AR design contemplations

K

kduffy

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New to this forum, and this design of the rifle. I would like to pick some brains about the things that kept me away from the AR design for many years.

I posted this in the AR15 forum, but thought that the likelyhood of finding people knowledgeable about actually scratch building an AR rather than "assembling" one would be higher in a gunsmithing forum. Sorry to those of you that had to read it twice!

I have resisted until recently buying an AR (an LR-308 came up reasonable), I always figured to build one from scratch in my overly equipped home machine shop. My question to all those with many more years in the know: Is there any reason the buffer tube is on the lower? Do you really have to tear down and clean them that much more than a Garand or a bolt gun when used for general hunting and target shooting? Could an upper and lower be just as effective for these purposes built in the form of a stick with a lower that pins on below? It would in the bolt gun world be the equivalent of blueprinting, truly aligning the buffer tube with the receiver bore. Coming from the traditional muzzle loading, bolt gun, and falling block world, it seems that there could be some improvements that the bench rest folks have done, applied to the AR design.

Also being of old school and having several 30-06, 270, and 25-06 around would one not just as well stretch the action a little further and chamber for cartridges that I already have in the family. I am a bit stubborn and thought that the .223 was a nice cartridge in the Contender pistol, but not so much in a rifle, where I prefer the 22-250. For that matter, why is the 22-250 not a top pick in AR chamberings?

I did not find any answers to these questions after searching, I may have missed them though, and they may be questions put to bed years ago.

I have a bit of a rind, so let the flogging commence!
 
Good contemplations.

ARs were designed to be high use, and as such, the ability to drop out the BCG for cleaning and lubing is desirable. IF you wanted a low use, say less than 500 rounds a year and an annual cleaning, then moving the buffer tube assembly to the upper receiver would probably be fine. However, you would not gain any accuracy improvements. The accuracy is all about the fit and stability of the barrel to the receiver and having the sighting system rigidly attached to that stable system.

Where some accuracy gains were made in this area were the timing of barrel nuts and the monolithic uppers, but not a lot. Creating an interference fit between the upper and barrel extension while having enough torque to overcome thermal expansion differentials is the most fundamental place to improve the platform accuracy. When I did that with my barrels, I found I could cut group sizes in half.

People have stretched the actions, but there are two basic issues to overcome. First is magazines, or lack thereof, and the second is the gas system. Most 5.56 ARs are significantly overgassed, less so the M4s than past generations, but still a LOT. When we step up to the AR-10 style, they are even more overgassed. It takes some careful planing, which can be, and has been, done, to limit the gas system within the proper parameters for a cartridge. Pressure, gas volume and dwell are all interrelated. Open too soon, or too late, you have problems.

The 22-250 just burns barrels up too fast in a high use weapon system. Now that the general population is starting to use AR platform weapons more and more for hunting and low volume target shooting, we will see more cartridges and factory offerings and a wider appeal of cartridges. I can get match grade .223 barrels for under $300 and rack grade for $100. Can't touch a .22-250 barrel of any quality for less than about $500. The body taper and adjusting the gas system are also set-backs for the 22-250 in the AR platforms. A 22-243 or one of the WSSMs necked down to .22 would be an easier and more reliable choice for a 3500+ fps AR.

No flogging, just stuff to think about. The AR platform is very easy to work on and wildcat. Barrel extensions are usually the only thing you need to modify with actual machining to make a AR wildcat work. The rest is tuning the system to your load/use/preferences.
 
Thanks for the reply Mark, good considerations, I had read some of your posts and hoped you would chime in. I knew that I had a lot to learn, but the AR platform does seem to be the simplest unit that I have disassembled. Some of my old Stevens come close, but there are some timing difficulties to understand in a Visible Loader, at least when repairing broken lock works parts.

You are right, I am considering a low annual usage, 500 rds/yr would be optimistic even. I was thinking that the buffer would integrate with the BC to provide a longer straighter bearing area thus driving lockup to the best possible perpendicular bolt face.

I actually felt all AR's were ugly until I saw Doug Turnbull's TAR-10 and realized that they could look nice. In that thought, a 4140 upper would not have the differential expansion issue, and an interference fit would nicely stabilize the barrel extension. Good information there on the accuracy improvements!

I had considered the magazine issue, as I have even considered cutting 10 rd mags to a minimal extension below the mag well for my LR-308. I rarely need many shots in hunting, and bench rest target shooting would be fine with 5 or so rounds, so integrating the mag well as the magazine like an ADL 700 Remington would suffice for that work. Sounds as though for such a project that it must be piston driven or have an adjustable orifice for a DI system. A “long” barrel would further complicate the over gassing, would it not? The dwell would be dependent on BCG mass I assume, that would have to be adjusted, as would spring rates (sounds like a lot of trial and ERROR!).

I had not considered the case body taper of the 22-250 to be too extreme, but figured that it would have to be built on the .308 action, maybe even shortened to the AR-15 length. Receiver and BCG parts would be have to be specific and custom made in that case. I had seen the 22-243 and wondered why. That would be an explanation. You have to admit that 3500 fps is a nice figure for hunting!

Yeah, the tuning for preferences thing, I have already started setting up to cast lead .309 diameter bullets, for now I think I can keep myself away from trying Goex FFF..........maybe.

Thanks for the input. I guess I do have a winter coming and a machine shop, unfortunately, work will get in the way in a couple months, but it will provide some additional funding as a sole side benefit.
 
I better start with a plain Jane standard build. Dad had found a raw lower forging that someone else had bought then figured out they didn't have any way to machine them. It sounds like a good mill exercise for my boys. They have to learn on something, they have been watching on a few simple projects! A cheap lower forging would be useful and relatively easy. I have some good aluminum already, need to see if any is the right size, now that I found drawings.
 
Digging around in my piles of future fabrications, looking for material to make a set of Stevens: Side Plate Favorites for my boys and I. I ran across a couple pieces of AL plate, one an 1.280" thick x 6'' x 16" and one 1.75" thick x 3" x 16", hmm, wonder what I was thinking, from maybe 7 or so years ago. Seems to be 7000 series too, Aviation grade by the place I got it. I found most of the reamers and all the end mills needed in my stash. I have a piece of 1 1/4" diameter 4140, sure looks like it could be a 1 3/16-16 tap in a short time, I may have to buy a 1" reamer, and a long 3/32 drill, but pretty much all else was there. I didn't realize how much stuff I had around for a project like that already. I just finished wiring one of the last machines tonight (a vertical band saw yet to go), I had a rented shop sold out from under me 7 years ago, I moved my equipment to a shop for storage, and finally built my own, been pretty slow, but I am about ready to be in project mode.
 
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