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So I switched all my brass over to a new batch of Starline. Previously I had a load of 26.8gr of imr8208xbr that was pushing 123gr SST at 2325ish fps. It showed no pressure signs in the hornady brass or in a few starline pieces I had then.
Did a new ladder with the 10 shot method and found a node b/t 27.7-28.3 at 2380fps. None of those pieces had pressure signs.
I loaded up at 27.8 with a base to ogive of 1.653" and shot one of the best groups the gun has ever shot.
![[Image: ZyFokKX.jpg]](https://i.imgur.com/ZyFokKX.jpg)
I got super excited and then looked at the brass, slight ejector swipes and extractor marks :mad:
![[Image: yj6OJaL.jpg]](https://i.imgur.com/yj6OJaL.jpg)
![[Image: motxYpF.jpg]](https://i.imgur.com/motxYpF.jpg)
I had some loaded with the old load of 26.8gr into my new batch of Starline and now I'm getting 2250fps and seeing ejector swipes and extractor marks on random pieces with those as well.
I refuse to believe I can be that much over pressure with such low velocities. Am I crazy or is there another explanation?
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02-20-2020, 01:23 AM
(This post was last modified: 02-20-2020, 03:12 AM by kmon.)
Check your bolt face. I have seen swipes before that was from carbon buildup or grit on the bolt face
Also check your chamber for fouling, both something on the bolt face and dirty chamber can cause what looks like pressure signs but is not.
Like someone says below that should not be into pressure unless the new brass has less case capacity then I could see pressure being the issue.
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I think starline brass is a bit thicker than hornady brass, I've heard the same thing before about pressure when switching brass brands just cant remember where. I see some cratering on the primers too, 8208 is spikey which could be the case with the thicker brass.
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Re-size a few of those 27.8 cases, to see how stiff they are going into the die.
Or measure just above the case web, and compare to some of your old Hdy loads, see whether there's a lot more expansion there.
I also wonder if Starline might be somewhat softer than Hornady. They don't all use the same brass alloy, each mfr has its specs, hardness, %compositions, etc.
I remember a while ago comparing Win brass to Remmy, and the Remmy was thicker and softer, the Win harder and thinner. Neither was a problem, just different. Rem brass primer pockets expanded faster for me than Win's, tho'. (Had the same thing happen in some 6.8 brass, SSA harder vs Rem softer. Both had their place to use however.)
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Yes it was the first firing on this starline brass.
Previously I had a batch 20rds of starline that had 26.8gr of 8208 with no marks and several firings.
Today I also fired some of this new starline with 26.8 and had marks just like you see here at 27.8.it makes me wonder if there's a factor other than pressure, especially given the velocity changes
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That looks like virgin brass compared to the 28.5gr I spit out. Lol. I can still get 5-6x loadings before the primer pockets blow. If you?re worried about pressure, you still have a ways to go
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Difference in brass hardness between lots? Is too bad that hardness testers are about $700 ish.
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imaguy3 Wrote:Yes it was the first firing on this starline brass.
Previously I had a batch 20rds of starline that had 26.8gr of 8208 with no marks and several firings.
Today I also fired some of this new starline with 26.8 and had marks just like you see here at 27.8.it makes me wonder if there's a factor other than pressure, especially given the velocity changes
Fire them again at the same charge and see if it gets worse.
Could be a difference in brass thickness in this lot of Starline brass. They may be fine with that load after they are shot and the case volume increases from being stretched on fireing.
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One other thing that could be going on that many AR shooters don't know or understand is that your rifle might be over gassed. It might not be a high pressure problem but too much gas being allowed to function the action hard and this new "softer" brass is getting marked by the harder slam bang operation. If you are getting truly high pressure with 26.8 grs something is VERY WRONG.
On the other hand Star does have less capacity than Hornady cases. New cases no matter the make will usually have greater capacity than previously fired and full length sized cases.
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Looks an adjustable gas block may be in my future after all. It's a midlength ballistic advantage barrel with a can.
I have seen these marks on factory hornady loads too, so it's likely overgassed then.
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If you look at your primers, they are textbook.
Sharp surfaces on a mass-produced bolt face and extractor will do this to brass as the norm.
If you are a brass-conscious reloader who wants brass coming out of a gas gun with minimal damage, you need to tune the bolt and extractor so that the sharp surfaces no longer scrape it during firing.
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That brass looks like it has serious "frosting" indicating a very rough chamber. Does the brass feel rough on the outside?
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Lemonaid Wrote:That brass looks like it has serious "frosting" indicating a very rough chamber. Does the brass feel rough on the outside?
no the brass is smooth... It's a combination of the soot from the can and the dirt from the desert floor. They are slippery smooth when clean. But they come out of my gun filthy.
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If you're shooting suppressed, it would help to know that information up-front and what gas system length you have, gas port diameter, buffer weight, spring, and bolt carrier.
Right now, I'm not seeing anything alarming, especially with the speeds you're getting.
It's just a case of a bolt with sharp surfaces interfacing with the brass under pressure.
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LRRPF52 Wrote:If you're shooting suppressed, it would help to know that information up-front and what gas system length you have, gas port diameter, buffer weight, spring, and bolt carrier.
Right now, I'm not seeing anything alarming, especially with the speeds you're getting.
It's just a case of a bolt with sharp surfaces interfacing with the brass under pressure.
my fault, I thought I mentioned it... I was tired.
midlength gas, ballistic advantage hanson 16" barrel (don't know gas port diameter), h2 buffer, standard spring and carrier, sandman K can.
The bolt was a group buy.
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I’m in the same camp as 52. Clean up the bolt face and extractor, chamfer ejector, and tune gas for the suppressor. May require adjustable gas block as well as heavier buffer.
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Took apart my bolt.. Touched the inner edge of the ejector hole, as well as the sharp edge of the bolt under the extractor with 2500grit sandpaper. I shot 10 rounds... these are the 1st 5. The 2nd group of 5 were the same (one showing an ejector mark).
![[Image: OSA7so8.jpg]](https://i.imgur.com/OSA7so8.jpg)
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Me likey. Looks like you've found your issue here.
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