Dirty optic glass constantly... How to plug the chamber witness hole?

[shojivic]

Stock/OEM barrel on the M&P (2.0 5" in 9mm) has the witness hole, and the stock factory optic slide is equipped with Trij RMR type 2.

It doesn't take too many rounds to produce a dirty carbon residue on the optic glass, no matter how "clean" or "dirty" the ammo being used is.

How would one be able to fill in this area of the barrel hood? Swapping out the barrel is not an option, for work.

Is there a solution, besides resorting to aftermarket barrels and slides?

Any advice is appreciated.

(BTW, I have a couple of Glock MOS platforms, so I do have the ability to compare with a pistol that does not possess this annoying feature, and therefore doesn't suffer this optic residue build-up.)

[SkyHawk]

I don't see why it would be the witness hole, since that is at the rim of the case. More likely it is just the way the M&P works and has some gas blowback.

Comparing to a Glock you are comparing more than just the presence or absence of a hole. The way the barrel locks and unlocks, timing of the cycle, the chamber dimensions etc

Anyhow I don't see any way to plug it unless you weld it. You could try taping a thin piece of credit card or something to the slide which overhangs just a bit to cover the hole, and see if blocking the hole really helps before you go too far down the rabbit hole.

Also is your barrel & slide ported like a P.C. M&P?

[SkyHawk]

You could also try attaching a shelf to the front of the optic to cover the hole, or sandwiching something thin underneath the optic that extends out, but who knows if this would interfere with holstering.

If such a cover worked, you would need to use something very rigid if you went to war with it, because there must be no chance it can dip down and prevent the slide from going into battery.

[OIF_VET]

A $3 lens cloth. Problem solved.

[shojivic]

Originally Posted by OIF_VET

A $3 lens cloth. Problem solved.

I expect more constructive input from a veteran member. Disappointing. Moving on...



Sky, thanks for more beneficial consideration. It's not a ported M&P, though.

And this buildup is equivalent, whether it be the 4" compact or the 3.6" SubCompact (now sold). The fact that it is a carbon based residue leads me to conclude it's from combustion: therefore, the witness hole is the only logical explanation. I would venture that the chamber tolerances around the case are loose enough to allow blow-back from ignition to exit via the opening. Notice in the pic the comparison of the relative location of optic to chamber and the differences in proximity...

In comparison, the only residue seen on the Glocks' optics is a light spattering of excess gun oil (I'm guilty of excess oiling at times).

I like the idea of some sort of deflection method, but I really wish there were some practical method of eliminating the orifice..

Glock vs M&P.jpg

[DaveInOroValley]

would it possible to make a small aluminum protrusion that would in effect be like a roof over the witness hole? Something that would mount under the optic and extend out.

[shojivic]

Originally Posted by DaveInOroValley

would it possible to make a small aluminum protrusion that would in effect be like a roof over the witness hole? Something that would mount under the optic and extend out.

You may be on to something that's simple enough to fabricate and still maintain reliability!

I found this pic:

Alexmount_cmore_tanfoglio_grande.jpg

[SkyHawk]

That is also what I was talking about ^^^

something that clamps underneath the optic, although I wasn't thinking of anything that big, but hey if it works

[shojivic]

Sky! That pic was only for reference.

Is a dab of JB Weld a possibility? Anyone?

[eaglemike]

Hole maybe contributing a little. How old is the recoil spring? years ago I lightened 1911 slides and found they unlocked earlier with the lighter weight - I had a lot more crud on the bottom of the scope and mount. The mount was to the frame rather than slide, but stuff came out of the chamber just the same. I put a little more spring into the recoil system and the hammer spring, and this decreased the amount of crud on the optic parts. Just a thought.
Good luck!

[SkyHawk]

Originally Posted by shojivic

Sky! That pic was only for reference.

Is a dab of JB Weld a possibility? Anyone?

I would not use JB Weld, no way it holds for very long.

