Open letter to BDC designers

BLUF: stop making M193 20” barrel BDCs. Just stop. Save your time and money.

55gr at ~1000 M/s shoots flat. Crazy flat. All the way to distances that it should never be used for. Its a laserbeam, but with wind drift. In fact, it sucks in wind past 300M. And in every other way, past that. I can’t think of many more ways to say that there is no need for a BDC for a fast-and-cheap short range load with piss poor BC. Even if everything else I say is dismissed as a crazy rant, know that 193/20” BDCs are dumb for duty optics. Every single one of them.

Honestly, its such a stupid application that I would instantly be turned off from a brand for even offering it on a “duty focused” optic, if it weren’t for the fact that nearly every manufacturer does it. Tells me that the dude who designed it neither shoots, nor studies ballistics. Certainly, he or she does not pay attention to who’s loading what, or why.

.Mil doesn’t care about 193. Cops that are issued 55gr ammo and near-roached M16 uppers aren’t shooting anyone at 500+meters. 3 Gunners have the Vortex JM-1 reticle, which you can’t do better than for this niche, and is sub-optimal outside its niche. Basically its the only BDC that makes sense for light/fast on a medium-range UKD 10” target with short ID/engagement times, and thats the ONLY place such a BDC makes sense.

Soooo, when does a BDC even make sense? Easy. Medium engagement distances with a velocity and BC where drop is more of a concern than wind. Simple, right? Ok, lets define that. Call it 300m-600m. 800 is stretching it, IMO, and I only rarely use LPVOs for this. 400m-600m is what I mostly like them for, but I do like to have the extra 700 and 800 hashmarks for screwing around, as an optional “luxury”. You’ll use a slightly heavier, higher BC bullet at more modest velocity to design an optimal reticle. Like, a 68-70 grain (full power)223 or 5.56 16” would split the difference between M855a1 14.5” and Mk262 18”. I tend to shoot from 62-70 gr, myself, as do many professional users. Upside down Cristmas trees on autoranging reticles such as Steiner LPVOs/prisms and Triji ACOGs have are the best kind of BDC, IMO. The whole point of a BDC is to get quick hits without clicking dope, right? So, right-side-up Christmas trees make less sense. Because if I’m measuring my wind, and I have an alternate method of ranging, I should just be clicking dope.

Steiner accidentally does a really good job with this. I say accidentally, because they offer both M193/M16 and slow/heavy .308 options on their more expensive optics. Strangely enough, they split the difference on their entry level P4Xi, and arrived at subtension values on an auto-ranging reticle that very well match everything from 12.5”-16” with 62-70gr bullets. It’ll even work well with light 62gr -69gr 3-Gun loads from an 18” or 20”. It looks like they did this to cut down on SKUs, but it actually works really well. Be more like Steiner. Keep your 308 reticles. They might even work OK for AK dudes. I know they work pretty well for Grendels. They do OK, but not great, on Mk18s. I’m sure they’re great for LE snipers trying to make that difficult 87yd shot with a .308 F-class gun. But ditch the M193 reticles in favor of something more middle ground, like the P4Xi has.

TLDR? Just do M855/14.5” autoranging instead of M193/20”, and I’ll make it fit the other guns. No one has a M16 loaded with M193 and topped with a 1-6x. No one. Thats been obsolete since the year after I was born. Until then, I’ll continue to prefer the 3 or so brands that roughly do that. As will the DoD, who rather obviously agree with me.

Sidenote, fiber optic illuminated center dots are sweet. I assume there is a reason so many choose the other methods, but I prefer fiber dots for several reasons.

M193/20-inch M16A1 was the standard when the ACOG was introduced. It got Trijicon their intro to the US military and helped win them their initial M4-NSN SOPMOD contracts. The rest is history.

M16A2 and A4 with Green Tip got them their Marine Corps contract and Army RFI sales.

M4A1 with M855 got them their Big Army contract and supports Euro military contracts (HK416 countries/armies).

Mark 18 and IPSC/USPSA? Rounding error numbers. Does the potential market justify a whole new product line? TA01B meets your barrel and bullet weight variances, and Steiner, Vortex, and others are following their generic arcs.

