Licensed Production of a Krytac Origin 12 Airsoft

Fridley Dolow1936 · Tuesday, March 1, 2022

Licensed Production of a Krytac Origin 12 Airsoft

Phase iv: Ability source conversion

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The gas port: in stock form (Fifty) and after removing the taper, drilling, and tapping with 1/4-28 thread (R).

I play yr-round, so my equipment has to suffer everything the eastward coast of the Us can throw at information technology. That includes temperatures ranging from 20 to 105 F (-7 to 41 C). Additionally, I needed a lot of propellant readily available due to the loftier attendance at my abode field. Much as I hated to admit it, HPA was the simply way to make this shotgun feasible for my purposes.

How does i go nigh converting the TM M870 to HPA? The most pop method I've seen involves running a HPA line through the fixed stock, as illustrated in eagle258's guide:

https://world wide web.airsoftsociety.com/threads/the-real-and-dirty-on-the-tokyo-marui-m870-gas-shotgun-hpa-tm-m870.120317/

While uncomplicated and cheap, this method won't piece of work very well when adapted to non-TM M870 stocks. Function of my project involved modifying a real stock to fit the gun, so the easy option was out the window.

I devised a dissimilar way to HPA tap the gun, i that doesn't rely on a gas-tight seal between the stock and mechanical box. I drilled and tapped the gas port at the rear of the mechanical box, and then screwed an Amped Airsoft Integrated Grip Line (IGL) directly into information technology. In this way, I am free to modify whatever stock without concern for refitting whatever parts of the original gas arrangement upstream of the mechanical box.

Mechanical box gas port dimensions: all approximate dimensions are +/- 0.01 in

Stock configuration: outside of gas port is tapered, so ii OD and wall thickness values are provided.

Inner bore: 0.181 in

Outer diameter: 0.307 in

Outer bore (at taper): 0.27 in approximate

Gas port wall thickness: 0.063 in

Gas port wall thickness (at taper): 0.045 in approximate

Depth of gas port available to thread: 0.39 in approximate

The gas port dimensions listed above were what drove my selection of IGL. All Amped IGLs are 10 inches long and utilize i of the following 3 thread patterns:

¼-28-2A thread: used on the Jack ane.1, F1, and F2 IGL. ¼-28-2A thread characteristics are 0.2490 in max major bore and 0.2110 in min minor bore.

M8x0.75 thread: used on the Fusion Engine IGL. M8x0.75 thread characteristics are 0.3150 in/eight.00 mm major bore and 0.2787 in/vii.08 mm minor bore

⅛" NPT thread: used on the M249 Fusion Engine IGL. 1/8" NPT thread characteristics are 0.403-0.405 in major bore and 0.39 in pocket-size diameter (approximate values, since threads are tapered).

¼-28-2A thread was the merely option whose major diameter didn't exceed the outer diameter of the gas port and small diameter was greater than the inner bore of the gas port. As such, I bought a Jack ane.ane/F1/F2 IGL, a ¼-28 drill and tap set, and a tap wrench to modify the gas port.

If you decide to alter your shotgun in this manner, at that place are a few things you lot should know:

This is a relatively risky modification. Use a drill press, if at all possible. If non, at least use a vice to secure the gas port block. If your drill or tap go off-centrality, you lot tin can irreparably harm the gas port block. The only mode to fix a damaged gas port block is to replace the whole back end of the expansion chamber assembly.
I'm reiterating the above indicate because it's of import. It's far also piece of cake to misalign either the bit or the tap when doing this modification by manus, unassisted. At a minimum, secure the gas port cake in a vice.
Disassembling the expansion chamber is advised, as is plugging the internal macro line (between the gas port block and expansion chamber) with tape or something like. I recommend having some compressed air on mitt to accident out the metal shavings when finished.
Measure twice, cut in one case. Figure out how deep you lot can drill before bottoming out in the gas port. I recommend clearly marking the maximum condom depth for your drill bit and tap. This will let you know when you're in danger of drilling completely through the gas port block, which would be bad. Wrapping tape around the fleck at the appropriate distance will work, but I recommend a sharpie or pigment pen since they won't slide effectually on the fleck. Be meticulous, mistakes can cost you lot.
If attempting this method, you lot should grind off the tapered portion of the gas port (facing the stock stop of the gun). Afterwards threading, the minimum wall thickness in this area would be less than 1/64 in. This is a 76% reduction in wall thickness, which will likely to pb to structural integrity issues (i.e. not bad or snapping off function of the gas port). Removing the tapered portion of the gas port nevertheless allows you to utilize the original stock and gas system, meaning you tin can go along your gun pressurized with the stock parts when not in use.
Tapping the drilled gas port by paw took much more force than I expected. Make sure the handles on your tap wrench are long enough to exert a lot of force when threading the port.

