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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2015 at 14:03
Dawgdad View Drop Down
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New rules in CMP rifle competitions now allow a scope with a maximum of 4.5X and 34mm objective to be used in what has always been an iron site competition. These matches are shot at  6 moa round paper targets at 200-300 and 600 yards.

I assume most of the currently available scopes that would meet this criteria have a fixed parallax set for something less than 200 yards.

My question is What is the effect of a parallax setting of 100 yards when shooting at 600 yards?


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2015 at 14:34
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There might be a mathematical answer, I'll let someone smarter give it.

I'd say the effect is decreased precision.  That would need to be experimentally quantified.  It'd be roughly the same as taking any 6X scope with parallax adjustment, setting it to 100 yards, then shooting at 600.

Let us know what you find.  I don't shoot competitively, but I do run 1-4 and 1-6 scopes.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2015 at 14:51
Dawgdad View Drop Down
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Thanks for the reply.


I am looking for the mathematical answer to know if I need to custom order a scope with a different parallax setting that would minimize the effect across all three distances. If the effect would need to be less than 0.5MOA for my purposes.

I want as few moving parts and as little weight as possible so an adjustable parallax is not a likely answer either.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/26/2015 at 17:39
koshkin View Drop Down
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The effect of parallax setting is a function of several factors on the scope and of how consistent your eye position is.

A good way to estimate the maximum possible error is via the following equation:

0.5*[Obj Diameter]*([Distance to target]-[zero parallax distance])/[zero parallax distance]

That gives you the maximum possible error in the same units as the objective diameter of the scope, typically millimeters.  To get the error in radians, divide by the distance to the target (also in millimeters).  In practical terms, the error is smaller than that since your eye pupil diameter is not infinitely small and there is a slight self centering effect when you set up behind the scope.

For a scope with a 24mm objective with a parallax setting of 150 yards, the maximum error at 600 yards is 36mm or 1.42 inches (or 0.067 mrad).

Now this is how you estimate the maximum theoretically possible parallax error given distances, i.e. the boundary conditions.

If you know the range of deviation from the optical axis of your eye's position inside the exit pupil, the calculation has to take into account magnification.

For example, if i Have a scope with a 24mm pupil set at 4x and if my eye pupil diameter is 2mm (assuming we are in the middle of a bright day), then the most my eye can be offset from the optical axis without clear image quality deterioration is about 2mm.

In that case, the maximum parallax error at 600 yards with zero parallax distance of 150 yards is 24mm at 600 yards.

Lastly, all of that assumes that your eye piece is setup with zero error for your eye.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/27/2015 at 05:02
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You da man Ilya. Wow!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/27/2015 at 11:57
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He said what I said, just with more words. 
And smarter.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/30/2015 at 15:08
Dawgdad View Drop Down
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That is the answer I needed.

Not enough to worry about ... The X-ring is 1 MOA (6") wide so less than a 1/4 MOA.


Thanks.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/30/2015 at 16:45
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Dawgdad;

I'm concerned that you are taking 24 mm as the parallax error for your specific set of factors, and if so, that isn't correct. 

Koshkin gave you the information needed to answer the specific question you asked, but he left it to you to solve for your specific circumstances. Please note that he used a 24 mm objective, 4X, and a 150 yard parallax correction distance for his examples, not 34 mm, 4.5X, and 100 yds.

As Ilya noted, when ones eye is not all of the way to the edge of the exit but is offset a certain amount (he used a 2mm offset from the scope's optical axis), then parallax error is not maximum.   Under these realistic circumstances, the P.E. for this offset can be calculated as:

P.E. = Eye Offset x Magnification x (target dist - parallax correction dist)/parallax corr dist.

For the specific set of values you set out:  4.5x, 34mm Objective, 100 yd parallax corr dist, and shooting at 600 yards, P.E. = 2 mm x 4.5 x (600 yd - 100 yd)/100 yd = 45 mm or 1.77 inches. 



Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/01/2015 at 21:56
koshkin View Drop Down
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The title of the thread says "1-4x scopes", so I did the calculation for the 24mm objective since that is the most common objective for a 1-4x scope.

That is also a popular configuration, so there are many good designs there.

Offhand, I can not think of any 4.5x34 scopes. The closest would be one of the 4x32 fixed power designs, but most of those are not set up with turrets to dial in the distance.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/01/2015 at 22:07
koshkin View Drop Down
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Actually, now that I think about it, I wonder if the rules were changed to open the field up to ACOGs and similar sights since many of the more recent veterans are well acquainted with them.

