[99Tarbox]

I'm likely going to have a custom barrel cut by Lothar for my 6.8 build. I was thinking of either a 16" or 18" barrel. What specs would you want in a custom barrel? BTW, this will be a hunting rifle more than anything else.

 

[ron169]

FOR me, 12 twist, 3 groove, 18 inches, mid length Gas, with an SPR profile. Then send the barrel to AR15performance and have a DMR chamber reamed into it. Then install barrel and do your best to deplete the over crowded GA deer population.

 

[constructor]

I would get the LW50 stainless, 18" with a mid length gas system , if you want light go with what Woody calls a "recce" contour .760/.600 or maybe a "SPR".840 under the guard and .730 out front for something a little heavier.

 

[99Tarbox]

Thanks for the info folks, but I have another request. Ordering a barrel is a bit more complicated than I expected! You can't just ask for a barrel, the folks need little things like dimensions! I can sure tell I'm an idiot about this stuff, but learning...or at least trying to learn!

So, when describing a barrel, I figured I would work from the chamber forward. The chamber should be easy enough, it is the other dimension that I'm curious about! How would a this be described? With the chamber, I expect the description would read something like “6.8 SPCII chamber with an installed barrel extension with M4 feed ramps, headspaced with bolt.”

The only dimension I'm sure of is the gas block since I plan on using a PRI Flip Up Front Sight with .750 Crossbolt. Would the diameter of the barrel at the block be .730 (described by Woody at LW as standard) or .7495? Is there a reference that describes optimal dimensions? What is a “recce” dimension? I’d like the barrel as light as possible without sacrificing to much accuracy.

Another question that has come to mind. With a 16" barrel I get the rifling in poly, in 18" I believe it is 6 groove, 1-11.25 twist. I've been reading up on the poly and, while intrigued, I noticed that are some issues that come with poly. What is the group’s opinion on poly in the 6.8 round? Would the poly rifling be worth the decrease in FPS?

Finally, I’m asking for 5/8 X 24 muzzle thread, but what is the shoulder dimensions? Is it standard to the 308?

I thank you for any assistance you all can provide! This is a great learning experience building this from “scratch.”

 

[99Tarbox]

Found some dimensions, and it looks like a great source! of course, this is a rifle legth gas system, I'm planning a mid-length gas system.

 

[rushca01]

Thanks for the info folks, but I have another request. Ordering a barrel is a bit more complicated than I expected! You can't just ask for a barrel, the folks need little things like dimensions! I can sure tell I'm an idiot about this stuff, but learning...or at least trying to learn!

So, when describing a barrel, I figured I would work from the chamber forward. The chamber should be easy enough, it is the other dimension that I'm curious about! How would a this be described? With the chamber, I expect the description would read something like "6.8 SPCII chamber with an installed barrel extension with M4 feed ramps, headspaced with bolt."

The only dimension I'm sure of is the gas block since I plan on using a PRI Flip Up Front Sight with .750 Crossbolt. Would the diameter of the barrel at the block be .730 (described by Woody at LW as standard) or .7495? Is there a reference that describes optimal dimensions? What is a "recce" dimension? I'd like the barrel as light as possible without sacrificing to much accuracy.

Another question that has come to mind. With a 16" barrel I get the rifling in poly, in 18" I believe it is 6 groove, 1-11.25 twist. I've been reading up on the poly and, while intrigued, I noticed that are some issues that come with poly. What is the group's opinion on poly in the 6.8 round? Would the poly rifling be worth the decrease in FPS?

Finally, I'm asking for 5/8 X 24 muzzle thread, but what is the shoulder dimensions? Is it standard to the 308?

I thank you for any assistance you all can provide! This is a great learning experience building this from "scratch."

I totally understand what you are doing but it's a tough thing to do. Your best option is going to buy a custom barrel from someone like AR Performance (Constructor), Noveske, Denny's Guns etc...

These custom shops order the barrels from the manufacture and though they may order their barrels from the same company Lothar, Pac Nor etc...each custom builder has them build to their specs. So AR Performance could get a set of Pac Nor barrels in using their specs and Noveske could get a Pac NOr barrel but built to their specs, theirwill be differences. Those differences will be the specs that are used to build the barrel which inlcude the land to groove ratios (trade secrets usually to that custom barrel shop) twist ratios and number of grooves and barrel profile.

I guess what I'm trying to get at is these custom shops have done all the research and testing. Now I also understand if you are trying to get one sooner due to demands but I still think you would be better off ordering a barrel from a custom shop in the long run.

Just my .02 but if you are up for the challenge go for it!

 

[99Tarbox]

The rifling is based on what LW has available. I don’t have any experience to even start going down that path, other than a discussion on the finer points of a poly vs 4 or 6 groove. The outer dimensions are more cosmetic, to a point, than anything, at least according to my understanding. Am I missing something?

 

[deacn dan]

new barrel

I totally understand what you are doing but it's a tough thing to do. Your best option is going to buy a custom barrel from someone like AR Performance (Constructor), Noveske, Denny's Guns etc...

These custom shops order the barrels from the manufacture and though they may order their barrels from the same company Lothar, Pac Nor etc...each custom builder has them build to their specs. So AR Performance could get a set of Pac Nor barrels in using their specs and Noveske could get a Pac NOr barrel but built to their specs, theirwill be differences. Those differences will be the specs that are used to build the barrel which inlcude the land to groove ratios (trade secrets usually to that custom barrel shop) twist ratios and number of grooves and barrel profile.

I guess what I'm trying to get at is these custom shops have done all the research and testing. Now I also understand if you are trying to get one sooner due to demands but I still think you would be better off ordering a barrel from a custom shop in the long run.

