Stormrider with offset LDC

[naptemp]

John,

Your Chaser front sight base image (below) appears to have a step at the front face, indicated by the slanted blue line spanning red lines 1 and 2.  Your measurements for barrel stub length measured two ways also seem to have a 1 mm disparity.

I am using the shorter of the two dimensions to avoid contact between moderator and front sight base; using the barrel muzzle face as depth stop instead.

Now, it is possible that what I am seeing in your image (below) is plastic flash or fuzz, rather than solid material.  If it is solid material, then I have to leave a larger gap at the top of the sight base than the bottom.  I certainly do not want to use the sight base as a shoulder for the moderator to bear against, as it would probably kick the moderator off at an angle.

Anyway, perhaps you could take another image at a slight angle to show if that apparent step is just thin plastic fuzz, or something more substantial?  For now, I am treating it as "solid".

I have added another photo of the barrel muzzle.
Most people would just be happy to have a good LDC.
I do not think it is important to have the LDC perfectly fit the size/shape of the sight.

[subscriber]

John,

I used the info you provided and the specs you requested to designs the .177 and .22 Chaser LDCs shown below.

STLs are attached below.  .177 STL in this reply.  .22 STL in next reply.

[subscriber]

Zipped .177 STL attached directly above.

Zipped .22 STL attached directly below:

[naptemp]

Thank you.
I will print the top threaded part to check for fitness.
I will let you know the result.

[naptemp]

I printed the threaded end at 100% scale.

The thread works.
The only issue is that there is a gap of 1.5-2mm between the LDC and front sight.
See photos.

[subscriber]

Thanks John

I will add material to reduce that gap substantially.  If the gap was not so variable I would use it as the mounting stop.  However, I want to keep the barrel muzzle as the shoulder for this design.

[subscriber]

Version 2 of these LDCs have the tail end extended by 1.5 mm.  You might want more, but there should be no contact at the front sight base, unless that is flat and perpendicular to the barrel.

Most of the original rear cone is exactly the same as the designs above.  I added a parallel 1.5 mm section to V2, then blended the cone to the short cylinder via a 10 mm fillet.  The rear face then has a 1 mm fillet applied.

The .177 STL is attached as a zip file below.  The .22 STL is attached in the next reply.

[subscriber]

.22 STL V2 attached below as zip file:

[naptemp]

I printed the top threaded part of V2.
For some reason it was much tighter than the first version.

I am reprinting it after scaling to 101.5%

For those who print threaded moderators, always print the threaded part first and scale all dimensions up (101%, 102%, etc) until you get a good fit.
Then you print the LDC using the scaling factor that works.

In Cura you can print only a vertical part of the model by sliding the model under the printing bed using the blue arrow (Z axis).

[subscriber]

John, if you scale the X and Y axis you will change the  barrel stub bore ID and thread OD.  If you also change the Z axis, that will change the thread pitch.  Unless you know that your prints are short, scaling up the Z-axis will change the printed thread pitch.  That will make the part go tight before it is threaded on all the way.

I added 1.5 mm to the length of the barrel channel, but kept the barrel channel diameter and thread OD at 10.3 mm in CAD.  See image below from latest design.

Are you printing at the same resolution as before?  What about the ambient temperature and humidity?

[naptemp]

John, if you scale the X and Y axis you will change the  barrel stub bore ID and thread OD.  If you also change the Z axis, that will change the thread pitch.  Unless you know that your prints are short, scaling up the Z-axis will change the printed thread pitch.  That will make the part go tight before it is threaded on all the way.

I added 1.5 mm to the length of the barrel channel, but kept the barrel channel diameter and thread OD at 10.3 mm in CAD.  See image below from latest design.

Are you printing at the same resolution as before?  What about the ambient temperature and humidity?

Screwing the LDC in works fine until it reaches the barrel portion and then it gets very tight.

In the last print I only decreased the number of walls by 1 compared to V1, everything else was identical.

So, if the threads are too tight I should only scale up the X and Y axes?
In the last print I scaled up X, Y and Z.

[subscriber]

A:  So, if the threads are too tight I should only scale up the X and Y axes?
B:  In the last print I scaled up X, Y and Z.

A:  Yes

B:  There is your problem.  Leave Z at 100 percent.

[naptemp]

A:  So, if the threads are too tight I should only scale up the X and Y axes?
B:  In the last print I scaled up X, Y and Z.

A:  Yes

B:  There is your problem.  Leave Z at 100 percent.

I will try printing V2 with the correct scaling (no Z scaling).

I attached a photo of all the prints so far.

[naptemp]

I printed V2 again with X and Y scaled at 102%, Z is still at 100%.
The threaded part fits well.

Just like before it gets very tight when the end of the LDC is about 4-5 mm from the front sight.
To get through the last 4-5mm I used some big plumber pliers :}

I can definitely live with this as is.
I do not intend to remove it very often.

[subscriber]

Now the question is, how well does it shoot?  Sound and grouping....

[naptemp]

Now the question is, how well does it shoot?  Sound and grouping....

I will print the entire LDC tomorrow.
Will update.

[subscriber]

I will print the entire LDC tomorrow.
Will update.

Well? 

[naptemp]

I am printing it tomorrow over night.

Once it's printed I will install, test and take photos

[TorqueMaster]

I printed up the 177 V2 version.  Just the threads at first, at 100% scale, and it fit very well -- just a slight friction all the way to seated.  I can't tell if it's hitting the muzzle or the front sight first it's so close. 

I printed the whole thing.  It's quite light for it's size, which is great.  Since my pistol barrel is not installed, it is very easy to check alignment -- and unfortunately it appears to be canted a bit, far enough that I might get clipping.  As I rotate it around the barrel, the cant moves, so it isn't just droop.  A minor nudge does allow it to center, so I may be able to tweak it with some thin tape on the unthreaded portion of the barrel if I don't find the cause.

TLDR: check your alignment with the bore best you can before shooting through it!

[subscriber]

Thanks, Bob

If it seems that the rear face of the moderator is contacting the front sight base, is there perhaps a raised area at the print seam that is canting the part off?  Something that could be filed off.

You might file or sand the rear face of the moderator until a small but obvious gap opens up relative to the sight base, when the moderator is fully screwed on.  Then we know that the barrel muzzle is the stop.  The overall moderator length to achieve that, might be good for a version 3...

The same concern about a raised print seam would exist at the shoulder intended to stop the barrel muzzle face, except it would be harder to reach.  Except perhaps with a 9 mm endmill - twirled between fingers.

I designed the radial clearance for these moderators the same way I have been doing for some time:  1 mm radial clearance over caliber, plus 0.15 mm for print shrinkage.  This is for the first baffle bore after the barrel muzzle.  The radial clearance then increases towards the front at a rate of 0.25 degree - or about 0.1 mm per 25 mm of length.

The above would seem generous, compared to what many assume is best, but it is intended to take care of any misalignment that is below canting that is obvious to the naked eye.  If there is obvious canting, then the cause/s should be found and corrected.  Certainly, clipping would not only shoot poorly, it would probably be louder; and might lead to complete failure of the baffle bores towards the front end of the moderator.