Need Advice - Ejector Swipes with reloads suppressed, Creedmoor AR10

[SMTGWKD]

Alright Hide - I have an AR10 in 6.5 Creedmoor with the following key components from tip to butt:

SICO Omega
Griffin Plan A & Ti Minimalist Brake
20" Proof Carbon Cam Gas Creedmoor
SLR Ti Sentry Gas Block
JP VMOS (standard weight) with JP HP Bolt
Heavy Silent Captured Spring

All of the pictured rounds were shot with the same load as follows:

Temperature was 20 degrees F
Hornady Brass - full length sized
Federal 210 primer
41.5 of H4350
140 ELD-M seated at 2.805 COAL

The first shots with no marks were fired with gas set too low to fully cycle (they were manually cycled). I turned up the gas to cycle reliably (ejection at 4:00) and noticed nice marks in the brass at the base.

Should I remove weight from the system? Add weight? Can't reduce gas in current setup as I'm as low as I can go and cycle. Send the barrel and bolt to Proof to test?

 

[cloverleaf22]

Since you have the VMOS I'd be inclined to try adding weight. I had a similar problem and I believe it was that between the gas system length and amount of reciprocating mass, the bolt was unlocking too early before chamber pressures dropped requiring even more gas to rip the case out of the chamber and cycle.

 

[SMTGWKD]

Since you have the VMOS I'd be inclined to try adding weight. I had a similar problem and I believe it was that between the gas system length and amount of reciprocating mass, the bolt was unlocking too early before chamber pressures dropped requiring even more gas to rip the case out of the chamber and cycle.

Thank you for the hands on insight - to be clear, you recommend adding weight and adding gas as I'll need more gas to fully cycle the system, but the added lockup time will allow the case to stay in the chamber long enough to allow pressure to dissipate before extraction?

If I didn't love 6.5 so much this would all be souch simpler with a .308

 

[troupe]

If you have the way to work on your ejector and if it has sharp 90 degree edges on it, take it out and place a small, smooth bevel around the entire ejector edge. Robert Whitley that is involved with 6mmAR explains it better in his post. It may help some.

 

[cloverleaf22]

Thank you for the hands on insight - to be clear, you recommend adding weight and adding gas as I'll need more gas to fully cycle the system, but the added lockup time will allow the case to stay in the chamber long enough to allow pressure to dissipate before extraction?

If I didn't love 6.5 so much this would all be souch simpler with a .308

Mine actually was a 308 but it sounds like the same problem. Despite adding over 6oz to the reciprocating mass I was able to use the same gas setting. My theory is that the extra mass kept the bolt locked longer allowing easier extraction.

 

[Odysseus1911]

I would actually go the other way. Replace your heavy spring with a regular or even a light spring. Then you can use less gas and cycle reliably. Should be easier on your brass.

 

[SMTGWKD]

I would actually go the other way. Replace your heavy spring with a regular or even a light spring. Then you can use less gas and cycle reliably. Should be easier on your brass.

May be time to test JP's claims about weight and lockup. I may strip off the weight to test and add weight to do the same with the same loads.

If others have experience, steer me straight with some added data points.

No doubt the brass is filthy so weight to the system may be the answer.

 

[mtrmn]

I'd add weight myself. Slows down the reciprocating mass for a smoother operating gun in addition to helping with the timing.
Also, I've always been under the impression 4350 was not ideal for gas guns. But I may be confused by all I've read in the past about M1a loading, M1 loading, ad nauseum. The primers don't look like too high pressure, but the duration/timing of the pressure (4350) could be something to consider.
And make sure that ejector has rounded edges.

 

[TonyTheTiger]

I'd try brass other than Hornady and see what happens. My Hornady 6mm Grendel brass looks the same even with light loads and barely enough gas to cycle.

 

[SMTGWKD]

I honestly haven't messed with ejectors before. May have to learn something new. Here is a picture of my ejector - should I head down that rabbit hole?

 

[SMTGWKD]

I'd try brass other than Hornady and see what happens. My Hornady 6mm Grendel brass looks the same even with light loads and barely enough gas to cycle.

That's a great point - I have the exact same thing as you with my grendel and I've just accepted it on that platform. Also Hornady brass.

