Ejector swipe on multiple ammo brands

[pnutty]

Hi again;

I’m having a few more issues with my build, specs are:

Aero m5 receiver set

BA 6.5CM 20” barrel rifle length with .0785 gas port with ar15 rifle gas tube in the middle of cutout

Kak 308 bcg dual ejector with small firing pin/hole, oring and 2 ejector springs installed

Kak extended buffer tube 7-11/16 deep with H3 buffer and EA1095 spring 

Cmmg lpk

What is happening is that I am getting ejector swipe on 4 different brands of ammo and a scenario where the extracted round doesn’t eject but stays in the receiver and the bolt travels rearward enough to pick up a new round. If I single load a round the bolt locks on an empty mag but the empty round still stays in the receiver. This build has around 100rds through it so nothing should be worn out.

Ammo is S&B 140g, Aguila 129g, Hornady 140g and my reloads in the Lapua brass which has 42g of staball that puts its right in the middle of the reload book spec.

My unprofessional opinion is that the cases are still expanded while trying to extract and that’s why they aren’t exiting the upper, I doubt it is undergassed because the bolt goes rearward enough to pick up a new round or lock backnon an empty mag.

 

[shooterrex]

I was having similar problems with 1 build. The ejectors in the bcg are they flat faced or rounded on the end?

I replaced the ejector with KAK rounded tip and the gun started running right. Almost seems over gassed and the emptiness are not shrinking fast enough to allow extraction. 

[98Z5V]

Does the pic of the brass directly follow the ammo listed, in order?  Like, left to right?  First ammo listed is the first piece of brass on the left, etc. 

You have a dual ejector bolt, but only one swipe on the brass - and the swipes seen are big enough to catch your fingernail, where you'd have to file them off to reload them.  

That 3rd piece of brass has no ejector marks on it at all, left to right, 3rd one.

[pnutty]

7 hours ago, shooterrex said:

I was having similar problems with 1 build. The ejectors in the bcg are they flat faced or rounded on the end?

I replaced the ejector with KAK rounded tip and the gun started running right. Almost seems over gassed and the emptiness are not shrinking fast enough to allow extraction. 

Yes they are both rounded, and I agree with what you are saying about it not shrinking fast enough.

 

4 hours ago, 98Z5V said:

Does the pic of the brass directly follow the ammo listed, in order?  Like, left to right?  First ammo listed is the first piece of brass on the left, etc. 

You have a dual ejector bolt, but only one swipe on the brass - and the swipes seen are big enough to catch your fingernail, where you'd have to file them off to reload them.  

That 3rd piece of brass has no ejector marks on it at all, left to right, 3rd one.

The brass is randomized in the pic, I shot Aguila, S&B, Hornady then reloads in that order. There are 2 ejector marks on the cases but only one of the ejectors is showing up much more pronounced than the other one.

On the S&B case the marks are on the “cr” and “oo” in Creedmoor but it’s hard to tell from the picture, I can try to get better pictures for you if needed.  But I do not know why one ejector mark is showing up much more than the other one…

Edited October 5 by pnutty

[Magwa]

also that bolt looks dry as street pavement, and maybe dragging due to how dry it is soak the bolt in mobile 1 synthetic oil for a couple of weeks the oil will adhere to the metal i the bolt and remain slick but breaking in a new gun you want it dripping wet....

[pnutty]

7 hours ago, Magwa said:

also that bolt looks dry as street pavement, and maybe dragging due to how dry it is soak the bolt in mobile 1 synthetic oil for a couple of weeks the oil will adhere to the metal i the bolt and remain slick but breaking in a new gun you want it dripping wet....

Ok sounds reasonable, I usually put some oil on my fingertip and smear it all over the outside as a film coat but ill do what you said 👍

[pnutty]

15 hours ago, 98Z5V said:

Does the pic of the brass directly follow the ammo listed, in order?  Like, left to right?  First ammo listed is the first piece of brass on the left, etc. 

