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Discussion Starter · #1 ·
I just finished my first 68 build a day or so ago, a 22" Triad, A-2 stock with an adjustable gas block; off of the build bench with factory 120gr SST's and 2-1/2 turns open on the gas block everything worked as expected, just a little over 1" groups at a 100 and 2600 plus FPS, bolt locks back every time on last round...
I picked up some of my hand loads, 100gr AB's loaded for my 18" DD-Ambush @ 29.1gr of 2200 My most accurate for my DD @ 2730 FPS and they would not lock the bolt back on last round.
So thinking Triad and light projectile I need more gas, well I'm up to 29.9gr's of 2200 2.285 COAL @ 2900 plus FPS, the Gas Block opened at four rounds open, as for as the instruction say to go and the bolt will still not lock back on one or last round.. I thought maybe something went wrong so I had a few factory 120 SST's left to try and the rifle works flawlessly,, what the heck I'm I doing or thinking wrong????
I do have a cheap Chronograph so don't take the speeds as truth but it does gives me an Idea of what going on for now ..
 

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Discussion Starter · #3 ·
Did you not try it with full gas?

Sent from a final firing position, the crosshairs are on you!
Full gas ? I opened the block as for as the manufacturer said to go (four treads showing or four rounds open) the factory 120 SST worked great at 2-3/4 turns open on the block ?? scratching my head, what up here ??????
 

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Full gas ? I opened the block as for as the manufacturer said to go (four treads showing or four rounds open) the factory 120 SST worked great at 2-3/4 turns open on the block ?? scratching my head, what up here ??????
That's what I'm referring to, if you were wide open with the block allowing full gas.

Must not have enough pressure to cycle the 100's
 

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Discussion Starter · #5 ·
That's what I'm referring to, if you were wide open with the block allowing full gas.

Must not have enough pressure to cycle the 100's
Well that's my thoughts but how can I get more pressure with out over doing powder charge, may be a different powder for light bullets? I have a few Hand loaded 120 SST's @ 2500 fps plus out of the 18" DD and can all most make them touch with 27.3 of 2200 ,,,, I will try them this weekend some time and see what happens ..
Thanks for your thoughts, if yea think of something let me know,,,,,,, The 100gr AB have done all I needed to do around here, I would like to make them work.....
 

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So thinking Triad and light projectile I need more gas, well I'm up to 29.9gr's of 2200 2.285 COAL @ 2900 plus FPS, the Gas Block opened at four rounds open, as for as the instruction say to go and the bolt will still not lock back on one or last round.. I thought maybe something went wrong so I had a few factory 120 SST's left to try and the rifle works flawlessly,, what the heck I'm I doing or thinking wrong????..
I've found two situations that can cause the bolt not to lock back. Not sure they apply to your situation.

1. there is excess tolerance inside the magazine between the follower in magazine walls. On recoil (at those velocities, the 100 AB has more than the 120 SST), the follower moves forward inside the well putting all the tolerance in the back and the bolt catch is not engaged. Solution if you suspect this, disassemble mag and apply soft Velcro across the front of the follower to help keep the follower aft in the magazine during recoil.

2. Your charge could be too high causing increased chamber pressure that is strong enough to hold the brass against the chamber as the bolt initiates extraction. Extraction is then delayed and insufficient gas pressure remains to cycle the bolt full aft. This situation will leave the fired brass looking cloudy instead of shiny. Solution if you suspect this, Drop charge two gains and test bolt cycling.
 

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I am running my 90 grain gold dot loads for my 16 in Bison thru my 22 in Triad.
They run 3050 to 3100 fps and lock the bolt back. Full wide open gas. They run 2850 in the Bison.
I built the rifle with a spare no name buffer spring.
I decided I would put a Wolff standard pressure spring in it.
With the Wolff spring it does not lock back on the last round.
I put the no name spring back in and functions perfectly again.
So it's right on the edge with the 90's as to gas port size in my rifle.
Try it with the block all the way open, if that doesn't work ask H which size you should open the port to.
Rifle gas can take some adjusting for light projectiles.
These barrels were set up around the 130 grain projectiles.
 

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Longer dwell time with too fast of a powder, I use H335 in my 24" barrel and am closed 10 clicks.


