form 1 300blk

Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.

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cedwards04
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form 1 300blk

Post by cedwards04 »

Just efiled my form1 for a 6.5" 300blk suppressor. I understand i cannot build any parts at all until it is approved, so for now i am just planning and learning to use the lathe. Have been a long time lurker/reader here. I have learned a ton by reading everyones builds and want to say thanks.

I recently aquired a harbor freight brand 9x20 lathe, and have a small drill press. I would like to build a very simple monocore design that i will pin to a 10.5" upper to get me at a legal 17" barrel. I want to make the outer tube threaded on the inside so that it can be removed for cleaning the core while still attached.

The plan is to use 1.5" od pipe for the outer tube. I have some 1.5" solid round bar that i will turn down and thread to go inside the tube. I am thinking of drilling 1" holes in the bar stock to create the baffles. I am thinking i will drill the first 2 1/4" apart and then drill the last few 1/8" apart. I plan to drill the holes, rotate the bar 90 degrees, and drill again. This will hopefully increase the volume. Thoughts?
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CMV
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Re: form 1 300blk

Post by CMV »

I would leave a shoulder on the core at the end that will attach to the barrel that's as high as your tube thickness. That way when you slide the tube over the core it buts up against it. Then on the other end of the core leave about a .600" nub .497" in diameter. You can thread that and then make a screw-on cap (with a shoulder just like the 'front' end). THat way you can permanently attach the core to the barrel and then unscrew the cap from the end to remove the tube.

As to the baffle idea of 2 intersecting holes, I don't see that working. If the 2nd perpendicular hole doesn't cut the core in half, the first hole isn't nearly large enough. Just make 1 big hole instead of 2 small ones.

This is for a .22 but same concept. You can picture what would happen if you tried to make perpendicular holes to these chambers.

Image

Image

Image

Pictures also show what I'm talking about for your end cap. In my case the tube butts up against the receiver but the threaded nub at the end screws on and holds the tube in compression. Same concept, just this example is a lot longer. No idea if the design would work well on yours though. My 300 BLK is 60° smooth cones w/ spacers and it works very well. If this were my project, I'd make a similar sealed can and permanently attach the whole thing.
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BlwnGazkit
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Re: form 1 300blk

Post by BlwnGazkit »

You could easily drill several smaller holes similar to the below quick & dirty drawing I drew to show my thought to you...

It would take more time, but probably be more effective. Readily done on a drill press if you pilot drill the holes and are careful.

Image
cedwards04
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Re: form 1 300blk

Post by cedwards04 »

Thanks for the replies. Both are very good ideas. I will have to give this some thought.

The smaller holes would give me room for more baffles. It would take considerably longer to execute, but thats nots really a problem to me.

I like the idea of leaving a ridge at the back of the core to butt the tube against. Is there any reason i cant just thread the tube and the core instead of making an endcap? Seems like it would be simpler but im an extreme novice so i am probably overlooking something.
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BlwnGazkit
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Re: form 1 300blk

Post by BlwnGazkit »

I suppose you could thread the tube and core. I've seen it done that way elsewhere I believe.

Just remember to use o-rings to prevent gas leakage.
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CMV
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Re: form 1 300blk

Post by CMV »

If you try to thread the entire length of either part - core or inside tube - you will have several hard to overcome challenges on a 9x20 lathe. You don't have a large enough spindle bore so the whole tube is in the chuck jaws & extended out from there so you'll need a steady rest to support it. Then you'll need a long threading boring bar to cut the threads. You will run out of room if you have ~5" of tube sticking out + ~7" of boring bar from the tool holder. The carriage won't be able to pass the steady rest - you don't have enough distance between centers. It would also take a pretty stout boring bar to extend that far & not deflect so you might have a hard time getting on center with a large enough tool depending on the size of your toolpost.

That's plenty of machine to make a nice silencer, but you'll have to stay within it's capabilities. What you're describing sounds easier - only 2 parts need to be made. But in reality, making one of those parts will be very difficult. I think the core would be difficult also. If you thread it first then go to the drill press you will most likely damage the threads. If you do the holes first, that's a lot of interrupted cuts doing the threads. Then consider assembly & disassembly. If the final result is 6.5" long & you use 20TPI threads, you're going to be spinning the parts together/apart a very long time. Then once it's good & dirty, taking apart may be very difficult. Picture the gun in a vise & you with a strap wrench on the tube spinning 130 revolutions with the threads badly fouled with powder residue. Like many people I use A1680 for my 300BLK sub loads. While it works well, it's very dirty. Adding the suppressor sure doesn't help the cleanliness. With about .006" clearance, by baffles insert easily when clean but need 'encouragement' to come out when dirty.

