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Gunsmithing How to Install Flush cups, Pics inside.

USMCj

Gunny Sergeant
Full Member
Minuteman
May 1, 2008
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Nazzifornia
I got the threaded flush cups from GrovTech today, so I figured I would do a how to.

First thing is to measure the OD of the cups to see what size drill bit you will need. The GrovTec threaded cups are about .55" so I went with a 5/8" bit (.600")

I measured the cups length (1/2") and put tape on the drill bit so I dont drill too deep.

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Then I drill the hole, After I drilled the hole and checked to make sure it is deep enough for the cup, I installed a ball mill on my Dremel and made some cuts on the inner wall of the hole all the way around so the bedding can create a mechanical lock and not pull out

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Then take a allen wrench that fits the flush cup, and tape it leaving just a tip of the wrench exposed. Make sure you put enough tape on the wrench so it fits the cup snug, this will keep any bedding compound from seeping into the cup.

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insert it into the cup

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Now mix up whatever bedding compound you are going to be using, I used JB QUICK, you can use anything you want, ie: Steel Bed, Devcon or Marine Tex. Apply the epoxy in the hole making sure you get it on the walls of the hole, and also apply it to the flush cup makeing sure it goes in between the threads to create a good lock.

Insert the cup in the hole until it is flush with the stock, make sure it is flush, if you insert it too deep, your swivel will not seat/lock in properly. Clean all the extra epoxy that oozed out and let it set.

Sice I was using JB QUICK, I didnt have a lot of time to take pics of some of the steps because it sets in 4 minutes.

Here is the finished project

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Re: How to Install Flush cups, Pics inside.

Outstanding! Thank you for posting this!
 
Re: How to Install Flush cups, Pics inside.

tag. thanks for the step by step photos.
 
Re: How to Install Flush cups, Pics inside.

Hey! these are working hands!
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a little dirt under the nails never hurt nobody
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Thanks Will.
 
Re: How to Install Flush cups, Pics inside.

Excellent post. Thanks for the writeup.
 
Re: How to Install Flush cups, Pics inside.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">Hey! these are working hands!</div></div>

You should see my hands
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Re: How to Install Flush cups, Pics inside.

Dont need to see it to know how it looks Will
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Re: How to Install Flush cups, Pics inside.

Thanks for the post I am just getting ready to order some of the flush cups from GrovTec.

Ken
 
Re: How to Install Flush cups, Pics inside.

Welcome, glad you guys found it useful.
 
Re: How to Install Flush cups, Pics inside.

Thanks for this. I've been planning on doing mine for awhile but I was always uncomfortable with the hole the bedding compound would have. Your solution of undercutting the hole to create a mechanical lock solves that problem for me.
 
Re: How to Install Flush cups, Pics inside.

Thanks guys! response like this makes doing a how to worth it.
 
Re: How to Install Flush cups, Pics inside.

You don't have a problem drilling holes in your Manners (I think, or McMillan?), but you have to work up the nerve to paint the scope???
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Just kidding, the stock is definitely much easier to fix than an USO with paint inside. Great job!

Are you in So. Cal?
 
Re: How to Install Flush cups, Pics inside.

LOL, yah Pete, still cant get myself to drop paint on the USO. Oh and its a McMillan A5.

Ya Im in SoCal, near Van Nuys.
 
Re: How to Install Flush cups, Pics inside.

would love to hear how these are holding up now, a few months down the track, im interested in doing this myself.

cheers mate, looks the goods.

jimi
 
Re: How to Install Flush cups, Pics inside.

Nice write up thanks heaps for it

Can you confirm they are the GT Heavy duty push button swivel set?

Looking to order some soon for a future project
 
Re: How to Install Flush cups, Pics inside.

TAG Thanks for doing this post, this is exactly what I was looking for! Only bitch is I want to do this to a Sendero stock and I think it's hollow. Any ideas from anyone on how to get cups set if the darn stock is hollow, something I can pump into the stock to solid it up?
 
Re: How to Install Flush cups, Pics inside.

