View Full Version : MR1 ACS Bolt MOD!

06-26-2008, 05:09 AM
Hey guys. Just wanted to let you all know that I have completed modifying a rear cocking Pilot SCA bolt to work with the MR1.

Photo obtained from PaintballGI.com

I did not do a detailed HOW TO, but here are a few pictures and a brief explanation of what I did. There might be better ways to do this, if there is please post your thoughts or ideas.

• Fine tooth hacksaw.
• Dermal.
• Bench Drill.
• Bench Vise
• Set Screw (8-24 x 3/8” or 10-24 x 3/8”)
• TAP & Drill bit for the set screw.
• Teflon tape.
• Stanly Knife.
• Sandpaper.
• ¼” Drill bit.


NOTE: The groove you see half way down the bolt is a bad bad job I did at making a groove for an O-Ring. I normally do that on a lath but I decided to use the dremel. It still works just not as sexy looking.

What I did:

1. Cut off the ACS rear cocking mechanism. If you compare the stock bolt and the ACS bolt side by side you’ll notice that the only difference in the overall length is where the cocking mechanism is installed on the ACS bolt. Since we do not need that for the MR1, you can put the bolt in the vise and use a fine tooth hacksaw to cut that part off. Where to cut? Make your cut where the outer diameters of the ACS bolt changes to a smaller diameter.

2. Disassemble the bolt by undoing the screw that holds the ACS mechanism and the Delran bolt together. Make sure you do not lose the spring or the O-Ring.

3. The next step is to remove the pin that connects the ACS bolt and the striker together. This is where our MR1 cocking pin is going to go. You can remove the old pin by undoing the mini set screw and pushing it out using a punch. The tolerance is tight so it might need a little humph

4. Once you get the striker pin out the next step is to make sure the MR1 cocking pin is going to fit smoothly. You may need to put a ¼” drill bit in a bench/hand drill and run it thru the hole a few times to get the cocking pin to slide up and down smoothly.

5. Now we need something that will hold the cocking pin inplace while playing. The easiest thing I could come up with was to use a set screw. The idea is that I loosen the set screw to get the cocking pin out and I tighten it to hold the cocking pin in place, the set screw will fit into the groove on the cocking pin. As you can see in my photo, the set screw is wraped in Teflon tape, this stops the set screw from working loose while playing. You can get a set screw and a tap kit at Home Depot. I got a 10-24 x 3/8” set screw and tap for $5.

6. In-order to install a set screw, you will need to drill the back of the aluminum ACS mechanism in dead center and drill it all the way thru until the drill bit pops out into the cocking pin hole. Make sure you de-burr any aluminum that might stick out into the cocking pin hole. Once the hole is drilled you need to tap it. Take your time so that you do not strip the threads. Once you tap it make sure the set screw screws in/out smoothly. As you’ll notice, the screw is very free, you will need to wrap Teflon tape around it so it does not fall out during play.


Now, at this point you’ve completed the cocking mechanism. Now you need to carve/drill out the slot for the cocking pin to slide back/forth. When you look at the original ACS bolt you’ll notice that there is only one slot for the cocking pin to slide, we need to make the other slot on the opposite side. The dimensions of the 2nd slot needs to be the exact same as the original one.

7. To open up the 2nd slot for the cocking pin, you can use a ¼” drill bit in a bench drill and drill several holes in the Delran as close together as you can. Once the holes are drilled you can use a Stanly knife to cut the excess meat between the holes. When your done it’s going to look rough, you can use the knife to smoothen it out and then use 600 grit sanding paper for the final touch. Make sure the cocking pin slides back and forth without sticking.

8. Once you’re done making the cocking pin slot, we need to make the detent grove. On the Pilot the detent is on the opposite side of the marker from the MR1. All we need to do here is put the stock bolt and ACS bolt side by side and mark where the DETENT groove needs to be. Once you mark it out, get the Dermel and the appropriate bit and Dermel the groove. Make sure you do not go too deep, as the walls of the ACS bolts are not as thick as the stock bolt or aftermarket bolts.


NOTE: I put the bolt in the marker, took out the detent, put a pen in the detent hole and slid the bolt back/forth until I had a clear mark on the bolt, then I dremled where the line was left by the pen.

We are almost done, now we need to do the usual upgrades to the bolt. We need to make sure that the front of the bolt is cupped so it has a snugger fit with the paint, but I will not get into that here.

Once you’re all done you need to reassemble the ACS bolt. Now put the bolt in the MR1, put the cocking pin in and tighten up the set screw. If you drilled the set screw hole in dead center, the set screw will fit nicely into the groove on the cocking pin and hold it in place until you loosen it. If the screw seems to be loose, wrap more Teflon around it.

Total time 2 hours.

So far this bolt has been amazing.

Hope this helps.


slim and shady
06-26-2008, 09:36 AM
Great how to that is very impressive and very usefull. Once again great thread!

07-02-2008, 07:09 AM
Great how to that is very impressive and very usefull. Once again great thread!

Thanks! No more chops for me even in full auto with a HALO Frontman hopper. :-)