barrel porting question

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John A.
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barrel porting question

Post by John A. » Sun Dec 15, 2019 9:21 pm

I am wanting to ask you guys a question, which I hope someone may know the answer to.

I ported the barrel with about 1.5mm holes, but they're shaving some of the jacket. Not down into the lead of course, but I had a lot of copper slivers laying on my shooting table when I finished so I'm certain that it is in fact shaving them.

My question is, if I enlarge the ports to say 1.9mm and then finish ream to 2mm and essentially make them bigger while the bore was filled with cerrosafe so I can essentially be certain that I am not leaving burrs or anything, will that help stop that? Or would it just make bigger shavings?

It hasn't hurt accuracy and like I said, it's just a sliver of the jacket and not deep into the lead. So, other than just having to clean out the integral portion of the can more often is about the biggest negative that I would see if it doesn't change anything.

I think the culprit is the bullets themselves. I'm shooting the 9x39, which the wolf bullet measures .364".

But the 9.3mm mauser bullets that I am using from speer to handload for, are .366" which just simply extend into the grooves more between the rifling lands. I haven't shot any of the wolf bimetal bullets through the gun since I made the ports because I didn't have any with me the other day and I'm going to take a handful with me just to make sure they're not shaving anything. I don't see any burrs and I've never had a problem making ports before either, but I just wanted to ask for opinions.

I don't really think that enlarging the ports would stop it from shaving some of the jacket, but I wanted to ask you guys what you thought before I make any changes to it.
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Re: barrel porting question

Post by T-Rex » Mon Dec 16, 2019 8:37 am

How many rounds have you put through the barrel, after drilling? What's the shaving's size and quantity look like, as you continue to shoot? Are they diminishing?

I would think enlarging the hole would exacerbate the issue. You'd be offering a greater cutting edge to be exposed to the jacket.Ideally, you'd want to use an interior deburring tool, like this

Image

Another easy way to go about it would be to angle the drill bit, slightly towards the muzzle, to eliminate the sharp forward edge. I understand it's too late for this.
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Re: barrel porting question

Post by John A. » Mon Dec 16, 2019 9:08 am

It's not too late to angle it if I enlarge the holes a little more. This would elongate the hole similar to how semiauto shotgun ports look and was why I was asking. Though would it matter if I angled the bit forward or backward in relation to the muzzle. I would think angle it forward would round more of the edge that is probably shaving it ??

I have only shot about 15 or 20 rounds since porting just while working up some of the Clays powder loads. And to test the velocity that I was getting with the Titegroup load that I had already worked up.

They are just little tiny slivers of jacket.

They look about like pencil shavings, only much much smaller. Squiggly I guess is how I would explain them. Very short. And very narrow. Very much smaller than what you would see while turning down a piece of metal on your lathe.

I have thought about firing some of the wolf bimetal bullets through it just to try to smooth out any imperfections that may be present between the lands where I can't really see down into. But like I said; I don't see any burrs while looking up through the barrel toward a light.

I think the slight extra diameter of the bullets themselves is also contributing to the problem because I didn't run into this with my blackout or my 9mm integrals and they were drilled the same way as this one.

Like I said, the accuracy of the gun seems unaffected. And it's not even deep enough to get down into or shave the lead. It's just the very micro edge of the jacketing and not even through it entirely.
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Re: barrel porting question

Post by T-Rex » Mon Dec 16, 2019 9:20 am

If the porting is working, in relation to gas flow, I'd fire a bunch more rounds and see if that cleans the edge of the hole up a bit.

As far as drilling on an angle, you want the end of the drill bit, that goes into the chuck, closer to the breech. The hole, essentially, would be pointed towards the muzzle and venting the gas back towards the shooter. You'd be removing the hole's sharp edge, on the muzzle side.
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Re: barrel porting question

Post by John A. » Mon Dec 16, 2019 9:52 am

The porting is working wonderfully where gas flow is concerned. With each pull of the trigger, a gas cloud suddenly appears around my barrel, so that's good and should work well in the integral once I get the approval signature.

Currently, the port holes are about 1.5mm.

