Advice on integraly suppressed barrel

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John1992
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Advice on integraly suppressed barrel

Post by John1992 »

If I was going to build a simple integraly suppressed barrel using drilled ports with a sleeve covering it should I wrap the barrel in steel wool before putting the sleeve over it? And if so should I wrap the entire barrel? And how tight if I do?
a_canadian
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Re: Advice on integraly suppressed barrel

Post by a_canadian »

Steel wool will burn up fairly quickly. Perhaps you mean the mesh ribbon type scrubbing pad, such as 'chore boy' made of copper plated stainless steel? Or copper mesh? Any sort of plain steel wool is highly flammable. Not something I'd recommend for use in a suppressor even for .22lr.

If you do use some sort of mesh make sure it can withstand flame of fairly high intensity. Test it with a torch, outdoors. If it holds up to a bit of heat torture it'll probably be okay.

Another factor to consider however is the flexibility of the mesh. If it's very easy to form, you should assume that it will be pulled into the bore at some point, though with very small barrel ports this wouldn't likely happen. A bit of broken stainless steel ribbon from a scrubbing pad pulling into the bore would make a mess of your rifling next time you fired a shot, the bullet dragging the hard steel down the bore. So if choosing some sort of mesh it's probably best to pick a welded type, or whatever is very stable. Look at the old WWII integrally suppressed subguns with stiff mesh wrapped in layers around barrel ports. There's a reason for that very firm mesh roll.
John1992
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Re: Advice on integraly suppressed barrel

Post by John1992 »

Do you think adding the mesh will help reduce the db at all?
a_canadian
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Re: Advice on integraly suppressed barrel

Post by a_canadian »

My experience is limited to 2 related efforts both in .22lr, one a 10" barrel ported with 8 x 1/8" holes between 5" and 7" from the chamber, the other a 6.5" barrel ported with 7 x 1/8" holes between 4.25" and 5.25". In each case I used K baffles ahead of the muzzle. In the shorter sample I also tested entirely blocking the ports for comparison, using a stainless steel sleeve which fit quite closely. Mesh used for both was copper-plated stainless scrubbing pad carefully unwrapped then twisted into a long rope then wound around the barrel tightly as indicated by Ciener.

I found very little difference in either case between with and without the mesh. And frankly the speed with which filth built up was dismaying. I typically use a thin smear of white lithium grease on the first few baffle faces to ease cleaning the 7075 aluminum and slightly enhance suppression efficiency for the first magazine or so. That along with the usual grime of rimfire makes a stinky mess of the mesh within a couple of hundred shots. Not fun to deal with.

In the case of the shorter barrel, I found a similar slight improvement in suppression (about 1 to 2dB) by making a pair of slip-on aluminum rings with slots in each to receive a thin walled stainless tube, the three part assembly fitting snug between the suppressor tube's rear plug and the threaded muzzle plug. This stainless tube was drilled with about 50 x 1/6 holes, in a pattern not lining up with the barrel ports. The 304 stainless tube was easy to clean so it made a lot more sense than the mesh. The design of the longer barrel profile did not permit use of such a buffer sleeve, but the difference in noise level wasn't sufficient in that case to continue using mesh, barely effective if at all.

It seems to me that things like mesh wraps or grommets filling a portion of a suppressor over a barrel are old tech which is not nearly so effective as the use of a modern baffle design. In the case of the shorter barrel above, on a semi-auto pistol, I found improved suppression after shortening the barrel to 4" and using a 5" stack of 7 short K baffles with effective cross-bore gas redirection features. Quieter than the longer barrel with ports and an 11" OAL tube with 1" OD and 5 K baffles about 1" long each. Longer K baffles are not great. More is better, with minimal metal at the bore, limited of course by porting and strength requirements. Seems that the most important element is face and porting shapes. Nesting the baffles helps slightly in getting more into the stack and easing disassembly/cleaning a bit. By all means go to a mesh or other fill if you like, just don't expect much in comparison to a truly modern baffle design.

