Frequently Asked Questions
- What is the 6.8 ARP chamber and what can I shoot out of it?
In short you can shoot any factory 6.8 ammo loaded from 2.26-2.295" long and the hottest handloads. In 2006 I found both the 6.8SPC and 6.8SPCII chambers to be kind of a sloppy military chamber. The body of the chambers were fine but the freebore was not optimum to produce accuracy. I redesigned the freebore to align the bullets on the bore better and shortened the freebore a little so the bullets would not have as much jump to the lands. It comes from 20+ years of experience in designing wildcats and chambering custom barrels. The ARP chamber design has proven to be more accurate than the other designs on the market. Check www.68forums.com for reviews. Do not use bullets larger than .277 in ARP barrels. Nosler, Hornady, Speer, Federal and Barnes all run .2765-.277, Sierra and Berger are dead on .277". It has been reported that some Cavity Back solid copper bullets are .278" in diameter and they are causing high pressure problems, the loaded ammo is popping primers. To achieve the best accuracy with Barnes bullets we have found it is best to do a deep clean removing all copper from the barrels then shoot Barnes bullets and nothing else. If you shoot a different kind of bullet you should deep clean again before going back to the Barnes.
- What causes swipes?
Swipes can be caused by a few things but in order for swipes to occur the case MUST be stuck to the chamber walls while the carrier travels to the rear far enough to turn the bolt 22.5 degrees where it unlocks. It is not always excessive high pressure.
the prt in the barrel could be too large. It could be because the pressure is higher and over-gassed because of it. The carrier moves before the case can shrink back down.
It could be that the case is sized a little long and it being pinched between the bolt face and shoulder keeping the case from turning. I once read where a guy(Yondering I believe) that frequents another forum sizes his cases for a .008" crush fit in an AR chamber. That is just asking for trouble.
It could be that the neck of the case is thick and the case can't turn in the chamber.
The chamber should be cleaned AFTER the bore is cleaned. Any junk cleaned out of the bore is drug back into the chamber and that grit could cause the cases to stick.
It could be that the gas port in the barrel is a little larger than it needs to be for that load.
It could be because the melonite chamber is sticky. New Melonite chambers get sticky when first heated up. They will smooth out after broken in or the chamber can be lightly polished with Iosso, JB or Flitz paste. A couple of patches wrapped around a brush on a short cleaning rod spun by a drill for a minute. Be sure to clean the abrasive out of the chamber.
Some look at posts online and wonder why they can't get the velocity others are getting without getting swipes. It isn't always high pressure like most believe. It is timing more than anything with the exception of sizing the cases incorrectly.
An adjustable gas block can fix the issue some times. A heavier buffer or stiffer spring. Primers make a difference. Powder burn rates make a difference. Using a faster burning powder will cause a pressure spike early. Using magnum primers will light more of the powder at once and cause a pressure spike.
In 07 when I was testing the 6.8 so much I figured out I could get more velocity by using Russian primers and more powder. A smaller spark ignites less powder slowing the pressure spike in some cases.
- Build an upper? quick tips
Please, when building your upper use good building procedures it will save a lot of headaches later. Many think the AR is like legos and anyone can slap them together on the kitchen table and they will run perfect. Maybe if you're lucky. It's better to be a good builder than a lucky builder.
*When assembling the gas tube and gas block MAKE SURE the gas port in the gas tube aligns with the port in the top of the gas block. Remove the rear set screw and look down through the hole into the top of the gas block. IF ANY part of the gas tube covers the hole in the gas block drill it out with a 5/32" bit.
*Use a sealer(not silicone) between the gas tube and gas block to prevent gas leaks. Blue loctite works.
*Use a sealer between the gas block and barrel. Any gas leaks in either location will cause problems when the pressure is 14,000psi.
*align the rear set screw with the dimple in the bottom of the barrel. That is what makes sure the gas port in the barrel aligns with the port in the gas block. The dimple is exactly 180* around the barrel from the gas port.
* If the barrel is a loose fit in the upper receiver use bedding(blue loctite is simple and works, been using it for 27 years)around the barrel extension not the threads. That helps make the connection between the barrel and receiver more rigid. The scope is connected to the receiver and the receiver to the barrel that connection between the barrel and receiver is critical. Use 40 ft lbs minimum torque then turn to the next hole to align it for the gas tube but do not go over 80lbs.
