IR laser zero on CD COR Rail

[danieljmaunder]

Hey ya'll

I have a DBAL D2 thats going to be mounted on a cloud defense cor rail in the recessed lower section. I'm pretty familiar with zeroing IR lasers using the constant offset method and targets from telluric, my question is with the lower rail changing the HOB of the laser, whats the best way to figure out how to zero properly so I have a constant offset with no divergance at distance?

TIA

[birdkiller]

Just stick your muzzle against a target, circle around the muzzle device, turn on your laser, mark its location on the target, and you’ve got a pretty good reference point of what your offset is.

Alternatively, there’s a pretty good argument that within realistic engagement distances with a laser, that a converging zero may be preferable if you’ve got the distance to do it.

[Red*Lion]

Just stick your muzzle against a target, circle around the muzzle device, turn on your laser, mark its location on the target, and you’ve got a pretty good reference point of what your offset is.

That is what I do on a target. Then I go to the range, shoot at 25 yards and zero laser for the same offset. Then do the same at 50 yards. I do not see the benefit in doing a coverging zero.

[titsonritz]

I also prefer to parallel zero my lasers, but a little trick I picked up on a converging zero is to fire the laser into the night sky and adjust it to your zeroed optic. It helps having a buddy giving you a hand.

[Defaultmp3]

That is what I do on a target. Then I go to the range, shoot at 25 yards and zero laser for the same offset. Then do the same at 50 yards. I do not see the benefit in doing a coverging zero.

The benefit of a converging zero is that you can do it without firing a shot, and have a zero that is entirely sufficient for almost any realistic usage of the pointer.

[Red*Lion]

The benefit of a converging zero is that you can do it without firing a shot, and have a zero that is entirely sufficient for almost any realistic usage of the pointer.

Really? What range do you decide to zero at then?

[Defaultmp3]

Really? What range do you decide to zero at then?

I do 100 yards, same as my optics, though I'm also kinda cheating, since I use the Wilcox RAID-X and RAID-Xe, which has the pointers over the bore. That being said, even with something like a ATPIAL or MAWL it should be fine. From an unpublished AAR of mine:

Chuck [Pressburg] then jumped into the typically contentious debate between parallel zero and converging zero with the laser. Chuck came out and said that if converging zero is done properly, it is for all practical purposes going to give the same results as a parallel zero, with factors such as the inherent accuracy of the gun combined with the ammunition chosen, shooter skill, and the reasonable distance that headborne NODs with zero magnification can be used at. The key thing for Chuck is to choose a reasonable distance to do a converging zero at; the problem that many run into is that they attempt to do a converging zero at 25 yards, simply because that is the only range they have access to. Chuck likened this to trying to zero an MP5 that has a 4” height-over-bore at 7 yards; while it will work okay for extremely short distances, it quickly falls apart at realistic longer distance engagements. For example, if a laser has a 2” horizontal offset from the bore (which is approximately what the offset is for the MAWL), then a 25 yard converging zero would mean a 6” offset between the pointer’s POA and the POI, which is fairly significant to keep track of; the 6” calculation comes about because for every 25 yards, the POA would shift 2” (0 yards would be -2”, 25 yards would be 0” since that was the convergence, 50 yards would be +2”, 75 yards would be +4”, 100 yards would be +6”, etc.). That being said, the parallel zero can be a bit more conceptually difficult for some folks to wrap their head around, as Bill had found with his team, where it took an excessive amount of time to try and explain the concepts, time that would have been better off on some other training. Thus, Bill’s team ultimately decided on a converging zero at 50 yards, which would mean a 2” horizontal offset at 100 yards, and a 6” horizontal offset at 200 yards, which the team found to be acceptable, given the limitations of seeing 200 yards with unmagnified NODs to begin with.

For Chuck, if zeroing at a decent distance anytime the POI is reasonably on the opposite side of where the pointer is mounted in relation to the bore, and the horizontal offset of the POI is less than the horizontal offset of the pointer, than the zero should be fine, e.g., for a MAWL mounted on the right side of the gun, which would have approximately 2” of horizontal offset, if the POI is roughly 1” to the left of the POA at 50 yards, than the zero is fine (and will likely converge at approximately 100 yards). For a convergent zero at 50 or 100 yards, there is typically only two to three clicks between that POA/POI and one for a parallel zero. On the other hand, if for the same setup, but the POI is roughly 1” to the right of the POA (so on the same side as the pointer), then this is completely unsatisfactory, as this means that the laser will never converge with the POI (and would arguably be called a divergent zero).

Due to all the various factors at play, Chuck typically finds that zeroing with the visible pointer is just fine if it’s coaligned with the IR pointer. Though there are slight discrepancies in the exact POI between the two pointers even when coaligned, these differences are almost certainly too minute to be detectable in any meaningful fashion, given shooter ability, the gun’s intrinsic accuracy with a specific round, etc.

That being said, Chuck did note that even at extended distances, it may be possible to PID a target as hostile and fire upon as such, even if it was outside of the realm of traditional PID techniques, by taking into account the totality of the circumstances. For example, a real life application of this was when Chuck took fire from multiple DShK MGs from range, while having intel that there were absolutely no friendly forces in the vicinity that weren’t inside the compound that was taking fire. This is why Chuck advocates for knowing exactly what the laser is zeroed for, to be able to accurately fire upon targets that were further than what unmagnified NODs alone could reliably PID, which will typically be between 30 to 40 yards (dependent on tube quality). Chuck stated that some of his previous units would regularly train to utilize MFALs on rifles at distances beyond 300 yards. He did acknowledge at these extreme distances, the weakness of the convergence zero can arise, depending on the distance of the convergence.

For the vertical offset, Chuck advised to simply have the same elevation at the distance one’s day optic is zeroed at. This will generally minimize the amount of retraining needed to account for external ballistics and bullet drop; there simply is no need to overcomplicate factors here.

Bill [Blowers] then interjected to state that one must be careful to take Chuck’s story in context; Chuck did not engage simply based off of muzzle flash that sent bullets his way, but sustained fire along with intelligence that there were no other friendlies; muzzle flash alone in an LE context may simply be a CCWer responding to a threat, or perhaps a teammate whose position one was not aware of.

[1168]

I do convergent at like 200 or greater. That keeps you within a couple inches of your day optic to 400, by which point PID and ballistic drop makes it decreasingly likely that I’m squeezing a round off, and increasingly likely that this is a job for a clipon or comms. People worry about convergence too much. As long as you avoid full divergence, or too close of convergence, the results on target are indistinguishable from parallel, and within the expected limits of practical precision at night with a GP fighting carbine.