Stormrider with offset LDC

[miksatx]

so I changed out my polygon rifled barrel off my Buck Rail 2nd gen stormrider. replaced with a .22 barrel i picked up from WesBob. I needed a ldc so subscriber took on the job. and what a job.

[subscriber]

Just so folks can get some idea of what is being attempted, see the images below.

The challenge is to create an offset reflex LDC for a modified Stormrider PCP, that can be installed and removed, without removing the barrel from the receiver.  This implies not being able to rotate the LDC more than a few degrees before it fouls the air cylinder below the barrel.

The concept is to split the rear LDC insert, so that it can capture the barrel in a non-rotating sandwich, while still using the barrel stud threads to retain the insert.   Secured, after the outer tube is slid on to hold the parts together. 

Then the front insert is slide in, to mate with the clocking dimples on the rear inserts.  There are also shallow alignment cones to help with the alignment of the rear inserts with each other, before the tube is slipped over them.

The front to rear insert dimples may look "oversize" in the last image, but the nominal 3.3 mm diameter holes are expected to close in during 3D printing, to leave perhaps 0.002" clearance for the mating features.

Mike has his work cut out, printing the parts and making them work.  If he has trouble, I may need to tweak the design in some areas to achieve a just tight fit on all the important interfaces.

The dimensions are somewhat arbitrary, but Mike wanted at most a 5" reflex length, using a 1" OD tube.  The section ahead of the muzzle is also 5" long, as this is a 12 FPE application.  If the muffler had been intended for 20 to 30 FPE, I would have wanted an 8" long forward section.   Considering the split sections inside the tube, I don't yet have confidence that a longer front overhang could be used, without droop.  Certainly, the outer tube needs to be a snug fit; as needs be the barrel inside its nesting features.

[dan_house]

love the look of ecentric cans...

used one on my P17 micro-carbine build and working on one for my chaser chassis system build

[miksatx]

So with some filing and a bunch of sanding in the right places lol. only hear the pellet hit the back stop.

[subscriber]

Excellent, Mike.

How much of a gap is there between the LDC outer tube and the air tank at their ODs:

After getting very deep into the design I was wondering if the gap at the air tank OD was large enough to avoid contact on firing.  If groups are tight and not way off from where you expect, then the gap must be large enough.  Positioning of the barrel band and some tweaks there might help a marginal situation, if required.  As another intervention; the LDC tube or insert flanges could be dressed with a file, if there happens to be suspected or actual contact with a given air tank.

I was thinking about the job of aligning the front and rear sections, blind inside the tube; and what I could do to help make that process easier.  But if you did it, then it can be done by those skilled in the arts; as they say on patent applications.

I can imagine that the split line between the two rear sections would need a bit of cleaning up, to remove flash and fuzz. 

How was the fit into your nominal 0.930" ID tube?  If you could measure the tube ID around the perimeter and provide an average ID measurement, I could fine tine the CAD model to help; if there are any other interested parties?  This assumes deburring and chamfering the cut edge of the tube first.

I used the nominal tube ID of 0.93", and then added 0.002" to the OD of the insert in CAD.  Largely because the OD of printed parts tends to be a little smaller than the CAD spec; and because I was aiming at a snug fit between inserts and tube ID.  This was so the front insert would not launch on firing.  It may need to additional retention over just friction for higher FPE applications, such as a cross pin. 

If there is any interest in printing the above bits are Mike has done, the STL files are attached separately (or zipped); due to file size limitations per post. 

Note that the front section needs to be printed with its "flange" down on the printer platen; while the rear sections need to be printed with their flanges up, away from the platen.  This is to enable printing without supports.  It may be useful to print both rear inserts at the same time, spaced a short distance apart on the platen.  The idea being that they better match each other, if there is any variation in as printed lengths.   Mike may be able to offer the best advice here, as he has actually produced a working set of parts.

Front section STL attached directly below:

[subscriber]

Rear section STL files attached in ZIP files

[subscriber]

Mike,

In looking at your image (close-up below) I get the impression that you used a foot long section of aluminum tubing.  Is that correct?  Certainly, doing that eliminates the need to match and insert the front and rear insert pip and dimple alignment.  It also means that you need to sight down the assembly bore to ensure clocking of the front section relative to the rear and barrel bore.  Easy enough for anyone who has used a peep sight, I suppose.