*Do not over torque the muzzle device, 15 ft lbs is all that is needed.
* OIL the bcg and keep it wet.
See below for short stroking problems.
- Short stroke? Align gas block/ port location and the dimple.
Most gas blocks have a hole .298-.300" from the rear of the gas block. That matches the port in our barrels +- allowing for a little manufacturing tolerance of holes in gas blocks. If you use a handguard with a cap the cap forces the gas block forward another .033" unless you use a FSB with a hole at .265" from the rear.
The rear set screw in the gas block is where the gas port in the top of the gas block is drilled. To align the holes place the rear set screw in the dimple on the bottom of the barrel. Remove the rear set screw, align the hole in the dimple and tighten the front set screw then replace the rear.
http://68forums.com/forums/showthread.php?55097-SHORT-STROKING-PROBLEMS-build-tips ***FYI- The hole in the top of most gas blocks is .1495" If the port size in the barrel is .082 you can slide the gas block as much as .034" toward the shoulder on the barrel to close the gap if need be.
ARs cycle from pressure created by the ammo. Different ammo and different loads create different amounts of pressure at the gas port which cause the carrier to move at different speeds. If everyone used the same ammo porting a barrel would be easy. We try to port the barrels with the combination most people use(carbine stock, standard springs and buffers with Hornady, S&B and Federal xm68 ammo). Any ammo or handload that produces 4000psi less or using heavy buffers and springs may cause the rifle to not cycle or strip cartridges from the mag. Remington and Federal Eagle ammo and many starting book loads do not produce as much pressure as Hornady, S&B or Fed XM68 ammo.
- Checking Headspace
GO: Corresponds to the minimum chamber dimensions. If a rifle closes on a GO gage, the chamber will accept ammunition that is made to SAAMI's maximum specifications. The GO gage is essential for checking a newly-reamed chamber in order to ensure a tight, accurate and safe chamber that will accept SAAMI maximum ammo. Although the GO gage is necessary for a gunsmith or armorer, it usually has fewer applications for the collector or surplus firearms purchaser.
NO-GO: Corresponds to the maximum headspace Forster recommends for gunsmiths chambering new, bolt action rifles. This is NOT a SAAMI-maximum measurement. If a rifle closes on a NO-GO gage, it may still be within SAAMI specifications or it may have excessive headspace. To determine if there is excessive headspace, the chamber should then be checked with a FIELD gage. The NO-GO gage is a valuable tool for checking a newly-reamed chamber in order to ensure a tight and accurate chamber.
FIELD: Corresponds to the longest safe headspace. If a rifle closes on a FIELD gage, its chamber is dangerously close to, or longer than, SAAMI's specified maximum chamber size. If chamber headspace is excessive, the gun should be taken out of service until it has been inspected and repaired by a competent gunsmith. FIELD gages are slightly shorter than the SAAMI maximum in order to give a small safety margin.
From PTG website- Exact same wording...
Pacific Tool and Gauge offers three lengths of headspace gauges per rifle caliber. In order from the shortest to longest, they are: GO, NO-GO, and FIELD:
GO: Corresponds to the minimum chamber dimensions. If a rifle closes on a GO gauge, the chamber will accept ammunition that is made to SAAMI's maximum specifications. The GO gauge is essential for checking a newly-reamed chamber in order to ensure a tight, accurate and safe chamber that will accept SAAMI maximum ammo. Although the GO gauge is necessary for a gunsmith or armorer, it usually has fewer applications for the collector or surplus firearms purchaser.
NO-GO: Corresponds to the maximum headspace Forster recommends for gunsmiths chambering new, bolt action rifles. This is NOT a SAAMI-maximum measurement. If a rifle closes on a NO-GO gauge, it may still be within SAAMI specifications or it may have excessive headspace. To determine if there is excessive headspace, the chamber should then be checked with a FIELD gauge. The NO-GO gauge is a valuable tool for checking a newly-reamed chamber in order to ensure a tight and accurate chamber.
FIELD: Corresponds to the longest safe headspace. If a rifle closes on a FIELD gauge, its chamber is dangerously close to, or longer than, SAAMI's specified maximum chamber size. If chamber headspace is excessive, the gun should be taken out of service until it has been inspected and repaired by a competent gunsmith. FIELD gauges are slightly shorter than the SAAMI maximum in order to give a small safety margin.
