Having a mental block, doubling reticle value in a 3-9X mil dot scope.

[pmclaine]

Going to take a Sig "Reach for 1000" class and I want to take a retro rifle.....

This one......

The reticle in the scope is your basic mil dot - 4 dots up and down with the fifth mil being the top of the duplex stadia.

Im going to set my 100 yard zero with a 2 mil holdover at 9X, the highest magnification as well the power that the SFP reticle reads true.

That will give me 7mils of elevation in the reticle. As about two thirds of the shooting is 750 and in I can shoot the bulk of the course at 9X magnification.

For distance that will require more than 7 mils Ive marked the spot on my magnification ring where I have doubled the distance between mil dots in relation to the target using this style target....

So at 9X distance between two mil dots is one mil but at approx 4.5X the distance between two mil dots is 2 mils.

So my mental block is the following.....

My zero at 9x is good at the 2 mil holdover dot.

Is my zero at 4.5X still that same 2 mil holdover dot that I used to zero at 9X?

Im assuming zero reference stays the same, only change is my mil dots are now 2 mils apart instead of one, allowing me 14 mils of elevation hold.

Ill be shooting this next week to confirm zero and check the doubling marks Ive made, just looking for assurance so I dont waste ammo having either over thought or under thought this.

Shot this class a few other times using "better" gear, this is going to be a challenge but it will pressure me to learn. Ill get some good data.

 

[Diver160651]

Only the center of the intersecting strata in a SFP remains the same value as you zoom in and out. If you choose to zero as a hold above or below that will change with the zoom ratio

 

[pmclaine]

Only the center of the intersecting strata in a SFP remains the same value as you zoom in and out. If you choose to zero as a hold above or below that will change with the zoom ratio

Damn I was afraid there was a complication...

I dont know if Im wording this right.....but your saying - Center is always a center reference but the aspect ratio of everything else changes in relation to that center when you adjust magnification?

I messed with this a bit today and I was finding at 9X I was getting predictable POI using the bottom of the target as my POA than increasing one mil hold for each consecutive shot.....

But when I went to 4.5X and held a 10 mil elevation up from my original 2 mil holdover zero I was not getting impact at or near 10 mils on the target.

I know my doubling of the reticle is correct at 9X the mil dots fall exactly in the center of the next adjacent diamond 1 mil to the side or 1 mil higher/lower.

At 4.5X the mil dots cover 3 diamonds - One mil dot in the top diamond, one mil dot in the bottom diamond and one diamond centered between the two dots - this represents 2 mils.

So how do I do this?

I could "zero" at the top duplex having me holdover with ten mils of elevation below zero. This kind of sucks as the scope is probably about maxed out in the erector housing.

Dont have time to figure each distance that corresponds to a change in magnification to create a sort of BDC scope...

I thought the doubling thing was genius and would work fantastic.

 

[Diver160651]

Can’t you just zero in the center of your scope?

I do much the same with my PCP (air rifle) but I still need to map the zoom ratio as you do. the markings on the scope are not exact.

If you have a 2mil old over zero and found a perfect 1/2 power, so 2mils now represents 4mils on the smaller target. Your new zero should be 1mil.

here is an example:

 

[pmclaine]

This is somewhat how I was ""guesstimating" the shift to work....

So when I power down to my 1/2 scale ratio my "zero" than becomes 1 mil?

So at full power POI for zero at 2 mils will be same POI for 1/2 scale POI at 1mil?

That would explain my confusion at the range as I was assuming 2mils would be zero.

@D_TROS any input, I think you have done this.





EDIT ADD - just noticed an error on my reticle page.......the 1000 yard data (12.3) should be in the box below the 600 yard reference. Hoping to true this up some when I shoot a tall target next week. This chart is wrong anyway as those holds written in red need to use the 1 mil hold under as starting reference. I used 2 mils when I made this.

 

[308pirate]

So when I power down to my 1/2 scale ratio my "zero" than becomes 1 mil?

So at full power POI for zero at 2 mils will be same POI for 1/2 scale POI at 1mil?

That is correct. Go confirm with live fire at both magnifications/holdovers at your zero distance.

Don't be surprised if your zero at 4.5X needs some tweaking. There's manufacturing variation in every man makes including the erector cam and the exact location of 4.5X on the zoom ring.

 

[pmclaine]

That is correct. Go confirm with live fire at both magnifications/holdovers at your zero distance.

Don't be surprised if your zero at 4.5X needs some tweaking. There's manufacturing variation in every man makes including the erector cam and the exact location of 4.5X on the zoom ring.

Thank you for the input.

Im setting up one of those long targets with a course of fire to confirm my 9X, 2 mil hold zero/holdover values as well Ill do similar for the 1/2 magnification zero/holdovers.

