509T on a G5 23 in the morning sun, using the circle dot reticle.
509T on a G5 23 in the morning sun, using the circle dot reticle.
Likes pretty much everything in every caliber.
Today we finished up another two-day pistol optic class. We had ten students from our department, two from a Sheriff’s department a bit of a drive away, and two from different Federal agencies. Like the last class it was a good group of shooters and a fun two days, especially since the weather is being nice to us, which seems rare around here.
Pistols/optics used were as follows:
Staccato / SRO
Glock / Holosun 508T
M&P / Holosun 508T
Glock / Holosun 507C
Glock / Leupold DeltaPoint Pro
M&P / Trijicon RMR-Manual
M&P / Holosun 508T
Glock / Leupold DeltaPoint Pro
M&P / Sig Romeo 1Pro
Glock / Holosun 507C
Sig P229 Legion / Sig Romeo 1Pro
M&P / Holosun 508T
Glock / Trijicon RMR-Manual
M&P / Trijicon SRO
None of the optics had any issues and nothing came loose. The batch of practice ammunition we’re using has some issues which resulted in a bunch of across-the-board malfunctions, including with the Staccato I was shooting and my Glock. You could feel and hear the difference in the powder charges. That said, it gave students (and an instructor) things to distract and challenge them so I’ll take it. I mentioned in my previous post that one of the Sigs in the prior class was getting sluggish by the end of day 2, but the Sig P229 in this class ran like a top and I never saw a malfunction even with the bad ammo.
One student from another agency was using a modified Glock 17 with an Apex trigger. The trigger safety broke during day 2 which caused the center “safety” portion to swing freely. It didn’t affect firing the pistol except for the first shot where the safety could move forward and impede the shooter’s finger from being able to get into the trigger guard. Luckily it was about lunch time so his trigger was switched out to a stock one at lunch and he had no further issues.
In the past couple weeks, we ran a firearm instructor school (12 students, 7 optics) and a pistol optic certification course (9 students, obviously all with optics).
The instructor school guns/optics were as follows:
Glock 17 / Trijicon RMR manual
Glock 17 / Holosun 508T
Glock 34 / Trijicon SRO
Sig P320 / RMR manual
Glock 19 / Holosun 509T
Sig P320 / Romeo 1PRO
Glock 17 / Holosun 507C
There were no optic issues during the class, though the round count isn’t very high in this course since it’s more about learning to teach. That said, we had one student whose agency is looking at optics and he borrowed one of our instructor’s dot-equipped guns for the class. His improvement and performance throughout the week in a class not designed around the dot was interesting and impressive. I know it’s shocking, but shooting a dot is largely about doing the fundamentals really well and when you’re forced to learn AND teach the fundamentals, the dot thing seems to kinda work into that.
During the week I discovered something interesting. A department member asked me to look at his Staccato P-DPO because he said something was up with the magazine release. When he brought it in he showed me that when he pressed the magazine release the whole mag-release assembly started to protrude out the right side of the frame. I removed the magazine release and looked at the polymer frame/grip module. I saw that the magazine catch lock had dug a trench through the plastic in the forward portion (where it would be in the locked position) of the magazine release channel. This obviously occurred over time, and he’s used the pistol in multiple training classes, but I’d never seen this before. I told him to send the pistol in for warranty work and I’m sure they’ll take care of it, but it’s now going to go on my list of things to inspect on a 2011.
The pistol optic class consisted of eight students from my department and one from a local department from the same state. Pistols and optics were as follows:
Sig P226 Legion / Romeo 1Pro
Glock 17 / Trijicon SRO
M&P 2.0 O.R. / Holosun 407C
Glock 17 / Trijicon RMR – manual
M&P 2.0 O.R. / Holosun 407C
Sig P226 Legion / Romeo 1Pro
Glock 17 / Trijicon RMR – manual
M&P 2.0 O.R. / Holosun 507C
Shadow Systems MR-920 / Holosun 508T
There were no optic or pistol issues in the class but our ammunition continues to be an issue. I’m hoping this extent of problems is limited to the current pallet of ammo and once gone will improve.
The two Sigs came from the factory with the optic installed. While my experience with Sig factory-mounted optics is limited, I don’t recall seeing one of their mountings fail. That said, we had to remove both optics to install the steel shroud. We did this at the end of day #1 to allow as much cure time as possible for the Loctite while still being able to zero the morning of day #2.
I removed the optic from one of the pistols and re-installed with the same factory screws and the steel shroud without issue. The other instructor used the screws supplied with the shroud as he’d attempted to do previously a few days prior with another shroud and the screws did not work – they started to engage and basically spun as any minimal torque was applied. While many of you already know this (I researched later and discovered it), the screws supplied with the shroud are for the older Romeo 1 and will not fit the 1Pro. The original screws were then used and no issues occurred on day #2 with either optic.