My Elcan Specter OS would make a good match for this kind of competition I am sure, and it is a 4x32 design.

I've taken that scope out to 600 yards and parallax was the least of my concerns.

ILya

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/02/2015 at 17:15
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I can see, and appreciate, the point being made about the details of the post, what is currently available, etc.  That said, I did not see it as unreasonable to address the maximum magnification and the 100 yard parallax correction distance as a simple exercise. 

Using your example 4x and a 32 mm objective and of putting the outer edge of a 2 mm pupil against the outer edge of the scope's exit pupil, with a 100 yard parallax correction, would yield an offset of 3 mm for the scope's 8 mm exit pupil and a parallax error of 60 mm, or 2.36 in, at 600 yards. 




Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/10/2015 at 10:17
Dawgdad View Drop Down
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Thank you both. I appreciate all of the input. Even with the maximum error you have calculated I am still inside the 1 MOA X ring at 600 yards on the Service Rifle targets.


Ilya - that is part of the equation on opening the rules. 

USMC requested they be able to shoot the rifles they train with (A4 or M4 with ACOG) in Service Rifle class in CMP and NRA competition. Certainly does also encourage veterans with experience using these systems to participate.

The secondary impact is it allows shooters who have a scoped AR (3-gunners and such) to compete with the rifles they already have. Many have said they never tried Known Distance shooting with service rifle because they don't own an A2 or A4 with carry handle sights and front sight base. This takes that obstacle out of the way for them to try the sport.

Tertiary impact... Older shooters who quit shooting service rifle when they could no longer see the post clearly enough to shoot their rating can use the optic to get back in the game. Many of these shooters are running match rifles with round sights now and still shooting, just not service rifles.

The shield and  the sword part of the addition of optics as a service rifle is now it becomes and arms race with scopes and mounting systems adding to the cost of building a competitive rifle.  My attraction to service rifle was I knew that the $1300 rifle and ammunition I was using was pretty much identical to the ones being used by the national champion shooter from the US Army AMU team on the line next to me. Any difference in the scores was purely the shooter. The Indian, not the arrow or the bow. That and shooting 20-300 and 600 yards across the course of fire with iron sights on an AR is just plain cool.

White Oak Armament,  Compass Lake Engineering, Keystone Accuracy and several others all make these uppers for about $800 and anyone of them will shoot 1/2 MOA with the proven loads that everyone knows. No load development required. A2 lower and a Geissele NM trigger for another $500 and you are in business.

90% of the rifles on the line at a Service rifle match are an A2 with pinned 1/4x1/4 MOA sights, Float tube under the handguards and over a 1:7 or 1:8 Wilson, Kreiger, Pac Nor, Shilen or other quality maker barrel with a Wylde chamber with a 2 stage Geissele  or Rock River trigger  set at 4.5 # shooting a 75 or 77 grain OTM bullet from a red green or black box at 2750 fps with 23-24.5 gr of Varget, RE-15, H4895 and IMR 8208XBR as the most popular powders.

I do not expect  a 4x scope to make a huge difference in scoring as no scope holds the rifle still for you but I do not see how using a scope would not increase X count of a shooter capable of shooting a good score with iron sights.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/10/2015 at 11:50
koshkin View Drop Down
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Thanks for the explanation Dawgdad.  I wonder if I should try it it now.
Opening it up to scopes makes it more interesting for me.
I already have a couple of lowers with Geissele triggers, so all I would need is a compliant upper and an A2 buttstock.

Either way, I need to look up the exact rules, I suppose, to see what exactly is allowed for different disciplines.

Thanks
ILya
Post Options Post Options   Thanks (1) Thanks(1)     Back to Top Direct Link To This Post Posted: November/11/2015 at 14:22
Dawgdad View Drop Down
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Proposed new rules will also allow collapsible rear stock if using and optic. No adjustable cheek pieces. 11.5# weight limit though.

Here are the highlights of the proposed rules changes for AR's. M1, M1A still same iron sight rules.

Are chambered for the 5.56 x 45 mm (.223) NATO cartridge.

  • Are designed or modified for semi-automatic fire only.
  • Have either a gas-impingement system or a piston-operated gas system.
  • Have a barrel that is no longer than 20 inches, with or without a flash suppressor (16” barrels are permitted).
  • Use one upper receiver and barrel for the entire match.
  • Have a trigger pull of at least 4.5 pounds.
  • Use standard service magazines or commercial equivalents that do not contain added weights.
  • Have a fixed or collapsible butt-stock that may vary in length and even be adjusted between firing stages. Butt-plates or cheek-pieces may not, however, be adjustable.
  • Have a standard A1 or A2 pistol grip.

