SLR build and issue

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Skel

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Southern Ontario
I just completed an SLR build
MRA 18.6 Nitrided match fluted barrel
SLA adjustable gas block
MRA gas tube (rifle length)
MRA V1 handguard
Carbine buffer and magpul furniture
Brownell TiN BCG
ALG ACT trigger
Vortex strike Eagle 1-6x24

Problem is the gas block has to be adjusted wide open in order to lock open on last shot. Works great with factory ammo, but identical velocity handloads won't eject as far and won't feed the next round of lock open on the last round.
Does the rifle just need to be broken in? I didn't expect that I'd need the gas block wide open to cycle factory rounds.
I installed the SLA as per instructions using a .025 feeler gauge.
I'm using a standard Carbine buffer and spring. Thinking I might need to try a different weight buffer. Suggestions?

 
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Pull the gas block and see how the carboned up circle aligns with the gas port in the barrel. If by the .025" means accounting for the delta ring, you may need to slide your block back, the hole might be getting eclipsed.
 
In before the flamers.

You said it works great with factory ammo? What kind of hand loads are they? Fairly light? As mentioned, check the port alignment. If you rotate the block 180 you can see how centered it is on screw hole.
 
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You probably don't need to set the gas block away from the seat. The MRA barrels don't seem to have the gas block saddle cut for a delta ring.
I have a MRA barrel and I seated the gas block against the shoulder and it cycles perfectly.

If that's not the fix try a different powder. When dealing with a semi auto it's not just about velocity, you need a powder with a burn rate that creates the right pressure curve to cycle the action. I can't remember if I've ever used 4198 in an AR, I do use it for my 223 bolt action but can't remember trying it or those loads in an AR.
 
cr5 said:
You probably don't need to set the gas block away from the seat. The MRA barrels don't seem to have the gas block saddle cut for a delta ring.
I have a MRA barrel and I seated the gas block against the shoulder and it cycles perfectly.

If that's not the fix try a different powder. When dealing with a semi auto it's not just about velocity, you need a powder with a burn rate that creates the right pressure curve to cycle the action. I can't remember if I've ever used 4198 in an AR, I do use it for my 223 bolt action but can't remember trying it or those loads in an AR.
Click to expand...

I agree about the gas port location as the MRA offerings appear to not be machined to mil-spec standards. Secondly I use 4198 in AR’s of 30 caliber as this is to slow a powder for a 22. 4227 is quicker and has a optimum pressure curve for a smaller projectile.

Any particular reason you chose an adjustable gas block? It really isn’t required.
 
Thanks for the responses. I now believe my issue is my choice of powder used. 4198 is a relatively fast burning powder that functions fine in Carbine length gas systems, but doesn't produce enough port pressure to cycle reliably in a rifle length system.
I will load up some new handloads with xbr 8208 and win 748 to verify.
I may also change out the fancy SLA gas block for a fixed gas block if it doesn't really matter for this configuration.
 
If you're running a lighter than normal carrier or BCG then an adjustable gas block will serve you well. Plus since you're running handloads it will also be nice to be able to adjust the gas system once you develop an accurate load.
Also try CFR223 if it's available and one of your other choices isn't available. I've found it works very well under a Nosler 60-62 grain pill.

Good luck
 
It’s the barrel, I have the same set up. I was running an adjustable gas block but just put a regular on because it wouldn’t cycle with any gas cut off. I also had a titanium carrier that wouldn’t lock on an empty mag. This was all with a carbine buffer, it won’t cycle with a Geissele 42 buffer. The gun is super soft shooting with a full mass carrier.
 
Sudbury shooter said:
It’s the barrel, I have the same set up. I was running an adjustable gas block but just put a regular on because it wouldn’t cycle with any gas cut off. I also had a titanium carrier that wouldn’t lock on an empty mag. This was all with a carbine buffer, it won’t cycle with a Geissele 42 buffer. The gun is super soft shooting with a full mass carrier.
Click to expand...

Ok another why waste the money on an adjustable gas block. Nobody in Canada is running suppressed.
 
Didn't know wanting a smooth running AR that has less reciprocating mass was a waste of money. The things you learn on CGN ...lol...
 
DILLIGAF said:
Didn't know wanting a smooth running AR that has less reciprocating mass was a waste of money. The things you learn on CGN ...lol...
Click to expand...

It’s all about properly tuning and AR with the correct components and not hiding the deficiencies. This all can be achieved with a minimum amount of money.
 
Sqr said:
It’s all about properly tuning and AR with the correct components and not hiding the deficiencies. This all can be achieved with a minimum amount of money.
Click to expand...

If you think an adjustable gas block is hiding deficiencies Im lost for words buddy !
 
DILLIGAF said:
Again you fail to understand that some of us are using lightweight components. And adjusting the reciprocating mass is needed.
Click to expand...

Need to adjust the gas when you change the reciprocating mass. But I know what you meant, just mixed it up going from brain to type :p

Sqr, you are 100% correct that with an AR with standard components an adjustable gas block is not needed and simply changing a buffer or buffer spring is usually enough to smooth out a hard cycling gun or get one locking back reliably if it's short stroking.
The op mentioned a titanium carrier which while I like you see no need for this guy wanted one so now he has to be able to compensate for throwing the system out of balance.
I personally think the only issue he has since it cycles factory loads well is his reloads may need a different powder. I use 4198 in my bolt action under a 36gr Varmint grenade it may not be the best choice for an AR with 55gr projectiles. I'd have to go check my burn charts and loading logs to see if I've ever used it in a semi or with heavier bullets but I seem to remember it being pretty fast.
 
Skel said:
I just completed an SLR build
MRA 18.6 Nitrided match fluted barrel
SLA adjustable gas block
MRA gas tube (rifle length)
MRA V1 handguard
Carbine buffer and magpul furniture
Brownell TiN BCG
ALG ACT trigger
Vortex strike Eagle 1-6x24

Problem is the gas block has to be adjusted wide open in order to lock open on last shot. Works great with factory ammo, but identical velocity handloads won't eject as far and won't feed the next round of lock open on the last round.
Does the rifle just need to be broken in? I didn't expect that I'd need the gas block wide open to cycle factory rounds.
I installed the SLA as per instructions using a .025 feeler gauge.
I'm using a standard Carbine buffer and spring. Thinking I might need to try a different weight buffer. Suggestions?
Click to expand...

That's because you're using powder that is incompatible with the AR rifle-lenght system. Powder burn rate and gas port pressure is everything. That and lenght of barrel past gas port (dwell time).

If it's not cycling with a carbine buffer and lightweight BCG (the lightest cycling components setup possible), you're absolutely positively underpressured at the gas port.
 
DILLIGAF said:
Again you fail to understand that some of us are using lightweight components. And adjusting the reciprocating mass is needed.
Click to expand...

And again us who use low mass components have custom barrels with the correct gas post size. Who has had an instance where an improperly adjusted gas block cost them grief during a competition? Raise your hands.
 
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