Originally Posted by eaglemike

Hole maybe contributing a little. How old is the recoil spring? years ago I lightened 1911 slides and found they unlocked earlier with the lighter weight - I had a lot more crud on the bottom of the scope and mount. The mount was to the frame rather than slide, but stuff came out of the chamber just the same. I put a little more spring into the recoil system and the hammer spring, and this decreased the amount of crud on the optic parts. Just a thought.
Good luck!

This is what I am talking about. I have no doubt the build up is carbon from combustion, but I just can't see that hole being a big problem. I am thinking it is a timing problem. The empty case is being extracted while there is still some gas in the barrel and it is venting back out the chamber. Maybe it can be fixed or maybe it is what it is, who knows.

[shojivic]

Although I've owned this gun for approx 2 years, it's not the most heavily used, as I rotate thru several M&Ps for training. Plus, after coming off an extremely reduced usage at the range due to Covid ammo conservation, I can confidently say this pistol (all stock) has seen less than 1500 total rounds: mixed duty hollowpoint Speer Gold Dot G2, Winchester Ranger SXT, FMJ ball ammo (Aguila, Blazer brass, Winchester white box) etc etc etc.

I have had ZERO malfunctions in this pistol, other than induced malfunctions for training purposes. Been an absolutely flawless performer. The only red dot that has ever been mounted since my transition to Optics, remains attached, save for a few battery changes.

I have not experimented with changes in barrels, recoil spring weights, guide rods, etc. Truly as stock as the day I purchased, save for the Trijicon RMR, adapter plate and the factory flat trigger replacing the original hinged OEM.

Therefore, hardly worn out...

[ar15barrels]

Originally Posted by shojivic

Stock/OEM barrel on the M&P (2.0 5" in 9mm) has the witness hole, and the stock factory optic slide is equipped with Trij RMR type 2.

It doesn't take too many rounds to produce a dirty carbon residue on the optic glass, no matter how "clean" or "dirty" the ammo being used is.

How would one be able to fill in this area of the barrel hood? Swapping out the barrel is not an option, for work.

Is there a solution, besides resorting to aftermarket barrels and slides?

Any advice is appreciated.

(BTW, I have a couple of Glock MOS platforms, so I do have the ability to compare with a pistol that does not possess this annoying feature, and therefore doesn't suffer this optic residue build-up.)

Gas is not coming out of the witness hole at the breech unless gas is leaking around the outside of the case and all the way back to the breech.
The outsides of the cases would be dirty if that were happening.

Have you photographed your gun in high speed to actually see where the gas is coming from?

The more likely cause is gas coming out of the chamber while the spent case is being extracted and ejected.

If you have a comp on the gun, the comp will cause more gas to come out the back of the barrel after the case is removed from the chamber.
Get/make a deflector that sits ahead of the optic and angles any excess gas from the chamber around the sides of the optic.

[ar15barrels]

Originally Posted by shojivic

And this buildup is equivalent, whether it be the 4" compact or the 3.6" SubCompact (now sold).
The fact that it is a carbon based residue leads me to conclude it's from combustion: therefore, the witness hole is the only logical explanation.

Post a picture of your fired cases that are covered in carbon on the outside.
Because if your theory is correct, the cases would HAVE to be covered in carbon.

In a normally operating handgun, the brass case acts as a gasket to seal the breech end of the barrel until the bullet leaves the barrel.
Once the bullet leaves the barrel, the pressure in the barrel subsides as most of the gasses leave the barrel behind the bullet.
Depending on the unlock timing of the gun, the case may be extracted while there is still notable pressure left in the barrel.
In this case, you get gas coming out of the back of the chamber as the case is being extracted and ejected.
The most often cause of that is a compensator at the muzzle end but some gun designs simply do it more than others because of their unlock timing.

The longer you can hold the breech closed after the bullet leaves the barrel, the cleaner the back end of the gun will stay.

[shojivic]

AR, your logic seems sound. I'm not sure if my lousy Samsung has a high-speed camera function capable of capturing the definitive answer, but I'll give it a try.