I don't want to open them up any more than 2mm,if I did at all, because I don't want to starve the DI gas port on the AR because right now I have the gun fully cycling the way it is now without a can, although it is a little weak. I left it where I did because I figured that once I make and install the integral can should add some more back pressure so it will cycle a little stronger, but like I said, I have it locking open and cycling properly now as it sits despite using the fast burning titegroup and clays.

I plan to work up some more loads using #2 powder trying to get a velocity boost. But it will likely be after Christmas and probably closer to New Years before I get a chance to order the powder and work on them. I'll shoot it some to see how it is. If the weather isn't too cold or muddy, I'll try to dig a few of the bullets out of the backstop so I can look at the jackets themselves if I can recover one.
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Re: barrel porting question

Post by T-Rex » Mon Dec 16, 2019 11:01 am

Yeah, I'd keep shooting it (maybe 100 rounds) and see if it lessens.

If you had to open the ports, you can always open the DI gas port a bit, too.
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Re: barrel porting question

Post by John A. » Mon Dec 16, 2019 11:34 am

That is true. When I made the gas port for the DI, I stopped at .109/.110'ish and I was surprised when clays and titegroup was fully functioning. As I said, it's a little weak there and ejecting about 5 o clock, but I think that it'll be about perfect once I get to make the can for it.

I could open up the DI port up to .125 if I had to. It wouldn't benefit me to open it up more than that because the gas tube itself is .125" diameter so I'd gain nothing by going further. But, I do have room to make it larger if I had to.

I'll try to shoot it in for a while and go from there with it because I am wanting to work up another load for it anyway that should net some higher velocities. But I do think that the larger bullet itself is at least helping contribute to the issue some too. But not much I can do with that though. Unless someone has a .364" swage or starts making 9x39 specific bullets.
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Re: barrel porting question

Post by T-Rex » Mon Dec 16, 2019 12:38 pm

John A. wrote:
Mon Dec 16, 2019 11:34 am
Unless someone has a .364" swage or starts making 9x39 specific bullets.
I'm disappointed, John.
You have a lathe:
Get some tool steel
Bore it .364
Externally thread it 7/8-14
Make a punch tool
Harden and polish
Done. :wink: :lol:
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Re: barrel porting question

Post by John A. » Mon Dec 16, 2019 1:02 pm

I suppose that would work LOL

While I'm at it, I should probably start making spoons to help end world hunger too.


:lol:
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Re: barrel porting question

Post by Capt. Link. » Mon Dec 16, 2019 8:23 pm

I'll buy a spoon and send it to my governor ,Its obvious he's a zombie starving for brains.

I'm not sure building a swagging tool will help much as the barrel itself is a sizing die....abet a soft one. You might try a lead lap charged with abrasive or fire lap it to remove burrs. I can provide details if needed.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This is boiled down information collected over several decades.

The AMF report details various porting including angled ports in both directions plus the British way of porting only in the grooves.The net results were all ports will "deform" the bullet.
H&K made studies when the MP5SD was in development.They found many small ports close to the chamber deformed the bullet the least.
Company's like KAC and others have found placement is critical.Theory is very small ports placed close to the chamber shave less lead and are kept clean due to pressure and heat.The early porting also lessens the bullet base pressure that "may" flare when a port is encountered causing the shavings.
(I have bore-scoped the KAC Amphibian pistol and found two very small ports in the throat). The accuracy of this pistol is match grade as is the MP5SD so both company's are doing something right.
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Re: barrel porting question

Post by John A. » Mon Dec 16, 2019 9:57 pm

Thanks for the replies gentlemen. As I have mentioned, accuracy seems largely unaffected and good.

My ports are between 7-10 inches of barrel. I can't really port nearer to the barrel with enough gas left to work the gas tube and the bolt. On the positive side, they are very small ports though. About 1/16" or 1.5mm

There are 20 ports.

The actual vintorez uses fifty four 2mm ports in the same location.
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Re: barrel porting question

Post by fishman » Mon Dec 23, 2019 2:31 pm

I have three words for you:

Electrical discharge machining
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Re: barrel porting question

Post by John A. » Mon Dec 23, 2019 3:58 pm

Sorry, I'm not set up for edm.
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Re: barrel porting question

Post by John A. » Tue Dec 31, 2019 7:44 pm

I just wanted to update the topic and probably put it to bed.

