ejection/extraction trouble shooting: adjustable gas blocks and powder burn rates

[georgehwbush]

i'm having issues with ejection/extraction on the new ar-10 243-win,
description: PSA 243-win 22" SS gasblock is 10" from muzzle. adjusted to full open.
factory ammo is ejecting at 2:00 with no marks on the brass, handloads (nosler 90g spr, H-4350 42.0gr, cci200 primers, winchester brass) are ejecting all over the place from 1:00 to 5:00 and have rotation/ejector marks, the last cartridge will not lock the bolt back.

my question is this: is the powder burn rate too slow for this kinda short gas system, or am i looking in the wrong place for this issue?

also is there any chance that reducing the gas might make the bolt lock back ? (sounds counter intuitive)

 

[Shadow9mm]

I use the Aero Precision adjustable gas blocks. Their instructions are basically, start full open, shoot 1 round, see if it locks open. repeat until the bolt does not lock back. Then open 3 clocks (has 15 clicks total) so closing it will only make it cycle worse.

If you getting erratic ejection, that indicates to me your load is inconsistent, or rather getting an inconsistent burn/pressure. Looking at Hodgdons site it shows a max of 44.5g with a 90g speer soft point. My suspicion would be that you are getting an inconsisten burn due to being 2.5g under max and not generating enough gas to cycle the system.

However your getting pressure signs so I wouldnt go any higher personally.

Id say its a bad combo for the gun imho.

 

[HiBC]

Its not convenient for me to look up your load right now.
You mention ejector/rotation marks.

If you are describing what I think you are describing, IMO,the issue is not about the gas block.

If I read you right, peak pressure is high enough to actually extrude brass into the ejector hole in the bolt face.Then,when the bolt rotates,it shears off the slight extrusion. I'd interpret that as your peak pressure is too high. Your gas block won't correct the extrusion of brass.
FWIW, the "scraping" ,a little crescent shaped bit of brass,may foul the ejector hole and bind up your ejector.
In any case,the day will come when you need to strip and clean your bolt. I suggest you order a Brownells/Sinclair bolt assy/disassy tool ahead of time,along with a kit of replacement springs and plungers, Its a learning curve thing. Think "boing" ,dang it!! and crawling around trying to find the launched bits. Stressful! There is peace in spares.

As far as your peak pressure, I respect Unclenick as our interior ballistics pro.

I'm not.

But I "read the track" of brass extruding into the ejector hole as high pressure. You might soon see loose primer pockets.

I could be wrong,but thats my guess.

 

[tangolima]

I have an ar10 in the same caliber. 24" barrel. A few things I have learned after monkeying with it for some time.

Check whether there is burr around the ejector hole. It can cause swipe mark prematurely. Do you see cratering on the spent primer? If you do, you probably have over pressure in your load.

.243 win published load data seem over aggressive. I could never reach the published MV. Mid way between min and max charge I started having pressure signs; swipe marks, cratered primers etc. In order to get a bit higher MV, I use slower powder (Ramshot hunter). It seems working better.

24" barrel with rifle length gas is not ideal. The dwell time is long. Action may started unlocking before bullet total clears the muzzle. It may cause the swipe marks. I deal with that by closing up the gas block. In my case, extraction/ejection/lock back is no problem. I don't pay much attention to clock position of the ejected brass, as long as it functions right.

-TL

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[Shadow9mm]

Hadn't thought about the dwell time issue. I knew it was a bit short for that system. But yes, if the bolt starts unlocking with the bullet in the barrel, and the pressure is still high that could definitely cause a problem

 

[HiBC]

We can respectfully disagree,

If the brass is extruding into the ejector hole,the root cause is excess pressure.

That has to happen first.

Gas blocks, buffers,dwell time, recoil springs, etc can tune the vigor of the cycle,

But if brass is standing proud of the case head, how does that happen short of excessive peak pressure? (Unless its a botched anneal job or othewise soft brass),

Agreed,if there is a steel burr standing proud of the bolt face, it could be misleading.

I don't know if its coincidence, but Shadow 9mm quoted data for a Speer bullet. The OP said "Nosler SPR" I assume "Spitzer"

I like the Nosler bullets I use, but I recall some Nosler "Solid Base" bullets vintage 1970's to 1980's that seemed to remarkably elevate pressure.

I don't know if those are still in the lineup.

 

[44 AMP]

A few points to consider...

First, IMR 4350 is a slow powder. Its not ideally suited to gas operated semi autos, though they can be set up to run it well enough.

Next point, is that .243 data is nearly always worked up using BOLT ACTIONS as test guns. Top end loads may simply not be suitable (or achievable) in gas guns.

finally, consider that if you get pressure signs on your cases you have excess pressure, for your gun and that combination of components. Doesn't matter WHAT the book says, if you get pressure signs, you have excess pressure.

WHY you have excess pressure and at what point in the cycle it happens are different questions.

Add in the complications of gas gun timing and there are now lots of possible factors that need to be considered.

 

[tangolima]

Action unlocking under pressure can change the swipe pattern. But I agree the load is probably on the warm side anyhow. I always want to correlate that with primer cratering to determine when to stop.

OP said the factory rounds worked ok. That's interesting. I haven't shot factory rounds at all. What's the make and model? I may want to give it a try as benchmark.

BTW, converting .308 win brass to .243 win is piece of cake. It will be my source of brass after I exhaust my batch of Hornady.

