Friday, June 28, 2013

M261 dedicated .22 LR upper build Prototype part 2

 Now that we have the barrel turned to the correct specs we need to focus on the "barrel extension" part of the build and mill it so it will work in combination with the M261 bolt conversion. We will need to make four cuts (5 if you are using a blank barrel) the first cut will be at the top dead center, this is made to clear the charging handle as the extension goes further into the receiver. The second cut is made on the bottom to clear the magazine you just need to cut away enough to offer proper clearance. The next two cuts are made using a woodruff cutter. Luckily I had the two sizes I needed already on hand so for once I didn't need to buy tooling for a project! The right side of the extension gets a 1/8" slot milled for the extractor and the same for the left side for the wire that helps retain the case (this cut may need hand finished with a round file so the wire does its job). The left side is then cut again for the bolt guide rod. You must measure this cut correctly or the bolt will not seat in and cant possibly causing undue stress and twisting on the whole unit.  I will get more detailed pictures up of each cut. This was the prototype so its not really pretty.

Top has been milled off, slot for extractor is milled (note new garage walls being put up)

View of extractor slot, over sized a little but it will work.

Left guide rod slot being milled

Wednesday, June 26, 2013

M261 dedicated .22 LR upper build Prototype 1

The M261 .22 LR conversion is great for what it was designed for....general familiarization of the weapon platform with accuracy taking a backseat to trigger time and dynamics. With this in mind more and more "designated uppers" as they are called in .22 LR have been manufactured. Some of these are costly and take proprietary parts which may be hard to obtain from time to time. My idea here is to make my own dedicated upper in .22 LR using the M261conversion bolt as a host bolt and a "demilled" A1 upper receiver.  I acquired a pair of these A1 upper receivers cheap and needed to put them to use . I wont say my idea here is original, however I have not seen an example in person and I'm pretty sure this has been done using the M261 bolt before.  I'm starting with a Marlin 60 take off barrel I happen to have a few of in the old parts box. The idea is to use M16A1 upper parts to build a trainer rifle that is more accurate than just the barrel conversion used in the M261.

Since barrel length is not so much of an issue with .22 LR we will go with a 16.25" barrel. I've kind of always liked the looks of the dissipator AR-15 sight radius and shorter barrel length but have never felt the need to have one in .223/5.56 I thought the design could be applied to my project here.

Below is mostly pictures of my yet to be tested prototype. I need to spend another hour or two on it and it will be up and running. I put this all together in about a day...most of that time spent hunting for tools and putting the shop back together as we just had a new garage floor poured.

Shortened barrel with muzzle end turned to fit M16A1 triangle end cap and Front sight.
Bushing needs fitted, final length determined and threaded. 

 Above and below we see the start of what is to be the modifications needed to morph the old Model 60 barrel into what we need it to be for our project.

Barrel being turned to fit M16A1 front sight and end cap

 We started with 1 1/4" mild steel round stock for the barrel bushing (pictured below) Since the shank on the barrel was close to 5/8's I chose to drill the center of the bushing to 5/8's and then fit the dedicated barrel closely to that.

Roughed out barrel bushing ready for final fitting.

Final turning of the bushing collar.

Above we see the bushing being shortened up a little, Here is where my prototype took a wrong turn but more on that further down.

Test fit

Ready for a barrel

Barrel bushing fit is very important as it must be tight since this is where the accuracy comes from. Note on above picture the upper receiver is missing the area under the ejection port, this was bashed in to "demil" the receiver, why? I'm not sure. I have it on good authority you can not bend and weld 7075 alum so I removed this lower section, it should not greatly hinder anything with this particular build.

Barrel press fitted into the bushing, for future designs this should be pinned into place.

Note barrel bushing stick out into upper rec.

The place where this prototype took a wrong turn was in the distance the bushing goes into the upper receiver. I measured wrong somewhere and made the bushing nearly 1/4" too short, what happens is the bolt goes too far forward and binds on the magazines. This will be a easy fix 

Upper mocked up to take a look at the progress. The "Ohio" hand-guards were the only spare ones I had around, they were left over from team shoots.

Threaded for 1/2x28 

Now politicians can worry.......its the dreaded bird cage. 

The flash hider and threaded barrel are really not needed for this particular build but I chose to thread it and put one on as it makes the build look more complete and is a nice finishing touch. The fact that this is a trainer upper also pushed me to put one on as when I'm working with trainee's this will be closer to what they may find "off the shelf" also it protects the muzzle which tends to find its way into the floor from time to time if shooting prone.

Mocked up again with the flash hider installed. Rubber bands make a dandy quick delta ring.

So from here we will need to mill the barrel bushing to accept the M261 bolt, drill and pin the front sight base in. The fix for my mistake can be done one of two ways, either make a whole new bushing which wont be hard or further modify the barrel to extend a little farther into the receiver. either way I will have to pin the front sight base a little farther forward than initially intended as the distance between the delta ring and the end cap would be too short. I plan on making a few more of these uppers once I get all the kinks worked out. Recycling has never been so cool......

Tuesday, June 18, 2013

SKS gas valves

Parts get corroded and wear out, especially if those parts are on firearms fired with corrosive ammunition from countries where cleaning may not have been top priority. I have a Yugoslavian SKS that has severe gas leakage and causes the rifle to short stroke the bolt carrier sometimes. Now I have heard that Yugoslavian ammo tends to be a bit hotter than the Russian Tula and Wolf imported ammo but I have not shot any in my rifle so I do not know if that is necessarily true or not. I have only shot Wolf/Tula through my gun which short cycles from time to time.

If you have a SKS that is short cycling one easy way to see if you need a new gas valve is to slip a O-Ring over the gas valve and re-install it into the rifle and shoot a few rounds and see if it cycles more reliably, the O-ring will not last long as it will "blow out" or be forced out of the excess space between the gas valve and the gas tube. I used this quick test on a few SKS's before deciding to machine my own gas valves out of 5/8's Stainless.  I may choose to do other gas valves out of carbon steel in the future as the stainless is a little harder to machine as it is "gummy", that is a technical term....NOTE: I had planned to do a part 2 to my gas valve experiments however I figured it was better to just let the SKS's I had go down the road, even with the gas valves I machined and increased reliability, I realized I wasn't happy with the accuracy of the rifles and sent them on their way. Life is too short for headaches such as this.

What the O-Ring looks like after a few rounds.

Blown out O-Ring for testing purposes.