First 308 AR Build - Issues

[Turd Furgeson]

.) Do you have Armalite AR10 Recoil System: Yes

 

6.) Gas System Length- Rifle, Midlength, Carbine, Pistol, Other?

Rifle – Using Faxon 20” Big Gunner, 6.5 Creedmoor

 

7.) Gas tube Length – 15.5”

 

8.) Photo looking directly into the magwell

 

9.) Photo of the Bolt Face

 

10.) BCG Clearance at the ears and bolt stop

11.)  Gas Journal Dia and gas Port Dia

 

12.) Photo and Description of the Malfunction or Issue

With one round chambered and empty magazine:
1-spent round ejects back into the receiver
2-spent round ejects 2-3 o’clock, about 1 foot
3-bolt does lock back

With round in chamber and multiple rounds in magazine:
1-Stove pipes or stove pipes with another round half way in the chamber
2-Can feed and fire up to 2-3 rounds then does #1
3-At least once round ejected then new round jammed half way into the receiver

 

Edited February 19, 2023 by Turd Furgeson
bad video link

[shooterrex]

Gas port is probably too small.

Ejector has a square face. My Creedmoor did some similar malfunctions till I changed the ejector to one w/a rounded face.

https://www.kakindustry.com/kak-bcg-ejector-308

[Turd Furgeson]

1 hour ago, shooterrex said:

Gas port is probably too small.

Ejector has a square face. My Creedmoor did some similar malfunctions till I changed the ejector to one w/a rounded face.

https://www.kakindustry.com/kak-bcg-ejector-308

Thanks shooterrex. After all the threads I read, I suspected the port size.  Interesting info on the ejector.  I'll order one.

[98Z5V]

5 hours ago, Turd Furgeson said:

 

100% and then some - that gas porti s the issue.  For a 20" rifle gas 6.5 build with a 0.750" gas block journal, you need 0.080" minimum, and that's my .260 Rem running a 5.15oz buffer, as an experiment.  You, with a proper 5.4oz buffer, might need 0.085" port diameter, to run it right.

It's worth the cost of the 2 numbered drill bits to try it.  Run it at 0.080" first, and see how it does.  It it doesn't work at 0.080", punch it to 0.085" and it WILL work, properly.

Get back in here with details, from those steps, and prove my "proof of concept" here. 

Edited February 19, 2023 by 98Z5V

[Turd Furgeson]

23 minutes ago, 98Z5V said:

100% and then some - that gas porti s the issue.  For a 20" rifle gas 6.5 build with a 0.750" gas block journal, you need 0.080" minimum, and that's my .260 Rem running a 5.15oz buffer, as an experiment.  You, with a proper 5.4oz buffer, might need 0.085" port diameter, to run it right.

It's worth the cost of the 2 numbered drill bits to try it.  Run it at 0.080" first, and see how it does.  It it doesn't work at 0.080", punch it to 0.085" and it WILL work, properly.

Get back in here with details, from those steps, and prove my "proof of concept" here. 

Will do... You da man!

[98Z5V]

10 hours ago, Turd Furgeson said:

Will do... You da man!

No worries - it's close, at 0.075" - it wants to work, it just can't quite get enough going.  You'll see a difference just going to 0.080", so try it there.  It still might need a little more to be "perfect" so don't be afraid of the 0.085" bit, if it's not perfect at 0.080." 

[Turd Furgeson]

Thanks... exactly what it looks/feels like... anemic.  Ordering bits now.

[98Z5V]

This thing is gonna run like a striped-ass ape after you drill it out.  Everything else is already there, done, and perfect for a "running gun." 

[308USK]

On 2/19/2023 at 3:04 PM, 98Z5V said:

This thing is gonna run like a striped-ass ape after you drill it out.  Everything else is already there, done, and perfect for a "running gun." 

Pictures/video ... or it doesn't happen!  

(LOL, I couldn't help myself...I apologize)

[98Z5V]

He'll crush it, once this port is drilled.  Might take one drill bit, might take the second one, to make it perfect.

I know these things - not my first rodeo with these big bitches... 

Edited February 20, 2023 by 98Z5V

[Turd Furgeson]

Here we go:

 

Drilled port to .080 done.

So much better, but I don't think I'm quite there.  Rounds are ejecting between 3:00 and 4:30.  Tossing them 5-10+ feet. 

Only issue now is I'll fire off 3-4 rounds and then jams (between mag and feed ramp). 

Is it still a little under gassed?  Maybe feed ramps need some work?  Other?  Thanks.

 

[shooterrex]

If you change the ejector to the rounded one I bet it straightens up.

[Turd Furgeson]

1 hour ago, shooterrex said:

If you change the ejector to the rounded one I bet it straightens up.

Ordered.  thanks.

[98Z5V]

You'll probably have to blow that gas port up to 0.085", as well.  My thoughts. 

[Turd Furgeson]

My thoughts too.  Like it's enough gas to work sometimes, but then short strokes and jams the new round?  More to come.  Thanks.

[98Z5V]

5 minutes ago, Turd Furgeson said:

My thoughts too.  Like it's enough gas to work sometimes, but then short strokes and jams the new round?  More to come.  Thanks.

