Picatinny Rail & Wedges

[rsterne]

I needed a scope mount for my .183 cal Benchrest rifle, capable of shooting up to maybe 800 yards.... Here is what I printed.... The Picatinny Rail has a groove in the bottom to match the ridge in the center of the wedges, and the outside of the rail fits inside the wider groove in the wedges.... It is a beautiful slide fit in all of the wedges.... The curve on the bottom of the wedges fits a 1.25" OD barrel.... and the height clears the objective of a 50mm scope by 1/16" to the bottom of the scope cap with all of the wedges....



The wedges, from front to back, are 30 MOA, 60 MOA, 90 MOA, 120 MOA, and 180 MOA (yes, a full 3 degrees).... If the rifle is sighted at 100 yards with the lowest rail, using the other rails should put me on the paper at about 265 yds, 415  yds, 550 yds, and 760 yards.... This is assuming a MV of 1000 fps and a BC (RA4) of 0.27.... I think those should be appropriate for the 39 gr. BBT I will be shooting at about 1000 fps....

Bob

[TorqueMaster]

Very nice!  CF PETG or something even higher end?  I saw the "V" pattern on the parts and figured there was some slope involved, nice that it's got swappable wedges. 

I did something similar for shooting at 100 yards only -- rotatable tubular shims that fit between a 1 inch scope and 30mm scope mounts.  As I recall I added a bunch of up and a wee bit of windage to keep the scope fairly mechanically centered.  Just plain old PETG.   18 grain pellets, 900ish fps.



 

[rsterne]

Yes, CF-PETG.... Made in Canada by Matter3D Inc. in Victoria BC.... One of the nicest filaments I have used, is now my go-to CF-PETG.... They have a 10% CF (cheaper) and a 15% CF (stronger) for a bit more money, both come in 1kg. spools....  Both are on sale right now.... These parts are the 15%, printed at 0.2mm layer x 0.6mm width, with a 0.4mm nozzle at 260*C, and 80*C bed PEI temperature.... The Rail is 94% Lines infill with a 3mm wall, the wedges are 30% Cubic infill with a 2.4mm wall.... Top & bottom thickness is 1.2mm on both....

https://www.matter3d.com/products/carbon-fiber-petg?variant=42692098097329

I talked to the guy who engineered the filaments about using a Nylon, he spent quite a bit of time asking me questions, and then said "although I'd love to sell you more expensive filaments, stay with the CF-PETG, it's way easier to print and perfect for your needs".... Honesty goes a long ways in my book!!!!

I'll probably never use the 3 deg. wedge, but I wanted to make sure they all cleared between the scope cap on the objective and the top of the barrel....

Bob

[rsterne]

Here is an .stl file for the Picatinny Rail and four wedges, 0.5, 1.0, 1.5 and 2.0 degrees.... If sighted with the 0.5 deg. wedge at 100 yards, most PCPs shooting slugs should get roughly 250, 400 and 500 yards using the other wedges, depending on velocity and slug BC.... The tube profile on the bottom of the wedges (they are printed upside down) is to fit a 1.25" OD tube.... You should be able to modify the models to fit a smaller barrel / receiver in something like Tinkercad, which is what I used to design them.... I printed with CF-PETG....

You will need to clean up the bridged area in the slots of the rail and wedges so that the rail fits down solidly and slides smoothly on the wedges....

Bob

[subscriber]

Bob,

The main benefit I see when using CF PETG for a sight rail is stiffness and creep resistance, rather than strength.  The load on a sight rail is not much, but regular PETG may change shape over time, causing a drift in your sight zero.

10 percent CF should have much better stability than the base material.  But, as I know nothing about the performance of this material, I would choose the higher CF content for such an important set of components; assuming it prints as well as the lower CF content PETG.  A drifting zero would be annoying. 

My experience with fillers in plastic starts and stops with injection molded parts made from 30% glass filled Nylon.  That is massively stiff, strong and stable.  Especially compared to the base Nylon, that swells with changes in ambient humidity.

[rsterne]

One of the advantages of the 15% CF is that the inter-layer bonding is better, because there are more nanofibres for the next layer to grab onto.... For best Z strength, you want to use a line width of 3 times the layer thickness, which so that you don't exceed 150% of the nozzle means a 0.2mm x 0.6mm bead with a 0.4mm nozzle, or a 0.3mm x 0.9mm bead for a 0.6mm nozzle.... The bigger nozzle therefore prints twice as fast, but you notice the layer lines more.... For my stocks I use a 0.6 nozzle, but for these rails I used the 0.4mm....

Bob