- Phone calls -
We are a small business... Sorry, we have 1 phone line and only a few guys that have many tasks. At this point in time we can't add someone to just sit and answer phones, it's tough to find someone that knows enough about AR15s to answer the questions correctly so it would just being them saying hello and handing me the phone anyway. Emails are the best way to reach us.
- gas port size
Gas port size, calculated and what works.
First this really isn't a troubleshooting post but an explanation. Some believe we can use a formula to figure the correct size gas port in a AR15 barrel. Engineers are taught to calculate everything. Sounds good to a guy sitting at a desk but not to someone who actually builds ARs.
There are too many variables for a formula to actually work. First the pressure in the barrel changes as the bullet moves down the bore therefore the flow through the port changes. The volume of the cylinder whether it be a carrier in a DI system or the cylinder in a piston system changes as they move. You can't figure pressure after the port because of the change in pressure in the bore and the downstream volume.
In addition the op springs rate are not the same in every build, the carriers and buffer weights are not the same. Some gas block to barrel connections are air tight and some leak, same goes for the gas tube to gas block junction. I would bet 99.999% of all builders never check the diameter of the tail of the bolt or the ID of the hole in the rear of the carrier to see how much gas will pass the rear seal but they will buy 1 piece gas rings to keep gas from exiting the front seal.
That is just the beginning, Every powder produces a different byproduct with a different specific gravity. The specific gravity of the spent gas is needed to use the critical coefficient of flow formula used in common engineering.
Every powder and every powder charge along with every bullet will produce a different pressure at a specified gas port location and every gas port location will produce a different pressure due to the volume in the barrel. A port at the carbine location will need to be much smaller than a port located at the mid or rifle length location.
Sure we can get close using a formula but then we throw "close " out the window and go with experience of what works for most people using most ammo.
The military can get very close to making every firearm work properly because they tell you what ammo to use and it is all the same, the rifles are all built to specific specs.
If we consider all the different build specs of all the rifles being built at home and every powder burn rate and charge from H110 to H4350 and bullet weights from 38gr to 80gr for a 5.56 there is no way one port size will work as designed for all of the possible combinations and even a lesser chance of a formula telling us what size should work.
ETA- There is no way one port size for each gas system length will work perfectly for every combination. All we can do is try to port the barrels so they work with most common combinations. When the final load combination is found it may require an adjustable gas block to tame it down or the port may need to be enlarged slightly to get the rifle to lock back on the last round but not be over-gassed.
- We will only ship to the billing address of the CC card.
There are too many fraudulent attempts to allow any other type of transaction. The street address and zip code must match the billing address of the card. This protects the card owner, card issuer and this business.
- NEW BARREL Cleaning and break in
AFTER building the upper run a patch through the bore to remove the protective oil, grit and dust that accumulated during shipping and building the upper to make sure there are no metal particles that may destroy your barrel on the first shot. DO NOT try to remove the black surface, that helps keep copper fouling down and provides a barrier between the copper bullets and the bare metal. Clean the protective oil out of the chamber. It will be brown, the oil mixes with the Melonite. Do not leave any excess oil in the chamber or barrel after cleaning or before shooting.
Melonite treated barrels usually do not copper foul like stainless barrels and no "break in" is needed. If(IF is the key word) there is a little copper fouling, use a good foaming copper cleaner when you come back from the range. A blue patch means there is some copper fouling in the bore so you should repeat the process until the patch comes out white. 1 patch with solvent to remove harsh copper cleaner thenrun 1 patch with alcohol. Then 1 patch with light oil like Rem oil or WD40. Then follow with 1 dry patch to remove the excess oil.
The barrel will copper foul less and become easier /faster to clean each time. When the day arrives that you clean and no blue comes out you can ease off of the cleaning and shoot until the barrel loses accuracy, when it does clean it again with copper remover. Keeping the copper out so a good layer of carbon can coat the bore is the objective.
- Can I shoot 600 to 1000yds?