How many are you proposing buying from them, OP? Maybe a half-dozen over your lifetime?

I believe that you and I agree on each of your points, but we may have arrived at different conclusions. Allow me to explain:

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Originally Posted by sinister

M193/20-inch M16A1 was the standard when the ACOG was introduced. It got Trijicon their intro to the US military and helped win them their initial M4-NSN SOPMOD contracts. The rest is history.

M16A2 and A4 with Green Tip got them their Marine Corps contract and Army RFI sales.

M4A1 with M855 got them their Big Army contract and supports Euro military contracts (HK416 countries/armies).

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In this contract timeline, the reticles have kept up with the ammo in use at the time. They have evolved in the direction that I advocate, and today have arrived at exactly what I described in my OP. Matching M855a1 and 14.5” barrels; close enough for 12.5”-16” with most “medium” weight .224 bullets.

Quote:

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Originally Posted by sinister

Mark 18 and IPSC/USPSA? Rounding error numbers.

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Please don’t allow my points about these niches to distract you from my main point, which is about a more middle ground, common in duty weapons. I only included those topics for relate-ability with a larger range of people. Competitors helped prove that LPVOs are useful; what I’m talking about is the duty adaptation of this technology during the past couple decades. Which is focused on 10.3”-16” barrels. Rarely are 55gr bullets relevant.

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Originally Posted by sinister

Does the potential market justify a whole new product line? TA01B meets your barrel and bullet weight variances, and Steiner, Vortex, and others are following their generic arcs.

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Lets flip that. Does the potential market of M193/20” shooters justify a whole product line? Certainly not more so than 62gr/14.5”-16” combos. If the former is true, so is the latter. But not necessarily vice-versa.

We can debate on why the m193/m16 reticles sell well, but I suspect its because most buyers don’t know better, not because that's actually what they shoot. Says .223 on the scope box; so does the ammo, so it should work, right?Kinda like the existence of 7mo NREMTP accelerated courses.

Quote:

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Originally Posted by sinister

How many are you proposing buying from them, OP? Maybe a half-dozen over your lifetime?

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I don’t matter as a purchaser, hence my point about the DoD agreeing with me. I can name 3 recent contract magnified optics that have the type of BDC reticles I’m advocating for, and zero that use a M193 BDC in current use. You have access to info that I don’t, so maybe you know of some.

I wouldn’t be surprised to find that Sig only put those mil-dots in there to distinguish their reticle from Triji, Steiner, and Elcan. Notice that there’s no mention of the somewhat popular budget brands in there. They all do the M193/20” thing exclusively instead, but seem to be running a little low on contracted models for door-kickers.......

An example of what annoyed me into this post: “The ranging reticle is calibrated for 5.56 (.223 cal) flat-top rifles to 800 meters.”
Spec sheet says: .223/5.56. Details end.

The takeaway? This manufacturer knows so little about ballistics that they think 223 is 223 is 223 and a barrel is a barrel is a barrel out to 800 meters. Yeah, sure.

Obviously that isn’t true, given the manufacturer. And I could email them for clarification. But why the $&@% are they not more specific when interfacing with the COTS buyer? Given the fact that almost every designer of reticles that just non-specifically says “.223” really means “55@3k”, it would be easy to dismiss that optic as not suited for me.

I can't speak for Trijicon. When I worked government tenders and contracts the old saying worked, "Money talks and bullshit walks."

The entity (whether a government buyer or commercial distributor) that says, "I'm willing (or am going) to pay $10 miilion dollars for the product that does X, Y, and Z, and will put down the payment no more than 90 days to the manufacturer who gives me close to (or the exact specified) product I want when I sign the contract" will either get manufacturers to kick-start their design and manufacturing departments or ignore the proffered tender. Simple.

SIG has learned from the field that they'll make money giving the customer what he wants, instead of telling them what they should buy.

The customer is always right, since he's paying. His requirements may be stupid, or wrong, and confusing -- but it's still HIS money.