You have a dual ejector bolt, but only one swipe on the brass - and the swipes seen are big enough to catch your fingernail, where you'd have to file them off to reload them.  

That 3rd piece of brass has no ejector marks on it at all, left to right, 3rd one.

I took the best pictures I could of the case heads, the marks dont like to show up for the camera though. You can see the spots where both ejectors are making an imprint but one ejector is much more pronounced than the other one, why that is I have no idea. I also took a picture of the extractor indent on the case if that would help as well. 
S&B had the least amount of swipe and I could not get that to focus at all on the camera.

[Albroswift]

Soak in mobile 1

See what you have under the extractor- Dougnut, spring, tiny spring inside the spring?

Weigh the H3

The swipes do not look like rounded ejectors

When it locks back does it lock on the bolt face 100% or maybe just the bolt carrier?

100% sure EA1095?

Look through the questions on the waterboarding thread, maybe find a clue there

 

[98Z5V]

21 hours ago, pnutty said:

On the S&B case the marks are on the “cr” and “oo” in Creedmoor but it’s hard to tell from the picture,

That doesn't mean anything, because of springs.  Springs twist when the expand and contract, so they turn things, in motion.  Even if you very carefully lined up every round in the magazine, exactly the same, all the wording directly matching in the mag, same angle - the springs will twist 'em.  Where the marks are, compared to the words on the headstamp - not an indicator of anything.

You have hot loads, plain and simple.  Maybe the ammo is hot - maybe the gun configuration isn't handling the pressure of the ammo you're using.  Something is causing that to be hot ammo in that specific gun. 

[98Z5V]

That extractor mark on the rim - that's telling of a hot load. It was trying to rip that stuck brass out of the chamber. 

So, if it's not the ammo causing this - it's the gun not being able to handle the ammunition.  Something is making all those loads look like hot loads - and it's not always ammo.

Have a chrono you can shoot these thing through?  That will give you some immediate answers, right there.

[pnutty]

18 hours ago, 98Z5V said:

That extractor mark on the rim - that's telling of a hot load. It was trying to rip that stuck brass out of the chamber. 

So, if it's not the ammo causing this - it's the gun not being able to handle the ammunition.  Something is making all those loads look like hot loads - and it's not always ammo.

Have a chrono you can shoot these thing through?  That will give you some immediate answers, right there.

I do have a magnetospeed sporter so when I get to the range again ill report back. 
Just curious if the ammo isnt an issue, could the gun parts be out of spec and that would cause this?

[98Z5V]

2 hours ago, pnutty said:

Just curious if the ammo isnt an issue, could the gun parts be out of spec and that would cause this?

Absolutely.  A recoil system that's too light, not up to the task, lets that BCG start unlocking early.  That rips rims off brass - brass that hasn't cooled and released from the chamber walls, sticks to the chamber walls.  Too large of a gas port, too much pressure going through - that's typically not the issue seen with gas systems - usually, the ports are too small.  Could be a few things...

Based on the specs you listed for your gun, I'm not going to condemn the parts, or port size.  You selected very great parts.  Focus on the ammo, with that Magnetospeed...  

Edited October 7 by 98Z5V

[shooterrex]

Weigh the buffer too

[pnutty]

8 hours ago, shooterrex said:

Weigh the buffer too

I did, the buffer is 5.5oz so that should be right in spec for an H3

 

On 10/5/2026 at 9:50 PM, Albroswift said:

Soak in mobile 1

See what you have under the extractor- Dougnut, spring, tiny spring inside the spring?

Weigh the H3

The swipes do not look like rounded ejectors

When it locks back does it lock on the bolt face 100% or maybe just the bolt carrier?

100% sure EA1095?

