Short stroking?

**HwyKnight** · 02-27-13, 21:27

Attachment 15658
Is this a short stroking failure? In addition the bolt isn't locking back on an empty mag. I was testing a lower that I built and had this malfunction. What do you think buffer or buffer spring? The upper is tried and true from another AR.

**308sako** · 02-27-13, 22:26

There are many possible causes, and springs are critical in the buffer and the magazine.

Does all ammo cycle well or only weak slow carrier moving ammo?

**thopkins22** · 02-27-13, 22:31

What ammo, action spring, and buffer? In the known good lower as well?

If it's not locking back on the last round then it's either short stroking, or outrunning the magazine spring.

**HwyKnight** · 02-27-13, 22:47

The only variable in this equation is the lower. The upper, mags, and ammo are all consistent, and tried/true. I lubed the buffer/spring with a waterproof marine grease. Looks like I over did it, so I'll clean it out and try again. I thought it felt a little stiff before testing.

**Iraqgunz** · 02-27-13, 23:39

Well I suppose we could guess all day but maybe if you provided us some detail about the make, model, ammo used, etc... it would help us.

**HwyKnight** · 02-28-13, 00:37

It's a Noveske lower with a Bushmaster LPK (bush was all I could find), std buffer, and carbine spring. Geissele SSA-E trigger, LMT Sopmod stock. Federal XM193 55gr fmj 5.56 ammo . After working the buffer spring a few times the feeding problem went away, but it still wouldn't lock back on an empty mag. The upper from my S&W MP15, as well as the pmags are tried and true.

**BufordTJustice** · 02-28-13, 01:57

Std carbine buffer (~2.9oz) is too light for that ammo in a 16" carbine gas barrel. Try an H buffer or even an H2. Buffer spring is also suspect if it is from Bushy. Try a Colt carbine, Springco WHITE, or Springco BLUE.

Also what extractor spring are you using?

**Iraqgunz** · 02-28-13, 02:20

If you are using a black O-ring, take it off as well.

**Iraqgunz** · 02-28-13, 02:42

I am pretty sure you will want to run an H buffer in that carbine. I would probably take a look at the various points of contact for the gas system.

1. Gas rings.

2. Gas tube.

3. Bolt Carrier Key.

4. FSB.

Originally Posted by HwyKnight

It's a Noveske lower with a Bushmaster LPK (bush was all I could find), std buffer, and carbine spring. Geissele SSA-E trigger, LMT Sopmod stock. Federal XM193 55gr fmj 5.56 ammo . After working the buffer spring a few times the feeding problem went away, but it still wouldn't lock back on an empty mag. The upper from my S&W MP15, as well as the pmags are tried and true.