Sanity Check: 20MOA Cant Mount with Sig Sierra3BDX (40H/40V MOA adj)

[MegaHurtz]

Good day.

My gray matter hurtz, megaly (how Trumpfelidanian of me). Admittedly, I am quite probably making this harder than it needs to be.?.

I am putting together an AR-based 6.5G solution which is, obviously, not an uber-precision bolt-action weapon. BUT, I am still interested in being able to reach out to tickle sumtin quite some distance away.

I've bought a nicer mid-range laser rangefinder - the Sig Sauer KILO1400DBX. Unbeknownst to me at the time of purchase (priced better than some non-smart LRFs), it is a 'smart' product that can have comms with a scope and provide some technical wizardry with automagic illuminated holdover calculations on their BDX flavored scope's reticle. When I got the LRF and realized what the BDX platform offered, I started to do some research, endeavoring to get a bit smarter regarding optics and to see if there was any merit to these new products that Sig is offering to their customers. Based on reviews, and what muh noggin deems reasonable, it seems that their line of BDX products may hold water. With the price point of the BDX glass, coupled with the functionality it presents to have, I have decided to move forward with acquiring one for this build.

The BDX scope I have settled on has vertical and horizontal MOA adjustments of 40 MOA stop to stop, I understand. While the scope provides illuminated windage/drift holdover indications over the entire horizontal range of reticle, only the lower half of the reticle's vertical scale has the illuminated hold-over indications. I believe that the intent is to zero the scopes reticles such that the round's POI will always be lower than the POI at the range where the rifle was zero'd (i.e. 100yds). And this makes sense to me.

I ran some numbers at ShootersCalculator.com, with data taken from this post and this post (guestimating 2800 fps as the velocity on a 28" bbl), and have arrived at what I perceive to be a reasonable representation of what the Hornady 123gr AG performance will be like.

It looks like I would run out of indicative elevation holdover (20 MOA (based on only the lower half of the reticle being illuminative)) at some 725-ish yards, if I adopted an approach to leave the reticles zeroed (not playing twisty-turrets) and relied on the hold-over indications entirely. While that is pretty good, the 123gr Hornady AG round stays supersonic out to some 1025-ish yards (on a standard day), and I would like to have the means to utilize the optics to shoot out to those ranges, which would require a hold-over of some 38-ish MOAs.

So, is it reasonable that if I procure a 20MOA Cant Mount that I might be able to have (possibly-cue'd) optic performance that is consistent with the entire supersonic range of the round?

...

I acknowledge that I need to RTFM to see if there is a means to have the BDX ballistics calculator in the LRF account for such a mount, when calculating and displaying hold-over cues on the scope's reticle, if I will need to adopt a less dynamic BDC approach with the scope's reticle cues (which the BDX software supports), if I need to do the mental gymnastics and offset by 1/2 VFOW to account for the 20MOA of cant, or adopt an approach to use the hold-over cues only when range to target is <~725 yards and play twisty-turret otherwise (when reaching out to the edges of the supersonic envelope). HMM, the hold-over cues also account for the optical zoom, so it might make sense to dial back the zoom a bit when setting up for the longer-range shot.?. I find it an interesting problem set, from an academic perspective.

[centerfire]

The Grendel isn't really a 1K cartridge so while it may be fun to use it for such the reality is that you may get a little frustrated doing it. With that said, there is some optical degradation at the end of the scope adjustment and you're better off if you can help not using the scope with the elevation maxed out. Also, you may not get the exact amount of range out of the elevation claimed by the manufacturer, it could be more or less. That is the long way around saying that given your set of criteria I'd opt for the canted base/mount. However, 20MOA is the max adjustment so unless you plan on never shooting at your 100yd zero and will always be dialing elevation you should probably look at less cant such as 10 MOA. Personally I'd look at scopes with more adjustment range given your criteria.

[LR1955]

Good day.

