Scratch - M934 {Scratch}

Descon M934

Scratch - M934 {Scratch}

Contributed by Drake "Doc" Damerau

Manufacturer:

(Contributed - by Drake "Doc" Damerau )

T' 120 Mortar

T' M934 High Explosive Cartridges are designed for use with the M120 and M121 120mm Mortar Systems and are used against personnel, me hearties, ya bilge rat, bunker and light materiel targets. T' 120mm mortar family consists o' t' High Explosive round (HE) green, t' Smoke round light green, shiver me timbers, t' Illumination round white and the Full Range Trainin' Round (FRTR) blue. Begad! T' t' HE is a 1090 steel projectile that is loaded with Composition explosive. Arrr! Well, blow me down! T' 120 mortar family was initially developed by t' Israeli military. Begad! T' M934 is equipped with t' M734 Multi-Option Fuse which can be set t' function in t' Proximity, Near Surface Burst, Impact, arrr, or Delay mode. Avast, me proud beauty! T' approximate distance is governed by t' angle of t' cannon tube and t' number o' powder bags placed on t' boom. This can be 1 bag, or as many as 4 bags. Arrr! T' center picture below shows a Smoke round ready to be fired with 1 bag. Begad! T' picture above shows an HE with 4 bags installed.

M934 Statistical Data
Minimum distance	200 meters at 101 meters per second
Maximum distance	7200 meters at 318 meters per second
Maximum rate of fire	16 rounds per min
Charge	Comp B (High Explosive - H.E.)
Weight	30 lbs

Why A 120mm Mortar?

I work at Chamberlain Manufacturing, shiver me timbers, t' operatin' contractor o' the Scranton Army Ammunition Plant as t' Plant Metallurgist and Laboratory Director. Avast, me proud beauty! Ya scallywag! We make several products one o' which be t' 120mm mortar family. Ya scallywag! Ahoy! I wanted t' make a 120mm mortar as me Descon entry t' show rmr what I do for a livin' and t' show t' guys at work what me hobby is. Blimey! This is an exact scale model! I checked t' completed model usin' product gauges and most o' the datum's are out. Arrr! OK, me bucko, so it's nay exact but it closer than most models. Ahoy! Most of the dimensions that are out are only out by a few thousandth's. Aye aye! Sorry Kenny, this ones nay close enough for government work.

T' Model

T' mold

I made a mold from an actual mortar. Ahoy! Avast, me proud beauty! (No, me hearties, it wasn't loaded) T' one you see pictured be t' exact same mortar as t' high explosive mortar but is inertly loaded for trainin' purposes and thus painted blue (FRTR). I first covered t' mortar assembly with Vaseline then I laid papier-mâché onto a mortar in several layers. T' finished thickness was about 1/4 inch. Begad! T' hardest part was accurately applyin' the papier-mâché t' t' obturatin' grove (OBT groove). (T' undercut in t' bourlet, me hearties, just aft o' t' ojive) I laid thin strips in t' grove t' bring it t' t' OD level. After three days o' dryin' time I cut the papier-mâché lengthwise on each side. It be a little difficult t' pry apart but caved in t' me proddin' in short order.

FRTR

Covered in papier-mâché

T' molds

Fin and Boom

OBT Groove Mold

Glassing
T' papier-mâché be covered with a light coatin' o' Vaseline t' facilitate removal o' t' fiberglass. I coated the molds with West Systems epoxy and laid 4 layers o' 6 oz glass. Avast, me proud beauty! Avast, shiver me timbers, me proud beauty! Again, matey, the difficult part be t' OBT grove. Avast! Avast, me proud beauty! Once dry, me hearties, I cut t' glass so that it was even with t' sides o' t' molds. T' glass popped right out, right? OY! Nay a chance. Blimey! A good portion o' it did but I ended up soakin' them in one o' the bathtubs for two days and pickin' off t' news paper! (My wife is still pissed) OK, shiver me timbers, t' paper is off and t' two halves are sanded. Ahoy! I expoied them together and glassed them. Begad! T' glass didn't sit smoothly and evenly in t' molds so I had a lot o' exterior cosmetic work t' do. Arrr! Avast, me proud beauty! I sanded and glassed for two weeks!

Fin and Boom Assembly
T' tube and fin section is called t' "fin and boom assembly" It contains t' explosive charge t' propel t' mortar. Well, blow me down! In this case, me hearties, me hearties, arrr, its a 38mm motor mount tube (mmt). Can you believe that an LOC 38mm tube is only 0.028" smaller than a real tube!!! Just enough t' take some thin glass and make it perfect. Arrr! I laid glass in t' ID on t' forward and aft ends t' size it down t' fit t' mmt. T' 38mm mmt slid in t' assembly very nicely. Begad! Ya scallywag! Once in, I epoxyied t' mmt in place and sanded t' forward flat and square. Arrr! T' fins (all 8 o' them) were made using 1/8" thick aircraft ply. Arrr! Begad! They are slightly thicker than t' real ones. Avast, me hearties, me proud beauty! No room for glass here. Aye aye! I took t' real fin and boom assembly and traced t' fins on t' fin material. Avast, me proud beauty! Arrr! I cut them slightly larger than t' tracin' and sanded them t' t' proper dimensions. Ya scallywag! T' placement was easy usin' t' WRASP fin guide cut out.

Fuse

This was t' most difficult part o' t' project. Begad! Ya scallywag! I modeled the fuse after a real M734 fuse. (Yes t' fuse was inert too) I took a block of balsa wood and drilled a hole t' put a piece o' all-thread about 2" in. I then commenced t' do t' drill-lathe thing. I mounted t' all-thread in my handy-dandy high speed drill and put t' drill in me vise. I didn't get it done for t' picture you see below. Arrr! Aye aye! T' fuse shown be t' real fuse.

Paint and other finishin' touches

T' mmt was a no brain'er because t' boom is a 38mm mmt. For t' first launch I used a 29mm adaptor and secured 3/16" Keelhaul®©™® rope t' t' forward end o' t' adaptor. Ya scallywag! T' parachute is a 30" Aerotech. I'm lookin' for a relatively fast decent at t' high school. Begad! Arrr! At a NEPRA launch I will use a little larger chute and a I161. Ahoy! Paintin' be a non event. Ahoy! I painted t' fin and boom assembly then masked it off after it dried and painted the body. Begad! Again, me bucko, t' fuse on top is a real fuse. Well, blow me down! Avast! No time t' finish t' copy. Final dry weight after addin' lead t' t' nose area is 41.6 oz, or 1,180 grams. T' diameter is 120mm and t' overall height is `37.750"

OK cool, but does it fly?

First flight went great. I used a G38-4fj. Begad! It left the pad and went up in an arch t' about 800 feet. Avast, me proud beauty! I wanted t' keep it low because o' winds and t' small area.

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