You can always efile for the SBR. Yeah it's another $200 but it gives you the option of using that can on other things instead of having it permanently attached. You'll be spending that $200 if you later want a .308 can for something else.

http://vimeo.com/75717721 This is my 300BLK shooting subs suppressed @ 100 yds on a piece of steel sheet. Camera is zoomed way in but is only a few feet away from the muzzle. The can is nothing fancy - just smooth, unclipped, 60° cones & spacers. It does have a reflex chamber back over the barrel instead of a typical expansion chamber but otherwise is very basic in construction.
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BlwnGazkit
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Re: form 1 300blk

Post by BlwnGazkit »

You can turn down all but say 1/2" of the core on either end and thread on of those 1/2" sections.

The just thread one of of the tube to match.
cedwards04
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Re: form 1 300blk

Post by cedwards04 »

I wouldnt dream of trying to thread the entire thing. Sorry if i was unclearcon that. Im thinking i would thread somewhere between .5-1" at the very end. The rest would just slide down over the core. I am thinking of turning an angle at the muzzle end to help with seating/sealing.
cedwards04
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Re: form 1 300blk

Post by cedwards04 »

As far as doing an sbr, i thought about it, but i have the gun setup for a certain look, it would not be useable without the suppressor anyway. I have a 10.5" barrel and a full 12" rail system on it. Without the suppressor it would be blowing gases all over the rail.

I plan to do another form 1 very soon for more of a multi caliber suppressor to be used on a 6.8spc, 5.56, and 22lr. Will probably bore it big enough for a .30 caliber bc at some point i want to get an ar10. This next one will be built longer and bigger diameter. Figured i could thread it 5/8x24 and make an adapter to use it on 1/2x28 threads. I'll start a new thread for it once i submit that form 1 in a few weeks.
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Capt. Link.
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Re: form 1 300blk

Post by Capt. Link. »

I would not build a monocore.A more conventional suppressor would be more effective with the very short length you have specified. Making smaller simple pieces will raise the probability of your success as a screw up on a small part only requires remaking that piece and not the whole core.You might wish to look into milling on your lathe and you will need to rebuild or make a new steady rest to hold the suppressor tube while you work on it as the factory model will only hold small diameter pieces.Old school K baffles or smooth cones are both good choices and well within the skill of a novice with limited equipment.CL
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cedwards04
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Re: form 1 300blk

Post by cedwards04 »

I would really prefer to stick to a monocore design if possible for this can. It just seems like it would be much simpler for my first go at it. There are several companies that make monocore 300blk silencers in the length i am building. They may not be the best, but i think it would suit my needs for now.

My steady rest is plenty big enough for 1.5" od tube. I got the lathe used so maybe the previous owner already upgraded??? I did recently purchase a quick change tool post with vertical height adjustment, and some carbide cutting/turning bits and boring bars. I have been reading on littlemachineshop and watching youtube trying to learn as much as possible. I think threading everything is going to be my most challenging thing.
cedwards04
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Re: form 1 300blk

Post by cedwards04 »

My form 1 was approved a little bit ago, and i have been practicing on threading on my lathe. I have the external threads down, but i have really struggled bad with internal threads. Seeing as how this will not be the last suppressor i build, i decided to abandon the whole making it serviceable and i just welded it all up.

My new question is this, i used a tap to thread the portion that goes on the barrel, and threaded it with the suppressor chucked into the lathe, and the tap in the drill head. When i finished, i decided to chuck the tap into the lathe, and screw the suppressor onto the tap to check the run out. With a dial indicator on the exit end of the suppressor it measures .036 of wobble. I drilled the center hole .35. Does this all seem ok? With the lathe on and turning, it looks like a lot of runout with the naked eye. To check it i placed the dial indicator at the exit end, rotated the piece by hand until the dial indicator started to swing back the other direction, i marked this as 0, then rotated the piece by hand again one complete revolution. The dial indicator went up to .036 and back to 0. Did i measure that correctly? I just want to make sure it is ok. In my brain, the math appears to work out, but just looking at it rotating, it looks pretty far off.
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T-Rex
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Re: form 1 300blk

Post by T-Rex »

your runout is quite excessive.
you seem to have the tools to do the job, i would recommend practice.
I understand your excited to build your Form1, but I can guarantee a giant smile and whole-hearted satisfaction the first time you mate 2 parts with male-female threads.