The jacket shaving is settling down now. It's quite a bit less now than it was initially. The integral can is done, and the portion of the barrel is not filling up with jacket shavings. When I took it apart and cleaned it, there were some jacket shavings in there, but not near as many as when I first did the porting that was laying on my shooting table.

I did buy some 1.9mm jobber bits and a 2mm reamer, but I have not reamed the ports with them. Doesn't look like I'll need to after all.

That's OK, next time, I'll port the barrel at an angle to begin with. I just wanted to thank each of you who offered suggestions.
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Re: barrel porting question

Post by T-Rex » Tue Dec 31, 2019 8:53 pm

Glad to hear it, John.
Knew the edge would wear down, after a while.
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Re: barrel porting question

Post by a_canadian » Thu Jan 02, 2020 11:06 pm

Finally committed to porting a 9mm barrel today to scrub a bit of borderline transonic velocity off my 147gr of choice. Winchester JHP were averaging 1,100fps out of a 9" barrel but the odd one was going to the mid-1,120's, coming close to not sounding good and flirting with the accuracy issues inherent anywhere close to the speed of sound. So I put a soft steel rod down the barrel as a backer and drilled 4 x 0.060" holes at about the 5" mark. Dropped the average to 1,090fps but one still went to 1,123. Drilled a second row half an inch forward, following the rifling slant, and like the first row slanted my drill back 45 degrees after starting the hole. Another 8fps drop...

So I opened the first set of 4 holes to 0.100" - didn't want to drill more holes in either of those ring locations and weaken the barrel too much, and obviously going further from the chamber wasn't going to slow it down as much. This brought the average down to 1,070fps and the peak to 1,079. Probably acceptably slow unless I decide to go shooting in really cold weather. I can always open out the second set of holes the same way.

Evidence of burning shows up as sooty circles inside the 1.375" ID tube, but nothing a finger won't wipe off. Decibel reading on my little modified SPL meter shows about a 1.5dB average drop from un-ported condition, confirming my auditory impression which is slightly less unpleasant. It's just a shallow clipped cone stack up front, 10 of those plus a contoured 'baffle' front cap, with 4 x 1/4" holes in the threaded mid plug to vent back into the over-the-barrel section. A LOT of sooty buildup happens in the OTB volume after a few dozen shots. Guess I'll be using big bottle brush now and then. Fixed rear plug in the tube provides a decent labyrinth seal against the front of the action, no sign of gas leaking there.

The main reason to add this nonsense, my two cents, is the angle of the holes. Going at 45 degrees left no swell inside the bore at all along the front half of the 8 holes, and only a very lightly distorted sharp edge at the backs. After a dozen test shots and a bore wipe I couldn't see any trace of distortion in reflected light. Seems angled towards the muzzle is the way to go with these ports. I hear no little shavings of copper rattling in the foot-long tube, none came out when shaking over paper.

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Re: barrel porting question

Post by T-Rex » Fri Jan 03, 2020 8:51 am

a_canadian wrote:
Thu Jan 02, 2020 11:06 pm
.
You should try using some copper mesh, in the OTB section. It will not only help disperse heat, but aid in the cleaning process. :wink:
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Re: barrel porting question

Post by John A. » Fri Jan 03, 2020 11:43 am

Thanks to both of you.

Copper mesh may help but I couldn't tell that it did much on mine. I even stuffed some aramid/Nomex material up in underneath of my handguard. The worst part of that was the smell of the stale powder smoke when I took it apart. Shew-wee it was bad.
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Re: barrel porting question

Post by a_canadian » Fri Jan 03, 2020 2:01 pm

Yeah, my experience with copper mesh some years back was similar. Didn't seem to make a difference in noise level, and cleaning it was just nasty. Ended up tossing it instead, unravelling a new scrubbing pad and twisting and wrapping that. Several cycles, maybe 150 rounds of .22lr each time, before I gave up on the stuff. A thin walled stainless tube, drilled with about 100 x 1/16" holes and captured by two slotted aluminum spacers to spread out the expanding gases worked slightly better but still didn't impress my ears. In the end I gave up on OTB for that gun and chopped the barrel, threaded, and it suppressed very well with a simple 5.5" front mounted can.