My gray matter hurtz, megaly (how Trumpfelidanian of me). Admittedly, I am quite probably making this harder than it needs to be.?.

I am putting together an AR-based 6.5G solution which is, obviously, not an uber-precision bolt-action weapon. BUT, I am still interested in being able to reach out to tickle sumtin quite some distance away.

I've bought a nicer mid-range laser rangefinder - the Sig Sauer KILO1400DBX. Unbeknownst to me at the time of purchase (priced better than some non-smart LRFs), it is a 'smart' product that can have comms with a scope and provide some technical wizardry with automagic illuminated holdover calculations on their BDX flavored scope's reticle. When I got the LRF and realized what the BDX platform offered, I started to do some research, endeavoring to get a bit smarter regarding optics and to see if there was any merit to these new products that Sig is offering to their customers. Based on reviews, and what muh noggin deems reasonable, it seems that their line of BDX products may hold water. With the price point of the BDX glass, coupled with the functionality it presents to have, I have decided to move forward with acquiring one for this build.

The BDX scope I have settled on has vertical and horizontal MOA adjustments of 40 MOA stop to stop, I understand. While the scope provides illuminated windage/drift holdover indications over the entire horizontal range of reticle, only the lower half of the reticle's vertical scale has the illuminated hold-over indications. I believe that the intent is to zero the scopes reticles such that the round's POI will always be lower than the POI at the range where the rifle was zero'd (i.e. 100yds). And this makes sense to me.

I ran some numbers at ShootersCalculator.com, with data taken from this post and this post (guestimating 2800 fps as the velocity on a 28" bbl), and have arrived at what I perceive to be a reasonable representation of what the Hornady 123gr AG performance will be like.

It looks like I would run out of indicative elevation holdover (20 MOA (based on only the lower half of the reticle being illuminative)) at some 725-ish yards, if I adopted an approach to leave the reticles zeroed (not playing twisty-turrets) and relied on the hold-over indications entirely. While that is pretty good, the 123gr Hornady AG round stays supersonic out to some 1025-ish yards (on a standard day), and I would like to have the means to utilize the optics to shoot out to those ranges, which would require a hold-over of some 38-ish MOAs.

So, is it reasonable that if I procure a 20MOA Cant Mount that I might be able to have (possibly-cue'd) optic performance that is consistent with the entire supersonic range of the round?

...

I acknowledge that I need to RTFM to see if there is a means to have the BDX ballistics calculator in the LRF account for such a mount, when calculating and displaying hold-over cues on the scope's reticle, if I will need to adopt a less dynamic BDC approach with the scope's reticle cues (which the BDX software supports), if I need to do the mental gymnastics and offset by 1/2 VFOW to account for the 20MOA of cant, or adopt an approach to use the hold-over cues only when range to target is <~725 yards and play twisty-turret otherwise (when reaching out to the edges of the supersonic envelope). HMM, the hold-over cues also account for the optical zoom, so it might make sense to dial back the zoom a bit when setting up for the longer-range shot.?. I find it an interesting problem set, from an academic perspective.

MH:

I have little or no idea what the majority of your post was about other than you can't get past 750 yards without using a hold over. Nothing uncommon with that. You need a 20 minute base.

They don't cost much and are a necessity if you intend on shooting past about 700 yards with most if not all cartridges.

LR55

[Bigs28]

I have a March optic for sale in the for sale section with 56 mil or 189 moa of travel.

Problem solved.

[Sinclair]

MegaHurtz, As LR55 has stated, if you want to shoot past 700 yds with just about any load, you need some sort of ramp style scope mounting rail. 20 MOA is most common, but there are others. Be aware that the scope centerline height comes into play here. At say 300 to 400 yds, you can use just about any setup and make it work; however, to stretch out 700 to 1000, everything must play well together. So your scope centerline height is a factor in your come up calculations.

