight height of 2.3" and my optic is 2.75", then the MOA holds won't line up.

The drop subtensions of your reticle in your scope are a constant. They don't change based upon sight height. They are based off of drop below centerline.

Your ballistic solution will have to take in to account the sight height when you input the data in to whatever solver you use.Your firing solution is what needs to consider the sight height.

Provide me your load data and let me run the numbers against the reticle. That may help explain the issue you are having.

I need a confirmed muzzle velocity, bullet type or BC, and atmospherics( altitude, temp, humidity or your density altitude) of the area in which you are trying to confirm your reticle. Also please provide your sight height from the center of your scope tube to the center of your bore. Try to be as accurate as possible.

We have the data for the reticle. I can match it exactly to your load.

[Onagoth]

MV - 2905 ft/sec, Cartridge AE223 55gr BC = 0.269, altitute 800 ft, temp = 60*, humidity unknownn. Sight height is 2.75".

Actual results, at 300m/330y....POA was the 400y bullet drop mark to hit a 5" area with 5 shots.

Edited May 17, 2012 by Onagoth

[co-exprs]

Burris web site shows the reticle set up for a 62gr FMJ at 3025fps. In addition, with the 69gr SMK at a BC of about .305 I would be hard pressed to believe .307 from any 62gr FMJ. Either way it doesn't matter. What matters is the actual dimensions of the reticle. According to my math, using Hornady 55gr FMJ at 3000fps and a BC of .243, if you zero your 300yd mark at 300yds, splitting the error between close and far shots, your POI will only be off by:

.06" @ 100yds (.06 moa)

.12" @ 200yds (.06 moa)

.48" @ 400yds (.12 moa)

1.5" @ 500yds (.3 moa)

3.18"@ 600yds (.53 moa)

About the same for a Hornady 68g BTHP doing 2750fps.

If you're good enough to care about a 3" POA/POI shift, at 600yds, with a 4x scope then you are a better rifleman than I am.

[co-exprs]

Using your numbers and a 300yd zero with your 300yd mark, you should be running a POA=POI variance of about:

.39" @ 100 (.39 moa)

.56" @ 200 (.28 moa)

1.56"@ 400 (.39 moa)

4.4" @ 500 (.88 moa)

8.9" @ 600 (1.48moa)

This was using Strelok for the chart and of course using 1" per 100yds as my MOA multiplier. I know it isn't exactly 1", but it's close enough for me to hit 4moa targets out to 600yds.

By zeroing at 300 with your 300yd mark, you should be able to use your scope practically as POA=POI out to 400 with only a slight correction (hold the top of the target) at 500 and 600yds. 400 is kind of common, but beyond 400 is kind of rare, so I would just make it work.

[pjb45]

Incredible work. Great information.