Products that don't sell usually get discontinued. I have no idea if the TA01-NSN ACOG still makes money for Trijicon, but I do see LOTS of manufacturers cloning others' products with common features (mil-dots, Christmas-tree reticles, BDC reticles, parallax adjustment knobs on the tube's left, counter-clockwise adjustable knobs, cantilever mounts, Docter-style open red-dots, etc.).

As for 55@3K -- those designers are probably long-retired, and the staff that works at Trijicon may not have even been born when the originals hit the street for the Contra wars.

Closed letter from BDC designers...

Mil/MOA reticles exist.

I guess I’m all wet then. I’ll stick to optics using the type of reticle I described that have recent DoD contracts (Trij, Elcan, Sig). Maybe they buy them just for me, since apparently I’m the only one that wants that sort of BDC reticle. Hobby manufacturers can just keep making hobby reticles for hobby shooters, who probably enjoy them.

Well, that, and the P4Xi. It also has a nice reticle, though its not of the same grade as a Razor.


Edit: you both make points that I’d like to discuss in a more postive manner. I’ll update and edit later.

Edit: try not to read this in a hangry basement dweller voice. Use Morgan Freeman’s instead. It was not my intent to sound so negative.

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Originally Posted by ggammell

Closed letter from BDC designers...

Mil/MOA reticles exist.

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The first half of of your reply makes a ton of sense. These manufacturers are telling me that I am not their target market. So, ****’em. I’m honestly not sure why I felt like any of them deserve my business, anyway. I’ll continue to use DoD contracted optics, on and off duty, and stop hoping that the commercial-focused market will cater to me. Perhaps I’m just spoiled.

To address the second half of your reply, yeah, sure that works. And for a long-range shooter that may suddenly need to engage 300m targets, thats probably the most sensible gear choice, with some practice. But, going the other direction, a short range setup that can stretch a little, or a GP carbine, an auto-ranging BDC makes sense. You can argue that point, but the profession of killing has spoken already. Magnified medium range optics that are issued to roided out twenty-somethings on 14.5” guns have a tendency to have EXACTLY the reticle I’m asking for.

Quote:

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Originally Posted by sinister

I can't speak for Trijicon. When I worked government tenders and contracts the old saying worked, "Money talks and bullshit walks."

The entity (whether a government buyer or commercial distributor) that says, "I'm willing (or am going) to pay $10 miilion dollars for the product that does X, Y, and Z, and will put down the payment no more than 90 days to the manufacturer who gives me close to (or the exact specified) product I want when I sign the contract" will either get manufacturers to kick-start their design and manufacturing departments or ignore the proffered tender. Simple.

SIG has learned from the field that they'll make money giving the customer what he wants, instead of telling them what they should buy.

The customer is always right, since he's paying. His requirements may be stupid, or wrong, and confusing -- but it's still HIS money.

Products that don't sell usually get discontinued. I have no idea if the TA01-NSN ACOG still makes money for Trijicon, but I do see LOTS of manufacturers cloning others' products with common features (mil-dots, Christmas-tree reticles, BDC reticles, parallax adjustment knobs on the tube's left, counter-clockwise adjustable knobs, cantilever mounts, Docter-style open red-dots, etc.).

As for 55@3K -- those designers are probably long-retired, and the staff that works at Trijicon may not have even been born when the originals hit the street for the Contra wars.

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You're absolutely right. Except that part about the 55@3k designers being retired. A brand new company that started up in the past few years has exactly that reticle, so they’re not ALL retired just yet. You’re definitely right about the customer always being right. As I’ve thought about this, I’ve realized that I was totally wrong. For all the bluster on the internet about “hard use” and “duty grade” most people don’t and never have carried a M4 for a living. And most people don’t shoot much. And when they do, no shit, many tend to shoot 55gr. None of this is meant to offend anyone in particular, because it certainly doesn’t apply to everyone, and there’s no shame in that, anyway.

Increasingly I realize that M4c is not the place to share lessons learned from actual intended use of the carbine. And I have to learn to read an audience better when I toss out what my homies and I believe to be those pearls.

Stay safe and have fun!