I had the opportunity to try out the Shadow Systems MR-920, and I like it. The grip felt very comfortable and the magazine well really helped lock in my grip. There were no issues with it during the class and It’ll be a tempting addition if I need another pistol to host an optic. I got the bug to impulse buy but combined with the fact there is no dealer anywhere near me and that I really don’t need it right now I was able to regain self control... go me.
Some other recent experiences with pistols/optics:
A few weeks ago one of our people brought in a Sig P365XL with a Holosun 507K for inspection. Right now we require the pistol and optic be brought in to be mounted by specific authorized people in our unit. Since the optic was installed on the pistol I asked who had installed it and the response was “the gun store”. I let the person know we’d have to remove it and re-install and he said he was ok with that.
I started to remove the screws and both felt like they had abnormal resistance but did move. About halfway out one of the screws sheared, leaving the remaining small portion in the slide, breaking even with the surface. I noticed the broken screw and the intact screw (once removed) had a LOT of what looked like blue Loctite all over them. I told the owner the slide would have to go to our armory to see if we could extract the screw, and with his permission I brought it down there later that week.
Our armory staff figured out an interesting fix for sheared screws. Our main guy had purchased a laser engraver. I joke that they set it from “stun” to “kill” and they engrave a slot into the top of the screw so that a slotted screwdriver will fit. I got to watch it done this time and it’s a pretty slick idea.
Here are some pictures:
The contraption:
The laser doing its thing:
The slot:
After:
Also, this week when working transitions in a patrol rifle course, one of the students noticed his 508T was loose on his M&P 2.0 Optic Ready. I took it to the office and examined it. Just like some of the previous incidents with 508Ts, the indicator markings did not show movement but the optic was clearly loose. One screw moved easily but the other seemed “tight”. Once turned, however, both screws were easily removed.
So… here’s my hypothesis and I’d appreciate any input from those knowledgeable on this forum:
I have installed a LOT of Holosun optics on various platforms with the McMaster-Carr screws. The screw head is definitely larger on the McMaster screws compared to the factory Holosun screws. There is less “room” in the optic for the screws compared to a RMR or SRO as well.
I’ve never had an issue with McMaster screws in any of my Aluminum Holosuns to include a 407A, 507C, and 407CO, nor did I have any issues with an older titanium 508T V1. My problem is I can’t remember whether I was using the factory or McMaster screws in that one as it was my first Holosun.
I’m guessing that since the construction of the 407/507 line is different from the 508T, there may be just enough more room for the screws to work, while there isn’t in the 508T, and there may also be a little something to do with the Titanium not having as much give as the aluminum, but I don’t have anything to look at right now. I’m going to check out my 407CO (currently not mounted since I let someone borrow the RMR plate from my CORE) when I get back to see if there are any marks in the metal from installing with the McMaster screws.
I think the screws are contacting the side of the optic body prior to seating in the recessed pocket and therefore seem tight. Once enough rounds are fired to deform the screw head or body enough the optic comes loose and the screw doesn’t need to turn for that to happen.
I know there was some discussion in the below thread several months ago (starting on post #48) about McMaster screw heads not fitting Holosuns, but I thought it was a compatibility issue with aftermarket milled slides and it didn’t match my experience with the 407s and 507s I’d used and mounted. Now I’m thinking there’s more to that story…
https://pistol-forum.com/showthread....ster%20Holosun
In short, I think there’s no reliable solution for Glocks with the 508T that I can find. All the McMaster screws in alloy steel or stainless, hex or torx, all have the wider 0.307” head. I’m going to be using factory Holosun screws for those. I’ve mounted several 508Ts on M&P Optic Ready pistols recently and used the factory screws. I did some research this morning and the McMaster 18-8 Stainless flat head screws have a smaller 0.262” head (in the 6-32x1/2”) so that is probably a solid option for the 508T on an M&P. I already have the stainless screws so I’ll have to get hold of a 508T and do some checking.
Awesome idea with the broken screw! Brilliant even! (laser pun dad joke)
I have a 508T myself but I used the factory screws and haven't changed them out yet.
Odd, as I have a number of 508T optics in use, and have never had one come loose. I am in elk camp, but will have to see what I am using. I know I have one 508 on a Zev Gen 5 slide, and another on a direct milled M&P 2.0.
Likes pretty much everything in every caliber.