For the 9mm filth accumulation isn't such a concern, but it's still going to need cleaning in the OTB area. There's enough pressure with this thing to make that volume play a significant role, but nothing's getting out anywhere besides the front cap bore so I'm not worried about spreading out gas flow in the tube. Got the ports now moving pressure forward, the 4 vent holes in the muzzle plug pushing backward from the blast chamber, so some good destructive interference going on in there I suspect.

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Re: barrel porting question

Post by T-Rex » Fri Jan 03, 2020 3:07 pm

Hmm. I've used the mesh on several projects and find it very helpful. Not a noticeable sound reduction, but, as I said, dissipates heat and aides in cleaning. The crud doesn't stick to the interior of the tube, as much, and makes it easier to slide a tube off. Throw the mesh in a small, plastic, tube or coffee can and soak w/ brake cleaner. Let it sit, while you clean everything else, and it's usually done after that. Let it dry and throw it back in. You can soak it in vinegar, too, and get that bright shine to it.
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Re: barrel porting question

Post by John A. » Fri Jan 03, 2020 3:20 pm

acanadian, I ported my 9mm integral barrel just forward of the front of the chamber. Maybe 1.5" ?

I only made a single row of ports around the barrel, but it was enough to help port off some of the gas while still giving good velocity down range while still splitting some of the gas out of the bore making the rest of it more effective. I sure didn't want to port off too much gas and make the gun useless or be able to port off 115 supers down into subsonic territory. I didn't want to go there. I don't remember my before and after chrono readings, but I think it was about 40 fps less after the porting.

I don't recall the size of the ports either because it's been so long, but I'm wanting to say mine were closer to .075 or .080 but don't quote me on that.

Oh, and I have no shaved jackets on this gun either or on my blk integral. Go figure !?! :roll:

Image

T-rex,I've tried the chore boy on a couple of different projects and both times, I couldn't tell a difference with or without it so I stopped packing it back in there after a while.

I think where copper mesh is concerned, it's better at just displacing oxygen and taking up space in a large chamber. Kind of like using all of those shoelace eyelets in the old sionics cans but with less weight and no rattle.
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Re: barrel porting question

Post by a_canadian » Fri Jan 03, 2020 3:33 pm

Makes sense if you're using chore boy to keep the tube clean. In the case of my 9mm integral that's not relevant really, as the can is one piece, permanently assembled. The larger hole at the back is turned into a profile which matches the front of my receiver and nestles fairly snug into that, providing a good seal. I'm able to do a bit of scrubbing through that opening as needed. I might make a multi-piece insert to bond into the area outside the barrel ports with a high temperature epoxy, but only if after shooting for a time there seems to be some wearing of the 6061 tube. If it's just soot build-up I won't bother. The fmj and jhp stuff I'm shooting is a bit dirty, but nothing like .22lr.

John A. - I'd have done something similar if it were an option, perhaps going as close as 2" from the front of the chamber, but mine's a PCC with removable barrel and the way it's laid out, holes drilled anywhere closer than I did would vent into the body of the carbine, making a heck of a mess and perhaps degrading the action. No matter. At the distance I drilled and with the 0.10" holes first it's working well enough. And I have no intention of using anything besides subsonic 147gr.

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Re: barrel porting question

Post by John A. » Fri Jan 03, 2020 4:29 pm

Yeah, that wouldn't work like how I did mine. I understand why you had to do it differently.

I never intend to shoot supers in mine either and didn't want to lose too much velocity while shooting subs so that's why I only ported it how I did.

Sure, we can do like HK and make about 30 ports to drop supers down into subsonic, but that's just stupid. They only did that because when they were designing the SD, the military was using 124's and there wasn't an abundance of subsonic munitions even available at the time so they wouldn't have to have specialty ammo. But technology has advanced and it's counter productive to do that now and completely unnecessary.