Yep, that BCG almost came rearward enough to strip the next round, but just "almost."  Bolt over-run.  Bolt ran over the round before it could fully strip it from the mag, because it just barely caught the rim - because it wasn't back far enough, but almost.

There's alot of "almost" in there.  Just because the gas is almost there...  

[Turd Furgeson]

Drilled  to .085

First session was with factory S&B FMJ 140grs – only thing in stock.  Seems like crappy ammo to me.  Doesn’t operate well in a semi-auto.

Results:  Definitely ran better than with the port at .080.  Shot 3 strings.  Jammed on 4, 7 or 10 depending on the string.  

Second session with reloaded ammo – new Hornady brass, #34 primers, Hornady 130 grs ELD Match.  Load was for max powder in Hornady #11 manual.  Loaded 50 for test.

Results:  Better than the S&B by far.  Two issues out of 50 rounds.  One case of the bolt running over the round and two rounds with a light primer strike.  Re-firing both rounds was successful.

Most rounds went between 2:00 o’clock and 3:00 o’clock… 3-6 feet in distance.

It appears to me I might need a little more gas?  Assuming the maxed out reloads were producing more pressure than the S&B ammo, the rifle ran much better.  I can’t explain the light primer strikes.  Or, is it what shooterrex recommends (or both)?

Thoughts?

S&B ammo jam pics.  Video is with reloaded ammo.

[Turd Furgeson]

57 minutes ago, Turd Furgeson said:

Drilled  to .085

First session was with factory S&B FMJ 140grs – only thing in stock.  Seems like crappy ammo to me.  Doesn’t operate well in a semi-auto.

Results:  Definitely ran better than with the port at .080.  Shot 3 strings.  Jammed on 4, 7 or 10 depending on the string.  

Second session with reloaded ammo – new Hornady brass, #34 primers, Hornady 130 grs ELD Match.  Load was for max powder in Hornady #11 manual.  Loaded 50 for test.

Results:  Better than the S&B by far.  Two issues out of 50 rounds.  One case of the bolt running over the round and two rounds with a light primer strike.  Re-firing both rounds was successful.

Most rounds went between 2:00 o’clock and 3:00 o’clock… 3-6 feet in distance.

It appears to me I might need a little more gas?  Assuming the maxed out reloads were producing more pressure than the S&B ammo, the rifle ran much better.  I can’t explain the light primer strikes.  Or, is it what shooterrex recommends (or both)?

Thoughts?

S&B ammo jam pics.  Video is with reloaded ammo.

Light strikes due to the #34 primers?

[shooterrex]

You are also dealing with a BCG that is not really broken in yet.

The problems being about every other round kind of points to the square ejector.

[Turd Furgeson]

45 minutes ago, shooterrex said:

You are also dealing with a BCG that is not really broken in yet.

The problems being about every other round kind of points to the square ejector.

Good point on breaking it in.  Appreciate it.

[shooterrex]

The square face ejectors seem to mess up feeding from the right side of the magazine on some guns.

[Turd Furgeson]

Hey Guys,

I now have a good balance between gas and recoil systems.  However, I am still seeing the bolt over run the next round... then jam. 

With reloads at 2.800 OAL, I can manually get/cause the bolt to run over the round as it fed from the magazine.  If I let the magazine hang naturally via gravity, I can make it over run the case.  If I support the magazine (push up on it from the bottom of the mag) it will not over run the case, then jam... so a very small tolerance between jam and not jam if the mag was being supported or not.

I then surmised that the OAL of the round (2.800) and the long style of the bullet in the case (6.5 Creedmoor), may be creating an excessive attach angle as the bolt stripped the case out of the magazine, that would allow the bolt to over run the round, thus causing the jam.  Again, I was able to do this manually with some dummy rounds.

Next, I loaded some 6.5 Creedmoor rounds with a bullet (140 grn kSST Hornady) that called for a shorter OAL of 2.690".  I was thinking from an angle of attach perspective, it would be less than the rounds at 2.800 and then not allow the bolt to over run the round.  I tested (live fired) around 40 rounds, and it definitely helped.... but still occurred (3-4 rounds).

Thoughts?

I suspect the upper/lower is out of spec in some way and the mag is just not high enough to allow for 100% proper purchase of the bolt lugs on the case head. 

I'm using PMAGS.

Not sure what to do at this point....   thanks.

 

 

[98Z5V]

Measure the top of the bolt catch slot to the top of the lower receiver - find out what that distance is.  We ran into something like this here before with 80% stuff, and posted a bunch of information about it in a discussion thread.  I'll try to find that thread again.

[Turd Furgeson]

Distance - .675"

 

Other lower measurements:

Another brand 80 .654"

Another commercial 308 .668"

[Turd Furgeson]

BTW, the width of the bolt  catch (where it mates with the mag) on the commercial  308 is .2475".  The width of the bolt catch (same spot) on the problem 6.5 is .2455" (diff of .002").  Wondering if a .002" delta might raise the mag high enough to fix the issue.  If not, I think I'm screwed 😡