I have about 300 pieces of Hornady 6.5 that I've planned to use for 6.5 gas guns, but also have Lapua for PRS stuff - I could sacrifice a case of two in the name of science.

I'll start with weight - crap those tungsten weight are pricey though!

 

[troupe]

If you tackle the ejector, just round the very edges. It does not take a lot. Hornady brass is softer than Lapua. The AR10 platform is tough on brass how ever you look at it. I had the same issues years ago and I just cleaned the burrs of my brass with a flat file and kept going.

 

[mtrmn]

I honestly haven't messed with ejectors before. May have to learn something new. Here is a picture of my ejector - should I head down that rabbit hole?

View attachment 7774413View attachment 7774414

That ejector doesn't look too bad as is, most I see that cause problems are totally flat faced with very sharp edges. If you wanted to break the edges just a little more you could remove the ejector and chuck it in a drill. Hold it against a cheap sharpening stone at a 45* angle just long enough to put a tiny chamfer around the edge. I've seen ejectors that were totally spherical on the face.

And really, that brass looked pretty typical for the large frame ARs. JMO

 

[GreenGO Juan]

I believe, Its the Hole for the ejector on the bolt face that is causing the mark not the ejector rod.

The brass is flowing into the hole the ejector sits in during firing causes a small impression in the case head from the pressure inside the case. If you look close at the brass you hand cycled you can see that impression, but no bur. The pic is out of focus, but I bet the others have this too.

When hand cycled, its not nearly as aggressive as gas cycled, so it doesn’t leave a bur from the small impression but its still there. When gas cycled with some pressure still in the barrel/case its enough to leave an ejector swipe from the small impression left from the bolt face.

Semi autos are tough on brass.

You could try playing with seating depth. Bullet jump/jam can have an effect on pressure. Try different/slower burning powder. That doesn’t build as much peak pressure.

My .02 take it for what its worth.

 

[SMTGWKD]

I believe, Its the Hole for the ejector on the bolt face that is causing the mark not the ejector rod.

The brass is flowing into the hole the ejector sits in during firing causes a small impression in the case head from the pressure inside the case. If you look close at the brass you hand cycled you can see that impression, but no bur. The pic is out of focus, but I bet the others have this too.
View attachment 7774646

When hand cycled, its not nearly as aggressive as gas cycled, so it doesn’t leave a bur from the small impression but its still there. When gas cycled with some pressure still in the barrel/case its enough to leave an ejector swipe from the small impression left from the bolt face.

Semi autos are tough on brass.

You could try playing with seating depth. Bullet jump/jam can have an effect on pressure. Try different/slower burning powder. That doesn’t build as much peak pressure.

My .02 take it for what its worth.

Bingo - I'm actually going to try a couple shots with Lapua and the same load before messing with mass, etc. Like changing spark plugs before bigger adaptations. If not, RL16 has been phenomenal in this regard by comparison. I may use that moving forward.

 

[GreenGO Juan]

Bingo - I'm actually going to try a couple shots with Lapua and the same load before messing with mass, etc. Like changing spark plugs before bigger adaptations. If not, RL16 has been phenomenal in this regard by comparison. I may use that moving forward.

Cool beans!

 

[gixxer822]

For what it’s worth I have a 308AR that does the exact shame shit with H4895. I tried BLC and the rifle absolutely loves it. Sometimes certain powders just don’t work well with the set up without lots of tuning.

 

[GreenGO Juan]

For what it’s worth I have a 308AR that does the exact shame shit with H4895. I tried BLC and the rifle absolutely loves it. Sometimes certain powders just don’t work well with the set up without lots of tuning.

I notice the trends from the powders I have tried with .308. Imr 4166 is the fastest powder I have tried and its hard on the brass. CFE.223 slowest powder I have tried is much easier on the brass at comparable, even high velocity. But I have not been able to get it to group well.

 

[Just-some-guy]

REASON EDITED: I re-read the post...


I recently had an issue with my AR10 and had brass that looked like yours with that ejection swipe and flattened primers. Most of my brass looked similar to yours, I thought it was not getting enough power to fully cycle the bolt carrier, that was not the case, fortunately I got help from the Hide before I blew things up.