If Wilson Combat and Bison Armory can call their barrels match grade we can damn sure call our barrels "AR match grade" The production barrels we sell for hunters and rec shooters are not made to shoot 600 or 1000 yds. I am not a used car salesman so I'm not going to lie in order to sell a barrel. Very very few people actually shoot that distance and those that do use a high end real "benchrest match grade" barrel like Krieger, Bartlein or Broughton. Our Socom 556 and 20" 556 barrels are very accurate with 69 and 77gr SMKs and they can be shot at 600 but If I was really going to shoot competition at 600+ yds I would use a purpose built barrel and not use a lightweight hunting barrel and be disappointed because of trying to do something that it wasn't designed to do. Buy the right tool for the job.
- Best mags for the 6.8
#1- Best mags for use with factory ammo-Barrett, they are only avail in hi cap 30 round mags. Great quality, apx $45
#2-PRI Gen 1 (old style, non-waffle)if you can find them(Precision Reflex inc), they allow loading to 2.3" very sturdy but no longer made.
#3 ASC- Stoner, Stag and others are rebranded ASC mags...the old CP mags.
- Scope mounts & accuracy
DO NOT mount 1 scope mount on the receiver and 1 on the handguard accuracy will be poor due to flex in the handguard. Use the proper cantilever scope mount and torque to 15 inch lbs, not ft lbs. Squeeze the trigger and follow through(hold the trigger back, do not allow it to reset until the bullet contacts the target)to get the best accuracy. Use a good sand bag or rest on a stable platform not the hood or tailgate of the truck.
Best accuracy is usually found when the brass is close to the chamber size. When setting up your resize die do not simply follow the instructions on the dies set. Try to adjust the die where it sizes (shoulder location)the brass .002-.004 under the chamber size. Screw the die up 1/4 turn above the shell holder and size a piece. Try it in the chamber, if it doesn't fit screw the die down 1/16th turn. Repeat until the unloaded brass fits and the bolt locks behind it. Size and try several pieces to make sure the size is correct before loading any, pulling bullets isn't fun.
- will you work on my upper or rifle?
No, we are not set up as a smithing shop.
We do not flute customer owned barrels.
ADCO's primary business is smithing try them.
- do you have reloading data for the 6.8? which bullets work?
Reloading data can be found at most powder manufacturers web sites. If you are an experienced reloader you can get much more velocity with careful loading.
The Speer 90gr TNT and Hornady 110gr HPBT seem to be accurate in every barrel I have shot or made.
To get the best accuracy requires hand loading to an OAL of 2.295- 2.3" except when shooting the Hornady 110HPBT (try it at 2.258") Pri mags allow loading to 2.295". We recommend the use of CCI 41 primers, CCI 450 or Wolf Magnum primers, any erosion to the bolt face by the use of other primers will not be covered under warranty.
- Can I use 5.56 mags in my XXX rifle?
No, the 7.62x39 requires 7.62x39 mags, the 5.45x39 use 5.45 mags, the 6.8 needs 6.8 mags.
In general most cartridges require a special mag except the 6mmx45 or other cartridges based on the .223/5.56
- cartridge stuck in chamber-
Just an FYI- If you have a cartridge stuck in the chamber and can't get it out by pulling on the charge handle do NOT stomp or beat on the charge handle. Mortaring(tap butt on ground while pulling charge handle) may be the military way but there is another way. Stick a big flat blade screw driver up through the mag well and place the blade between the front of the carrier and the barrel extension and twist it.
- FYI- overgassed barrel- adjustable gas block
If you have a firearm that is overgassed check out Black River Tactical's gas block with inserts to change the port size.- http://www.blackrivertactical.com/store.html#!/~/product/category=2710008&id=18000700 This IMO is the proper way to change the port size instead of a set screw that over time burns away.
DO NOT USE bullets that are larger than .277" in these 6.8 barrels, the chambers were designed for .277" bullets and all 6.8 barrels have a .277" bore so bullets larger than .277 will cause excess pressure and increased copper fouling. It seems some Maker bullets and Cavity Back bullets made by Maker are .278" and on top of that they are solid copper so check the diameter of the bullets before using them.
CURRENT SHIPPING TIMES 3-4 BUSINESS DAYS
AR Performance (ARP)
Hi performance 5.56 & 6.8 SPC barrels and parts since 2007
The best way to contact is by email
Phone: 801-750-4216 8am-5pm eastern time M- Fri only
Sorry we do not export anything and do not have a storefront. Everything must be purchased online.