Barrel and upper prep

[budlight]

It's the little things that all add up!

Just some best practises for anyone doing their own AR build. I'm Pro forged upper and lowers. I only use 20 inch SS barrels of 8 or 9 twist because a 223 is limited to really 75 grains. The 223 case has a short neck and not enough powder to drive anything heavier at acceptable velocities. Many years ago I bought gross bulk 62 gr HPBT very high BC bullets. You can't get them anymore. But they achieved dime size 200 yard groups. I'm very pro rifle length or even +2 inch piston or gas guns.

My friend bought an upper truing device from Midway which he loaned to me. Uppers might look nice out of the box, but sadly the barrel faces have always been off probabably because of the black coatings.

This is an upper after truing!

The next step I do is hand polishing the barrel inside with a bore snake and chrome wheel polish. I then polish the feed ramps. You don't want to scrap the copper on the beautiful bullets that you painstakenly loaded to perfection from days on the range and chrono work.

NO sharp edges anywhere not even the chamber.

One of my light weight 20 inch piston guns with a titanium brake and slick sided upper. Blue tape over my serial number. 3 pound trigger. This is a prairrie dog machine. 8X32 60 mm objective. Ambidextrous safety and long pull down ring pins

 

[gohring3006]

Yep! I've been truing faces for a few years now. I also do a tubbs final finish in mine to get a head start on smoothing out the gas port. I also shim and lockitite my barrels into the uppers if they are not thermal interference fit.

 

[Darryle]

I quit all of that and started using BCM uppers that have to be thermal fit.

Barrel in the freezer for 24hrs or more, heat the receiver up, apply a very thin film of high temp grease to the receiver bore and work fast getting the two together. I had a couple thread protectors made from a 1" diameter piece of pipe, one for 1/2-28 and one for 5/8-24 in case I need to seat the barrel extension with a whack.

I was a 620 guy for years, not anymore. Thermal fit and in some cases, custom fitted oversized barrel extensions.

The thing with the receiver face lap, you are using lapping compound, how much wear is happening to the lapping bar. I know that I took mine to work and had it CMMd on the face it had evidence of wear.

YMMV

 

[rpol98]

 

[Darryle]

I am just not convinced that lapping the face is squaring the face to the bore or adding meaningful benefit. This is where my thinking has evolved, I honestly do not think you can change the relationship of the 1" of BE length combined with the 1" length of receiver bore enough with the face of the receiver, barrel nut and torque, lapped or not on an interference thermal fit.

Now that it is routine to see prefit barrels for most all production 700 clones, I think this machine capability has migrated into the gas gun world and will only improve as we move forward.

The thread over on SH you posted in originally and several other previous threads over there changed my way of thinking about receiver/barrel extension fit. It also changed my entire upper assembly process. Joe's video was eye opening about their original receiver builds and barrel movement and POI shifts.

If you want brain ache and information overload, there are a few posts in this thread that will give you zombie spinny eyes.

Is bedding an AR barrel a myth

I haven't read every single response in that thread, so I will preface this, it may contain salty language and not be safe for viewing at work or with kids looking over your shoulder.

 

[budlight]

As velocity goes up though the use of longer barrel and modern powders the need for 7 twist dimishes. Up to 16 inch it's okay. I had a friend building Ar's. Those delta ring M-16 look a likes and he convinced me that I needed one. 20 inch 7 twist that keyholed every bullet less than 69 grains even with reduced powder loading.

When you could buy bulk 55 -62 grains for 7 cents a piece I was having to shoot 69-75 gr at 4-5 times the cost. The whole phoney Delta ring and fixed front site was not for me so I gave it away and went to the M-lok style front arm guards and the big barrel nut. I also saw the value of actually buying match grade stainless steel barrels.

 

[wwbrown]

I just bought two of the BCM uppers and two different barrel extensions fit right in without heating the receiver. There is nothing wrong with the quality of the receivers and I can't find what cuased the blem on either one, they just are not thermal fit. For these builds I will just shim and 620 them as I have done in the past.

Here is the link for the actual receivers I purchased

 

[Darryle]

Same ones I have bought. Every one I have used has been thermal fit and tight at that.

Can you measure your barrel extensions?

 

[budlight]

I only use no forward assist or dust cover uppers. It saves weight and the crap falling apart out in the field.

AM-15 Anodized Sport Upper Receiver, No Forward Assist or Dust Cover

No Forward Assist or Dust Cover

andersonmanufacturing.com

 

[Darryle]

I only use no forward assist or dust cover uppers. It saves weight and the crap falling apart out in the field.

AM-15 Anodized Sport Upper Receiver, No Forward Assist or Dust Cover

No Forward Assist or Dust Cover

andersonmanufacturing.com

I use the delrin plug from Bore Buddy, simply because I have seen people force a round into the chamber and then have to get someone to show them how to mortar it out.

I do like a slick side upper though

 

[wwbrown]

...
Can you measure your barrel extensions?

If I get out to the shop I can measure it to 10ths, but rarely get out.

 

[ARlife4me]

I 10 ton press mine in, so it fixes all issues .