Frankly, 40MOA of total adjustment doesn't sound like very much. My SWFA SS 10 x 42 Milquad has about 36 Mils of total adjustment (~ 124 MOA) and according to JBM, that is barely enough to reach 700 yds. You have a very good range finder, but maybe not the one that you really need. To get the most out of it you must now design a setup around it to achieve your long range goals. BTW, Applied Ballistics has some very good articles by Brian Litz. According to them it becomes very difficult to hit anything past 600 or maybe 700 yds with a cartridge such as the Grendel. Your estimation of the wind, range, DA, mv, etc have to be spot on (as in less than 1% error) to achieve a 95% hit ratio. Just to let you know that your expectations might be a little unrealistic. Mine were too, so I have pulled back my goal to ~600 yds. max.

So your ring height, rail thickness, and scope diameter must be considered.

[Klem]

Megahurtz,

Yes, you need a 20MOA rail to shoot 1,000 if you want your target towards the middle of your scope's field-of-view. The closer you are to the centre of the field of view will have the least distortion. Otherwise you will need to use hold-overs, which will work, but not as precisely as having a nice crosshair to assist.

Sounds like your whole settup is a handicap for what you are trying to achieve. An (unreasonably) long 28" barrel fixed to a light-weight/flimsy AR15 receiver, using the smallest popular 6.5 calibre, with a scope that only has 20MOA of usable travel.

What model is your Sig scope?

On a side note, where did you get the data for Hornady American Gunner in Grendel? I visited their website and AG is not listed. They advertise 'Custom', 'Black' and 'Frontier' in Grendel only. Is this a limited run or a discontinued line? (also, hardly anything mentioned in previous threads for Grendel AG).

[MegaHurtz]

Thanks to all who chimed in. Good points about keeping things in perspective and not expecting too much from the platform/cartridge pairing.

Being a jarhead that was used to hitting 10 for 10 @ 500 yds with the A2's iron sights back in the day, I may have unrealistic expectations.?. I am much older, not as lean, and certainly have poorer eyesight.

What model is your Sig scope?

I haven't coined up just yet. I am vacillating over one of three models (3 are in my cart at the moment), struggling to make a good decision about the zoom/objective size vs keeping optical boresight as close to the bore as possible. I'm currently leaning towards the 6.5-20x52 on a set of Burris Rings. Others being considered include the 4.5-14x50 and the 3.5-10x42.

EDIT: Here is where I got the 40h x 40v MOA figure.

On a side note, where did you get the data for Hornady American Gunner in Grendel? I visited their website and AG is not listed. They advertise 'Custom', 'Black' and 'Frontier' in Grendel only. Is this a limited run or a discontinued line? (also, hardly anything mentioned in previous threads for Grendel AG).

From a post @NugginFutz made. I too tried to find sumtin on Hornady's site - no joy.

[Klem]

MH,

Two thoughts; scope and ammo...

Scopes
Having shot 1,000yds in F-Class over the years with a Leupold 20x I can say it is possible, but not recommended. What helped was big 6ft square targets with big (44" x 44") black roundels. You can't see the individual rings through the scope but you can see them on a TV screen if using an electronic target (e.g. Kongsberg). Before the advent of TV screen shooting we used Butts parties and spotting disks, driving the string round the target based on the previous shots and wind. If you don't have this support you are going to suffer from not knowing where the hell your rounds are going. Steel splashes and splashes around the target can work but in your intended rig it's going to be like driving jelly. Your 123gn bullets are going to arrive at the target slower than a wet week, made worse by lower BC's than a larger 6.5 calibre typically uses.

60x scopes are normal for long range. 40x if it is a hot day and the mirage is killing vision. High magnification helps see what the wind is doing down at the target. Here it is either March 60x or Nightforce 55x with NF becoming more popular. March has a good reputation for repeatability. S&B 50x, Sightron's 60x and others make long range scopes. They tend to be big, expensive scopes but for long range you have to pay to play. Your 4.5-14 and 3.5-10 are just not going to cut it at long range.

