I am turning a barrel from a pull off bench rifle. It is 21" long and I plan on a rifle length gas system. Will some one verify that the shoulder for the gas block is 12.120" from the back of the barrel extension? I have a drawing with that measurement and have not found any other drawings. Also this will be a 6mmBR and any advice or information you have will be appreciated.

I found some people talking about barrel specs with a person who gave the measurements he used when turning barrels. They were 12.120" to the gas block shoulder also. I cut mine to 12.125" to give a little room for getting the gas port in the center of a land. Had to settle on 0.875 dia. at the gas port which only leaves me with Superlative Arms in the way of an adjustable block. If anyone used one of their block, what do you think about it? There was only one review and all he said was 5 stars. Attached File

can't help on the gas port location, but I'm curious about the 6br. are you going to run this in a .308 pattern AR or ar15? I seem to remember a few on here were trying to scarf up the 30 Remington ar's and 450 bushmaster uppers when they were cheap with br and .284 variant wildcats in mind. it had the beefiest bolt/different extension and bcg if my memory serves me right. to my knowledge those kind of dried up?

found one of the topic's about the differences. https://www.ar15.com/forums/t_3_121/602745_.html&page=1

garred, Thanks for the input and the link. I will have to read that again. I have a 450 bushmaster bolt. I should get a barrel extension from BAT. I will only be able to shoot 40 gr bullets as the barrel is 1:15 twist. It is far the most part a lathe turning project, before I build its big brother 7-08.

Thanks again for the link. I will have to keep an eye on the bolt and extension lugs.

Well I hope I said that I was a beginner at machining. My rifle length barrel is now a mid length barrel due to cutting the wrong thread pitch. I blamed it on my dog but for some reason he doesn't care.

Does any one have a suggestion as to how to time the barrel extension to the gas port and get the hole of the gas port in the center of a riffling groove? I have it drawn in CAD and don't quite see the solution just yet.

The smith I was going to borrow the 6BR reamer only has tight neck reamers. I guess I will go with a 6PPC if I have to rent a reamer to avoid any pressure issues.

I have the barrel chambered. I ended up going with the 6mmBR. I have a BAT extension on the way. Did you know that BAT will sell you a extension of many sizes. I have one coming that measures 1.0010. The receiver is 1.0015. Locktight for the rest. Now to build the brake. What design?

Attached File

Attached File

I test fired the upper today with 4 rounds loaded with Varget from 28gr to 29.5gr to check primer pressure. This is a low charge for Varget. I have heard of 6mmBR loaded with 34gr of Varget compressed. Much to high for me. I do not expect to have to load more than 31gr. I have attached a picture of the barrel nut that will allow me to tune the barrel harmonics. This idea was read from an articular in American GunSmith by Joe Carlos.
Attached File

I've got a superlative arms adjustable block on one of my Creedmoor builds. I'm pretty happy with it. My other one has a SLR block and if I did it again I would probably have two superlative blocks and $30 more in my pocket.

I looked at those but since this is a Smithing project and after seeing how easy JP makes their adjustable blocks I decided to weld up a block and make it adjustable myself.

Well the welded up block sounded like a easy job. Learned something when tapping the set screws. Any other REAL smith probably knows this but for those that don't , like myself, When you have a setscrew that will be safetied by another set screw. Drill and tap the first set screw before you drill the safety screw hole. Happened to have a carbide end mill I could use to get the broken tap out. I found that barrel nuts for free floating hand guards are not mill spec. I have 4 nuts with 4 different threads that also have 4 different gas tube hole spacing. You see I have a RRA free float HG I wanted to use on this project but they do not list replacement nut on their site. I did find that I can buy an Alu. nut at WalMart. It looked like a go and was $11. Sure nough it has a 1-15/16 thread not a 1-7/8 thread. O-well that's what I have a lathe for right. I have it together enough to test powder charge for grouping. Then I will work out the barrel torque.

Attached File

First off I am not a trained rifleman. Here are my exploits for info or entertainment.

I have made it to the range. Couple times. I first to test fired and managed to ruin two cases with the adjustable gas block. But it does cycle. At the range with the GB opened several turns I could not get what I wanted in a group with 55 gr bullets. 4" spread for 5 shots at best. As for grouping, besides the shooter, the rear part of my stock is hard to hold steady. I plan on a straight tube or rod extending forward to use a sand bag. Hope that will help. As for the 6mmBR chamber it is designed for a bolt gun. My measurement to lands is 1.830. With a 70 gr seated to fit the mag I have a 0.096 jump. Then the rounds from the 450 bushmaster mag would pop out and the rounds in a 6.5 Grendel mag run to low they won't feed. Frustrated. If I have to feed rounds one at a time I will build a bolt gun. Worked on the mag lips and I think both feed well now. When I get my rear rest build I will try again.

I add a rear support to my stock to help stabilize on the bench. It worked well. At the range with 5 shots groups set at jumps from 0.005 to 0.055 in steps of 0.010.

Attached File

Good for you man. You started an involved project and saw it through to fruition.
You own it now.
Best of luck in future endeavors.

I made a bag device for a Rifle I built my best friend a few years back. He wanted something for coyotes when he was living in Nebraska, needed the adjustable butt stock to compensate for cold weather gear, warm days, the wife, the kids, but wanted stability on the bag for long range shooting.

I made a little piece from aluminum bar stock milled to fit into the sling loop position and some aluminum tubing that bolted on  to settle the butt stock in a bag.

Worked good.

Only picture I could find of it....

Attached File

PR361, That is just like the add I made for my stock.
Attached File

I have 2 more thing that need accurizing. I have centered the bolt carrier to run straight with the bolt when loaded into the upper receiver.