Gas-Adjustable Rifles

29 Oct 07

Adjustable gas systems on military rifles:

The FAL is one of a number of military, gas-piston, autoloading rifles that feature and adjustable gas system. The user may adjust the amount of gas pressure, and thus the degree of robustness of the cycle of operation, by altering the size of the "purge vent," and thus amount of gas that is bled off and whose energy thus does not contribute to pushing back the operating rod.

This feature permits the user to alter the amount of recoil and literally " tune" the rifle to the particular ammunition being used. Instructions that come with the rifle advise the owner to adjust the size of the purge vent by measuring the distance ejected cases are flung.

For the recreational user, that is all fine, but my advise to the serious user is to close off the purge vent completely and leave it that way!

The only advantage associated with enlarging the purge vent is lessening the recoil and (at least in theory) lessening wear and tear on the rifle itself. Again, my advise is to stop worrying about any of that and concerning oneself more with the reliable operation of the piece, no matter what kindof ammunition is being used.

In a Vehicle-Defense Course last weekend in IN, a student brought a DSA/FAL and a mixture of 308 ammunition. With ammunition becoming ever more expensive and scarce, these days one needs to use whatever he can get! In any event, one round in a half-dozen short-cycled and created a stoppage, to the increasing annoyance of the rifle's owner! After witnessing the problem for twenty minutes, I asked the shooter where he had his gas-adjustment set. The purge vent, as it turns out, was half open. My colleague, Henk Iverson, and I both suggested he close it up completely. When he did, the short-cycle problem immediately went away, and the rifle ran normally for the rest of the day.

Serious users of FALs and other gas-adjustable rifles, never knowing what brand of ammunition they may be compelled to use, are thus well advised to forget about adjusting the gas system at all. Close it off and leave it that way!

/John