Ammo
I will let someone lese chime in here. I don't use factory ammo. Obviously something accurate with a high BC to buck as much of the wind as possible on the way to the target.

[LR1955]

Thanks to all who chimed in. Good points about keeping things in perspective and not expecting too much from the platform/cartridge pairing.

Being a jarhead that was used to hitting 10 for 10 @ 500 yds with the A2's iron sights back in the day, I may have unrealistic expectations.?. I am much older, not as lean, and certainly have poorer eyesight.


I haven't coined up just yet. I am vacillating over one of three models (3 are in my cart at the moment), struggling to make a good decision about the zoom/objective size vs keeping optical boresight as close to the bore as possible. I'm currently leaning towards the 6.5-20x52 on a set of Burris Rings. Others being considered include the 4.5-14x50 and the 3.5-10x42.

EDIT: Here is where I got the 40h x 40v MOA figure.


From a post @NugginFutz made. I too tried to find sumtin on Hornady's site - no joy.

Mh:

10 X and 14 X are not a good choice for precision work at 600, let along 1000.

20X would be the low end I would consider at 600 and having used 20X extensively, I went to 26X and will go to 30 X in an instant.

Hold overs are not the ideal solution for precision shooting and particularly with the low velocities found with a 30 grain 6.5mm cartridge as the Grendel.

The guys have commented on field of view and clarity when someone is using a stadia line far from the center of the optic. I will add four other problems when using hold overs.

First, if the distance is such that you are between lines, you are basically guessing at the hold. May not mean much but with a low velocity cartridge where the danger space is short and at longer distances, guessing where to hold between stadia is problematic.

Second, if your rifle is canted when using a hold over, you just put windage on it. Guys alleviate this by using levels attached to the optic. That assumes they mounted the optic perfectly in relation to the axis of the bore. Guys assume the axis of the bore is in line with a flat on the receiver and that the rail is also made perfectly. Not always true, particularly with cheap barrels.

Third is holding a stadia for wind when you are using a horizontal stadia that is well above the middle of the optic. Like using a three mil hold over for example, then a windage hold from that. Unless a guy is using a grid type of reticle that for many is too cluttered to be of value, he is guessing on where to hold for wind. And he will have a greater tendency to cant the rifle when using a big elevation hold.

Forth, we as humans are hard wired to look at the center of objects. It is our natural tendency so shifting our focus to something away from the middle tends to detract from precision. Even if there is a stadia line to look at. It requires a lot of focus to use extreme holds repeatedly and precisely.

If you want to use a Grendel at 10000 with any degree of success you are better off using the main cross hair located in the center of the optic and indexing the right elevation and windage. Or using the center cross hair and holding for wind. You are better with a Vari X that gives you up to 30X or so. At about 25X in most conditions you can dope winds through your optic providing the glass is of decent quality. Seeing mirage through the optic is a good thing because the Grendel will not give you anything at that distance so your holds for wind will be constantly shifting and most likely you will have to depend on mirage to see shifts and to estimate speed.

LR55

[centerfire]

You might want to define "precision" because I'm rarely over 12x 1K and in. Connecting up on an IPSC head at 700 yards doesn't require any more than 10X. I don't shoot BR or own a Joy Pod though so my perspective might be different than some.

[MegaHurtz]

... They tend to be big, expensive scopes but for long range you have to pay to play. Your 4.5-14 and 3.5-10 are just not going to cut it at long range.

Ammo
I will let someone lese chime in here. I don't use factory ammo. Obviously something accurate with a high BC to buck as much of the wind as possible on the way to the target.

Yep, understood on importance of using quality match-grade or, more preferentially, custom loads. The latter is next on my list of capabilites to invest in. The Dillon 1050 looks like a nice unit that is receiving my initial consideration.

I hear ya 5x5 on the optics zoom. For my initial endeavors, i think the Sig glass might pass muster for optical quality, with the 6.5-20x52 setup proving to provide a budget friendly solution on this initial investment.