Would the optic's location, so close to the chamber, have any part in contributing to the problem? The Glock MOS optic mounting area, by comparison, is definitely further away. My Glocks remain pretty clear, shooting back-to-back, when compared to the M&Ps. My pic shows this difference.


Edit:
Randall, I'll gather the spent cases throughout my time at the range tomorrow, and post some pics.

And I forgot to clarify earlier, as you brought up the idea: I don't run any compensators on this pistol. It's not ported in any way. Completely stock components.

[ar15barrels]

Originally Posted by shojivic

Would the optic's location, so close to the chamber, have any part in contributing to the problem?

Yes.
Make a simple little deflector from a piece of aluminum to deflect the gas.
The deflector can be held down by the RMR.

[PLINK]

FWIW I run a G17 with a Zev slide and Trijicon SRO for competition and training. With this set up the optic is closer to the ejection port. The glass does get dirty the more I shoot during a match or class but not enough to prevent me from seeing the dot. It can be annoying to look through dirty glass so I get that. I also shoot with both eyes open if that provides you with any helpful information. I have also taking a pistol optics class where we would put tape on the FRONT of the optic and engage targets with BOTH eyes open. What this shows is you can engage and still hit your target accurate enough even though the glass is completely occluded. I never really found a solution to preventing the dirt accumulation other than the occasional wipe with a lens cloth between stages or when I can. I do use a lens pen that has a compound in the cap that does seem to clean the glass well.

[hambam105]

shojivic,
Great question and great response all around.

If you reload please let us know the load particulars. And did you try using some elses reloads or factory loads?

Can you chronograph your loads? A weak primer spark causes all kinds of issues.

I think AR15 Barrels has the answer. He usually does on gun issues.

[shojivic]

Originally Posted by PLINK

FWIW I run a G17 with a Zev slide and Trijicon SRO for competition and training. With this set up the optic is closer to the ejection port. The glass does get dirty the more I shoot during a match or class but not enough to prevent me from seeing the dot. It can be annoying to look through dirty glass so I get that. I also shoot with both eyes open if that provides you with any helpful information. I have also taking a pistol optics class where we would put tape on the FRONT of the optic and engage targets with BOTH eyes open. What this shows is you can engage and still hit your target accurate enough even though the glass is completely occluded. I never really found a solution to preventing the dirt accumulation other than the occasional wipe with a lens cloth between stages or when I can. I do use a lens pen that has a compound in the cap that does seem to clean the glass well.

Well, Plink, I hear all that you said, and I experienced similar training points/lessons when I went thru my transition class. All valid arguments, and I suppose I've just reached the point where you guys have reminded me to accept the inherent drawbacks to optics!

I guess I've been to willing to blame the M&P barrel too much, thinking erroneously it was the culprit alone! Which is good.. this gun still runs like butter and out-shoots my capabilities.

Apparently my OCD was creeping up on me, and the rather dirty-shooting ball ammo I've been burning thru made the issue worse than I'd recalled seeing before.

[shojivic]

Originally Posted by hambam105

shojivic,
Great question and great response all around.

If you reload please let us know the load particulars. And did you try using some elses reloads or factory loads?

Can you chronograph your loads? A weak primer spark causes all kinds of issues.

I think AR15 Barrels has the answer. He usually does on gun issues.

Hams, I don't reload. Although I wish I had taken up that hobby long ago! I shoot mostly factory stuff, but the minimal reloaded stuff I picked up here from various Calgunners over the years has been stored mostly.

Therefore, I also never invested in a chronograph. Additionally, I am mainly an indoor shooter, as the local indoor range options for me have better hours and accessibility for a family guy trying to get in some practice at odd hours.

Again, I offer my thanks to all the insight provided. It all boils down to some of life's simplest lessons: Sometimes you have to take the bad with the good, and Nothing good (optics) comes easy (cleaning regimen).

