Light weight AR rimfire build

[55fairlane]

So my latest project is a new AR rimfire build, I am a competitive rifle shooter, and I want a CMP national rimfire sporter championship. Last year was my best showing 9th out of the 179 people in my division (16th overall out of 709 people). My current rifle JUST makes weigh,  we are limited to 7½ pound with magazine,  and the gun is a little front heavy, so I cannot add weigh to the rear for counter balance.
So I went looking for a light weight barrel,  and I found one 1½ pounds cost.....$350 ouch!! As I pondered my options,  I said, I have a match chamber reamer,  plenty of barrel blanks and I am a machinist,  let's make a barrel.
But first I need an upper, a bolt and a handgaurd.....found a set new unused (with a bull barrel)  for about half cost. Off to a great start.
Apon receiving the parts I found the barrel nut was steal and weighed over 3 pounds. Ok to heavy over weight all ready, so step 1 was make a new barrel nut out of aluminum and have it hard anodized.

[55fairlane]

Ok barrel nut done, let's move on to the barrel.
I determined that a 9/16 diameter,  17 inch barrel should tip the scales at 1.2 pounds....perfect!
I found an old Remington 510 score master barrel. On went the 4 jaw, on went the offsides "spider! In went the barrel and using a gauge pin inserted in the chamber I dailed the barrel in (on both ends) , cut the chamber off, turn the trunion for the bolt carrier group (there is a co..ar on the CMMG pattern bolt)  turn the barrel a few Inches to 9/16 dia and chamber.
Chamber is a bentz type and the floating chamber reamer holder I made

[55fairlane]

Now you may have noticed there is "trunion "for the nut to hold the barrel in to upper.....I made that out of aluminum and glued it on with 648 Loctite.  648 has a 15k psi shear strength the aluminum has like 8500 psi shear strength......this glue will hold.
Loctite advised me .002 clearance,  60(ish) surface finish, full cure 20 hours.

I'm ready to shoot for groups

[Jo]

I find the techniques for building all sorts of firearms fascinating and they inspire us for techniques that may help build our own engines.


It should be noted that: In many countries it is illegal to make or convert a "de-activated" firearm and if you do will find yourself having a long holiday at your government's pleasure if you are not appropriately licensed (in the UK this would be to be a Registered Firearms Dealer).

If you try making one and get it wrong, i.e. use the wrong material for a barrel, you are more likely to kill or maim yourself than any target you may be shooting at 

Jo

[simplyloco]

It's a sad fact of life that our modern systems of Limits and Fits was invented solely to benefit the weapons industry by ensuring the interchangeability of parts and ammunition...

[Jo]

It's a sad fact of life that our modern systems of Limits and Fits was invented solely to benefit the weapons industry by ensuring the interchangeability of parts and ammunition...

I assume you refer to Egypt's development of interchangeability for their bows around 3000BC to enable arrows to be used on more than one bow

Jo

[petertha]

Sorry for diversion, but can you tell me about what I suspect is floating reamer holder? I understand they are very important for reaming straight holes. I've been meaning to make one myself, but I have no way to gauge if one design is better than another. The commercial ones cost a fair dollar AFAIK. I figure if its good for precision holes that go Boom, it surely belongs in my engine building tool arsenal haha. Did you make it from plans?

[55fairlane]

Sorry for diversion, but can you tell me about what I suspect is floating reamer holder? I understand they are very important for reaming straight holes. I've been meaning to make one myself, but I have no way to gauge if one design is better than another. The commercial ones cost a fair dollar AFAIK. I figure if its good for precision holes that go Boom, it surely belongs in my engine building tool arsenal haha. Did you make it from plans?

That is a floating chamber reamer holder,  in the machine shop I work in we have similar tools for reamer, use on very picky tolerance holes.
Chamber reamer holder and plans will be in the August/ September issue of machinist workshop,  in fact I made to cover and I am the featured article.

I designed this one based on one a friend has, he made when he worked at Sinclair gunsmithing (yes the same one Brownell owns)

These will allow for both radial & axial misalignment,  especially when used with a piloted tool...

Shoot me an email or PM and your phone number if your in the USA and help ya out

Aaron