Modernized M72 Build - coming along nicely

[r.erichsen]

Another nearly complete build awaiting some finishing touches.

I have some welds to finish on this one (the slot for the sling loop won't be used, the spot welds on the front and rear trunnion) but this one gets the fancy Black T coating from Birdsong when it's done.

ModernizedM72-4.jpgModernizedM72-Receiver-3.jpgModernizedM72-M70B2Companion-2.jpgModernizedM72-1.jpgModernizedM72-5.jpg

Regular flavor RPKs don't have the style of the Yugo M72 - the barrel is heavier and a few inches shorter (21.5" vs. 24") and those cooling fins are reminiscent of the stylish Thompson SMG. I decided not to add the bipod lug and there is no provision for an old-fashioned cleaning rod. I'm building a semi-traditional M72 free of "cheese grater" attachment rails that will have all of those traditional features present.

A brief list of components include:

* DEZ adjustable gas block, milled out for the larger M72 barrel
* KNS dual crosshair front sight
* Solar Tactical muzzle brake (hardly needed given the weight)
* Texas Weapon Systems Dog Leg 2 picatinny rail top cover
* Midwest Industries Forearm MI-AK-Y quad rail system, designed for the M70, milled out for the larger barrel diameter of the M72 barrel
* Tromix skeleton stock, ACE Yugo stock trunnion adapter
* Red Star Arms adjustable 2 stage trigger
* Solar Tactical grip strap for compliance (yes, a Cali thing)
* Wolf extra power recoil/action spring
* Power custom hammer spring

Yet to be done:
* Drilling rear sling swivel
* Picking a low profile adjustable rear aperture sight base, so far all of them are too tall
* Attaching the low profile Leupold QD throw rings and fitting an optic
* Fitting the Cadiz Gunworks LRBHO lever and catch
* Attaching the Snipershide left-side selector switch
* Media blasting and sending to Birdsong for Black T coatings inside and out

R

[M1 Tanker]

Looking good. How is the weight and balance on it now?

[r.erichsen]

Looking good. How is the weight and balance on it now?

Thanks M1 Tanker. It's about 11 lbs without a magazine in it. The Midwest rails aren't as heavy as some because of the short length and the amount of metal removed to make that fat barrel fit. The DPH buttstock (billet aluminum) was a bit heavier and I may still use it - the Tromix, even though it looks aluminum it's actually some type of Zytel polymer (which I didn't know when I bought it). There is a bit of excess on the left side where it meets the trunnion that I'll need to grind off to make it symmetrical. The buttpad is a 1.5" thick Limbsaver that is overkill for recoil on a 7.62x39 mm weapon weighing close to 13 lbs loaded - it's too heavy to recoil, but the extra thick pad addressed a LOP issue for me since I'm tall and the shorter stocks aren't comfortable for me.

The balance point is just in front of the magazine well, one finger under the back of the handguard where it teeter-toters at the fulcrum. I was surprised how well that worked out, since it's not much different from the traditional M72 build (just a bit more barrel heavy on this build). After I attach the rear swivel I'll loop my 1.25" Andy's Leather "Guerrilla Sniper" sling through the new rear loop and attach the two front points on the handguard I expect everything balance to remain good from shoulder to ready. The sling is pretty cool, I'm using the shorter "Ching Sling" on the M70 builds - these are 3-point slings that create a loop for your forearm to go through for a supported off-hand hold. Mostly I wanted this to free me up to firing positions other than supported on the bench (which gets boring fast).

R

[Planning]

YEP! It is looking very good.
ron

[holescreek]

I love the look of the RPK barrel fins I used one on my x39 build. I wish I had an other excuse to get another one.

[DaCapster]

Anyone have to cut the barrel for the ejector? IS it hard to do nice?

[r.erichsen]

I love the look of the RPK barrel fins I used one on my x39 build. I wish I had an other excuse to get another one.

Rechamber it in some other caliber and put it in another CETME build - that'll do it.