Don't give up yet! More than a few of us share your observations. My next purchase (hopefully today, actually) is a Steiner P4xi for reasons very similar to you. There's really no reason that medium range optics shouldn't be point-and-click out to 400-500 with boring regularity using the common loads for these platforms.

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Originally Posted by opngrnd

Don't give up yet! More than a few of us share your observations. My next purchase (hopefully today, actually) is a Steiner P4xi for reasons very similar to you. There's really no reason that medium range optics shouldn't be point-and-click out to 400-500 with boring regularity using the common loads for these platforms.

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Yup. To me, a dude who is not a Sniper or PRS type, the autoranging feature of 18” wide lines on an upside down Christmas tree are worth as much as the drop compensation. Which, as you put it, is point and click.

I’m not leaving M4c. Never was smart enough to know when to quit. Besides, I like y’all, and I don’t use most other social media. I’m just going to take a step back and think more about how, where, and why I post. I may return to mostly using the the portions of the forum that discuss the technical aspects of the weapon, and only speak of how to actually use it better when I’m being paid to do so. The replies in this thread aren’t even the real source of my frustration, and some debate was desirable.

***Next day edit: thats enough whining from me. I’ll go ahead and own the problem below and make efforts to resolve it. Maybe I’ll start posting in Training and Tactics more. We’ll see.***

If more than like 10 people here actually shot their guns at UKD ranges in the second half of an Infantryman’s “pie are squared” of point target effectiveness, I’d have gotten more replies. I’m certain about that, because I deliberately left my OP open to being curb stomped with a fatal flaw in my argument. Nobody took the bait, because they simply don’t know what they don't know. I’ll PM that flaw in my argument to you, just so you know what I mean. You may already know it and are just polite. I’m fairly certain Sinister knows it and is just being polite.

The problem here is expectation management. You and the manufacturer’s have two different standards of accuracy. The manufacturers and .gov are satisfied with minute of man at those distances.

I'm re-visiting this thread.

Based on 1168's threads here and on other LPVOs, I've endorsed the Steiner P4Xi to a number of young kids shooting the M4A1 with M855A1 (the new Army 5.56 round) to get the flexibility of both an ACOG and Aimpoint in a single scope. When I reload for my kids and we shoot ACOGs, since we don't have access to M855A1 when we're not working/training on Uncle's dime I load 69-grain Tipped Matchkings or regular 69 Matchking BTHPs to match trajectory.

I like quick, and I like a generic BDC that'll kill an E-type, but most of all (for new shooters) I like simple. 1168's technique to zero at 200 and follow the BDC (against GI E-types) works like a charm.

I'm feeling inflation pressure -- our local gun shop has a P4Xi on the shelf for around $650.

Here's a bit of good news: I found this article titled "The Convenient Overlap of M193 and the 77 gr Sierra TMK" < https://thenewrifleman.com/the-conve...gr-sierra-tmk/ >. You don't have to buy the more expensive T5Xi for the 7.62 reticle. This guy found (on Strelok) if he zeroed his 1-6 Vortex (JM-1) at 200 for the 77 TMK the BDC tracks with 55-grain M193 / commercial Ball zeroed at 100.

This should also work with both the P4Xi and ACOG BDCs.

Nice.

The only problem is, if you're not independently wealthy you'll have to handload (if you can even find 69 or 77 TMKs). I'll bet you can get fairly close with other bullets, too, while we're in covid shortages.

So, I was eyeballing a Credo and saw the BDC model. Well, $&@%. 55gr. But then I looked at the drops in it. Distance in yards, drops in MOA. BCs from Litz.
200 z
300 3.3
400 6.5
500 10.7
600 16.1
Well, that looks familiar. So I punch 77SMK, 2600fps, 3” optic height into my calculator.
200 z
300 2.9
400 6.6
500 10.9
600 16.1
Neat. How about 69 SMK @ 2700fps?
200 z
300 2.8
400 6.3
500 10.7
600 16
Sweet. This is really close also to the 7.62 T5xi. Crank it up to 2850fps, and its nearly spot on to 600 in the P4xi. I’m guessing Sinister is somewhere in that range, or maybe a little slower with the TMK.