Post-modification:

Inner bore (min) = small thread bore = 0.2110 in

Inner diameter (max) = major thread diameter = 0.2490 in

Outer diameter is same as above; outer diameter (at taper) is no longer applicable due to removal of taper

Gas port wall thickness (min) = [outer diameter - inner diameter (max)] / 2 = 0.029 in (54% reduction in thickness from stock configuration)

Gas port wall thickness (max) = [outer diameter - inner diameter (min)] / 2 = 0.048 in (24% reduction in thickness from stock configuration)

Depth of thread within gas port (after removal of taper) = 0.35 in judge

Thread length on Amped Airsoft Jack ane.i/F1/F2 IGL: 0.xix in approximate (less than 0.35 in, so the IGL tin completely screw into the modified gas port)

Now that I had information technology hooked up to external air, I needed to figure out what output pressure was safe to utilise without blowing upwards the gun. There'due south a warning that comes in the box, stating that the gun shouldn't be used in temperatures warmer than 40 C. It'southward off-white to assume that the pressure of the propellant gas becomes besides high at this point, which causes damage. How can I utilise that information to HPA?

Simple, actually. Figure out the guess pressure of HFC134a (the only gas approved by TM) at 40 C and you've got your upper limit for pressure. This came out to exist almost 133 psi gauge (psig).[xiii] As such, I determined my maximum allowable pressure at the regulator would be 120 psi in order to maintain a small (9.8%) factor of safety.

I followed Ballahack chrono SOP to adjust my output pressure. Per their procedure, all gas/HPA weapons and sniper rifles are chronoed with 0.40g bbs. I tweaked the regulator until I achieved my desired muzzle velocity. The results are as follows:

For reference - HPA @ 72 psi, 0.20g bbs in iii-shot mode, xx shots:

Field limit: 400 fps/one.49 J

Boilerplate: 363.vi fps/1.228 J

Muzzle velocity standard deviation: 9.8 fps

HPA @ 72 psi, 0.40g bbs in 3-shot manner, twenty shots:

Field limit: 283 fps/i.49 J

Average: 267.2 fps/ane.326 J

Muzzle velocity standard difference: x.four fps

Joule creep: approximately 8.0% more energy with 0.40g than 0.20g using HPA @ 72 psi

HPA @ 72 psi, 0.36g bbs in 3-shot mode, xv shots:

Field limit: 298 fps/1.49 J

Boilerplate: 284.1 fps/1.350 J

Cage velocity standard difference: 11.five fps

Joule pitter-patter: approximately nine.nine% more energy with 0.36g than 0.20g using HPA @ 72 psi

Ammo pick and range: using WiiTech hopup unit, TM hopup rubbers shimmed in accordance with my notes in Stage three, WiiTech extended inner barrels, and all upgrade parts listed in Phase 2.

3-shot mode, HPA @ 72 psi: 0.40g bbs work best, approximate range 200 ft

half-dozen-shot mode, HPA @ 72 psi: 0.36g bbs work all-time, approximate range 180 ft

I was besides interested in the number of shots I could get out of my HPA tank setups. I found an equation[fourteen] that should provide a ballpark figure:

N = (V * P_t) / P_r

where

N = number of shots

Five = volume of tank (or tanks, if more than than one), in cubic inches (ci)

P_t = pressure inside tank(s), in psi

P_r = output pressure of regulator, in psi

Plugging in the values for my First Strike Hero 2 48 ci 4500 psi tank yields:

N = (5 * P_t) / P_r = [ (48 ci) * (4500 psi) ] / (72 psi) = approximately 3000 shots in 3-shot manner per 48/4500 tank, equivalent to 300 shells

Similarly, substituting the values for my dual tank rig using two Commencement Strike Guerilla xiii ci 3000 psi tanks gives me:

N = (V * P_t) / P_r = [ (13*two ci) * (3000 psi) ] / (72 psi) = approximately 1083 shots in iii-shot mode with dual thirteen/3000 tanks, equivalent to 108 shells

This increased shot chapters is a massive improvement over the 100 shots/10 shells[15] available from the stock gas tank. A bit overkill, admittedly, just I'd rather have besides much propellant on hand than too fiddling.