[saudadeii]

Originally Posted by shojivic

<snip> And this buildup is equivalent, whether it be the 4" compact or the 3.6" SubCompact (now sold). The fact that it is a carbon based residue leads me to conclude it's from combustion: therefore, the witness hole is the only logical explanation.<snip>

Attachment 1154062

I must be missing something. The "residue" appears to be concentrated at the front of the hood not by the LCI.

I have 3 M&Ps, a Full, a Compact and a Shield (all 1.). My full has a 5" ported CORE slide kit and RMR. None of them exhibit that much residue after a range sessions. Now, admittedly, I've never shot more than 100 rounds through anyone of them in a single range sessions. However, the RMR remains clear. I always clean/lube after each range session.

[shojivic]

^^^
I agree with you on those two points. But I think you'd see more residue after shooting more than a hundred rounds.

The cheap ammo I'm trying to use up, plus the 200+ rounds I'm shooting at a time, was just becoming something I thought could have a solution.

It wasn't something that was an impediment to effective operation, rather just an issue that I thought could be somewhat remedied. Randall and the crew set me straight!

[therealnickb]

Just put a little piece of clear tape on the optic when you’re shooting the dirty stuff.

[saudadeii]

I wonder if that ceramic coating you can put on windshield might help.

[naz]

Not sure if it?s feasible for your slide but how about using a large optic like romeo3xl where the base of the optic will cover the hole

Or if there are any barrels available without that lci hole, switch to that

[hambam105]

OP,

One shooting session firing 200 rounds, indoors, probably from the same point within a hour or two, right? Most indoor
shooters probably shoot less than half that amount in the same time period.

Comparing your situation to Action shooters, they mainly shoot outdoors from different positions. So these shooters aren't
exposed to the level of smoke you're in so the particles do not have the time to settle on the optic screen.

Remember, more than likely AR15 Barrels found the main cause of your situation.

As for OCD, perhaps NON-OCD shooters are experiencing the same situation but just do not notice it.

[shojivic]

Originally Posted by therealnickb

Just put a little piece of clear tape on the optic when you?re shooting the dirty stuff.

Actually, not a bad idea, but like OIF Vet said, just wipe and be done.

Originally Posted by saudadeii

I wonder if that ceramic coating you can put on windshield might help.

Interesting thought, but aren't ceramic coatings more for protective/impact protection rather than just a barrier to dirt? I have zero experience in this stuff.

Originally Posted by naz

Not sure if it?s feasible for your slide but how about using a large optic like romeo3xl where the base of the optic will cover the hole

Or if there are any barrels available without that lci hole, switch to that

I'd definitely use a factory M&P barrel that eliminates the witness hole, if they made it, but no luck as far as I know. And like I said, I have to stick with factory. And I understand the idea of using a different optic that might cover the witness hole, but that also puts the optic very close to the ejection port and flying brass.. chipped optic glass?

Originally Posted by hambam105

OP,

One shooting session firing 200 rounds, indoors, probably from the same point within a hour or two, right? Most indoor
shooters probably shoot less than half that amount in the same time period.

Comparing your situation to Action shooters, they mainly shoot outdoors from different positions. So these shooters aren't
exposed to the level of smoke you're in so the particles do not have the time to settle on the optic screen.

Remember, more than likely AR15 Barrels found the main cause of your situation.

As for OCD, perhaps NON-OCD shooters are experiencing the same situation but just do not notice it.

Hambams, you're probably right in the indoor vs outdoor range argument and the concentration of dust within an enclosed area that contributes to the buildup.

At this point, I'll look for a disposable, pre-moistened wipe/packet product that would make it easier to clean between reloading, and would be more convenient than breaking out the spritzer solution bottle and microfiber towel... so tiresome.

[therealnickb]

Originally Posted by shojivic

Actually, not a bad idea, but like OIF Vet said, just wipe and be done.



Interesting thought, but aren't ceramic coatings more for protective/impact protection rather than just a barrier to dirt? I have zero experience in this stuff.