Look through the questions on the waterboarding thread, maybe find a clue there

 

Alright, thought I had all the important info but here is more;

The bolt does have the dual ejector spring setup with the oring setup that way from KAK.
The buffer does weigh 5.5oz so that is in spec for an H3 and the EA1095 spring was purchased from everygunpart which Armalite uses as their oem so I highly doubt its a knockoff.

The bolt locks back properly on the boltface everytime so I doubt that it is undergassed. I am going to follow 98Z5V’s advice and chrono the ammo im using and hopefully will have some answers after that.

[98Z5V]

 You are on the right track, man - and you have the tools to find out the info.

FWIW...  In the future, I have a MagnetoSpeed that I can send out, when people run into this kind of issue.  I'm not saying I'd send it out just all WillyNilly, to any random jackass that shows up on the board...  But I would send it out to reputable, trustable, known members of the board.  

[Albroswift]

Maybe things to check, does unfired ammo that has been chambered from full back bolt extract easily? Can you slowly chamber a round fully? Do you have access to chamber gauges?

[Magwa]

1 hour ago, Albroswift said:

Maybe things to check, does unfired ammo that has been chambered from full back bolt extract easily? Can you slowly chamber a round fully? Do you have access to chamber gauges?

I am wondering the same ,maybe a tight chamber or rough one.

[shooterrex]

or overgassed

[pnutty]

13 hours ago, Albroswift said:

Maybe things to check, does unfired ammo that has been chambered from full back bolt extract easily? Can you slowly chamber a round fully? Do you have access to chamber gauges?

No issues with chambering and extracting a unfired round, I did rent headspace gauges when I first built it and no issues but I did swap the original dpms large firing pin bolt with a Kak small firing pin dual extractor bolt. The locking lugs thickness and the bolt face depth are identical on both so I doubt that would cause an issue.

[98Z5V]

I just went back and looked at these two pics...

Exactly what's happening right there is this - that hot brass hasn't contracted enough yet, in the cycle of operation, and it's stuck to the chamber walls still.  That BCG is already beginning it's rearward movement, forcing the cam pin cutout in the BCG to rotate the cam pin - and turn the bolt.  While the brass is stuck to the chamber walls.  That's what causes ejector swipes.

Commonly, it's not enough recoil system.  Not the case with your gun setup.  Secondarily, it's not a bad gas system that isn't balanced to the proper recoil system.  I wouldn't suspect that at all with your BA barrel, and your statement on gas tube length, ending in the center of the cam pin cutout in the upper receiver.  Your gas tube length is good.  Only other thing in the gas system that can cause problems is the gas port diameter - but I wouldn't suspect that coming from BA, not in the least.  Too much gas port, and you're running hot, too much gas.  Not on my radar, from BA.

That leaves hot ammo.  It's the only other thing that's easy to test, without putting tools to your gun to check the gas port diameter.  

Run 5 rounds each of all those ammo choices that you shot, document the info from each ammo brand (MV AVG, SD, ES), and let's see where this goes, or leads us. If all those ammo speeds check out, we're pulling the gas block screws, sliding it forward, and measuring gas port diameter...   

[Albroswift]

10 hours ago, pnutty said:

I did rent headspace gauges when I first built it and no issues but I did swap the original dpms large firing pin bolt with a Kak small firing pin dual extractor bolt. The locking lugs thickness and the bolt face depth are identical on both so I doubt that would cause an issue.

Never know, might want to re-rent and double check. Did you fire the same ammo with the DPMS bolt? Do you still have the DPMS bolt? Agree with above looks like overly hot ammo but different brands of commercial all doing the same thing seems unusual, but I don't shoot commercial except to test new builds. See what the chrono shows.

[pnutty]

23 hours ago, 98Z5V said:

I just went back and looked at these two pics...

Exactly what's happening right there is this - that hot brass hasn't contracted enough yet, in the cycle of operation, and it's stuck to the chamber walls still.  That BCG is already beginning it's rearward movement, forcing the cam pin cutout in the BCG to rotate the cam pin - and turn the bolt.  While the brass is stuck to the chamber walls.  That's what causes ejector swipes.

