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Posted: 5/18/2020 4:13:10 PM EDT
How is the distal chamber measured? I have an end cap that will be milled, will this effect the measurement? Or is it measured from cone to threads (just the spacer area)?
These are not mine but examples of the same end cap, one has been milled.  Attached File Attached File |
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Posted: 5/18/2020 7:09:33 PM EDT
[#1]
Are you asking about the blast chamber sizing, or how to size the spacer that forms the last chamber that terminates with the front cap?
Usually spacers are a little long and the stack is held in compression with the rear cap tight to the shoulder and the front cap a little proud. If the stack doesn’t compress under first firing, sand or trim a larger spacer that’s easy to get a hold of. |
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Posted: 5/18/2020 9:40:08 PM EDT
[#2]
Quote HistoryOriginally Posted By KalmanPhilter: Are you asking about the blast chamber sizing, or how to size the spacer that forms the last chamber that terminates with the front cap? Usually spacers are a little long and the stack is held in compression with the rear cap tight to the shoulder and the front cap a little proud. If the stack doesn’t compress under first firing, sand or trim a larger spacer that’s easy to get a hold of. I’m sorry, I guess the pic wasn’t the best without clarification. The cap in the pic that’s threaded for a barrel was just for reference of the material that’s in the cap when new. My question is, if I have a stack of spacers and cones figured out.... blast chamber size and all spacing figured already, and lastly I’m shooting for a certain “space or distance” from last cone to end cap. What would be the proper way to measure that distance. From the last cone to the face of the end cap threads? Or from the last cone all the way passed the threads to the inner face of the end cap. In this pic, would that distance be measured from cone to #1 or cone to #2? See what I’m asking? In an unmachined cone, #2 doesn’t exist, it’s taken up by cap material.  Attached File |
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Posted: 5/18/2020 9:45:30 PM EDT
[#3]
that picture made me go "wtf" for half a second
 the front face of your distal spacer (or cone if you don't have a distal spacer) will be compressed by the base of the front endcap. Counterboring the endcap won't affect any of your spacer measurements, you will just have move volume in your distal chamber. |
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Posted: 5/18/2020 10:14:13 PM EDT
[#4]
Quote HistoryOriginally Posted By TheShlouf: that picture made me go "wtf" for half a second the front face of your distal spacer (or cone if you don't have a distal spacer) will be compressed by the base of the front endcap. Counterboring the endcap won't affect any of your spacer measurements, you will just have move volume in your distal chamber. Yep, that’s what I’m asking, not about spacer length but more about the effect of the distal chamber by removing the material in the cap. If someone said “end up with your distal chamber .375”. Would that spacer be .375 no matter the cap design? If you change the cap design and volume, does that change where you want your last cone? Maybe I’m overthinking this? I just had a recommendation of .375 distal. My end cap hasn’t been milled. If I did have it milled for weight reduction, would this have an effect on what the recommended spacer length would be, internal design and functionality wise? I know milling it won’t changes threaded portion length and such, I’m asking from a functionality and theory point of view. |
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Posted: 5/18/2020 10:34:15 PM EDT
[#5]
Yea, you're overthinking it a bit. If you wanted a .375 distal length, you would need a ~0.01" spacer. I made the depth of those endcaps 0.36-0.37".
Your recommendation was likely for a .375" distal spacer with the assumption that your endcap will be counterbored, since I think SDTA is the only vendor that sells solid endcaps with that much material there. You will definitely want it counterbored (for both weight savings and sound improvement) regardless of what distal length you go with. |
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Posted: 5/19/2020 8:03:07 AM EDT
[#6]
I didn’t realize those were your end caps. Thanks for responding. Hope you don’t mind me using the pic.
I had a layout for 300 with subs. 13 cones in 7.8 tube. I thought my distal was going to be right at .375, but then when I realized the cap needs counterboring, and according roughly to your measurements, that’s going increase the distal to ~.7. Will that hurt performance? Should I try to tighten that space some? Closing the distal will mean shifting everything else, how will that trade off? Thanks |
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Posted: 5/19/2020 9:02:58 AM EDT
[#7]
I don't mind.