For further nerd joy,
M855 @2800fps with the same 3” height
200 z
300 2.6
400 6.1
500 10.4
600 15.8
Of course, precision and wind isn’t great at that point. How about 2900 fps?
200 z
300 2.4
400 5.6
500 9.6
600 14.5
A little flatter…could use either the 7.62 T5Xi or the P4xi successfully, especially at 500 and in. I’ve also been looking at the ACSS M2 on the PA Platinum 34mm LPVO:
200 z
300 3
400 6
500 9.7
600 14.2
Looks like with a 14.5” and M855, it should be on. It would also be perfect for heavier match ammo from a 16” or 18” barrel. Here’s 69gr 2850 fps:
200 z
300 2.4
400 5.5
500 9.4
600 14
And 77gr 2700fps, still with a 3” high optical HOB:
200 z
300 2.6
400 6
500 10
600 14.7
ACSS or 7.62 T5Xi will work nicely.

There’s no real point to this post, but, I crunched the numbers and wanted to share the data output. Keep in mind with all of this, wind is a thing. The ACSS has dots for 5mph that math out fairly reasonably with the above loads. Triji and Steiner do not.

Excellent post! I played with some of the same numbers concerning the Credo. If it's there long enough I'll probably want it.

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Originally Posted by opngrnd

Excellent post! I played with some of the same numbers concerning the Credo. If it's there long enough I'll probably want it.

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The BDC is appealing, but I need to get one in my hands to look at the illuminated portion before I pull the trigger. The PA looks like the center is more usable up close, but it is listed at an absurd weight.

Shot the PA PLX 1-8x ACSS yesterday. Zeroed it at 300yds with Frontier 68gr through a suppressed 14.5” Noveske. I made a few adjustments and then shot a 5 shot group centered about an inch or so high. Figured that was good enough and moved to steel at 200, 300, 400, and 480. It was pretty close, just needing to hold a little low on the 400 and 480 (using the 500yd hash). Obviously, I need to adjust it a bit and play with it on paper, but it looks like it might work pretty well.

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Originally Posted by 1168

Shot the PA PLX 1-8x ACSS yesterday. Zeroed it at 300yds with Frontier 68gr through a suppressed 14.5” Noveske. I made a few adjustments and then shot a 5 shot group centered about an inch or so high. Figured that was good enough and moved to steel at 200, 300, 400, and 480. It was pretty close, just needing to hold a little low on the 400 and 480 (using the 500yd hash). Obviously, I need to adjust it a bit and play with it on paper, but it looks like it might work pretty well.

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Does it still have that RCO-M4 ACOG feel to it, or does 8x magnification give it a more traditional scope feel?

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Originally Posted by opngrnd

Does it still have that RCO-M4 ACOG feel to it, or does 8x magnification give it a more traditional scope feel?

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At 8x, it feels more like a traditional scope, for sure.

Quote:

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Originally Posted by 1168

so it should work, right?Kinda like the existence of 7mo NREMTP accelerated courses.

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I laughed WAY to hard at this...... considering the quality of EMT and EMT-P's that are coming out now a days.

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Originally Posted by jwfuhrman

I laughed WAY to hard at this...... considering the quality of EMT and EMT-P's that are coming out now a days.

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Yup. The schools offer accelerated courses because they sell. The students sign up because they assume that the school has determined that this is an adequate amount of time for the material. If I ran NREMT……

In the year+ that has passed since I first posted this rant, I’ve made more of an effort to learn about commercial and military BDCs, and the specifics of bullet flight. I’ve shot ACOGs, PA PLx, Steiner P4Xi, ELCANs, VCOG, some dialy scopes, and of course Eotechs and Aimpoints. I’ve done this with a variety of 5.56, 223, and 7.62 barrel lengths, projectiles, and types/brands of ammo. Regular guns and belt-feds. Played with few brands of calculators, quite a bit. I also shot a grenade launcher a few times, but its lessons don’t carry over to this subject.

