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Now that you have the gas block alignment sorted out, I would look at the action spring and buffer. Are you sure the rifle length one is "normal" strength and not "extra" or "plus" strength?

Also, if this is a race gun rather than an alll purpose home defense/race gun, a lighter weight buffer would reduce reciprocating mass and rifle movement during recoil.

Since the rifle ran well with 223 ammo with the non adjustable gas block, wonder if there is something wrong with the SLR, as WFO it should mimic the fixed one in gas flow.

What does SLR say?

Most important, personally would not run the gun with carbine buffer and spring as gas key might impact the upper receiver in its rearward travel.

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11 minutes ago, mpom said:

Now that you have the gas block alignment sorted out, I would look at the action spring and buffer. Are you sure the rifle length one is "normal" strength and not "extra" or "plus" strength?

Also, if this is a race gun rather than an alll purpose home defense/race gun, a lighter weight buffer would reduce reciprocating mass and rifle movement during recoil.

Since the rifle ran well with 223 ammo with the non adjustable gas block, wonder if there is something wrong with the SLR, as WFO it should mimic the fixed one in gas flow.

What does SLR say?

Most important, personally would not run the gun with carbine buffer and spring as gas key might impact the upper receiver in its rearward travel. 

Yep, standard spec buffer and spring.  Nothing special.  I'm going to check the trigger install then see if maybe taking a weight or two out of the buffer will do anything.

SLR hasn't responded for a couple of days now, but since having an issue with the standard gas block, I suspect something else is actually causing the problem.

Agreed on the carbine buffer...I was just experimenting for a couple of rounds.

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Okay, so adjusted the trigger...same.  I even tried swapping lowers with a different rifle.  Same lower I used all of last season actually so I know it should work...didn't.

 

Can a muzzle brake cause this sort of behavior?  I also added an APA Answer, and haven't tuned it yet, so all of the ports on top are currently sealed, maybe causing a back pressure situation?

 

That's everything.  I'm going to grab a new gas tube, try taking out a screw or two on the brake and if none of that works, then I'm at a loss.  I've actually spent ~$500 in upgrades, only to have a non-functioning rifle.  Worked flawlessly before the new brake, trigger and AGB. 

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Doubt it's the muzzle device. 

Gas tubes are cheap, worth replacing, especially if old one has high round count.

If rifle runs well and locks on empty w original gas block, and empties are ejected between 3 and 5 O'clock, then I would call it good as you really dont want less gas then that.

So basically you are out the cost of the AGB.

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31 minutes ago, mpom said:

If rifle runs well and locks on empty w original gas block, and empties are ejected between 3 and 5 O'clock, then I would call it good as you really dont want less gas then that.

So basically you are out the cost of the AGB.

Totally agree, the problem is that I went back to the original gas block and still had the same problem.

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1 hour ago, clw42 said:

Can a muzzle brake cause this sort of behavior?  I also added an APA Answer, and haven't tuned it yet, so all of the ports on top are currently sealed, maybe causing a back pressure situation?

No, and if it did cause significant back pressure it would be causing more lock back, not less.

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A couple of things I would check while waiting for the gas tube to arrive: is the gas key showing signs of gas blow by as would happen if its 2 bolts were loose?

Do the bolt rings pass the stand up test, where you pull the bolt out and stand the assembled bolt carrier group on the bolt? Bolt should not collape into BC if rings are good.

Does the action operate smoothly when pulling charging handle back fully and lock into battery when CH is released slowly? Similar force required compared to another rifle/carbine?

Does BCG move freely with upper separated from lower?

Something is not right and I feel your frustration at trying to solve the issue 😕

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2 hours ago, mpom said:

Do the bolt rings pass the stand up test, where you pull the bolt out and stand the assembled bolt carrier group on the bolt? Bolt should not collape into BC if rings are good.

Are you saying the carrier standing upright on the bcg buffer face and the gas rings should support the bolt's weight, or that the bcg standing upright on the bolt lugs and the rings should support the weight of the carrier?

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Posted (edited)
3 hours ago, TonytheTiger said:

No, and if it did cause significant back pressure it would be causing more lock back, not less.

 

That's really what I figured, but wasn't 100% sure.  Thanks!

 

2 hours ago, mpom said:

A couple of things I would check while waiting for the gas tube to arrive: is the gas key showing signs of gas blow by as would happen if its 2 bolts were loose?