I'd definitely use a factory M&P barrel that eliminates the witness hole, if they made it, but no luck as far as I know. And like I said, I have to stick with factory. And I understand the idea of using a different optic that might cover the witness hole, but that also puts the optic very close to the ejection port and flying brass.. chipped optic glass?



Hambams, you're probably right in the indoor vs outdoor range argument and the concentration of dust within an enclosed area that contributes to the buildup.

At this point, I'll look for a disposable, pre-moistened wipe/packet product that would make it easier to clean between reloading, and would be more convenient than breaking out the spritzer solution bottle and microfiber towel... so tiresome.

And yet, you rejected OIFs answer and ?moved on?.

[shojivic]

^^^ Oh nickb,

If we only took the first response we ever got, we would be missing better results from the more constructive members, instead of just the guys who want to raise their post count. There WERE better responses and insight offered, but I weighed these and decided on the practical limitations of my restrictions. Vet didn't offer anything I didn't already know and practice. Get it? Don't be trite...

[therealnickb]

Originally Posted by shojivic

^^^ Oh nickb,

If we only took the first response we ever got, we would be missing better results from the more constructive members, instead of just the guys who want to raise their post count. There WERE better responses and insight offered, but I weighed these and decided on the practical limitations of my restrictions. Vet didn't offer anything I didn't already know and practice. Get it? Don't be trite...

Interesting. I took it as you not wanting to clean your lens. Hence, my simple disposal solution. Then you reversed course to only seek out the solution you previously dissed.

Be well and take care.

[lastinline]

What type of ammunition are using? Is it new factory, or reloads?

[Dr. Peter Venkman]

Rain X or Cat Crap with a combination of cleaning.

[Rover]

Originally Posted by ar15barrels

Gas is not coming out of the witness hole at the breech unless gas is leaking around the outside of the case and all the way back to the breech.
The outsides of the cases would be dirty if that were happening.

^This is the correct answer. If gas is shooting out of the LCI and clouding the optic lens, something else has gone wrong.

On high speed camera you should be seeing the bullet leave the barrel, then a ball of flame/gas behind it, then the slide will start to move, dropping the barrel and the case will start to move rearward, by the time that happens there's a gape between the barrel hood and slide, at that point the LCI is irrelevant.


I think the issue here stems as much from optic placement as anything. The further behind the chamber you can get the optic, the cleaner it will stay. M&Ps run the optic pretty far forward, MOS Glocks are a bit more reasonable, and that's still a bit of an apples and oranges comparison because they're different guns. However having Glocks with the same optic both irons forward and irons rear, moving the optic rearward makes a huge difference in how much junk gets blasted onto the glass. My Irons forward Glocks can go 1000 rounds without any appreciable build up.

[k1dude]

I wonder if using an aftermarket "match" barrel with a tighter chamber and no hole might help. Also, stop using dirty ammo.

To those of you recommending a metal plate to be mounted forward of the optic, doesn't that require a custom made optic mounting plate? Who would make something like that? Depending on the slide cut, there also might not be enough room. Taking a look at my pistol optics, some fit perfectly in the cut, and there's no extra room for the plate extension unless you machine the slide cut bigger.

BTW, I have a M&P CORE Gen 1 with an optic on it and have had no such optic fouling problems. I've put tens of thousands of rounds through it in competition.

[mej16489]

My wife and I have both been shooting M&P COREs with RMRs since the guns were released (over a decade ago now?) We've never experience any more or less fouling of the lens than any other platform (FN 509, Glock MOS, etc)

All of which have been to multiple 2 though 5 day classes shooting maybe as much as a thousand rounds or more with no cleaning...

[gsparesa]

S&W loves holes. Just look at their revolver designs with the "Hillary Hole".

The "blow hole" design lends itself to be problematic. It's a S&W issue. Even if you change to a third party barrel, only half of the problem will get resolved. The OP has a few options if he doesn't want the RDO lens getting trashed.