I also have a 9mm carbine with an integral suppressor. Improvement in decibel reduction was found after boring 8 x 3/32" holes at 45 degrees, starting at 4.5" from the chamber in 2 rings 1/2" apart and staggered, slanting from further back towards the muzzle to minimize cutting of the bullet jackets and direct gas flow back towards the rear plug of the can. The OAL on that barrel is 10". Up front is a centering plug with 5 x 1/4" ports to allow gas pressure exchange between over barrel and baffled volumes and burn marks inside show a very significant amount of activity in that area, the initial blast chamber before the first shallow clipped cone being only 1/2", so a lot of stuff comes backward. 6" with 11 shallow cones and spacers combined with the equally long section of open tubing around the barrel make for a very effectively suppressed report, ejection port noise approximately matching that measured at the front cap of the device. I considered some sort of mesh in the reflex space but dismissed it as impossible to maintain in this design. Glad of that, as no further noise reduction seems to have been possible.
John1992
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Re: Advice on integraly suppressed barrel

Post by John1992 »

Okay thank you that really helped out alot.. A lot of good insight also to some stuff I hadn't even thought about. One more question, on the ports, is there a certain distance I should stop the ports from the end of the barrel to keep my bullet more accurate? I have heard that having ports close to the end will cause the bullet to drift badly and I was not sure seeing as I have no personal experience with it yet
a_canadian
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Re: Advice on integraly suppressed barrel

Post by a_canadian »

The closest I've gone to the muzzle with ports is 1", on a relatively low powered .22" PCP which I've tuned to shoot 18gr pellets at about 500fps. With 3 x 1/8" ports from 3" to 1" before the muzzle, a 3/4" OD barrel shroud to contain that's expelled air, then a 3.5" aluminum monocore baffle thing in the tube ahead of the muzzle of that 14" barrel, the thing is darn near silent. When I drop a squirrel with it the impact on the side of the animal's head is vastly louder. Makes me worried people will hear that and be alarmed. Firing the airgun doesn't worry me. I could probably set up a soft target backstop and shoot in the yard all day with nobody noticing. Pardini and other airgun makers put tiny ports within a couple of inches of the crown, with no harm to accuracy on these competition guns. Has to be done cleanly of course.

But yes, do leave a bit of clean bore after your last port. If it's just noise you want to take away with the ports, further towards the muzzle is fine. If you also want to reduce velocity, then they should start at around 4" from the bolt face to dump more pressure early.
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ninoslavt
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Re: Advice on integraly suppressed barrel

Post by ninoslavt »

It's ok to use steel wool in a suppressors. There's no need to be feared of a fire hazard 'cause fire needs oxygen and there will be almost none in that part of the tube. Now... Is it a good way to go for a legal suppressor in the hands of civilians? I would say no. Even rolled mesh (brass, bronze, steel...) will get clogged very fast and pretty much useless. HuK changed their design for a MP5 SD because this.
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John1992
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Re: Advice on integraly suppressed barrel

Post by John1992 »

a_Canadian where did you get the 3.5" baffle you were saying you put at the end of your barrel? Or did you make it?
a_canadian
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Re: Advice on integraly suppressed barrel

Post by a_canadian »

Oh that's crudely home made, from some awful Home Depot stock, probably 1024 or similar crappy aluminum. Messy to machine with my little hobby tools. Sure works though. Seems I glitched on the length - looking at the picture in a plastic parts box and holding a ruler in about the same orientation in that box, it seems it was 4.5" not 3.5" long. Oh well, that was something like 8 years ago. Not taking it apart now. Those plastic plugs (one a barrel cap keeping the shroud centred, the other a spacer at the back of the shroud tube sealing at the receiver) are both glued and grub screwed in place. Thing is practically mouse far quiet while delivering an 18gr pellet at 515fps, for 10fpe. Plenty on squirrels, and a neighbour coughing in their kitchen makes more noise.

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