FAQ: My thumb doesn’t fit. The endplate, buffer tube, and/or castle nut, rubs my hand.

This is not really a FAQ, but this does come up enough to address it in a short article.

Sparrow Dynamics
4 min readMar 12, 2018

First off, please excuse this blogging platform and/or advertising and related stories at the bottom. This is an experiment and a quick way to create this page to answer your question.

Sore on knuckle from buffer tube and castle nut.

Let me start by saying I totally understand your disappointment and wish we all weren’t having to deal with this in California. Everyone has different hands and what might work great for someone else may not work for you. Especially with big hands, you can’t choke up on the grip; a more relaxed grip-hold is more comfortable (like how you would hold a shotgun stock with your hand kind of to the side and not behind). Remember there is a trade-off of ergonomics in California because it is NOT a pistol grip.

If the buffer tube or castle nut are the issue, there are some things you can do. You can wrap tape, or heat shrink tube, or a cut bicycle innertube around the sharp parts (see next 3 photos). Or you can wear a glove. AND, you can use a more relaxed hold where your hand is more on the side of the rifle and not so “choked up” into the grip.

Use of heat shrink tube to protect your hand from the sharp edges.
Customer on Calguns.net suggested using Forten tennis racket grip tape.
A bicycle innertube can cover the castle nut. Sharp edges of endplate can be filed down.

For these types of featureless grips that force your hand to be above the top of the trigger, this “unconfortableness” is typical. If the buffer end plate is sharp and rubbing the web of your hand, there are a few things you can do.

Sharp edges of buffer end plate rubbing web of hand.

Even Thordsen has this issue. They sell this rounded endplate to help… https://www.thordsencustoms.com/ergonomic-receiver-endplate/

We have been planning to make a smoother endplate also. But in the mean time, you can buy the Thordsen one, or DIY one with a dremel tool (while it is still on the rifle). Then use some Cold Blue on a q-tip to bring it back to black. https://www.brownells.com/guntech/cold-bluing-touch-ups/detail.htm?lid=11043

Or you can wear a glove. AND, you can use a more relaxed hold where your hand is more on the side of the rifle and not so “choked up” into the grip.

Alternatively, you can have a normal pistol grip on a fixed-mag rifle, but fixed-mag is cumbersome and the upper and lower receivers can wear out at the rear takedown pin hole, as they were never meant to be separated every time you do a mag change.

Any featureless grip is not going to be as ergonomic as your old pistol grip. California thinks that a pistol grip makes the rifle more “assaulty”, so we have been forced to come up with other solutions that work around their definition of “pistol grip conspicuously protruding”. We feel that our California legal rifle grip is much safer and more ergonomic than any fin grip solution that keeps you from using your opposable thumb. So, in short, there are trade-offs.

Use of tape to protect hand from sharp edges of castle nut and buffer tube.

It is a minor trade off compared to not being able to grip the rifle at all. I find it more comfortable to not choke up so much and have a more relaxed grip kind of like what you would use with a shotgun or “traditional” rifle. When you try to grip it tight, it just crams your hand in there (remember it is not a pistol grip).

You can always use the “cradle hold” kind of like the Monsterman grip. With that, your thumb is stuck to one side like a fin grip, but with the advantage of still being able to grab it with your opposable thumb if needed.

Maybe there is some information here that will help!