***TLDR: Doesn’t matter what cartridge the optic manufacturer writes on the box. Its probably workable if you have a gun/ammo between 2500 and 3000fps. There’s a good chance the reticle doesn’t even exactly match the advertising***

Pretty much my entire adult life, I’ve known that any little thing will make a BDC useless. Barrel length, projectile, HOB (Height Over Bore), the number of floats in a Mardi Gras parade, apparent vs actual height of movie stars, moon phase, etc. Simply not true. Within reason, most well-made ones are adaptable. In fact, within some limitations, you can change ammo weights without touching the dials and be fine.

So, what are those limitations? What is reasonable? A BDC made for 300PRC (I don’t think that is a thing) will probably not work for 55gr Tula and an 11.5” barrel. But one made for 55gr/24” might work with 62gr/14.5”. Here, I am talking about killing E-types, B/C steel, or even F-Types. Hits are hits, from 100-600 meters or yards. If you’re shooting past that, or even routinely past 400, you should probably be dialing. Because wind. If you’re shooting tiny targets with high-precision ammo where a minute or two of drop or drift matters, you should probably be dialing. If you are shooting 2-4 minute (10+shots, most of us aren’t shooting 1MOA ammo, even if you think you are) ammo at 2 minute or more UKD (UnKnown Distance) targets, and time is critical, a good BDC is rather what you need.

WTF am I talking about? Given the size of targets, the change in temp after zeroing, the dispersion of ammo, etc, most BDCs are close enough to literally not notice on most guns with most ammo and almost all shooters. The arc simply does not change as much as we think, within the usable ranges of most combinations. As an experiment, use a ballistic calculator with the zero set to zero yds and the HOB set to 0 inches to compare some of your favorite loads. Set max distance to 600 and intervals to 100 in order to not be overwhelmed. Now, pick projectiles and use Litz BCs to compare them. For every step in bullet weight (55,62,69,77), use a delta of 0-200fps. So, in Sinister’s example, with a 77gr ammo zero, lets say at 200yds, with 2600fps, there are a lot of 55gr loads that will get you hits at the distances you would cheap out on, at like 2800-3000fps. This is just for math purposes. As an extremely general rule, 100fps steps gets you similar drop ballistics between weights (like dropping from 62 to 55gr), and are common differences. Extremely general. Notice that I said drop, not drift. So the dude that handloads to near max with 62 or 68gr projectiles might be able to find some ballistic similarities in cheap factory ammo. Which is what I have found.

Remember being a kid and learning to throw rocks? Did we weigh them?

So, how does one use this nonsense? Find an app that does this shit. As our barrels get shorter, and our bullets heavier, a little extra HOB seems to help. On my 12.5”s I’ve been a little surprised at how few inches exist between prediction and observation of impacts. Both the PLx 1-8 (1.94”) and the VCOG 1-8 (2.05”) with 55gr reticles have worked quite well for me in SBRs with 62-69gr ammo. And I’ve checked the PLx with garbage 55gr after zeroing with 69 or 68gr ammo, and found that it works to the limit of that ammo. I would suggest using a calculator that has reticles in it to see if they will work, and then truing them at longer range, or at least figuring out the best strategy. Because if I’m trying to shoot out to 600, a one minute deviation means more to me at 500 than a two minute deviation at 300.

Turns out, its all OK, because its all so adjustable to the actual arc. If you’re a Military guy, just ignore all of this and refer to TC 3-20.40.

I truly appreciate a long post that is worth the time to read it!

Andy

My PA ACSS 1-8 does the best with 55 or 62 gr.
It's way off with with 5.56 77 gr.

I use Strelok+ that's pretty handy for seeing what the drops are and has a slider for 1-8 power that adjusts the reticle and ranges.
According to Strelok it's pretty close to the the other two when using 7 power.

So in practice you would range at full power and adjust to 7 for the correct drop for A zone hits.
I keep it simple and zeroed it for 62gr Mk318, 55 gr is close enough to not worry about.
Since 55 and 62 is what I shoot with this rifle it works out.

But for anything else I would rather have a tree type reticle for holdovers.

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Originally Posted by One More Time

My PA ACSS 1-8 does the best with 55 or 62 gr.
It's way off with with 5.56 77 gr.

I use Strelok+ that's pretty handy for seeing what the drops are and has a slider for 1-8 power that adjusts the reticle and ranges.
According to Strelok it's pretty close to the the other two when using 7 power.