Functionally, with a longer tube, you end up with a larger expansion chamber, following the reflex air stripper.  This is clearly not a problem; if my scaling by eye of your image is correct.   If I am correct, it sounds like something to be emulated by others who want to try this assembly - assuming the stock Stormrider barrel stud and shoulder lengths are compatible.

[miksatx]

Mike,

In looking at your image (close-up below) I get the impression that you used a foot long section of aluminum tubing.  Is that correct?  Certainly, doing that eliminates the need to match and insert the front and rear insert pip and dimple alignment.  It also means that you need to sight down the assembly bore to ensure clocking of the front section relative to the rear and barrel bore.  Easy enough for anyone who has used a peep sight, I suppose.

Functionally, with a longer tube, you end up with a larger expansion chamber, following the reflex air stripper.  This is clearly not a problem; if my scaling by eye of your image is correct.   If I am correct, it sounds like something to be emulated by others who want to try this assembly - assuming the stock Stormrider barrel stud and shoulder lengths are compatible.

with inserts nested 10 3/8"

[miksatx]

having clocking issues and changing poi lol. reprinting new inserts at a higher quality, the rear flange clocking into the tube.

[miksatx]

Mike,

In looking at your image (close-up below) I get the impression that you used a foot long section of aluminum tubing.  Is that correct?  Certainly, doing that eliminates the need to match and insert the front and rear insert pip and dimple alignment.  It also means that you need to sight down the assembly bore to ensure clocking of the front section relative to the rear and barrel bore.  Easy enough for anyone who has used a peep sight, I suppose.

Functionally, with a longer tube, you end up with a larger expansion chamber, following the reflex air stripper.  This is clearly not a problem; if my scaling by eye of your image is correct.   If I am correct, it sounds like something to be emulated by others who want to try this assembly - assuming the stock Stormrider barrel stud and shoulder lengths are compatible.

yep no need for the little divots. if the inserts are to tight for the tube i have only been sanding the flat side of the inserts.

[subscriber]

Thanks, Mike.

[miksatx]

Thanks, Mike.

Hopefully this next set of prints make things right lol.

[subscriber]

Not sure I fully understand the problem.  Else I would offer to help.

[miksatx]

Not sure I fully understand the problem.  Else I would offer to help.

they seem to be just a little fat for the tube sanding down the flat part of the insert skinnys them down. took off to much on my first set of inserts. 

[subscriber]

yep no need for the little divots.

The attached STL files have all divots and pips removed from the front and rear inserts.

Front insert - no dimples:

[subscriber]

Left and right rear insert STL files, zipped - no dimples:

[miksatx]

Inserts keep breaking in this same spot need reenforcing of some type. the bottom of the flange hits the air tube. takes me 9hrs to print theses insret.

[subscriber]

Frank,

I can thicken up the wall where it broke.

It seems there is not enough clearance between air tank and outer tube.  How much additional offset do you think would be enough to avoid contact?  It looks like I might be able to shift the offset an additional 3 mm.

[miksatx]

Frank,

I can thicken up the wall where it broke.

It seems there is not enough clearance between air tank and outer tube.  How much additional offset do you think would be enough to avoid contact?  It looks like I might be able to shift the offset an additional 3 mm.

I was going to say shifting the offset a couple mm should do it.

[subscriber]

OK, Mike; I increased the LDC axis offset to the max:  The most offset that will allow a 12 mm barrel OD to to work with a 1" LDC OD tube, with a 0.035" thick wall.

That worked out to the offset being increased by 3 mm over what you tried before.  That should clear the air tank and even allow a little barrel droop, without closing the gap between tank OD and LDC OD.  If not, then the tube OD would have to be reduced; or the LDC would have to be mounted ahead of the air tank.

You could reduce barrel droop by mounting the forward barrel band directly behind the LDC; or real close to it.

The three insert STL files are attached in the same ZIP file, below.

To reduce the fragility of the rear inserts, the outer wall is increased slightly, and the internal support ribs now run the full length.