...
If you want to use a Grendel at 10000 with any degree of success you are better off using the main cross hair located in the center of the optic and indexing the right elevation and windage. Or using the center cross hair and holding for wind. You are better with a Vari X that gives you up to 30X or so. At about 25X in most conditions you can dope winds through your optic providing the glass is of decent quality. Seeing mirage through the optic is a good thing because the Grendel will not give you anything at that distance so your holds for wind will be constantly shifting and most likely you will have to depend on mirage to see shifts and to estimate speed.

LR55

Well stated. Your other points are well received too.

Yeah, I am leaning towards just setting up a BDC config on the scope's smart reticle and not being lazy in considering heavy use of holdovers. And, doing so will very likely aid me in becoming a better marksman and lay a foundation for eventual transition into the ELR domain, should I decide to pursue such an endeavor.

-MHz

[MegaHurtz]

Ok, got the scope. Going to set it up on my 5.56x16" fraken carbine. While I await receipt of my new 6.5G upper.

The scope does indeed have only 40MOA of elevation and windage adjustment (160 1/4-MOA clicks, stop to stop).

As such, I am considering running the reticle down to one MOA off the bottom stop, and use a canted set of mount rings (Burris XTR Signature with various MOA ring-insert sets), and zeroing it at 100yds, slipping the turrets to zero, once sighted in.

The thought process is that the traj/poi will always be lower than the optical zero (except when shooting a target at 100 yards), which would nearly-always impute raising the reticle to push poi down. I'm thinking that adopting this approach, I should be able to get full use of the reticle's vertical field of adjustment enabling reticle-on-target out to the cartridge's 40MOA distance, and using hold-over for any distances from 40MOA to the bottom of the reticle's markings (or to the limit of the cartridge's Supersonic range, if less).

Does this sound like a reasonable approach? I can't conjure up a reason where I would want to have an ability to move the POI up above the 100yd zero'd POI (except for those rare instances where I may be shooting up or down a slope at a close target?).

Am I tracking true, or off muh rocker? What say ye?

-MHz

[centerfire]

Does this sound like a reasonable approach? I can't conjure up a reason where I would want to have an ability to move the POI up above the 100yd zero'd POI (except for those rare instances where I may be shooting up or down a slope at a close target?).

Am I tracking true, or off muh rocker? What say ye?

-MHz

No, your plan sounds poorly thought out and you disregarded every bit of good advice. At this point you're just fishing for affirmation. Run the set up and learn the hard way since you're already 100% financially committed.

[Klem]

Mhz,

Unfortunately you cannot change the angle of a scope by dialling the turrets. You can only change it by using an external angled mount.

Yes, the most efficient way to use the limited elevation in that scope is to mount the scope so the closest target appears in the middle when the elevation is dialled all the way to the end. Then you have the full 40MOA of the dial for all the further ranges. 40 is all you've got. If you want more you will need to come off the crosshair and use the reticle stadia lines (as long as your reticle has MOA stadia lines)

[MegaHurtz]

Mhz,

Unfortunately you cannot change the angle of a scope by dialling the turrets. You can only change it by using an external angled mount.

Yes, the most efficient way to use the limited elevation in that scope is to mount the scope so the closest target appears in the middle when the elevation is dialled all the way to the end. Then you have the full 40MOA of the dial for all the further ranges. 40 is all you've got. If you want more you will need to come off the crosshair and use the reticle stadia lines (as long as your reticle has MOA stadia lines)

Copy on using canted mounts for scope angle changes - the Burris rings' inserts do enable this.

Thanks for affirming my suspicions on the approach to zero with reticle at the bottom stop, to enable use as detailed. As an fyi, the scope can be setup with BDC-ish rigid stadia 'lines' (actually illuminated oleds). That will help with the longer ranges once i get it dialed to the other stop.

Thanks again, for your time and counsel, as I travel down the path of getting smarter.

-MHz