Ahh, ok, it's for a subs can. I don't shoot centerfire subs, so I don't keep track of what the design guys on the form1 board regard as best for sub cans. It depends on how much material you remove from your endcap I guess. Since it's a subs can, you shouldn't have an issue counter boring deep enough so that the endcap against your last cone makes your distal chamber .375". |
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Posted: 5/19/2020 9:38:18 AM EDT
[#8]
You're overthinking it. yes, a final expansion chamber can be beneficial, but not so much that a crappy design will see a drastic change. Your stack should provide 95+% of the performance.
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Posted: 5/19/2020 9:49:37 AM EDT
[#9]
Quote HistoryOriginally Posted By smokedoff: I didn’t realize those were your end caps. Thanks for responding. Hope you don’t mind me using the pic. I had a layout for 300 with subs. 13 cones in 7.8 tube. I thought my distal was going to be right at .375, but then when I realized the cap needs counterboring, and according roughly to your measurements, that’s going increase the distal to ~.7. Will that hurt performance? Should I try to tighten that space some? Closing the distal will mean shifting everything else, how will that trade off? Thanks In many instances a larger chamber (like equivalent to an inch or more of skirt or spacer plus front cap volume) at the front cap will deepen the tone. Depends on caliber, powder, and to a great extent your sensitivity to different frequencies. I wouldn’t worry about it as far as changing design to hit an exact value. Counter-boring is good to drop weight near the front, reduce the “tunnel” the projectile has to pass through, and the extra volume after that last baffle likely won’t hurt performance. With 13 baffles you may not hear a difference, but out in the end of the suppressor weight differences can be felt. |
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Posted: 5/19/2020 10:03:40 AM EDT
[#10]
Quote HistoryOriginally Posted By KalmanPhilter:reduce the “tunnel” the projectile has to pass through...likely won’t hurt performance. Several designs use this tunnel to increase final tone "performance". |
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Posted: 5/19/2020 10:50:46 AM EDT
[#11]
Thanks guys. I just checked something that I had neglected. On my sdtac tube and end cap, I have to have .300 for the distal spacer anyway to keep last cone out of the threads, so no matter what the end cap ends up being, it will be +.300.
I guess you have to work with what you have. But I have learned some more and that’s what matters. I’ll get a pic posted in a bit of my drawing. I’ve had to revise it again bc I messed up and got .180 off on workable space. I’m gonna have to tighten the plans up a little. I’ve had a great deal of help with the design from a couple guys on the f1 boards through email and such. I recognize some of y’all from over there as well. |
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Posted: 5/19/2020 12:23:23 PM EDT
[#12]
EDIT: Disregard these numbers! I have a working area of 7.06, not 6.88. My brain is stumbling big time this morning. Let me reconfigure and we can discuss further.
edit: refigured a few posts down I keep getting close but then run into snags. This is my first and I think I’m trying to get it too perfect?? I have a workable space of 6.88. I have to stay .310 off the the distal end cap. I’m I don’t up on both sides off 6.88 by .100-ish. What do you think? Here’s a basic layout of the suppressor, don’t look too much into the number on the graph paper.  Attached FileThis excel sheet is 13 cones, the first tip is .200 from the muzzle.  Attached FileThis sheet has 12 cones, the first .300 from muzzle.  Attached FileAs you can see, both are creeping up on the 6.88 but not quite there. |
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Posted: 5/19/2020 12:32:05 PM EDT
[#13]
This is for 300blk? On an Ar15? That's a tiny blast spacing and you're probably going to be a bit gassy. Supers will like that blast spacing even less.