Playing a bit with this yesterday my 9X results were as expected.

Changing down to 4.5X is where I got confused and it was the result of still using the 2 mil holdover dot as my starting reference. Ill use 1 mil now when at 4.5X.

Thats actually better as it gives me a tighter scale.

Shooting .308 to get 1000 yards it will be close whether or not I have enough holdover on the reticle.

JBM is predicting 12.3 mils and Ill only have 12 to use. Shooting at Sig previously I think Ive only used in the 11 mil range and that was using a shorter barrel .308. Im hesitant to zero on the 3 mil hold under dot as the adjustment screw would be looking kind of funky backed out any further than it is. Optically Id be pushing the scope engineering.

Regardless the targets are torso plates so they will be over MOA at distance and I should be able to still see part of them on the thin crosshair while the duplex obscures part. I want to be sub MOA all day but the only place it will show is at 100 yards when we shoot paper, all other distances are a noise reward on plates.

Im expecting there to be some sort of difference in zero shifting magnification from 9X to 4.5X. One of my exercises will be to fire a couple of rounds at 9X holding under 2 mil for group than do same at 4.5X holding under 1 mil. My expectation is I should see two pretty close groups and if there is a "shift" Im hoping it shows itself in the difference between the groups.

My effort to find the "doubling" magnification was pretty good. At 9X my mil dots are centered on targets that are 1 mil apart. At the location Ive assumed to double the same two dots are centered on targets 2 mils apart. Im sure its not exact but its close. Im more confident the "repeatability" is better using the reticle holds rather than trying to dial the erector. Id expect more error dialing from this level of scope.

Im expecting it to be a challenging day, having to wear Covid-19 PPE per order of Sig, shooting off bags, not having the crutch of the 15X magnification Im used to, the metal BP becoming a collar bone thumper shooting +/- 120 rounds in this class.

It will be tough but if I succeed Im going to have some great data and gain some utility out of an old school rifle. Ill get an appreciation for what the guys did using these in service.

Thank you to any that reply here with input.

and......

all this thinking will be for naught if it rains. I dont like getting my wood wet. Ill bring an old reliable in fiberglass stock if the Angels decide to cry.

 

[308pirate]

Im expecting it to be a challenging day, having to wear Covid-19 PPE per order of Sig

What, exactly, are they forcing you to wear?

I've resolved to not give any business to anyone who forces me to wear shit I don't need.

 

[pmclaine]

What, exactly, are they forcing you to wear?

I've resolved to not give any business to anyone who forces me to wear shit I don't need.

They will be handing out masks and.....

SIG SAUER ACADEMY COVID-19 QUESTIONNAIRE

www.sigsauer.com

 

[Gunfighter14e2]

If I am reading this correct you are wanting to double the ret holds on a SFP scope so that your 2 mill zero becomes a 4 mil target range? If that is correct you will have to locate your ret doubling location on the power ring. The following picture is of a device I built many years ago for shooting subs to 500yds. Leupold will tell you to set the scope at half power,..they are FULL OF SHIT on that. I have 2.5'sx8 3.5x10 6.5x20 an NONE double at half power. So I made whats in the photo for all of them. You can set it in the dark by feel w/o issue. We used this method long long ago on SFP scopes as a reverse BDC using the thick an thin as an aiming point an it played tag very well. With this doubler I can get to 400yds w/o knobing at all, past that I still have another 55 MOA of up to use. The stick has a 100 high speed zero, but it take 13 minutes of up to get the 217gr sub in the same place. If it was for subs only it would get to 450 w/o dialing anything set up this way. You can see in the top photo it is set to rock an the power setting is on 6.2X which is where most of my 10X's want to be for doubling.

 

[308pirate]

They will be handing out masks and.....

SIG SAUER ACADEMY COVID-19 QUESTIONNAIRE

www.sigsauer.com

The questionnaire is an easy one: no

 

[pmclaine]

If I am reading this correct you are wanting to double the ret holds on a SFP scope so that your 2 mill zero becomes a 4 mil target range? If that is correct you will have to locate your ret doubling location on the power ring. The following picture is of a device I built many years ago for shooting subs to 500yds. Leupold will tell you to set the scope at half power,..they are FULL OF SHIT on that. I have 2.5'sx8 3.5x10 6.5x20 an NONE double at half power. So I made whats in the photo for all of them. You can set it in the dark by feel w/o issue. We used this method long long ago on SFP scopes as a reverse BDC using the thick an thin as an aiming point an it played tag very well. With this doubler I can get to 400yds w/o knobing at all, past that I still have another 55 MOA of up to use. The stick has a 100 high speed zero, but it take 13 minutes of up to get the 217gr sub in the same place. If it was for subs only it would get to 450 w/o dialing anything set up this way. You can see in the top photo it is set to rock an the power setting is on 6.2X which is where most of my 10X's want to be for doubling.
View attachment 7319165

View attachment 7319166

Pretty slick.