So in practice you would range at full power and adjust to 7 for the correct drop for A zone hits.
I keep it simple and zeroed it for 62gr Mk318, 55 gr is close enough to not worry about.
Since 55 and 62 is what I shoot with this rifle it works out.

But for anything else I would rather have a tree type reticle for holdovers.

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My PA 1-8 is FFP, so I can’t try that. What I’ve found with Strelok: When evaluating a reticle and ammo combo, I put in all the most accurate data I can, including HOB, which is usually around 3” for me. I find that using 1.93” mounts seems to make a lot of reticles work better with SBRs and heavier bullets than 1.5” mounts. Although, thats not why I use 1.93” mounts. BUT, for zero offset, I use a vertical of -2 or -3…that puts me low at most or every point in the reticle.

Then I look at the reticle, zoom in, and turn the virtual elevation dial until it matches at the longest range I plan to shoot at. This usually gets me really close at most of the other distances. Then I go back to data input and try different zero offsets to match that. What I end up finding is that if I get a perfect zero at 200, I’m completely off at 600. Thats probably where a lot of the “BDCs don’t work” comes from. But, if I’m willing to accept zeroing 2-4” high at 200, I’m getting less error from the scope as I stretch it.

As an example (near worst case), here’s a 77SMK at 2600fps, 3” HOB, 3” high at 200 on a silhouette at 600yds: Attachment 69109

Of course, with calculators, you have to shoot it to be sure, but it sure helps figure out where to start.

14.7" barrel, 2.81" HOB at .5" high at 100 yards.
I noticed that the 77gr keeps up better until 800 yds.
55 and 62 seem to drop out around 500.

I suppose its not that far off.
https://i.imgur.com/pDeaiaEl.png
Better on 7
https://i.imgur.com/At7Macul.png

If all I ran was 77's through it could work out.
I had it on my 18" for a bit that gets fed 77's but never ran it out past 100 yds.
That gun wound up with a better scope that took me a bit of looking around for a reticle I liked that didn't have a BDC which is a NF 2.5-10x42 with the MOAR reticle.
I liked the SWFA 2.5-10 but the BDC killed it for me for that gun.

Although I may end up getting it and use it on the 14.7" instead of the PA 1-8

Quote:

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Originally Posted by 1168

In the year+ that has passed since I first posted this rant, I’ve made more of an effort to learn about commercial and military BDCs, and the specifics of bullet flight. I’ve shot ACOGs, PA PLx, Steiner P4Xi, ELCANs, VCOG, some dialy scopes, and of course Eotechs and Aimpoints. I’ve done this with a variety of 5.56, 223, and 7.62 barrel lengths, projectiles, and types/brands of ammo. Regular guns and belt-feds. Played with few brands of calculators, quite a bit. I also shot a grenade launcher a few times, but its lessons don’t carry over to this subject.

***TLDR: Doesn’t matter what cartridge the optic manufacturer writes on the box. Its probably workable if you have a gun/ammo between 2500 and 3000fps. There’s a good chance the reticle doesn’t even exactly match the advertising***

So, what are those limitations? What is reasonable? Here, I am talking about killing E-types, B/C steel, or even F-Types. Hits are hits, from 100-600 meters or yards. If you’re shooting past that, or even routinely past 400, you should probably be dialing. If you are shooting 2-4 minute (10+shots, most of us aren’t shooting 1MOA ammo, even if you think you are) ammo at 2 minute or more UKD (UnKnown Distance) targets, and time is critical, a good BDC is rather what you need.