Commonly, it's not enough recoil system.  Not the case with your gun setup.  Secondarily, it's not a bad gas system that isn't balanced to the proper recoil system.  I wouldn't suspect that at all with your BA barrel, and your statement on gas tube length, ending in the center of the cam pin cutout in the upper receiver.  Your gas tube length is good.  Only other thing in the gas system that can cause problems is the gas port diameter - but I wouldn't suspect that coming from BA, not in the least.  Too much gas port, and you're running hot, too much gas.  Not on my radar, from BA.

That leaves hot ammo.  It's the only other thing that's easy to test, without putting tools to your gun to check the gas port diameter.  

Run 5 rounds each of all those ammo choices that you shot, document the info from each ammo brand (MV AVG, SD, ES), and let's see where this goes, or leads us. If all those ammo speeds check out, we're pulling the gas block screws, sliding it forward, and measuring gas port diameter...   

If everything goes well, I will hopefully be testing tomorrow. Before I installed the barrel I measured the gas port and a #47 (.0785”) drill fits perfectly, a #46 drill would not fit (.081”) so that gives you the port size at least. I recall reading (possibly on here) that the 6.5CM runs higher port pressures than the 308win for the same barrel length and gas system, I wonder if that would have anything to do with it.

 

13 hours ago, Albroswift said:

Never know, might want to re-rent and double check. Did you fire the same ammo with the DPMS bolt? Do you still have the DPMS bolt? Agree with above looks like overly hot ammo but different brands of commercial all doing the same thing seems unusual, but I don't shoot commercial except to test new builds. See what the chrono shows.

I did fire the same ammo except the Aguila and the same thing happened with the DPMS bolt but I was getting pierced  primers so that is why I swapped. I figured if I had issues with 4 different ammo types then something has to be causing it in the gun. I was thinking maybe the leade or throat was very short and jamming the bullets in the lands but I colored in the bullet with a sharpie and loaded a few rounds and ejected them. No marks were on the bullets at all so there goes that theory.

[Albroswift]

I would think it doesn't necessarily have to jam the bullet into the lands to cause a pressure spike. Try handloading a dummy round with very little crimp, and 0.020 extra long or as long as you can fit in magazine, sharpie it up and see if it hits the lands or is pushed back. I have no idea wat a 6.5 in an autoloader should have but I'd guess 10 or 15 thou minimum. Internet is all over the place like 20 to  100 thou for AR's. The one we built a couple years back did pierce primers with a 308 bolt, went to the SRC dual ejector just because I had one on the shelf but later figured out somehow I had a 308 bolt with a small dia firing pin so that may have been the primer issue.  

[pnutty]

Update to the thread, did ammo testing today and have some numbers. I also made up a free float jig for my magnetospeed so now I can zero without effecting barrel harmonics or zero.

Hornady 140g eldm ; avg-2596 sd-7 es-15

S&B 140g fmj; avg-2566 sd-16 es-32

Aguila 129g SP; avg-2647 sd-12 es-29

Reloads 140g eldm with40g staball; avg-2575 sd-7 es-17

 

Barrel was cleaned and all residual oil wiped out of barrel before testing. I also soaked the bcg in oil and ran it very wet but still getting swipes and extractor marks on the case rim.

Edited Sunday at 07:22 PM by pnutty

[98Z5V]

On 10/9/2026 at 6:03 PM, pnutty said:

Before I installed the barrel I measured the gas port and a #47 (.0785”) drill fits perfectly, a #46 drill would not fit (.081”) so that gives you the port size at least.

That's what I had to come to on both my .260 Rem guns.  20" rifle gas barrels with 0.750" journals,both ported to 0.080"  That's good.

That ammo isn't hot.  Something else is going on.  I have 2650 fps with Hornady 147 ELD-M handloads going through both .260s, and there are no pressure signs.