Do the bolt rings pass the stand up test, where you pull the bolt out and stand the assembled bolt carrier group on the bolt? Bolt should not collape into BC if rings are good.

Does the action operate smoothly when pulling charging handle back fully and lock into battery when CH is released slowly? Similar force required compared to another rifle/carbine?

Does BCG move freely with upper separated from lower?

Something is not right and I feel your frustration at trying to solve the issue 

 

Gas keys are staked and firmly in place on all carriers

All bolts, rings and pins appear to be in good working order.  Nothing seems amiss.

Action works great, very smooth, locks back fine when pulling the charging handle.

BCG is buttery smooth with plenty of lube, slides into the chamber with a nice click and I can pull it free with my fingertips and minimal force.

 

Here's a picture of the gas block (standard not adjustable).   Does this look like maybe I'm leaking gas?

IMG_3370.thumb.JPG.b71821df395304402f8f281fe9c243c0.JPG

 

Not sure if I should bother putting the new gas tube back on that block or if I should get another standard one and wait for it to arrive.  If what's in the picture is normal, then I'll try the new tube.

 

Very frustrating.  I took the brake off and fired a few rounds just to work the process of elimination.  I was able to get lock back on a reload of mine (27 grains of CFE223), but two other different loads(25.5 Grains of TAC and 26 Grains of TAC) and factory PMC were a no go.  I'm not sure how much higher I want to push the TAC powder, the manufacturer maxes out at 25.8

 

Also, my ejections are between 3 and 4 o'clock when it cycles.

Edited by clw42

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Have you tried a different magazine for the lock back test?  I assume with an empty mag the action locks back when pulling back on charging handle.

While its apart see if you can blow compressed air through the gas tube to be sure its it's clear. 

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30 minutes ago, mpom said:

Have you tried a different magazine for the lock back test?  I assume with an empty mag the action locks back when pulling back on charging handle.

While its apart see if you can blow compressed air through the gas tube to be sure its it's clear. 

I've tried about seven different mags.

 

I actually did notice some resistance in the old tube compared to the new one.  I'm going to install the new tube and see what happens.

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Installed the new tube, and just for the heck of it went back to the SLR AGB, and it worked perfectly.  Six clicks out and I had the rifle locking back with one of my weaker loads and PMC.  Crazy, I wouldn't have thought I had enough rounds through the old tube to render it a problem part.  But maybe that coupled with "breaking the seal" on the old gas block was enough to cause fits.  I'm honestly not sure. 

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I searching many posts on the subject of FTL/cycle issues I came across this fourm and would like to get some feedback on an issue I had on my first time to the range with a new upper assy that I installed and problem experienced.  Old upper was shooting just fine but accuracy was not sub MOA I desired.  My gun started out from a Armalite rifle mid length gas system and standard rifle stock.  Since the front sight was mounted to the barrel and wanted to have my new barrel free floated I have replaced everything on the new upper with the exception of the BCG.  The new upper consists of Bear Creek Arsenal 16" carbine length 1:9 twist diamond fluted barrel, Smith Vortex flash hider, and Nordic NC15 extruded upper, carbine length low profile gas block, and Magpul free floated hand guard.  As I stated earlier reusing BCG from old upper.  Went to the range with it 2 days ago with the following results.

1)  Pull charging handle, round racks as it should

2) fires round down range and spent round ejects at about 4 o'clock and about 8 feet away

3)FTL new round, short strokes with the bolt stopped about mid way with next round still in Mag, and fails to lock action back with no rounds in Mag

This was consistent will ever round fired regardless of load, any where from 50g Nosler to 62g SS109.  Research has indicated that my issue is with the rifle stock buffer being too heavy to allow rearward travel far enough to be able to rack a new round.  I have since replaced only the buffer to a H1 but have not been to the range again to try it out.  About the buffer spring, it appears to be in good condition, well lubricated, is 12.25" long with 43 coils.  I have a question?  I am not wanting to replace the stock with a collapsible carbine stock, assuming the difference between a rifle and carbine springs has only to do with # of coils and length, should this set up fix my cycling problem, or should I install carbine length spring with a block installed inside the buffer tube to account for the differing length springs.

Thanks for any and all thoughts you may offer.

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