-TL

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[georgehwbush]

ok guys let me clear this up. using H-4350 not imr-4350 secondly 42.0 gr is the "starting" charge weight for that powder, not the max. at least according to hodgdon's load manual. thirdly i do not see any signs of over presure, and the velocity is in the starting velocity range for that load. fourthly the sd on th seven shot test i ran was 6 the pressure is not "all over the place" so more thoughts with this in mind maybe ?

 

[georgehwbush]

tangolima make and model ? gun or factory load ?

 

[georgehwbush]

tangolima assuming load is your qurry, federal 100gr sp "blue box" the cheapo stuff.

 

[tangolima]

Thanks. I was indeed asking about the factory ammo. I will get a box to shoot as benchmark.

-TL

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[44 AMP]

Generally speaking, gas operated semis run their best with medium burn rate powders. Gas guns require a pressure curve within their design tolerances, peak pressure may be within proper range, but the pressure curve / port pressure may not be what the rifle wants, with slower powders.

Slow powders are best in bolt guns where there is no concern about port pressure or the pressure curve.

I don't know H 4350 isn't it a tad slower than IMR 4350??

decide which is most important for you with that rifle, maximum accuracy? Maximum velocity? consistent correct functioning??

You may not get all three with some loads.

Personally, with a semi auto, I put reliable function first, accuracy second, and velocity last. If I have to give up some velocity to get better accuracy and reliable cycling, I will gladly do that.

If the last round doesn't lock the action open (and factory ammo does) your function is borderline.

 

[tangolima]

Slower powder has higher port pressure. That's about it. It can cause issues, or even break things, if the system is not adjusted. With proper adjustments it will work. It is true that MV will be lower than bolt action. Energy is indeed syphoned off to work the action.

On the other side of the coin, fast powder will have lower MV and lower port pressure, given the same chamber pressure. Without proper adjustments to system, it can cause issues of different sorts too.

I have been loading with Ramshot hunter for ar10 in .243 win. I like it better than the other faster burning powder I was using. I plan to try even slower powder if I get hold of some.

-TL

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[georgehwbush]

" I don't know H 4350 isn't it a tad slower than IMR 4350?? "

yes it is. as the 4350s go, it is : imr 4350 - h 4350 - aa 4350 : in order from faster to slower, although there are other considerations besides published burn rates. none of these are very much different but not alike either.

"Slower powder has higher port pressure." that is what i was thinking, and thinking that if i squeeze the port a little it will slow the amount of gas and thus reduce the overall pressure. i'm going to try it next time i have the chance.

so thanks to all for the input.

 

[tangolima]

Most adjustable gas blocks use set screw to reduce the orifice opening. It dynamically reduces pressure and cuts down the flow. Reducing the flow effectively delay the unlocking of the action. It takes more time to fill up the gas cylinder.

I also found it necessary to readjust after a couple hundreds rounds. Perhaps it is because of carbon build up or gas cutting of metal. It feels more like the latter. Faster powder probably has less problem in this regards.

-TL



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[44 AMP]

It dynamically reduces pressure and cuts down the flow. Reducing the flow effectively delay the unlocking of the action. It takes more time to fill up the gas cylinder.

I don't think you've got that exactly right. or I'm misunderstanding you.

It does take "more time" to fill up the gas cylinder/system with a smaller port, but the pressure is what the pressure is, and once the system has enough pressure in it to move the parts, they move.

The original idea of adjustable gas systems was to adjust the weapon to the smallest setting it would reliably run on (lowest port setting) and then have larger settings allowing more gas to dump into the system to continue operation when crud buildup began to foul the weapon in combat.

changing the setting doesn't change the amount of gas pressure, available, it changes the amount of time it takes for the system to fill to the necessary amount of pressure to operate. There is plenty more pressure available than that minimum, and generally speaking the systems today are made to dump or shut off the excess once they have "enough" to operate. There are exceptions.

 

[tangolima]

The pressure in the cylinder is ramping up as it is being filled. If the time taken to reach the threshold pressure to move the BCG is long than the dwell time, the BCG won't move at all.

The pressure on the other side of the orifice can never reach the port pressure instantaneously. That's what dynamic pressure means. Time taken to reach equilibrium depends on the pressure difference, the diameter of the orifice, and the viscosity of the fluid (gas).

There is also built-in time delay between BCG starts moving and action unlocking. That also depends on the above factors.

-TL

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[44 AMP]

The AR direct impingement gas system is what I call "long and thin", while most gas piston systems are shorter and wider. I believe that affects the timing of the system overall.

Every part of the design is a factor, / has some effect in the timing of the system cycle.

With the AR DI system the gas has to go a long way from the port to get to the point where it does the needed work. All the way from the port back to the bolt carrier. Then it has to move the bolt carrier, at the right time, so that the bolt doesn't unlock until after the bullet is out of the barrel and the pressure drops enough to extract the case. And that is where the timing of all the factors working together is critical.

The biggest "problem" using general reloading data for semi autos is that the semi autos are designed to run on a fairly narrow range of pressure curves.

Its not so much a question of safe, as it is a question of suitable.

 

[georgehwbush]

this is a non-issue un-needed point; but the gas starts to flow into the gas block port before the bullet ever reaches the port. the pressure ahead of the bullet is building up all the way to the muzzel.

if the gas pressure was instantly peak pressure on the gas port it would still have to build up in the tube and "piston". even though the buildup would be extreemly quick, gases do compress and cause a slight delay in pressure transfer. the tighter the port the longer it would take.

as op have pointed out if it takes too long the pressure would be falling to a point that it might not even function.

but; as i already posted, i will test with slight restriction when i get to shoot again. my job may have just ended, the owner of the company was med flighted out today and it doesn't look good.

if you are religious, please pray. thank you.