WTF am I talking about? Given the size of targets, the change in temp after zeroing, the dispersion of ammo, etc, most BDCs are close enough to literally not notice on most guns with most ammo and almost all shooters. The arc simply does not change as much as we think, within the usable ranges of most combinations. As an experiment, use a ballistic calculator with the zero set to zero yds and the HOB set to 0 inches to compare some of your favorite loads. Set max distance to 600 and intervals to 100 in order to not be overwhelmed. Now, pick projectiles and use Litz BCs to compare them. For every step in bullet weight (55,62,69,77), use a delta of 0-200fps. So, in Sinister’s example, with a 77gr ammo zero, lets say at 200yds, with 2600fps, there are a lot of 55gr loads that will get you hits at the distances you would cheap out on, at like 2800-3000fps. This is just for math purposes. As an extremely general rule, 100fps steps gets you similar drop ballistics between weights (like dropping from 62 to 55gr), and are common differences. Extremely general. Notice that I said drop, not drift. So the dude that handloads to near max with 62 or 68gr projectiles might be able to find some ballistic similarities in cheap factory ammo. Which is what I have found.

Remember being a kid and learning to throw rocks? Did we weigh them?

So, how does one use this nonsense? Find an app that does this shit. As our barrels get shorter, and our bullets heavier, a little extra HOB seems to help. On my 12.5”s I’ve been a little surprised at how few inches exist between prediction and observation of impacts. Both the PLx 1-8 (1.94”) and the VCOG 1-8 (2.05”) with 55gr reticles have worked quite well for me in SBRs with 62-69gr ammo. And I’ve checked the PLx with garbage 55gr after zeroing with 69 or 68gr ammo, and found that it works to the limit of that ammo. I would suggest using a calculator that has reticles in it to see if they will work, and then truing them at longer range, or at least figuring out the best strategy. Because if I’m trying to shoot out to 600, a one minute deviation means more to me at 500 than a two minute deviation at 300.

Turns out, its all OK, because its all so adjustable to the actual arc. If you’re a Military guy, just ignore all of this and refer to TC 3-20.40.

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Reviving a dead horse to refresh knowledge.

The new hotness the last few years is higher rings or mounts for a better heads-up position on the stock. I have since had neck fixation surgery as a result of decades wearing the Dome of Obedience while doing free-fall and static-line parachute jumps with ignorant loads.

Where standard 1.4-inch rings or Unimounts would have been "Normal" back in the 20th Century, fitting IR aimer-illuminators to the 12 o'clock of your Picatinny rail or tube fore-end might now call for a 1.93 or 2.3-inch (or higher) to get a clear view without your gadget (PAQ-4, PEQ-2, PEQ-15, Attilla, Vital, NGAL, etc.) blocking the lower 1/3 of your scope.

This may help stretch the service life of older scopes (the P4Xi, 1-6 Razor Gen 2, T5Xi, etc) as the slightly increased height, legacy BDC reticle, and evolving bullet lengths-weights norm-out closer with the higher Height-over-bore.

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Originally Posted by sinister

Reviving a dead horse to refresh knowledge.

The new hotness the last few years is higher rings or mounts for a better heads-up position on the stock. I have since had neck fixation surgery as a result of decades wearing the Dome of Obedience while doing free-fall and static-line parachute jumps with ignorant loads.

Where standard 1.4-inch rings or Unimounts would have been "Normal" back in the 20th Century, fitting IR aimer-illuminators to the 12 o'clock of your Picatinny rail or tube fore-end might now call for a 1.93 or 2.3-inch (or higher) to get a clear view without your gadget (PAQ-4, PEQ-2, PEQ-15, Attilla, Vital, NGAL, etc.) blocking the lower 1/3 of your scope.

This may help stretch the service life of older scopes (the P4Xi, 1-6 Razor Gen 2, T5Xi, etc) as the slightly increased height, legacy BDC reticle, and evolving bullet lengths-weights norm-out closer with the higher Height-over-bore.

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You mention a rise in height over bore could lead to slightly increased accuracy with a BDC and I think that is interesting, I might have to test this out when we don't have fog, freezing rain and 2.5 feet of snow on the ground.

As you revive this old thread I think about one of the first real lessons I learned through a rifle class after getting out and that is that "Perfect is the enemy of Good Enough", I realize that my ACOG stadia lines aren't exactly going to be a perfect representation of where my round will go as I send it down range at 400+ yards, but I like the understanding that it might be a good reference point for to utilize when engaging targets anywhere from 300-500 yards.

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Originally Posted by ggammell

Closed letter from BDC designers...

Mil/MOA reticles exist.

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This ^^^