The problem I had was essentially 2 things:

1. Gas block: This was not aligned correctly, and thus not allowing enough gas through. This was very hard to fit correctly on this build for some reason, as I tried several times and methods and it was still not 100% correct, thus causing "low gas" symptoms despite over power loadings. I Solved this by using a dimple jig sold by KAW Valley Precision (highly recommended).

2. Buffer weight: The standard .308 rifle buffer was not heavy enough, I swapped to a heavy rifle buffer / fixed cycling problem. I can't really describe the science behind this but something to do with mass and lock / unlock times.


Read all about my issues here...

6.5 Creedmoor AR10 Cycling Problem

So here is my issue... I built an AR10 (DPMS style) in .308 with a Criterion 18" rifle length gas system, standard weight rifle buffer and spring, and a Toolcraft BCG; this setup runs flawlessly with pretty much all my loadings and with the factory ammunition that I've (sparingly) used. I...

www.snipershide.com

 

[supercorndogs]

Does nocking the edges of the ejector actually work? I though it was the hole the ejector is in that makes the mark.

 

[GreenGO Juan]

This piece of brass with the red arrow was shot with the gas turned off, hand cycled. The ejector rod sits on a spring which I can push in with my fingers, below the bolt face.

I am curious where the impression in the brass came from? Surly not the 50-60,000 psi of pressure in the chamber.

 

[LRRPF52]

Brass is soft and not all brass is created equally. In a gas gun, we’re often not letting the brass rebound fully, but instead are unlocking the chamber with a rotating bolt (in the Stoner and Garand systems), so any residual pressure or brass flow into the ejector channel gets smeared or shorn opposite of the direction of rotation because it’s still trying to fill the void where the ejector channel is (a flow path).

There are several ways to approach this problem:

1. Use Lapua brass (mitigates but might not totally solve it)

2. Polish your bolt face and barely take the sharp edge off the ejector channel mouth.

3. Keep your bolt locked longer with Extended Length Gas System and/or heavier action spring weight.

There’s a long post from another Hide member from many years ago that takes you through a very detailed list of mitigating these and many other little nuances in the SR-25/AR-10/AR-15, complete with photos, called Hellbender’s guide.

 

[GreenGO Juan]

But he is still getting the impression manually cycled. Which is alot slower than any gas system. The bolt is not unlocking for likely a few seconds, and all the pressure is gone, yet still getting an impression of the bolt face on the brass.

Aggressive cycling is creating a bur, but the root cause is deformation of the case head from pressure. No amount of change to the gas block, buffer weight, bolt carrier is going to effect that fact the when the bolt stays locked and is manually cycled its still deformed the case head. The impression pointed out in the picture above.

 

[LRRPF52]

OP: How far are you setting back headspace?

Look at the difference between ejector channel shadow vs extruded shears.

There’s nothing wrong with shadow, but there is a problem when the brass is flowing into the channel and then being shorn during bolt rotation. The biggest problem that creates is brass shavings accumulating on the bolt face, into the extractor shelf, and into the ejector channel.

The next big problem is with case overall length readings in your gauges. The added material protruding from the case head will throw off your headspace measurements, as well as seat your bullets that much deeper during the seating process unless you sand off the extrusions.

In my .260 Rem gas gun, I started off using harder Winchester 7mm-08 brass necked down, since the Remington brass is so soft. I’ve never even messed with the Remington brass in that rifle. I then got Lapua .260 Rem brass when it came out.

Another way to approach this is to use Small Rifle Primers. Oh wait, I just checked and you’re already using SRP brass.

Reduce your charge weight or shoot 130gr like I do. Chasing performance with 140gr in a 6.5-08 class gas gun is really asking for a lot. That’s where I’m at with this and even for myself many years ago. I tested out every available 140gr class bullet back then and found that I couldn’t really expect to push max book loads with them. 130gr Berger VLD became my friend, although many said I wouldn’t be able to get it to shoot in a gas gun. My chamber was cut for 139gr Scenar, so 130gr VLDs worked like magic. Extremely flat, fast, minimal wind drift, less stress on the reciprocating mass, easier sight picture management.

 

[SMTGWKD]

I'm actually using large rifle primers in these rounds. Using up the remaining Hornady brass. Should be jumping 20 Thousandths based on initial look and COAL at 2.805.