How thick is the wall? Can you get to the back side? I'd try drilling the hole, roughing up the back side as best you can, then mound up epoxy compound on the back side of the hole, then put in the flush cup. If you can't get to the back side directly, you'll have to used hooked/angled tools to work through the hole.

Epoxy will not stick to some kinds of plastic, so that might be something to check also.
 
Re: How to Install Flush cups, Pics inside.

I'll get the recoil pad off and see, I have a feeling it's going to be thin based on pictures I've seen. Maybe I can put some kind of blockage part of the way up inside the stock and fill it with some resin. Hopefully I don't make mess. I have a cheap factory take off I'll practice with first. Thanks again, I thought you did a great job on this post.
 
Re: How to Install Flush cups, Pics inside.

I put the heavy duty threaded flush cups in a hogue buttstock. It is hollow and about 3/16" thick. I drilled a 1/2" hole and and threaded with appropriate tap. Threaded in cup. Then I cut a nut in half to make a thin nut and tightened it onto the cup from inside the stock. Very solid. I thought about putting devcon on the cup but figured the nut was easier. I just looked and tap size is 9/16-18. Just another option.
 
Re: How to Install Flush cups, Pics inside.

I thought you we supposed to cut threads into the stock with a tap. Then the cup screwed into the stock.
This way the cup screwed and then epoxie glued into the stock.
 
Re: How to Install Flush cups, Pics inside.

I ordered some HD swivels from Denise at Grovtec today to put in my A-2 stock. Also ordered one of the cute inserts that goes into the QD socket in front of the hand guard that looks like a regular swivel stud to attach a bi-pod to.
 
Re: How to Install Flush cups, Pics inside.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DaveD</div><div class="ubbcode-body">I thought you we supposed to cut threads into the stock with a tap. </div></div>

Well, that may be the preferred method, but as with everything gun related that is a bastard tap. So you can buy and oddball tap that you won't ever use for anything else, or just drill it oversize and glue it in. I used a tap on this install, but the insert threads into a magnesium block that also provides a mount point for a bipod:

http://www.snipershide.com/forum/ubbthre...387#Post2696387


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Re: How to Install Flush cups, Pics inside.

tag. awesome pics and thanks for the step by step.
 
Re: How to Install Flush cups, Pics inside.

a few guys have done this in an HS stock too and its foam and hollow in the butt. no one is doing chin ups but no one has lost a rifle from one pulling out either. i may have to nut up and do it too. if you dig around in a parts bin at most hardware stores you can find flat nuts in most sizes if cutting one isnt an option to some.

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Re: How to Install Flush cups, Pics inside.

Hey, i realize this is an old thread, but i wanted to say thank you for posting this tutorial/ how-to. I used it to install Grovtec flush cups on my HS Precision stock, and it worked out really well. thanks!

-Paulus


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Re: How to Install Flush cups, Pics inside.

Thanks for the write up!

Is there a place where the flush cups can be purchased online? I can't find them listed anywhere.

Do I just call grovtec?

Think a Bell and Carlson stock can take them? Probably also hollow like the HS Precision. (My guess at least, I know it's not a manners or mcmillian)
 
Re: How to Install Flush cups, Pics inside.

MadCap, i got my set of flush cups and adaptors right from grovetec. they are awesome to deal with.

The HS Precision's are not hollow, they are foam filled with a brittle, hard exterior that chips easily when drilled (as i found out). They also have an aluminum chassis internally that runs the full length of the fore end to the bedding block as well. i BELIEVE the Bell and Carlson's do as well, but i am not 100% sure of this, and i hope other members more familiar with the B & C's can weigh in on that.

-Paulus
 
Re: How to Install Flush cups, Pics inside.

Another tip is to use whatever your favorite release agent on a q tip to coat the inside of the swivel cup before install just in case some bedding material gets inside. If it squirts into the swivel cup you can then use a dental pick to just pop out whatever got leaked into the wrong place. I haven't had any yet that did leak but I still do it as I would hate to have to drill out a cup in a stock to replace it if I did happen to mess it up.