1) Remove the RDO and use metal sights. Problem: Why did I buy an OR gun?

2) Red Dot Cover - Problem: Won't be able to see the dot or target. Use the force Luke.

3) Jellyfish Transparent RDO Optics Cover - Problem: Gets ghostly shadows which might resemble your target.

4) OpticGard Scope Cover - Problem: Same as #2 above.
5) Lancer Airsoft Optic Shield Protector - Problem: Modification Required.
6) WML Flashlight Lens Cover - Problem: Some modification maybe required.

7) Sell the POS and buy a better designed pistol.

[FNGGlock]

The obvious fix is to just get a Glock

[1911su16b870]

This is a really great thread, sorry shojivic this is happening, and honestly should be a non-issue...but if this is a work/defensive pistol, I can understand the frustration.

Ideas:

Try a winclean ammo for training. Less carbon fouling overall in my experience...or maybe another ammo mfg/loading?

If duty ammo (ranger etc.) is causing it...remember you need to be able to focus on the threat/target, superimpose the dot where you want the hole and press the trigger without disturbing that...e.g. your optic is still up and you have the ability to fight through fouling from zero to the # of rounds that cause fouling and beyond until that target/threat is no longer so.

[shojivic]

I appreciate all the insight (and support of my OCD, 1911su), as there are definitely more experienced people here than me.

Just to clarify: The purpose of the thread was to determine if the witness hole could be "closed" in the attempt to prevent build-up on the optic. I erroneously thought it was the cause of the carbon build-up, but that's been made abundantly clear to me, thanks to the knowledgeable base here. For anyone who simply suggested "wipe and be done," I've been doing that, obviously. Don't be obtuse.

I've NEVER had the problem that the optic was simply TOO dirty to see thru/use; and yes, I've been instructed on the use of the optic in an occluded manner/worst case scenario. As I admitted before and hambam recognized, I simply have less tolerance for a dirty optic.. I've not been dramatic or overly sensitive to it and was merely sharing my displeasure.

I transitioned to the M&P from my previous duty Glock 34 Gen 4 simply because I wanted to have a gun that didn't have the notorious Glock "hump" even though it never impeded my competency shooting it. When my Dept finally offered transition to optics, I jumped at the chance and have made the switch permanent: both in recognizing the inherent advantages, and recognizing the astigmatism in my right/shooting eye favors using optics instead of irons. I don't flip-flop back and forth simply because I have an OCD-based displeasure of a dirty optic lens.. But I digress..

After having this CORE Pro Series for some time, I MERELY WAS TIRING OF THE OPTIC BUILD-UP as an annoyance; NOT A LIFE-ENDING PROBLEM. Too many peanut-gallery members here misinterpret a request for input as a sign of complete ignorance or lack of intellect!

I've recognized that different ammo contributes to the problem depending on how cleanly combustion occurs. Again, noted.

To the Glock fan-people: yes, I've begun running optic-ready Glocks again, simply because I'm very familiar with the platform, and quite frankly, they shoot just as accurately for me as my M&P CORE.

As stated earlier, running side-by-side alternating, the Glock-mounted optics just seem to remain cleaner, all other conditions being equal (indoors, same ammo and rounds shot, same RMR optic, etc).

THEREFORE, I've gleaned a few things, and like I said, ultimately I have NO problems functioning as is. Unlike GSP's thoughts, I don't plan on tossing this 5" ProSeries any time soon. I've got the Glock 45 and 19 MOS should I need a change of venue. But ultimately, this thread was about how/why the witness hole affects the optic, and I'm thoroughly convinced that it is a non-issue.

SO, at the end of the day, I learned something new, and I'm content to keep on doing what I've been doing... (Now, all I need to know is what is the best, clean-burning ammo for range/practice? But I'll GOOGLE that first.. thankyouverymuch!)

[Carcassonne]

You could try a heavier and lighter recoil spring so the barrel unlocks sooner or later than it is now.

Someone else posted something a while ago about too much oil causing the problem.

.