I have a wonderful load at 41.0 of h4350 behind a 147 that doesn't show these signs. Ive never shot 123s in my Creedmoor but may find a solid load and run with it since I may have a bunch if I sell my grendel barrels.

 

[SD Carpenter]

I've ran about 500 rounds of Lapua brass through my 6.5 creed gasser, and it definitely chews up my brass. It looks alot worse then yours with nicks along the case body.

 

[mtrmn]

Does nocking the edges of the ejector actually work? I though it was the hole the ejector is in that makes the mark.

The hole makes a mark or a raised area where the brass flows into the ejector hole. If the mark winds up actually being a raised area in the brass, then that raised area becomes a "swipe" when the brass is shifted sideways during bolt rotation and ejection

If there is also gouge in the brass with a raised lip of brass along one edge of the gouge, then this is a product of a sharp-edged ejector catching the brass during the feed cycle. This would look something like if you were to use a scraper on a freshly painted surface that's still soft.
As the cartridge is fed from the magazine, the head of the case will slide across the ejector under a good bit of force. If the ejector has a sharp edge it will gouge into the softer brass and leave a mark that is often mistaken for the dreaded "swipe."

Rounding the edge off on general principles won't hurt anything and it's really hard to overdo this. If you look at a lot of "enhanced" bolts you will likely see some well-rounded ejectors.

 

[LRRPF52]

I'm actually using large rifle primers in these rounds. Using up the remaining Hornady brass. Should be jumping 20 Thousandths based on initial look and COAL at 2.805.

I have a wonderful load at 41.0 of h4350 behind a 147 that doesn't show these signs. Ive never shot 123s in my Creedmoor but may find a solid load and run with it since I may have a bunch if I sell my grendel barrels.

Isn’t Federal 205 a Small Rifle Primer?

Does Hornady even make SRP brass for Creedmoor?

I see Federal 205s listed in the OP. Is that a typo?

Temperature was 20 degrees F
Hornady Brass - full length sized
Federal 205 primer
41.5 of H4350
140 ELD-M seated at 2.805 COAL

 

[supercorndogs]

I have read quite a few thread where @padom helped people make their big frame AR easier on brass.

 

[SMTGWKD]

Isn’t Federal 205 a Small Rifle Primer?

Does Hornady even make SRP brass for Creedmoor?

I see Federal 205s listed in the OP. Is that a typo?

Whoops! 210! Updated.

 

[SMTGWKD]

I have read quite a few thread where @padom helped people make their big frame AR easier on brass.

I believe I'm actually using exactly what padom recommended. I messaged with him while building this project.

 

[Kocher]

never saw an update.. i’m guessing all the fixes that have been talked about we’re trying.

The time I’ve spent with my AR10 I Believe gas port timing/length is the issue to solve. a +4 or +5 would be the way to go on most rifles.

If that’s not gonna work then adding weight and a heavy duty spring.

If I had the ingenuity I would make modifications to bolt carrier groups where it allows you to screw plugs in the back cavity it would allow you to place tungsten electrodes in or take out depending on what you wanna do for weight it’s a cheap fix and you can use the bolt carrier group already got you don’t have to go out and spend another 400 bucks on JP system.

I’m having trouble just reaching max velocities with max charges mine are not making case marks on most but I have found brass that is softer makes it worse.

Tungsten adding work good for me until the silicone that I used to hold it together started pulling loose so that didn’t work I’m going out today with two springs in my rifle length buffer tube system figure that’ll increase dwelltime.

 

[SMTGWKD]

never saw an update.. i’m guessing all the fixes that have been talked about we’re trying.

The time I’ve spent with my AR10 I Believe gas port timing/length is the issue to solve. a +4 or +5 would be the way to go on most rifles.

If that’s not gonna work then adding weight and a heavy duty spring.

If I had the ingenuity I would make modifications to bolt carrier groups where it allows you to screw plugs in the back cavity it would allow you to place tungsten electrodes in or take out depending on what you wanna do for weight it’s a cheap fix and you can use the bolt carrier group already got you don’t have to go out and spend another 400 bucks on JP system.

I’m having trouble just reaching max velocities with max charges mine are not making case marks on most but I have found brass that is softer makes it worse.