Do the countersink angles of the screws and optics match? That’s often a source of trouble any time I try to substitute a flathead machine screw.Originally Posted by SoCalDep
“ Countersunk-head screws that follow the Unified Thread Standard very often have an 82° angle, and screws that follow the ISO standard very often have a 90° angle. Throughout the aerospace industry, countersunk fasteners typically have an angle of 100°.” - wikipedia
This probably doesn't apply to your situation but I think it's worth bringing up; on a buddy's Staccato the factory screws that came with the 508T were a touch too long and bottomed out between the adapter plate and the slide. He figured it out after he found the Holosun loose.
The shorter screws supplied were too short and the longer screws looked just right until he found a small gap between the adapter plate and the slide on one side. One screw actually lifted the adapter plate away from the slide on one side. Sure enough, the 2 longer screws were a few thousands too long. He pulled it apart and took 0.005" off the one screw and a few thousands off the other screw to make them the same length and ensure that they didn't bottom out against the slide. Seems to have fixed it.
What ammo are you having problems with? We've been shooting some Fiocchi 124 grain lately that we are noticing issues from case to case.
I got my hands on a 508T X2 this week and compared it to my 407CO X2. The countersink of both optics is right up next to the side of the optic body. The McMaster screws did appear to at least touch the side when sitting in the countersink. When I removed the 407CO from my pistol, I immediately noticed significant wear marks on the inside of the optic body around the edge of the countersink. It appears that the McMaster alloy steel screws, with their 0.307" head diameter barely touch the body as the optic is installed and are able to move the aluminum enough to seat. In fact, the snug fit might even assist with keeping things in place. Here are pictures of both sides:
I "lightly" installed the 508T on a S&W M&P 2.0 optic ready (CORE) pistol. As I started to feel resistance when tightening the McMaster alloy steel screws into the 508T, I stopped, removed them, and saw that the side of the screw-head was indeed hitting the side of the optic body prior to seating.
There were wear marks on the edge of the screw-head. The optic body had two very small marks that were almost imperceptible, but that makes sense because I was purposely trying to avoid any damage to the optic.
So short answer to all of this is that I think that while the 0.307" head screws "probably" work reliably with the aluminum Holosuns, they don't reliably seat on the Titanium 508T (I think sometimes the tolerances work out... sometimes) and my guess is that once the reciprocation of the slide causes the optic to deform the small contact area of the unseated screw it allows movement and loosening of the optic. I'm no longer going to use them for the Holosun optics.
I looked on the McMaster web site and unfortunately, all of the 6-32x5/16" screws, whether alloy steel or stainless, hex or torx, have the 0.307" head EXCEPT the standard steel (part # 90920A274) torx screws (They have a 0.262"). They have the same 60,000psi tensile strength as the 18-8 stainless so that will be my go-to for Glock MOS going forward.
The 6-32x1/2" stainless torx screws (part # 92703A255) have the smaller 0.262" head diameter - with the same strength as the steel screws and increased corrosion resistance (we tested it and the stainless screws were better) so I'll be using those for installations in M&Ps going forward.
So the next question is whether 0.262" is small enough for the Holosun, and the answer is yes. I compared the stainless 0.262" head screws I have on hand to the factory Holosun screws and to my eyes (caliper? Pssshhh...) they are pretty close to the same size. Here's a pic (Holosun screw on the left, then McMaster stainless 0.262", and the 0.307" McMaster alloy steel on the right:
More or less yes. I'm familiar with the countersink angles of various components (ie: the metric screws that attach the Glock MOS plate to the slide vs. the imperial 6-32 screws that attach the RMR to the plate). That said, I'm no engineer and I don't have a great way to measure angles so I did the best I could to confirm. That involves a protractor and graph paper. Yep... Science. For sixth graders.
Here's the McMaster stainless screw with its quality controlled US made 82 degree angle:
Here's the Holosun screw... I'm including two pictures of that one. Also, yes...there's a wrapper for a Reece's Peanut Butter Cup. It's Halloween... Don't judge.
It's Speer 124gr Clean Fire. Most of the time it works just fine, but this specific pallet of ammunition has been wildly inconsistent. We had some issues recently as well with Winchester practice ammo as well (I think 115gr) that involved cases that were either too long or too short. I chalk it up to the fact that the ammo manufacturers are trying to keep up with demand and QC has dropped a bit across the board. It sucks but it's reality.
Awesome post.
I am snipping out everything but the above to ask this question. I'm trying to confirm the screw you'd suggest for a Holosun 507c, Dot to MOS plate, mounting screw. Is it a McMaster-Carr, standard steel, part number 90920A274, 60,000psi tensile strength, torx screw, with a 0.262" head and undercut profile, as per below?
Same question, for a Holosun 507k? Same screw?
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