Ejector marks always a pressure sign?

[aquinas]

My DPMS SASS shows ejector marks even with a mild load.

It has shot 42.6 grains of H4859 with a 168 Nosler CC, CCI BR2 Primer in a Winchester case without problem.

It was showing ejector marks yesterday at 70 degree temps with 41.5 grains in an LC case. Primers looked fine.

Was testing 42.6; 42.7; 42.8 and 42.9 grains with Win case, CCI BR2 Primer and 168 bullet.

42.6 seemed fine. I thought 42.7 was showing ejector marks but they look more like scrapes rather than punches. They are very clear with a magnifying glass but less so with unaided eyes.

Was thinking I need to slow the carrier down with Tubb's Carrier Weight System. Wonder if that would help.

Still trying to figure out how to get pictures loaded on this forum.

 

[SScott]

Re: Ejector marks always a pressure sign?

You might be on to something, gasguns are a different animal, and they are known for timing issues. ( ejecting before brass is ready to come out of the chamber). This site is generally based on the bolt action platform, although most guys will have a back gun in their stash. If you don't get alot of response here, you might check other forums that cater to the black gun community.
SScott

 

[sobrbiker883]

Re: Ejector marks always a pressure sign?

Scrapes are from the timing (unlocking a c-hair early). The brass hasn't "sprung back" when the bolt starts to unlock, causing the crescent shave of brass.

When the brass flows into the the ejector's hole and stay there leaving a high spot then its usually over pressured.

A carrier weight may help, as would a heavier buffer.

Look in the "site info" forum for how to post pics.

 

[CardiacKid]

Re: Ejector marks always a pressure sign?

I noticed this as well on another shooter's 7.62 gas gun in addition to some decent extractor marring. I'd like to see photos as well to see if it looks similar because like you, he wasn't running anything that would be considered a hot load by book standards.

 

[gunsnjeeps]

Re: Ejector marks always a pressure sign?

The AR-15 leaves the same type of mark on brass. I'd assume (remember, assumtion is the mother of all f^@k ups) that the AR-10 by most manufacturers would do the same thing. Same action, different scales.

 

[former naval person]

Re: Ejector marks always a pressure sign?

NO. Machines differ. So do the brass marks.

 

[ClayDirt]

Re: Ejector marks always a pressure sign?

I dropped a heavy 10 oz buffer from slash in my AR10. It makes the rifle a little easier on the brass. If you are interested I will be offering some 10 oz buffers for sale in the group buy section here on the hide. They will be made here locally and not by Slash. Made from the same material 303 stainless.

 

[Grump]

Re: Ejector marks always a pressure sign?

Been at this for 30 years now.

I now believe that the only reliable pressure sign is velocity. If it seems too fast for that powder and bullet from that barrel length, it's probably over SAAMI spec.

Some people are just more comfortable using up their safety margin than others.

That said, if factory ammo using the same brass shows the same ejector wipe, *I* don't worry about it--velocity NOT being "too good", that is. YMMV, take action based on this at your own risk. We're all grown-ups here.

 

[OutlawHoss]

Re: Ejector marks always a pressure sign?

I just recently encountered this issue. I was developing a load for my DPMS LR308-AP4, after seeing what seemed as excess muzzle flash and a velocity spread of over 300 fps using Varget. I pursued a bit faster powder for the stock 16" bbl. and I tried RAM-TAC next, using a powder burn rate chart to pick from, that was pretty inclusive of almost everything on the market. It was the ticket. I loaded up 5 rounds for each charge, going up .5 of a grain from 40gr through 43.5 grain of the RAM-TAC. The last three loadings (42.5, 43, and 43.5) spit out the brass with the same ejector-swipe marks described above. I assumed it was too hot a load. Keep in mind I have the Tubbs CWS installed, have had it for most of the life of the gun, and am a believer in it. Those last three loads chrony'd from 2470 (average, 27fps spread) 2504 (average, 74fps spread) and 2507 (average, but only got two rounds through the chrony before it threw up errors due to battery dying). The loads fired prior to the ejector marks were 42gr of RAM-TAC and averaged 2421, with a spread of 58fps. Interestingly enough, I have used the Prvi Partisan 168gr. BTHP prior and had chrony data for it. It averaged 2437 with a spread of 64fps, similar (close anyway) to the 42gr. load of RAM-TAC with a 168gr. Hornady BTHP-Match (my loads were all 2x fired LC brass). The Prvi Partisan did not leave the ejector-swipe marks on the brass either. So my conclusion, for MY DPMS LR-308 w/16" bbl. gas gun, is that approximately 2430 fps is what it can handle, including the fact that I use the Tubbs CWS.
To drag this out even further, I'm using the Leatherwood/Hi-Lux CMR on this gun and the BDC reticule works great with this 2430fps., 168gr. BTHP round, again with the 1:10 16" bbl. Hope this contributes the the conversation, or at least the confusion.