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Posted: 5/19/2020 12:34:56 PM EDT
[#14]
Quote HistoryOriginally Posted By User55645: This is for 300blk? On an Ar15? That's a tiny blast spacing and you're probably going to be a bit gassy. Supers will like that blast spacing even less. 300 subs. At platform. Direct thread. I was recommeded .200-.300 muzzle to 1st cone tip. That’s why it’s laid out like that. Open so suggestions of course. |
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Posted: 5/19/2020 12:57:28 PM EDT
[#15]
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Posted: 5/19/2020 6:31:42 PM EDT
[#16]
Quote HistoryOriginally Posted By smokedoff: 300 subs. At platform. Direct thread. I was recommeded .200-.300 muzzle to 1st cone tip. That’s why it’s laid out like that. Open so suggestions of course. That’s a good rule of thumb when you have a muzzle device protruding into the blast chamber. Or for rimfire to reduce first round pop. Otherwise a very common dimension is one diameter from muzzle to cone tip. Typically you’ll see about a 2 inch blast chamber spacer and a cone that intrudes anywhere from 0.4” to 0.75” into that spacer. |
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Posted: 5/19/2020 6:40:06 PM EDT
[#17]
Quote HistoryOriginally Posted By User55645: Several designs use this tunnel to increase final tone "performance". Oh, I know it can be done. For Form 1 builds if you get a front cap kiss it’s a lot easier to rework a flat front cap to a slightly bigger aperture. Flat caps are also easier to design for wipes. I think if you are going to spend time on a highly machined front cap the best pay-off (at least for shorter cans) is flash hider tines. Hoping someday the Pew Science guy does some metering on these design nuances, but not holding my breath. |
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Posted: 5/19/2020 6:44:56 PM EDT
[#18]
Quote HistoryOriginally Posted By KalmanPhilter: That’s a good rule of thumb when you have a muzzle device protruding into the blast chamber. Or for rimfire to reduce first round pop. Otherwise a very common dimension is one diameter from muzzle to cone tip. Typically you’ll see about a 2 inch blast chamber spacer and a cone that intrudes anywhere from 0.4” to 0.75” into that spacer. Quote HistoryOriginally Posted By KalmanPhilter: Originally Posted By smokedoff: 300 subs. At platform. Direct thread. I was recommeded .200-.300 muzzle to 1st cone tip. That’s why it’s laid out like that. Open so suggestions of course. That’s a good rule of thumb when you have a muzzle device protruding into the blast chamber. Or for rimfire to reduce first round pop. Otherwise a very common dimension is one diameter from muzzle to cone tip. Typically you’ll see about a 2 inch blast chamber spacer and a cone that intrudes anywhere from 0.4” to 0.75” into that spacer. Can you clarify “one diameter”? So if my first cone is .620, in a 2.00 inch chamber, it will protrude .560 (.620-.060 (flange thickness)). My muzzle is .150 beyond the spacer mating area of the endcap. 2.00 chamber spacer - .560 cone - .150 muzzle protrusion = 1.29” muzzle to cone tip. Sound right? |
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Posted: 5/20/2020 1:37:07 AM EDT
[#19]
Quote HistoryOriginally Posted By smokedoff: Can you clarify “one diameter”? So if my first cone is .620, in a 2.00 inch chamber, it will protrude .560 (.620-.060 (flange thickness)). My muzzle is .150 beyond the spacer mating area of the endcap. 2.00 chamber spacer - .560 cone - .150 muzzle protrusion = 1.29” muzzle to cone tip. Sound right? I was referring to the ID of the tube as the length of one diameter. So for example a Dead Air Nomad 30 if you look at the welds it’s about 2.25” from the rear of the tube to the first weld where the base of the blast baffle sits. With their cone that puts the tip about 1.4” from the rear of the tube where mounts thread in. The ID of their tube is around 1.6”. It’s just a rule of thumb. Having a blast chamber drops pressure, reduces flame erosion on the blast baffle, and allows room for muzzle devices if your design can accept QD mounts. Rugged has very long blast chambers and fewer baffles than most in many of their designs. Q and Sig and CGS on direct thread run the stack closer, but port the blast baffle or chamber to vent pressure. A longer blast spacer on a Form 1 is something you can get a grip on if you need to trim the stack. Shortening your last tiny spacer on a belt sander to get the front cap near flush is a pain. |
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