Tungsten adding work good for me until the silicone that I used to hold it together started pulling loose so that didn’t work I’m going out today with two springs in my rifle length buffer tube system figure that’ll increase dwellti

I haven't had time to recheck! I purchased a couple extra tungsten weights to mess around with mass first, then brass but haven't yet taken the initiative. Lame, I know.

 

[bobke]

Not going to claim expertise on dwell time, but the above suggestion of a +4-5” port location over rifle length would have your gas block sitting over your muzzle. There’s a good reason for +2 in a high pressure smaller caliber round like 6.5CM, but requires close attention to port diameter and balancing the entire gas system for proper function. Five 6.5CM barrels of different configurations and mfg’s tell me so. It’s a little bit of art and science to make it all work together.

 

[bigjake83]

The OP is running a Proof CF Barrel that already has the +2 Cam Gas system, and requires a Full mass BCG (1-1.2 LBs) and H2 Buffer. If you're not running the above configuration you're already off the mark, it is clearly stated on the Proof webpage it is required.

Proof has well and truly put in the RND to figure out the proper gas port size and location for the higher pressure 6.5 and 6MM rounds, after they invented their CamGas system JP shortly started moving to a +2 gas as well. So it will behoove you to follow their instructions.

As mentioned above you probably need to lower your charge weight, my last 6.5CM handload was 40.8grs of H4350 with a MZ of 2720 from a 22" barrel.

You don't chase performance in a Gasser, do your ladder test and as soon as you see signs of pressure, assuming your rifle has the proper BCG/Buffer weight and gas adjustment you stop and find your node/ best group under that charge weight.

And lastly yes use quality brass I personally use STARLINE Match SP brass and shit can them between 5-6 firings.

 

[msgriff]

never saw an update.. i’m guessing all the fixes that have been talked about we’re trying.

The time I’ve spent with my AR10 I Believe gas port timing/length is the issue to solve. a +4 or +5 would be the way to go on most rifles.

If that’s not gonna work then adding weight and a heavy duty spring.

If I had the ingenuity I would make modifications to bolt carrier groups where it allows you to screw plugs in the back cavity it would allow you to place tungsten electrodes in or take out depending on what you wanna do for weight it’s a cheap fix and you can use the bolt carrier group already got you don’t have to go out and spend another 400 bucks on JP system.

I’m having trouble just reaching max velocities with max charges mine are not making case marks on most but I have found brass that is softer makes it worse.

Tungsten adding work good for me until the silicone that I used to hold it together started pulling loose so that didn’t work I’m going out today with two springs in my rifle length buffer tube system figure that’ll increase dwelltime.

I have not seen a +4 or +5 6.5 CM barrel before. I'm sure one could be custom made, but do you have any examples? Also, I'm a bit confused on your tungsten/silicone buffer, can you elaborate? Same with the double action spring, what are the specific specs of the springs you are doubling (length, wire diameter and number of coils), and are they stacked or intertwined?

 

[SMTGWKD]

I have not seen a +4 or +5 6.5 CM barrel before. I'm sure one could be custom made, but do you have any examples? Also, I'm a bit confused on your tungsten/silicone buffer, can you elaborate? Same with the double action spring, what are the specific specs of the springs you are doubling (length, wire diameter and number of coils), and are they stacked or intertwined?

Following up here so my experience can help others.

I went to the range with a load I had tested previously that left marks on brass with the combination in the OP (Xanthos AR10, Proof 20" barrel, JP VMOS BCG, SCS, with Silencerco Omega).

147 ELD M with 42.2 gn RL 16 & Hornady Brass

I've messed with charge weight, Brass, BCG weights, etc and just stopped shooting it as I only shoot suppressed.

The only change this time was the use of a low back pressure can (CAT ODB Ti). WHAT A DIFFERENCE!

Here a photo of Brass and 3, 3-shot groups ranging from about .35" to about .6". I had to ADD quite a bit of gas to cycle the rifle with the CAT.

In short, the very high backpressure of the Silencerco Omega, in my setup, caused some really annoying pressure issues - all of which were solved with the can change.

Had a great, accurate range day after that! Hope it proves useful for others as they decide on silencers, etc. Knowing what I know now I would only buy a lower back pressure can for semi autos and a higher backpressure can for a bolt gun use.