I didnt find my "doubling" magnification based on any ring markings.

I found it by looking at a target with mil references than dialed the magnification to the point where two mil dots, 1 mil apart, rested on references that were 2 mils apart. I than hit that point on the ring with a dab of paint for reference. It is plus or minus 4 mils.

Unlike your high speed set up Ill be screwed in low light.

You are a crusty old killer arent you?

Guessing you and Sam Whittemore would enjoy drinks together.

 

[pmclaine]

The questionnaire is an easy one: no

Ive got the rinoest of governors in my state.

He is going to fight to be the last to open up.

Attended that Never Trump meeting on Jekyl Island in Georgia prior to the 2016 election.

This talk of "New Normal" is pissing me off.

"New Normals" have never turned out well for freedom respecting people.

Im guessing Sig has no choice in this just as my gun club has no choice in the bullshit it is doing.

We could refuse and just say "No" but currently if it comes to training vs not training....Ill take the training right now.

Restaurants wanting to take my temp though prior to service........only if its anal....I can cook my own burgers at home.

These restrictions are not to "protect our health" they are onerous demands to dampen the economy and show "orange man bad".

 

[Gunfighter14e2]

Guessing you and Sam Whittemore would enjoy drinks together.

Whittemore like many Americans just make do with that they have. I would have loved to be able to talk to him. Back in my day. we had to make the most with what we had, still holds true to this day with some.

While on the thread mill a little while ago I was thinking back to Hardrock matches long ago. A friend of mine whated to shoot it, so long short, he did not have a 1K yd stick, so I lent him my 300wm. To say he was nervous is a major understatement,... he shot the course with my side kick spotting for him an my data book. When his relay was over I ask why he shot the whole thing on 3.8X with the parallax at 750 yds, as I/we had watched him closely. He said he was nervous as hell do to the quality of shooters an gear there. Interesting things was,.... he finished,.... in the top 10% of the ATG class. Another time we had a young man win the whole thing an I think he was only 12 or 14 years old. Guess some just don't gee-haw with internet shooting reports.

 

[Gunfighter14e2]

Unlike your high speed set up Ill be screwed in low light.

Adding a cheap de-dent during mfg to a SFP scope as a doubler would cost at least 50cents,... full retail. They are very easy to make an during low/no light fool proof.

 

[supercorndogs]

Good thread, with a mind on vintage shooting.

 

[pmclaine]

Good thread, with a mind on vintage shooting.

Ive shot this class a few times with much more "modernly accessorized" rifles. Its great fun but little challenge. I know Im going to get my hits.

Ive been wanting to do this for awhile.

I think through 750 yards it should be pretty straight forward but 1000 yards will be where I make or break my day.

If this works I want to do this course with a Model 70 30-06 and external mount Unertl. With just straight cross wires that will require dialing. Ive checked it out and I should just make the elevation for 1000 yards using the scope blocks on my rifle. Ill have to dial 1/4 clicks into the hundreds and probably need to raise my cheek rest doing it but it should just get there.

 

[seansmd]

Wearing all that ppe may be a blessing with the black flys!

 

[pmclaine]

Wearing all that ppe may be a blessing with the black flys!

I think they all froze today.

 

[seansmd]

They never freeze, just resting!

Don't miss them

 

[pmclaine]

Went out with the rifle to try and proof my mil reticle shift.

Rifle.

New toy is spot on from the ConX RF.....have to see how it does at distance....

Sighted in using a 2 mil hold under at 9X on right. Used big box on left with a 1 mil hold under at 4.5X to sight in.

Starting at bottom of the target I fired zero at each magnification than walked my way up the target a mil dot at a time. I fired all the 9X holds first. I intended to than fire the 4.5X holds but I forgot to change the magnification so you will see to 9X shots on 4-5 of the POI spots.

Middle of target....

Top of target....

When I get to Sig Im going to tighten my zero because Ill be using a different lot of 175 FGMM.

It looks like today I had a .2 mil shift low when I changed from 9X to 4.5X.

I forgot to bring my 2 foot level so my target was off the reticle a bit. Hoping when the target is a plus MOA steel torso plate the hits will come.

Most of the shots look to be within two tenth of a mil, that could be a mess at 1000 yards. I should be able to shoot on 9X to 750.

Im in for a good challenge.

 

[Davo308]

Sweet rifle.

Whats the scope?

 

[pmclaine]

Sweet rifle.

Whats the scope?

Leupold 3-9X 40mm.

Its a pretty simple scope but the green anodizing makes it special for M40 rifle fans.