New build is short stroking

[LorinB]

New build is short stroking.  It ejects about 1' @ 3 o'clock and will not lock bolt back on empty mag or strip off next round.  .308, 20" Shilen barrel, rifle length gas system, .75 gas mandrel, JP adjustable gas block (wide open) 5.6 oz rifle buffer.  I suspect the gas port is too small at .076 (caliper measurement).  I am planning on buying numbered bits tomorrow to confirm size and possibly open it incrimentally until it runs.  Where should it be .093 - .096?

Also, I have only shot 50 rounds through it and I suspect the problem could be contributed to the fact that I am loading 130 grain Barns TTSX, which is very light for caliber but they are near max load at 3250 fps.  That gives a power factor of 422 vs 175 gr bullets @ 2600 fps (PF 455) which is the Federal load that Shilen uses as a proof load.  I know the easy answer to this question is to try heavier factory ammo, but is it likely that the 130 gr bullet is the cause of the cycle failure?  If so is it reasonable to attempt to tune for this load?  I really want to use a fast monolithic bullet for hog hunting at night wich is the primary reason for this build.

First post.... and thank you for any feed back!

[98Z5V]

2 hours ago, LorinB said:

.308, 20" Shilen barrel, rifle length gas system, .75 gas mandrel, JP adjustable gas block (wide open) 5.6 oz rifle buffer.  I suspect the gas port is too small at .076 (caliper measurement).  I am planning on buying numbered bits tomorrow to confirm size and possibly open it incrimentally until it runs.  Where should it be .093 - .096?

0.076" gas port is way too small, for a .308 Win calibered barred of your configuration. 

18" Rifle gas with a 0.750" journal diameter needs between 0.095"~0.098" to run.  Add 2" of dwell time to that for your barrel, and you'll need 0.090"~0.093" gas port for that thing to run.  Properly. 

Inspect your recoil system.  You only listed 5.6oz rifle buffer, nothing more than that.  Weigh it.  Common it's 5.4oz, and it's not easy to make it heavier than that, with common materials that most manufacturers use.  Just verify it.  List the manufacturer - Of your whole recoil system.  MEASURE the INTERNAL DEPTH of your receiver extension - shove a tape measure down there until it bottoms out.  Needs to be 9 11/16" internal depth.  Not close - right on.  Get rid of the recoil spring, unless you already possess the Armalite EA-1095 spring, or the Sprinco Red spring.  If you don't have one of those - find one and install it.

Welcome aboard, again. 

Here's the Intro Section, when you have time.  tell us a little about yourself. 

https://forum.308ar.com/forum/22-introductions/

 

Edited February 1, 2023 by 98Z5V

[LorinB]

Kitchen scale says buffer is 5.6 oz (but could be off) and 5.291" long.  Buffer tube is actually 9-11/16".  Spring, buffer and tube are some Joe Bob's fifle length set.  Before finding this sight I ordered a Tubb flat wire spring that has not delivered.  Should I give it a go or just go straight to Sprinco Red?  I also ordered a Kak LR 308 buffer body and an assortment of aluminum, steel and tungsten weights that I'm guessing I should probably return, correct?

 

I'm a wood worker by profession with a well appointed wood shop but little to no metal machining experience or machines.  I plan to jig up a wooden barrel clap on a table top drill press and drill out the gas port to .093 or .096.  Will an inexpensive high speed steel, Harbor Freight set of numbered drill bits do a fine job or would it be safer get a higher quality high speed steel or carbide bit?

[shooterrex]

You already have a pilot hole. A drop of oil and go slow. Let the bit do the work.

[NF1E]

I thought, from M14 experience, that my new Aero M5 20" build was short stroking too. Listening to shooterrex and the advice on this forum, simply closing my AGB half way solved my imagined problems and she runs like a top with all ammos. Thanks guys, you are the best. Lower rifle in the first photo is the M5.  Whatta Hobby!

Edited February 2, 2023 by NF1E

[dpete]

3 hours ago, NF1E said:

I thought, from M14 experience, that my new Aero M5 20" build was short stroking too. Listening to shooterrex and the advice on this forum, simply closing my AGB half way solved my imagined problems and she runs like a top with all ammos. Thanks guys, you are the best. Lower rifle in the first photo is the M5.  Whatta Hobby!

Is it my imagination, or how the picture was taken, but the muzzle brake on the M5 looks as if the ports are up and down (vertical).  They should be and are designed to be side to side (horizontal).  If they are vertical the muzzle blast is directed up and down causing one heII of a blast into the sky and down into the bench or dirt if your prone.   No such issue if ported side to side, other than foks next to you at the range may not like it as much.

[MikedaddyH]

Looks about 60° off. Shims can fix this problem. Get a set they are like 5$.;

[NF1E]

It is an illusion for sure. That is an OSS suppressor QD adapter brake and ports in 4 equal directions.

[dpete]

Ports to the side and top make sense.  Direct the major muzzle blast to the sides while smaller ports on top eject gas upward reducing muzzle flip .  Ports out the bottom make no sense at all.

[NF1E]

There are flats on the top, sides and bottom with the  4 sets of ports spaced equally between them. Works like a champ for me. I use them open most of the time and occasionally screw on the suppressor.

[dpete]

As long as it works for what you want it to do.  Thats what matters.