-Alexander
 

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I am running my 90 grain gold dot loads for my 16 in Bison thru my 22 in Triad.
They run 3050 to 3100 fps and lock the bolt back. Full wide open gas. They run 2850 in the Bison.
I built the rifle with a spare no name buffer spring.
I decided I would put a Wolff standard pressure spring in it.
With the Wolff spring it does not lock back on the last round.
I put the no name spring back in and functions perfectly again.
So it's right on the edge with the 90's as to gas port size in my rifle.
Try it with the block all the way open, if that doesn't work ask H which size you should open the port to.
Rifle gas can take some adjusting for light projectiles.
These barrels were set up around the 130 grain projectiles.
+1 with what Yama wrote on the buffer spring--it and the gas block are like heart and lung working together. I use JP's captured silent springs and find the black, "standard" weight spring they're strung up with at the factory will function within the range of my adjustable Syrac with any bullets/load, including subsonics that I've way underpowered.
Then, I've got a rifle with no fancy gas block or buffer gizmo that functions on anything perfectly and I've really come to appreciate that...so she runs a little dirty, so what. My JP/adj.gas block rifle runs dirty, too.
You'll get her right in the end.
 

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You may change powder with the 100's to create proper function.

As Yamaraja stated, you may have to open the barrel gas port up to reliably cycle the lighter bullets.


Sent from a final firing position, the crosshairs are on you!
 

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Discussion Starter · #11 ·
So far this morning I have tried my hand loaded 120gr SST's @ 2650 FPS, I tried a different lower with the lightest buffer I have, I loaded a couple of 100gr AB with H335 @2539 FPS and the rifle still failed to lock open on last shot, scratched my head put another factory 120gr SST in the rifle and it worked like a charm, locks open on the last shot.
I like the A-2 stock and wanted to do away with the rattling spring anyway so I will order the JP silent capture spring builders kit with a few different springs included and will give it a try among a few other things ,, the drill bit will be the very very last resort...
Thanks for the ideas and input on the problem
 

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Longer dwell time with too fast of a powder, I use H335 in my 24" barrel and am closed 10 clicks.

-Alexander
This! 2200 is too fast for the location of the port in the barrel.
 

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This! 2200 is too fast for the location of the port in the barrel.
Maybe, however I am using RL7 for my 90gr Gold Dots and its a faster powder with a lighter projectile and its cycling properly with the no name buffer spring.
I also have a Young Manufacturing N/M bolt carrier so its slightly heavier.
 

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Maybe, however I am using RL7 for my 90gr Gold Dots and its a faster powder with a lighter projectile and its cycling properly with the no name buffer spring.
I also have a Young Manufacturing N/M bolt carrier so its slightly heavier.
Yes, RL-7 is faster, but without comparing pressure curves at the port location, we aren't able to truly compare the two powders.
I don't have access to that info.
 

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Yes, RL-7 is faster, but without comparing pressure curves at the port location, we aren't able to truly compare the two powders.
I don't have access to that info.
Very true.
As I said my 90gr Gold Dot load is right on the edge of cycling the action properly.

I do have some 100gr AB loads for my Bison barrel I havent tried yet in the Triad.
They are 30gr of AA2200 in S&B brass, CCI 450, 2.295 OAL they run 2850 .8 MOA in the 16in Bison
I can take a few out to the range Monday and see how they run in the 22in Triad.
 

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So far this morning I have tried my hand loaded 120gr SST's @ 2650 FPS, I tried a different lower with the lightest buffer I have, I loaded a couple of 100gr AB with H335 @2539 FPS and the rifle still failed to lock open on last shot, scratched my head put another factory 120gr SST in the rifle and it worked like a charm, locks open on the last shot.
I like the A-2 stock and wanted to do away with the rattling spring anyway so I will order the JP silent capture spring builders kit with a few different springs included and will give it a try among a few other things ,, the drill bit will be the very very last resort...
Thanks for the ideas and input on the problem
Scan ARPs website on what they say about rifle length buffers, I want to say he recommends don't use them and use carbine buffer systems. Which can be done in a rifle length buttstock with a spacer btw.
 

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Discussion Starter · #18 ·
Scan ARPs website on what they say about rifle length buffers, I want to say he recommends don't use them and use carbine buffer systems. Which can be done in a rifle length buttstock with a spacer btw.
I looked at APR's site and didn't see anything on it, But I did take a shorter spring out of an adjustable stock and put it in the A2 stock tube just see what it felt like, very weak but very smooth, didn't want to try it and send the bolt out the back of the receiver..
 

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You need a spacer if you are going to run a carbine spring and buffer in the A2 can be bought pretty cheap.


Brett C.
IronworksTactical.com - owner
 

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Discussion Starter · #20 ·
I did open the Gas block another half turn @ 4-1/2 turns open (18 clicks) even though the instructions say not more than 4 turns open and the rifle locked back on the last round with 29gr of H355 but it still short stroked on next round and Not lock open with 29.7gr of 2200, Do I need to move to an even slower powder, CFE223 or something??? I had the same problem with my 18" Ambush with faster IMR4198 when first started loading for 68....
I was hoping to build a high velocity 95/100/110gr back porch 300 yard tack driver out of this thing.. View attachment 14402
 
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