Tips and Tricks
Tips and Tricks:
On this page, we are going to look at some ways to optimize the GFD AR-17HMR upper to your specific lower. Just a fancy way of saying we're going to Hot-rod the setup.
First, let me say what it is and what it isn't.
We have designed the upper receiver with the gas system to operate on a wide variety of lower receiver setups. We have seen anything from the Novenske Laru ilk; to polymer 80% lowers made with a mildly sharp Dremel tool- freehand. Brand new out the box, to the truck gun that has been handed down from cousin to cousin. Some people are decidedly meticulous in cleaning and oiling, others are content to run a patch down the bore annually if they remember it.
We do a good job, with most of our uppers working out of the box. However, sometimes some tweaking is in order.
One thing you can do is make sure the bolt is well oiled when new. We have attempted to make this an accurate system as most targets are going to be small and field accuracy is necessary for the intended task. We have kept tolerances fairly tight for this purpose. So some break-in is necessary. We are looking at some of the new Nickle Boron, Black Nitride coating on the market and have them out in the field with good results. Just use a light oil like CLP, Rem oil, or similar. Once things are working just keep things lightly oiled like you would on normal firearms. By the way, it is not recommended you lubricate the cases of ammunition. It is not necessary and promotes dirt in the chamber. You should have things running in the first 50 rounds or so.
Perhaps, after breaking in your weapon is still short cycling. Many things can influence this- different triggers, hammer spring rates, small variances in manufacturing tolerances between mil-spec parts, tight or loose fitting buffer tube, variances in ammunition -even from lot to lot.
Most of these issues can be addressed by clipping a few coils off of the buffer spring. Start with 2 and go up to 5 or so to balance the spring weight with the individual system. We are using a spring we determined to be on the heavier side of the bell curve to allow for things to work with some of the faster actions. Don’t worry about clipping too much as the lockup is controlled by the spring in the bolt (we will get to that shortly), just don’t cut so much that the bolt fails to return into battery. I would cut no more than necessary to function. We may develop a lighter spring for distribution, however, some actions would get pounded excessively.
Another check is to make sure the gas tube is aligned with the gas key in the bolt. To do this remove the bolt and charging handle. Remove the locking bearings and insert the bolt without the rollers in place, there should be little friction between the gas key and gas tube as you slide into battery. This is especially important if you have changed hand-guards or removed the gas block. They can be a little fussy especially with first production run uppers, we are making adjustments in manufacturing to address this thanks to the excellent feedback from our early adopters. Just flex the gas key to align.
If things haven’t worked yet give us a call.
The lockup is controlled by the relationship of the geometry of the gas key, locking balls, and locking cups located on the sides of the receiver. By the way, there is no reason to remove the lock cups from the receiver, they are Loctited in place and control head-space. Unlocking is controlled by the timing of the gas port in the barrel, inertia of the gas key, and the gas key spring. Just as with the buffer spring we have installed a gas key spring on the heavier side of the optimum bell curve.
At this point, my attorney wants to remind everyone that messing with the spring rates of the gas key spring may create an unsafe condition and is not recommended. So I will just explain what is going on with the spring and let people who know what they are doing make their own decisions.
The gas key spring is located in the bolt along with the gas key and firing pin. To disassemble the bolt requires removing 2 roll pins located at the back of the gas key. The best way to do this is from the bottom of the bolt. Depress the gas key and insert a 5/64” #2 roll pin punch into the small holes and drift out the roll pins on a bench block. Use the roll pin punch to push the firing pin out from the front of the bolt. The gas key can be removed at this time. I would not take off more than ½ a coil at a time as a small adjustment makes a big difference. If you see bulged case rims when testing you have gone too far. Call us and we will get you a new spring or send the upper in and we will set it up for you. Do not send in the lower. Also, I only add the gas key spring information as someone would attempt to do this anyway.
The good news is once you have the upper dialed into your individual lower system. It will operate very reliably for a long time.
If it still isn’t running like a sewing machine. Get in touch with GFD inc. and we will get you the latest advice over the phone or have you send it back for evaluation and repair. Your communication on any issues is helping make a better product.
I hope this helps.