6.8 SPC Forums banner

1 - 20 of 27 Posts

·
Registered
Joined
·
22 Posts
Discussion Starter #1
I finally finished my 6.8 Black Rain upper build with ARP barrel and JP Enterprises bolt. The rounds below are from the first time shooting the rifle. The are factory S&B rounds (green box). I noticed swipes or marks on the case head. Is that normal? Some actually gouged the head and pushed a small amount of brass up into a sharp edge as you can see in the picture below. I did not check the head space, don't have the gauges. Not sure if this is a head space issue or just normal wear. The marks look like swipe marks which usually indicates a max power load.
62440
 

·
Registered
Joined
·
290 Posts
Since you already have the gauges, it'll be easy enough to check headspace.
You can also measure the growth of your brass, from new to fired, to check headspace.
Are you running an adjustable gas block ?
 

·
Registered
Joined
·
836 Posts
The ejector marks looks like a sharp edge on the ejector. Most on here put a light radius on it with either a dremel tool or sand paper. The extractor marks looks like it's over gassed and the bolt is opening while the brass is still expanded against the chamber wall.
 
  • Like
Reactions: sfs13

·
Registered
Joined
·
1,148 Posts
Wrote this last night but never hit "post." Chamfer your ejector. There's some instructions on the site. I had the same issue with brass getting peeled up. Fixed it.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #6
Thanks for the info guys. I don't have head space gauges, so can't check that. I do have an adjustable gas block and it is set just high enough to lock back on an empty mag, so not over gassed. Maybe I'll put a light radius on it. Surprised because it's a $150 bolt. Shouldn't be marking the brass.
 

·
Registered
Joined
·
406 Posts
Thanks for the info guys. I don't have head space gauges, so can't check that. I do have an adjustable gas block and it is set just high enough to lock back on an empty mag, so not over gassed. Maybe I'll put a light radius on it. Surprised because it's a $150 bolt. Shouldn't be marking the brass.
Alot of things you pay for a name these days. A bunch of stuff is made by the same company, just different logos on it.
 

·
Registered
Joined
·
4,244 Posts
My experience with the 110 PTS is that it runs hot for a factory load, especially if your barrel has a shorter freebore. I've taken distance to the land measurements from the current 6.8s I have using the 120 SST. Included are two barrels I have passed on (and wish I still had).

SST COALs touching the lands

barrels from 7-8 years ago
18" 5r 2.358" (passed on)
20" 5r 2.345"
20" 5r 2.372" (passed on)
Note, the ARP chamber at this time had 0.015" less freebore than typical SPC II chambers.

Barrels from the past 24 months
18" 3r 2.307"
16" 5r 2.312"
12" 5r 2.310"

You can see that customer barrel makers have shorten freebore to maximize performance from factory ammo, i.e., achieve higher velocity and better accuracy. If your ARP is recently manufactured, you should have a shorter freebore and be seeing higher muzzle velocities and chamber pressures than an older 6.8mm barrel. This could be contributing to your swipes. It doesn't look like your primers are cratered and most still have some roundness. Removing the bolt's sharp edges should help.

This is a perfect example of why no one should use someone else's reloads ... and ... why everyone has to do load development for their specific rifle (and the brass they use). As reloaders, especially if you load longer than 2.260", we need to be aware of our freebore. I've had the same load that showed no pressure signs in the earlier barrels, pop primers in the new barrels with shorter freebores.

Also note, as a chamber reamer wears 0.001", the freebore in the chamber can change by 0.017" because of angle of the throat (freebore to the bore (full rifling)).
 
  • Like
Reactions: Pilot172

·
Registered
Joined
·
573 Posts
If your building rfiles and not ordering your barrels with a head spaced bolt then you need to at least invest in a go, no go and field gauge. When mixing random parts I want to know my headspace is correct before first round is fired. Most popular cartridges I have two sets, one for build bench and another for my range bag. I cannot count the number of rifles I have diagnosed headspace issues at the range for people who built a rifle on their kitchen table with mish-mash collection of parts.
 

