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I didn't see any pressure signs on the case, but there were gouge marks on the bottom, I guess from the ejector? I'm not sure what would cause that. Higher pressure?
Pressure signs typically show up on the head/base of the cartridge, not the neck or sidewalls. Yes, those gouge marks are indication of high chamber pressure often referred to as swipes. They occur when the chamber pressure is high enough to push/reform the brass back into the crevasse of the bolt, in this situation the ejector pin. Looks like there are extractor marks, also. Your primers are flat, too. Is there a "crater" around the primer strike, e.g., a lip that you can catch or feel with your finger nail.

Swipes usually occur when the bolt rotates to open. These marks don't seem to have much of a rotation indication with them. If they had, the gouge marks would have been sheared off and not be raised above the case head.

Did you bolt lock fully back with these, e.g., on the face of the bolt, not the lip of the bolt carrier?
 

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Discussion Starter · #22 ·
There is a very slight lip on the primer that I can catch with my nail. As far as the bolt locking back, I didn’t notice if it was on the carrier or the face of the bolt.
 

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I finally got around to testing these out. Overall they shot very well. I didn't see any pressure signs on the case, but there were gouge marks on the bottom, I guess from the ejector? I'm not sure what would cause that. Higher pressure? View attachment 63601 View attachment 63602
Yeah, those are swipes. Ive seen some light swipes on a couple of my rounds, nothing that pronounced. Which barrel do you have again?
 

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Definitely pressure signs: craters around the primer strikes, plenty of swipes, and multiple instances of carbon blow-by around the primers.
 

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It was PTG. IIRC- You said "You contacted them on the error. they fixed the issue quickly."
No, PTG never fixed the issue in the year I sent them 6-8 emails. I gave up trying to explain they transposed the number and assumed they were dyslexic. It wasn't until late 2009 that Ben from Bison talked to them and they changed the drawing. Used the same print number but changed the numbers on it just like they did the Valkyrie.
If you go back into the archives on arfcom Randall posted the first drawing with the first transposed number in 2006. Art from SSA and Randall had a thread going for 6 months or more.
When I first saw the drawing I thought the 45* note assured that cone angle was 45 but it did not it was just a note left from an earlier SAAMI print. When I ran the numbers it came out around 87* or somewhere close.


 

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No, PTG never fixed the issue in the year I sent them 6-8 emails. I gave up trying to explain they transposed the number and assumed they were dyslexic. It wasn't until late 2009 that Ben from Bison talked to them and they changed the drawing. Used the same print number but changed the numbers on it just like they did the Valkyrie.
The fact that they did not change the print number when they revised it has caused a lot of confusion over the years.

edited to add - This is one of the things that I meant when I noted in an earlier post: "there is more than one SPC II drawing".
 

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Discussion Starter · #30 ·
It’s not mine, but just in case anyone is looking, I came across 250 rounds of Druid Hill 90g gold dots on gunbroker with a starting price of $250. Ends n 9 hours. Has 0 bids.
 

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Browsing due to knee surgery and I’m grounded….so my question here is, I have 400 of these 90g gold dots from DHA. experienced the same swipes on brass from both my 16” scout 5r, and my 12.5” 5r.
Are these safe to shoot, or should I dismember them for components?
 

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Browsing due to knee surgery and I'm grounded….so my question here is, I have 400 of these 90g gold dots from DHA. experienced the same swipes on brass from both my 16" scout 5r, and my 12.5" 5r.
Are these safe to shoot, or should I dismember them for components?
Do you have an adj gas block on it? If you do adjust the gas down a little. In short the loads are safe and mild swipes are not dangerous, if you get flat primers then you need to take another look at things.
 

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I have shot the 90 GDs in 3 rifles, 12.5", 16", and 20" ARP 5Rs. I had signs of pressure though less than some others posted on the forum. I run the 12" and 16" ARPs with adjustable gas blocks but had their gas blocks full open. All rifles shot this load 1.5 moa or better but the most notable aspect of the range session was bolt cycling. The 12" locked back. The 16" would pick-up the next round but did not lock back (or catch the bolt carrier). The 20" with a rifle gas would not pick-up the next round and had to be manually cycled. I expected the 20" with its rifle length gas to not cycle. I wasn't expecting the 16" with mid-length gas to not lock back.

It is not easy to make a max pressure SPC 2 load that works in everyone's rifle. DHA has done a pretty good job with these but, IMO, the powder is too fast so turning down your gas will have no impact. The chamber pressure is a bit high but has subsided by the time the bullet reaches the gas port which is why cycling was an issue. I've heard that DHA is going to use a slower powder in the future. If these shoot well in your rifle, have fun shooting them.

73045
 

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Do you have an adj gas block on it? If you do adjust the gas down a little. In short the loads are safe and mild swipes are not dangerous, if you get flat primers then you need to take another look at things.
On my 12.5" I have an adjustable block, but not on my 16".
in both rifles the accuracy is sub 1.5 MOA and function flawless, even the 12.5" with my can on it.
I really like the speed…..in my 12.5 suppressed I'm still getting velocities hovering around 2930 which is surprising.
 

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Constructor or others can correct me if I remember the facts wrong, but the freebore was not the only problem with many early 6.8 SPC barrels. In particular, there was a sharp angle at the place where the chamber diameter steps down from the outside of the case neck to the smaller diameter freebore.* Brass/copper from the jackets would sometimes be shaved off the bullets here. In addition, the bores of a significant number of early barrels were undersized. Many early SPCII reamers did not address the sharp angle, but went overboard lengthening the freebore in order to drop pressure. This tended to reduce velocity and definitely did not help with accuracy with factory ammo.

ARP and some others fixed the sharp-angle problem and found that the cartridge worked better with less freebore than in some of the SPCII drawings (yes, there is more than one "SPCII drawing").

*There was an error in the chamber print (two numbers transposed), but some reamers had an even sharper angle, making the problem worse!
Does this apply to only ARs, or does it also apply to the mini 6.8. Thanks
 

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Does this apply to only ARs, or does it also apply to the mini 6.8. Thanks
Depends on your chamber. You're probably SAAMI SPC unless someone reamed it to SPCII. If you only use factory ammo (exception is CBB) or, if you reload, stay within "book" loads you will be fine.
 

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Depends on your chamber. You're probably SAAMI SPC unless someone reamed it to SPCII. If you only use factory ammo (exception is CBB) or, if you reload, stay within "book" loads you will be fine.
Is there any way to determine which chamber the rifle has, other than making a chamber cast, or having a gunsmith check it?
Thanks.
 

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If you reload there's a way to seat a flat base bullet backwards and measure it.

Post #4

 

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Greentick, Thanks for the info and posting the old thread. I'm learning a lot about the 6.8 and will learn much more before the rifle arrives about Feb. 1st. Had a busy day and haven't had a chance to do searches, yet.The rifle is a mini-14, I'm looking forward to shooting it, in April, when the MI weather allows.
 
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