I wish more barrels were ribbed like these - but an hour on a lathe could fix that.

Ever consider doing a smaller bore .243 Win or a bigger .358 Win CETME build? With the right brass and an appropriate locking piece - a caliber change within the .308 Win case based family could be interesting. A barrel blank could be cut to size and "ribbed" to suit - sounds fun huh?

R

[r.erichsen]

Anyone have to cut the barrel for the ejector? IS it hard to do nice?

Roccobro did mine, but its pretty regularly done by hand and eye with a dremel tool, prussian blue, a printout of the template and some abrasive wheels (obviously, plug the chamber so you don't have abrasives and metal shavings going down the barrels gullet!). This rifle's barrel is US made and "virgin" (Centerfire Systems if I recall, Green Mountain is the likely manufacturer), which is preferred since you can address any minor variations in pin location, do a proper gas port job and in my case no need for the handguard retainer notch since my handguards don't need one. The barrel has the typical 9.5:1" twist with a conical 13 degree crown, not chrome lined (Yugo barrels aren't). Like most of these barrels, it came as you see it, in-the-white. My other M72 is a Yugo original NOS barrel that had it's original finish and and was packed with a light coat of cosmo that hadn't turned into wax yet. Dimensionally the two M72 barrels were within .002" of each other on two of the journals, non-issue in my case since I'm only using the original front sight base.

Both of my M72 barrels will be headed for MMI Trutec to receive Isonite QPQ treatment in the next batch we do over at Calguns in a month or two. Given the hardness achieved, all barrel population chores need to be done prior to nitrocarburizing or you'll wear your tools out trying to cut through the case hardening. We've got the technique down so that pressing out the barrel results in minimal galling. A well deburred trunnion with properly reamed barrel pin hole and lots of grease seems to do the trick. This will be the 3rd sequence of pressing the barrel in/out on this rifle and the barrel shank appears undamaged. The first time was to headspace and populate it, when it came out I deburred the remaining edges on the cross-pin hole. The second time was to push out the barrel to rivet in the trunnion. This third time will be to get the barrel out for nitrocarburizing treatment and then back in again. The barrel pin hole is where most of the "tearing" you see on used barrels comes from.

R

[r.erichsen]

YEP! It is looking very good.
ron

Thanks Ron.

[r.erichsen]

UPDATE:

I drilled the stock sling swivel on the rear of the tromix and locktited the threads, pilot holed the selector switch hole on the left side to 1/4" (no going back now) and have found a rear aperture sight with adjustments that meets my needs (the NECG weaver base adjustable for elevation/windage with screw-in apertures). I have all but one weld left to do and have a finished bolt carrier media blasted it to a uniform gray. There is a 30x15 mm knurled drill rod for a charging handle which was TIG welded on after cutting off the curved finger groove handle. A single weld was forgotten (the slot on the left side for the sling swivel normally attached here) which I'll get to sometime next week.

Next on the list is drilling for the left side selector/safety switch and joining the selector switch stems together, then cutting the slot in the extractor within the bolt head for the Cadiz LR-BHO trip lever and fitting the catch. At that point it's off to Birdsong for the Black T anti-rust/dry lube metal treatment, I should get it back by end of year assuming I get my other tasks done by end of this month.

UPDATED 11/22: Well that did it, I cracked the lower truss of the stock drilling and tapping for my sling swivel. I didn't notice until I was screwing in the threaded portion of the swivel. I think I learned my lesson regarding polymer stocks. The DPH that has a similar appearance but solid aluminum construction is going on as soon as I cut my 1.5" thick Limbsaver buttpad off the Tromix to get the desired LOP on the DPH. For what the thing cost, it should have been aluminum, buyer beware.

My jumbo charging handle has a bit of an issue - I need to relieve a radius on the top of the handle for the top cover, it's smacking into the lower edge of the cover. Time to break out the dremel and remove a slot of 1/8" depth by 1/8" width, chamfered at both ends. A small price to pay for my wicked looking charging handle.

R