Just my .02 but if you are up for the challenge go for it!

I agree with Rushca. I think what he is trying to say (very diplomatically I might add) is that the custom shops on this forum with their tremendous experience and knowledge regarding the 6.8 barrels, twists, accuracy, and maximum ballistic performance, have already waded through all the minutia involving barrel length, diametor, gas systems and other potentially confusing technical stuff. They are the masters of this cartridge and rifle configuration. They've already conquered the learning curve and stand ready to discuss options and build you the best upper that can be made with the exact barrel that you are looking for because those specs are what the custom shops have insisted that the barrel companies make for them. But as always, if you desire the frustration and challenge of your own learning curve, they will patiently walk you through that also.

 

[BLACK LION]

I have to agree... I would go with someone who has already done all the legwork for you and let them walk you through all teh paces...rather than you trying to walk someone else through the paces. Wait time is most likely the same regardless of what they may tell you the turn around time is.
Besides going with a trusted source will lead to a relationship that can be built upon and if anything is needed or wanted then it can be configured to your taste... Going striaght to the manufacturer might leave you out in the cold later on when it comes to your needs.

just a thought as I went down this path when I wanted to build a .458 socom... the barrel manufacturers had no time and no patience for my lack of technical knowledge so I went somewhere who already did the footwork and all I needed to do was specify which barrel I wanted.

 

[99Tarbox]

Rgr copy all. Thanks for the input from everyone.

 

[BLACK LION]

Love the avatar btw...

 

[99Tarbox]

Why thank you! Wish i could claim it, but it was liberated from an evil power. BTW, how long where you navy. I'm a retired 22 year sailor.

 

[99Tarbox]

Well, took y'alls advice. Went with the AR Performance 16" barrel w/ the ITS9310 bolt. Wait till that comes in and get the pieces one at a time.

 

[deacn dan]

You won't be disappointed in your choice. Those barrels have majic powers. They help you shoot long, hard and accurate.

 

[BLACK LION]

Why thank you! Wish i could claim it, but it was liberated from an evil power. BTW, how long where you navy. I'm a retired 22 year sailor.

I was in long enough to adopt cursing as a primary language

 

[99Tarbox]

I haven't given up on my original quest. I want to know why the ODs are the way they are.

 

[Test_User]

99,

What are you wanting to know about the OD?

Here is a short overview:

All AR-15 barrels are 1" at the chamber

After that they can can technically stay that way to the muzzle.

Normally they drop down to .748-.749 at the gas block boss as this is by far the most popular diameter size but there is also .625 and .938 and a number of customs as well. As far as why the barrel dimension has to be at least .001 smaller than the hole of the gas block for you to be able to get it to slide on.

After that the barrel can step down to even as low as the mid .500's but it will cause it to be a whippy barrel. The deciding factor is the bore size as there is a min thickness the barrel walls have to be to handle the pressure.

If you plan to be adding a muzzle device than the muzzle had to to be a threaded diameter that the devices are made in. The standard for the 6.8 is 5/8x24.


So other than the chamber area gas block boss and muzzle (if a device will be used) the dimensions can be numerous. Obviously you would not want your barrel in from of the gas boss to be larger than the gas boss itself as it woudl make it hard to slide on the gas block. The real deciding factor on most profiles other than the extremes is barrel weight and balance.


To pick the correct profile for you you really need to know what you plan on using this upper for specifically. Is this going to be a range gun shooting from a bench most of the time. Are you going to be pakcing it miles to hunt at the top of a mountian. DO you want it to be a recreation of a particular mil spec like a MK12 Mod O or a RECCE. Strictly for home defense. Tactical carbine classes etc..

I can tell you unless you are going to be doing hunting were you need every FPS its hard to beat a 16" setup. If you want one to do the best fps hunting but also want it to work well tactically I suggest a 18". We are getting so much vel from the 6.8 now that 16" guns have more than enough vel to take jsut about any N American game less Brown bear and possibly bull moose out to and past 300 yards with out any issue. I think the best thing to do and you may have alkready done this is talk it over with Harrison of ARperf and he will give you his opinion.

 

[99Tarbox]

Thank you sir! That confirms some of what I suspected. I'm shooting for a lite system since I'll be carting it through the woods, yet one that maintains its rigidity under heavy use. I will call Harrison and see when and if he can schedule some time to talk.

It's a bit odd, my dad and grandfather were both machinists (tool and die makers) but wanted better for me so they never taught me the trade. Now that I'm getting older, I'm facinated by machining but have neither the time nor cash to actually learn it. We all have to admit our limitations I suppose, but I can sure learn learn as much about these systems as possible! I may have to dig up some gunsmithing books to learn some of the basics. Thanks again.

 

[Test_User]

That is very much what happened to me and I had to play catch up in the machining dept Thank god I have a sucker for a friend that keeps teaching me the stuff and hold my hand. Don't feel to bad as many of the AR manf out there do not do a lick of machining. Many even have their gas ports and aligent pins installed by others let alone cutting a crown or turning a barrel profile. Than there are those that do it all from barrel blank to squaring up and tweaking manf parts to making their own from billet. Its across the board but there is much more outsourcing than I think most realize. Then you have conpaniess that are more RD companies that actually manf. They put there name on them and design them but then outsource the building but still charge that premium. I still remember the chuckle I would get watching people argue over Ar lowers when they were both actually made by the same company which was not either of the named ones being debated.

 

[BLACK LION]

I ran into a guy at big 5 that kills black bear here in kommiefornia with his out of spec dpms 6.8.... dont know how big they are but they die just the same I take it...