 

limited alibis

11.5 lb weight limit for optics

Currently no weight limit on iron sight AR's - mine weighs about 16# with lead up front under the hand guard and in the butt stock.

Where are you located? Always glad to get new shooters on the line. I might even convince you to shoot irons..

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2015 at 19:20
koshkin View Drop Down
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Originally posted by Dawgdad Dawgdad wrote:

Proposed new rules will also allow collapsible rear stock if using and optic. No adjustable cheek pieces. 11.5# weight limit though.

Here are the highlights of the proposed rules changes for AR's. M1, M1A still same iron sight rules.

Are chambered for the 5.56 x 45 mm (.223) NATO cartridge.

  • Are designed or modified for semi-automatic fire only.
  • Have either a gas-impingement system or a piston-operated gas system.
  • Have a barrel that is no longer than 20 inches, with or without a flash suppressor (16” barrels are permitted).
  • Use one upper receiver and barrel for the entire match.
  • Have a trigger pull of at least 4.5 pounds.
  • Use standard service magazines or commercial equivalents that do not contain added weights.
  • Have a fixed or collapsible butt-stock that may vary in length and even be adjusted between firing stages. Butt-plates or cheek-pieces may not, however, be adjustable.
  • Have a standard A1 or A2 pistol grip.

 

limited alibis

11.5 lb weight limit for optics

Currently no weight limit on iron sight AR's - mine weighs about 16# with lead up front under the hand guard and in the butt stock.

Where are you located? Always glad to get new shooters on the line. I might even convince you to shoot irons..


I am in California, so chances are you are nowhere near me.  I am guessing you are pretty close to a different coast.

As far as iron sights go, I was actually considering entering some vintage military matches that we occasionally have around here.

My Mosin M28/76 is the right iron sight rifle for that.

ILya


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2015 at 19:24
koshkin View Drop Down
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Forgot to add: is there a limitation on the type of handguard used for this?  Are free floated handguards OK?

My only 5.56 AR right now is an ultra lightweight 14.5" barrel, so it might not be perfect for this application.
I might still give it a shot though since it is quite accurate with 77gr SMKs.

Ultimately, I might just build myself another upper.  With my Spectre OS, I think I can easily get into the 11.5 lbs weight limit with a medium weight 16" or 18" barrel.

Does that weight include a loaded magazine and sling?

I thought about it and realized that I have four ARs, all chambered for four different calibers.  I should get another 5.56 anyway.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2015 at 19:53
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Lots of service rifle shooters in California. Junior program is outstanding. I know a few shooters at Coalinga who could show you the ropes of you are in that part of the state. This is one of the friendliest sports I have ever been in. No secrets. National champs shoot along side newbies and give them coaching and tips if they need it. I always carry a spare rifle and ammo in case some one says they just want to watch. Much better to watch from behind the sights. Rules won't be final until January by weight will be with sling and an empty mag.

Swedes and 98's and springfields usually rule the vintage matches. Some Mosins shoot well but most struggle. Get a Garand and have some fun with that.

Check out nationalmatch.us for service rifle information. It is an Olympic sized pool of knowledge. Bunch of chatter and blather about the optics rules but great forum for learning about high power.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2015 at 20:25
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I have or had a lot of milsurd rifles of all sorts and Mosin 28-76 is easily the most accurate one I have ever shot.

I'll check out the website, thanks.  

Coalinga is in a different part of the state, but there are a couple of places around here where they do service rifle shoots, so I think I'll be OK.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/11/2016 at 19:59
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Fellows:  Im bringing  this post up again. The CMP has released the "new" rules concerning the use of "optics"  on the AR15/M16 family of firearms that they now allow in the competitive events they (and the NRA) conduct.

There is great interest (good and .... not so good) in equipping the AR's we have been using with optics.

With the information that Dawgdad about the "sport"  could some of you that have experience with "optics"  give us "newbies"  some suggestions about suitable scopes?

I think the majority of us that will venture to this side of the "sighting system" will be looking at "optics" in the $250 to $350 price range.

IMHO a "simple" reticle is what is needed.  I dont think a reticle with all sorts of "ranging" information is needed.

Thanks,   ptf18
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/11/2016 at 20:23
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