Shots Strung Diagonally

[JohnKSa]

I finally got my Imbel FAL to the range yesterday.

I shot it with a variety of surplus ammunition.

@ 100 yards, 10 shot groups were pretty consistently 4"

The interesting thing is that the groups were strung diagonally starting from point of aim for the first few shots then walking down and to the right.

I didn't get the gun for precision shooting, so the current accuracy is more than acceptable. However the fact that the groups are so consistent in terms of shot distribution intrigues me. If I let the barrel to cool after every shot, the gun shoots around 2"--maybe better. I had a couple of groups where the first two shots were touching. Then the barrel started heating and the stringing/walking began.

I did shoot one group trying to compensate for the stringing behavior, and enjoyed a modicum of success, but trying to eyeball hold off to compensate for a few inches of stringing at 100 yards with iron sights is a bit touchy--I'm not quite that good...

I thought maybe the gas tube was heating up and putting pressure on the receiver, but it floats at the receiver end. There's not really any way for it to push on the receiver.

The handguards are plastic (fiberglass/polymer) so I don't expect them to be a factor in heat-related stringing.

Anybody got ideas?

 

[Art Eatman]

If the end of the gas tube at the receiver doesn't touch, yeah, it's free-floating. How tight does it fit in the sleeve? It could be heating faster than the barrel and so exerting some force. The diameter of the tube will expand somewhat as it heats.

Sure, the stock's rate of heating is less than the steel, but if it's pressing on the barrel at all, it will exert some force.

As a generality, if shots string upward, it's pressure from below from the forearm. Downward? It's something from the topside of things...

Art

 

[nextjoe]

Could also be stresses in the barrel itself, although like Art I'd first check out everything touching the barrel...

Best,
Joe

 

[JohnKSa]

Ok,

I took the gas tube off and beveled the outside of the end where it fits into the tube that threads into the receiver. I removed a slight ding from the gas tube with a fine file.

Then I polished the engagement surface--both the outside of the gas tube and the inside of the tube that threads into the receiver. I got pretty vigorous with 400 grit paper to start with. That removed all the finish on both surfaces. High-temp paint on the gas tube and parkerizing on the tube that threads into the receiver. Next, I put a mirror finish on with 1000 grit paper.

I put a slight bevel on the inside of the tube that threads into the receiver.

Then I lubed the engagement surface with a high temperature moly grease.

Hopefully, that will ensure that the two tubes will slide and not bind, even if the gas tube expands a bit. They do slide a LOT easier than they did. The parkerizing and paint were not good complementary friction reducing surfaces.

When I reassembled the handguards, I pulled them as far forward as possible before tightening the screw. There was a little play which may be enough to keep the handguards from lengthening and putting pressure on the receiver.

I'll shoot it again Saturday--I'll update this thread then.

 

[JohnKSa]

No effect.

Shots are still stringing as before.

First two shots go into an inch or less at 100 yards, then they start stringing down and to the right.

I may play around a little bit more with the handguards, but I'm about to admit this is a barrel issue.

BTW, the bore looks rough, but it cleans up very easily. Virtually NO copper fouling was present after shooting 54 rounds.

I also found out that if you empty a mag pretty quick the handguards get so hot they're uncomfortable to hold. I got some looks from the other shooters when the smoke started curling out through the vent holes!

Neat gun. In spite of the stringing, I shoot it very well. It just fits.

This may not be my last FAL...

Good shooting!

John