·
Registered
Joined
·
55 Posts
If i were handloading, I would say those were hot. You have both ejector and extractor marks and some of the primers look kinda flat. I would shut the gas block completely off and just see if the marks are still there. If not, maybe a timing issue?? I am definitely not the most knowledgeable about timing, but closing the gas off seems like that would quickly give you an answer if that was the problem or if it was pressure.
 

·
Registered
Joined
·
3 Posts
I had the same problem even after polishing my ejector. I replaced the buffer spring with a Wilson combat flat wire for the 6.8 and it stopped all of my problems.
 

·
Registered
Joined
·
4,244 Posts
I can appreciate what hueyville is saying about go, no go, and field gauges. However, I have not found a critical need for them. If you take your fired S&B cases and use the Hornady tool to measure the case shoulder and compare to an unfired case, you have a headspace measurement. I've seen as much as a 0.017" difference between new and fired brass. If you don't have the tool you can use a 9mm case and your calipers to determine the measurement. For best accuracy, remove the spent primers as they can be proud.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #13
If your building rfiles and not ordering your barrels with a head spaced bolt then you need to at least invest in a go, no go and field gauge. When mixing random parts I want to know my headspace is correct before first round is fired. Most popular cartridges I have two sets, one for build bench and another for my range bag. I cannot count the number of rifles I have diagnosed headspace issues at the range for people who built a rifle on their kitchen table with mish-mash collection of parts.
I know the go/no go gauges are the correct way to go. I just couldn't see spending the $80 or so for a single build. Some say if you use a quality barrel and bolt, the head space "should" be good. My other thought is it's either going to work or not, or have some issues. If there's issues, then I'll get the gauges.
 

·
Registered
Joined
·
1,063 Posts
If you close the gas all the way off how is it going to mark the head or eject the case .

Sent from my moto g(7) play using Tapatalk
 

·
Registered
Joined
·
1,063 Posts
What does the side of the cases look like ? Shiney or cloudy ? Have you given the bore a good cleaning and polishing? My 12.5" ARP did the same thing with factory SST and S&B and I actually had to mortor a couple out before I gave it a good cleaning and polishing .

Sent from my moto g(7) play using Tapatalk
 

·
Registered
Joined
·
22 Posts
Discussion Starter #17
What does the side of the cases look like ? Shiney or cloudy ? Have you given the bore a good cleaning and polishing? My 12.5" ARP did the same thing with factory SST and S&B and I actually had to mortor a couple out before I gave it a good cleaning and polishing .

Sent from my moto g(7) play using Tapatalk
I did not polish the bore. I don't recall if the cases were shiney or not, already tumbled them for reloading. I will polish the bore anyways.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #18
I can appreciate what hueyville is saying about go, no go, and field gauges. However, I have not found a critical need for them. If you take your fired S&B cases and use the Hornady tool to measure the case shoulder and compare to an unfired case, you have a headspace measurement. I've seen as much as a 0.017" difference between new and fired brass. If you don't have the tool you can use a 9mm case and your calipers to determine the measurement. For best accuracy, remove the spent primers as they can be proud.
Are you talking about this tool in the video? What should the difference be between factory and fired brass, or what is the max allowed? Does it need to once fired or fired 2-3 times?

 

·
Registered
Joined
·
1,063 Posts
I did not polish the bore. I don't recall if the cases were shiney or not, already tumbled them for reloading. I will polish the bore anyways.
It is a common problem with Melonite barrels . Some people use fritz or other compound to polish , I used a battery powered drill and . 357 brush and rubbing compound on a mop . You don't want a mirror finish because cases need a little traction . Be sure to clean really good before firing to protect the barrel .

Sent from my moto g(7) play using Tapatalk
 

·
Registered
Joined
·
22 Posts
Discussion Starter #20
It is a common problem with Melonite barrels . Some people use fritz or other compound to polish , I used a battery powered drill and . 357 brush and rubbing compound on a mop . You don't want a mirror finish because cases need a little traction . Be sure to clean really good before firing to protect the barrel .
I have the 18" stainless barrel but will do a light polish.
 
1 - 20 of 27 Posts
Top