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Posted: 5/31/2015 2:33:29 AM EDT
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I just built a 6.8 for hunting. ARP 16" midlength barrel, geiselle High Speed trigger, Palmetto bolt carrier, and Joe Bobs adjustable gas block.
My worry is with the Taccom super lightweight buffer and 10% reduced power recoil spring. I had the gas block set quick and started setting the sights. The gas was just barely spitting out the empties and it only took a bit to have it barely loading the next round. I had used a copper cleaner on the barrel before ever firing it, but I did not clean the chamber out like I did the bore. I shot 10 rounds and the brass all looked like it had been rubbed with fine sandpaper on the straight walls of the case just where the barrel touches the case. Is this a sign of the case being pulled out too early? I saw no extractor marks. I had not heard of anyone using the TAccom set up with 6.8. I was doing it for less recoil, but I can not tell any difference to be honest. My other theory is just that I left some copper solvent in the chamber and it etched the brass. I wanted to know if its just the cleaner or if I should put in a regular CAR buffer and spring before locking the gas block set screw down. |
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Quoted:
I just built a 6.8 for hunting. ARP 16" midlength barrel, geiselle High Speed trigger, Palmetto bolt carrier, and Joe Bobs adjustable gas block. My worry is with the Taccom super lightweight buffer and 10% reduced power recoil spring. I had the gas block set quick and started setting the sights. The gas was just barely spitting out the empties and it only took a bit to have it barely loading the next round. I had used a copper cleaner on the barrel before ever firing it, but I did not clean the chamber out like I did the bore. I shot 10 rounds and the brass all looked like it had been rubbed with fine sandpaper on the straight walls of the case just where the barrel touches the case. Is this a sign of the case being pulled out too early? I saw no extractor marks. I had not heard of anyone using the TAccom set up with 6.8. I was doing it for less recoil, but I can not tell any difference to be honest. My other theory is just that I left some copper solvent in the chamber and it etched the brass. I wanted to know if its just the cleaner or if I should put in a regular CAR buffer and spring before locking the gas block set screw down. You need to clean the chamber on a new barrel. The marks on your brass are from residue left in the chamber. A .410 bore mop and Iosso or Flitz polish paste works very well to "lightly" polish the chamber. Be sure to clean out all remaining residue of the polish. The 6.8 barrels from ARP are designed to run a standard carbine buffer and spring. Most guys run a standard or H buffer and spring. |
| Get yourself the proper chamber brush and scrub it good. Avoid polishing the chamber. With a reduced power spring and light buffer if the gas is set right on the adjustable gas block it should have been flinging the empties out of the gun, possibly try bumping up the gas ratio. If after a good chamber cleaning and the brass still looks to be sand papered, send the barrel back to ARP for replacement. |
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Harrison polishes the chamber when he does custom barrels.
If you don't want to polish it at least scrub it good with a 6.8 chamber brush, or a .410 brush works as well. Highly polishing a chamber will make it sticky, this is why many say to avoid it. A very lightly polished chamber will remove any slight ridges left from the milling process and allow the case to release better. |
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With a reduced power spring and light buffer if the gas is set right on the adjustable gas block it should have been flinging the empties out of the gun, possibly try bumping up the gas ratio. I had initially adjusted the gas block close with a guess. I had it almost ejecting the first round, then a full turn had it ejecting the next case, but not grabbing the next round. I started going in 1/6th turn increments until it was barely cycling S&B 6.8. My logic was that if I had only just barely enough gas to cycle that the chamber pressure should be down before extraction EVEN though I was using a weightless buffer and reduced power spring. This is sound login with 5.56. Yama above says ARP designs around a CAR buffer and spring. Surely I am not doing anything extravagant. I'll try with a clean and dry chamber next time and if I still see rough brass I'll switch to a CAR buffer and spring and adjust the gas for that. My concern about early extraction is how it can affect accuracy. I saw no signs of high chamber pressure or extractor marks so I don't think this is a safety issue. |
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Quoted:
Harrison polishes the chamber when he does custom barrels. If you don't want to polish it at least scrub it good with a 6.8 chamber brush, or a .410 brush works as well. Highly polishing a chamber will make it sticky, this is why many say to avoid it. A very lightly polished chamber will remove any slight ridges left from the milling process and allow the case to release better. You are right about a potential sticky chamber and that is why it's very bad advice to give him for him to polish it, leave it up the maker so he has no outs by claiming "oh you over polished it and your screwed". |
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Quoted:
You are right about a potential sticky chamber and that is why it's very bad advice to give him for him to polish it, leave it up the maker so he has no outs by claiming "oh you over polished it and your screwed". Quoted:
Quoted:
Harrison polishes the chamber when he does custom barrels. If you don't want to polish it at least scrub it good with a 6.8 chamber brush, or a .410 brush works as well. Highly polishing a chamber will make it sticky, this is why many say to avoid it. A very lightly polished chamber will remove any slight ridges left from the milling process and allow the case to release better. You are right about a potential sticky chamber and that is why it's very bad advice to give him for him to polish it, leave it up the maker so he has no outs by claiming "oh you over polished it and your screwed". ARPs are Melonited ( about 70 Rockwell). So, it probably won't hurt it. Unless he uses a Dremel with a gritted polish or something like it. |
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On top of the suggestions in some of the other posts you need to set up your adjustable gas block the correct way. Load a mag with one round only. Fire and see if the BCG locks back fully. Don't adjust until it's appears to be ejecting correctly. You adjust until it just locks back then give it one more click.
And FYI the ejection pattern not only takes into consideration the gas but also Extractor and Ejector spring tension. How hard the Ejector is trying to push the case out of the bolt face and well as how the Extractor Claw is grabbing the rim affects ejection pattern too. And then there's the timing issue. i.e how fast the BCG is traveling rearward. |
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