Hey everyone.
With the Benjamin Gunnar going on sale for $499 from airgun depot recently (where I got mine), and $599 in many other places, I figure there are probably a few people that picked one up. One of the biggest complaints I have seen about this gun, is the lack of a hammer spring preload adjuster. So, I figured I would show how I very easily added one to my new rifle. The one downside to this, is you do have to remove your stock by loosening the castle nut to adjust it.....unless you get a folding stock adapter, which I plan on doing eventually. Not so I can more easily adjust my hammer spring, but just to make it easier to transport. Anyway....
First off, make sure your gun is safe, of course. Unloaded, hammer down, on safe. For the next step, do not have your stock fully collapsed, it *may* prevent the castle nut from being loosened enough.
Next, remove the stock by first loosening the standard castle nut.
If you don't have a castle nut wrench, get one. This is America.
All jokes aside, you can use a pair of channel locks and a strip of leather or something similar, to protect the finish on the nut and buffer tube. Mine was not on very tight. You will need to loosen the nut entirely, then lift up the retaining washer, before you can unscrew the stock. Take care not to loose the little plunger that retains the washer.
With the stock removed, you will see two allen head screws. While holding pressure down on the buffer tube block, unscrew both of these, as the hammer spring will have pressure against this. Once you remove the buffer tube block, you will have a spacer, then the hammer spring, and further down in, the hammer, seen in the picture below, minus the hammer itself.
Next, we will drill and tap the buffer tube block, so that we can use a screw to add preload to the spacer/hammer spring. I used a 5/32, or #25 drill bit, for a 10-24 tap. A 10-32 tap would also work just fine if you have one, but use either a #21 or 5/32 bit, not a #25. I went with a #10 machine screw vs a 1/4", because you need the screw head to be small enough to ensure the buffer tube still has clearance to screw in to the buffer tube block with the adjusting screw installed.
Also, while you could probably drill the hole in the center of the hammer spring spacer depression (seen below), I opted to put the hole closer to the center of the buffer tube hole, again, so I don't have any interference between the adjuster screw and the buffer tube.
This block is aluminum, so it is very easy to drill and tap. A little bit of cutting oil (which may not even be necessary) and it took about 20 seconds to have the tap ran through. Next, get an appropriate screw for whatever threads you tapped, and screw it in. I would recommend a 1" long or so screw, that should give plenty of preload adjustment. I added lock tight blue to the screw, so I wouldn't have it creep out on me.
This image is looking through the hole in the buffer tube block, reinstalled, without the adjuster screw in it. The inside track where the hammer spring spacer rides is a snug fit, so the adjuster spacer should not have any binding issues.
Reinstall everything, and your ready to tune it, using your regulator, hammer spring, and also your transfer port adjuster. If you wanted to, I'm sure you could tune your hammer spring preload with the stock off, using a bag under the grip, to make it easier, then reinstall everything.
This diy took me longer to gather my tools then it did to actually do the job, I would say pretty much anyone could do this with a quick trip to the hardware store. They have the screws there for you to use too, FYI.
Hope this helps someone out. Take care.
With the Benjamin Gunnar going on sale for $499 from airgun depot recently (where I got mine), and $599 in many other places, I figure there are probably a few people that picked one up. One of the biggest complaints I have seen about this gun, is the lack of a hammer spring preload adjuster. So, I figured I would show how I very easily added one to my new rifle. The one downside to this, is you do have to remove your stock by loosening the castle nut to adjust it.....unless you get a folding stock adapter, which I plan on doing eventually. Not so I can more easily adjust my hammer spring, but just to make it easier to transport. Anyway....
First off, make sure your gun is safe, of course. Unloaded, hammer down, on safe. For the next step, do not have your stock fully collapsed, it *may* prevent the castle nut from being loosened enough.
Next, remove the stock by first loosening the standard castle nut.
If you don't have a castle nut wrench, get one. This is America.
All jokes aside, you can use a pair of channel locks and a strip of leather or something similar, to protect the finish on the nut and buffer tube. Mine was not on very tight. You will need to loosen the nut entirely, then lift up the retaining washer, before you can unscrew the stock. Take care not to loose the little plunger that retains the washer.
With the stock removed, you will see two allen head screws. While holding pressure down on the buffer tube block, unscrew both of these, as the hammer spring will have pressure against this. Once you remove the buffer tube block, you will have a spacer, then the hammer spring, and further down in, the hammer, seen in the picture below, minus the hammer itself.
Next, we will drill and tap the buffer tube block, so that we can use a screw to add preload to the spacer/hammer spring. I used a 5/32, or #25 drill bit, for a 10-24 tap. A 10-32 tap would also work just fine if you have one, but use either a #21 or 5/32 bit, not a #25. I went with a #10 machine screw vs a 1/4", because you need the screw head to be small enough to ensure the buffer tube still has clearance to screw in to the buffer tube block with the adjusting screw installed.
Also, while you could probably drill the hole in the center of the hammer spring spacer depression (seen below), I opted to put the hole closer to the center of the buffer tube hole, again, so I don't have any interference between the adjuster screw and the buffer tube.
This block is aluminum, so it is very easy to drill and tap. A little bit of cutting oil (which may not even be necessary) and it took about 20 seconds to have the tap ran through. Next, get an appropriate screw for whatever threads you tapped, and screw it in. I would recommend a 1" long or so screw, that should give plenty of preload adjustment. I added lock tight blue to the screw, so I wouldn't have it creep out on me.
This image is looking through the hole in the buffer tube block, reinstalled, without the adjuster screw in it. The inside track where the hammer spring spacer rides is a snug fit, so the adjuster spacer should not have any binding issues.
Reinstall everything, and your ready to tune it, using your regulator, hammer spring, and also your transfer port adjuster. If you wanted to, I'm sure you could tune your hammer spring preload with the stock off, using a bag under the grip, to make it easier, then reinstall everything.
This diy took me longer to gather my tools then it did to actually do the job, I would say pretty much anyone could do this with a quick trip to the hardware store. They have the screws there for you to use too, FYI.
Hope this helps someone out. Take care.
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