Still, how well do you think your integral sounds? I'm betting pretty darn good.
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Re: barrel porting question

Post by a_canadian » Fri Jan 03, 2020 5:44 pm

I wouldn't quite class it as pretty darn good. My ears are overly sensitive, painfully so when it comes to things like ambulance sirens or construction air nailers as I walk by a site, so custom hearing protection is the norm for shooting unsuppressed even with something like CCI Quiet out of a long barrel. I'm not set up for machining anything quite so large as K baffles for a 9mm with an OD of 1.375", so I went with stupid-simple on this first 9mm can. Fat steel washers heated to orange and pressed in a pair of vise mandrels to a shallow (15 degree-ish) conical shape. And since most of those opened out to about 11mm centre hole from the pressing and needed slight correction for centering on the lathe, as a stack, average bore size ended up at 12mm, with just the first couple at 11mm. And the 10 baffles plus front plug only add up to 7", so again not optimum. I made simple symmetrical shallow clips on each baffle.

The result is pushing up close to my low pain threshold when firing indoors at 1,100fps. Outdoors it doesn't bother me. Not having proper metering tools I can only guess really, besides making relative measurements between tests with an SPL thing. With that I can see relatively small changes which are always in agreement with my ears. But comparing to published numbers and my .22lr testing I'd guess around 132dB for this 9mm setup at the muzzle, maybe pushing over 136dB at the shooter's ear due to the dual ejection ports. I may wrap my brass catcher in foam at the exit on that size and make some sort of port cover to slap onto the unused right hand side to further reduce that problem, after all else is finished.

I'm awaiting a piece of tungsten rod to let into the buffer weight, upping mass by a few ounces over stock, mostly to delay uncorking, reducing ejection port noise. I suspect that will play a larger role in quieting the beast than barrel porting/velocity reduction. Might also raise velocity again slightly, so I'll perhaps have to bore that second string of 4 holes to 0.100" to drop it again.

-------------------------------------------
edit:
Thought about that 1070fps for a couple of days and decided to knock it down a bit more, so this afternoon drilled the set of 4 holes to 0.100" and cleaned them up. Shots with Winchester 147gr JHP dropped to a 1,042fps average, from 1,037 to 1,053.

Surprisingly, FRP showed up for the first time, actually rising 1.5dB above my previous first shot average, but every shot after was between 1.5dB and 2.5dB quieter than with the smaller second set of holes, so a very significant improvement to go with the drop in velocity. Looking into the tube there's a spattering of unburnt flecks of powder. Guess a significant bit is burning as it's coming out of the ports, burning oxygen there like it would in an excessively large blast chamber. The first baffle is within 0.50" of the muzzle so this didn't arise before.

Not a big worry as even that first round pop is about 2dB quieter than the same setup with no barrel porting. And any edge to the sound is completely gone, sounds soft, very tolerable at about 7dB louder than .22lr CCI SV through a good rifle can. And at about 350fpe it's still a usable trajectory, no significant drop for 60 yards and only 6" at 100 yards, with 275fpe remaining at that distance. I'm guessing the added buffer weight to come will up velocity slightly, but have to wait for that in the slow mail...
Last edited by a_canadian on Sun Jan 05, 2020 7:59 pm, edited 1 time in total.

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Re: barrel porting question

Post by a_canadian » Sat Jan 04, 2020 1:43 am

Along similar lines, a very interesting H&K prototype being discussed on the Forgotten Weapons channel today. Thing has some kind of valve alternately blocking or opening what looks like maybe 5 large ports in the bottom half of the barrel, barely ahead of the chamber. Ian said it was designed to dump excess pressure into a vessel below the action, dropping velocity from 350m/s down to 305m/s, or from about the speed of sound at seal level to a hair over 1,000fps. Just by flipping a lever! Seems a very cool feature. Not sure I'd want to implement it myself, but for a 9mm police/special forces SMG designed specifically for suppressed use this seems kind of neat. The specific bit about the switch starts at 11:30 in this video, with a clear look down the chamber and bore at about 13:09:

https://youtu.be/e7hX2jWw8cU

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