If you're not already familiar w/ them, I suggest you check out mrpete222,Keith Rucker and Toms Techniques on YouTube.
They are all very informative when it comes to the lathe .

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cedwards04
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Re: form 1 300blk

Post by cedwards04 »

So my runout is too excessive to work? Mathematically it appears to me that it would work, but i could be thinking about it wrong.
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Re: form 1 300blk

Post by Kuraki »

cedwards04 wrote:My form 1 was approved a little bit ago, and i have been practicing on threading on my lathe. I have the external threads down, but i have really struggled bad with internal threads. Seeing as how this will not be the last suppressor i build, i decided to abandon the whole making it serviceable and i just welded it all up.

My new question is this, i used a tap to thread the portion that goes on the barrel, and threaded it with the suppressor chucked into the lathe, and the tap in the drill head. When i finished, i decided to chuck the tap into the lathe, and screw the suppressor onto the tap to check the run out. With a dial indicator on the exit end of the suppressor it measures .036 of wobble. I drilled the center hole .35. Does this all seem ok? With the lathe on and turning, it looks like a lot of runout with the naked eye. To check it i placed the dial indicator at the exit end, rotated the piece by hand until the dial indicator started to swing back the other direction, i marked this as 0, then rotated the piece by hand again one complete revolution. The dial indicator went up to .036 and back to 0. Did i measure that correctly? I just want to make sure it is ok. In my brain, the math appears to work out, but just looking at it rotating, it looks pretty far off.
First, by chucking the tap in the lathe, you're going to have runout between the chuck and the tap. Second, threading the part onto the tap will induce runout in the thread engagement, which might be mitigated by only exposing enough of the threads from the jaw faces to hold the part, and then butting the shoulder of the part up against the jaw faces. Third, you would want to indicate those jaw faces rather than assume they are perpendicular to the rotational axis. Fourth, a .350" bore leaves .021" of clearance per side, which is acceptable if everything was perfect. If your part truly does have a TIR of 0.036" however, that clearance is not sufficient.

Because of the way you're measuring run out, it's hard to say what your actual case is. At this point your best bet would be to attach the can to a rifle and use a range rod in the bore to check clearance.

If you do have interference, I think it is still possible to save the can. I would chuck up on a piece of stock, diameter at least as wide as the shoulder of your threaded mounting hole, turn and single point thread that stock, square up the shoulder, and leave it in the chuck. Attach the suppressor. Check runout as now you have a mounting point true to the axis of the lathe. Straighten the can by bending the exit end towards center in the opposite direction of the run out. Repeat until you have satisfactory results that clear the range rod in your bore with at least (in my opinion) 0.020" per side.
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Re: form 1 300blk

Post by 300sniper »

Chuck up piece of bar stock with just enough stick-out to thread a "muzzle thread". Thread it to your muzzle spec. Without removing the newly threaded bar from the chuck, thread on your suppressor. Now check your runout at the exit hole of the suppressor.
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cedwards04
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Re: form 1 300blk

Post by cedwards04 »

I tried chucking the exit end of the suppressor in the lathe, and screwing the tap into the muzzle end, and then set my dial indicator on the shank of the tap. Set up this way i am getting .018 of runout. I can wiggle the tap up and down the the threads about .005. I think the slack in the tap is what is throwing me off so much set up the other way. Does it sound like this method of measuring would be more accurate?

If its worth anything, i cant visible see any wobble in the suppressor if i clamp the tap in a vice and screw it onto the tap. It visible appears to screw on nice and straight.

I'll try to get some smaller bar stock and thread it like the muzzle and see how well that works. Going out of town for a few days so it will probably be a week or so before i can report back.
cedwards04
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Re: form 1 300blk

Post by cedwards04 »

I decided to thread the suppressor onto thd barrel and check it with a rod down the barrel. The suppressor screwed onto the barrel with no noticeable runout, the rod sat nice and centered in the suppressor. After seeing this i decided to test fire it. The suppressor performed very well in my opinion. No baffle strikes, and very little poi shift. I shot it with 110 supers, and 220 grain subs. It is still pretty loud with supers, but is hearing safe. With subs all i hear is the gun action and the thud of the lead hitting down range. My wife actually thought something broke when i shot the subsonic due to hearing the bolt slam and not hearing the bullet haha. Thanks for all your help guys. I've got a little cosmetic work to do to it still when i get some free time and then I'll post a pic.
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Slow Hand
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Re: form 1 300blk

Post by Slow Hand »

Good to hear. I may have missed it, but why kind of design did you end up going with? Monocore, Ks, Cones?

Looking forward to another first time builders pics!
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