adding bolt hold open option on a MKI ?????

[xtratoy]

I am wondering if the MKI A100 frame can be retrofitted with MKII parts to use the MKII hold open on an empty Magazine feature. I was just eyeballing the one I got with a 12-***** serial number (1974-75). It looks like all the parts would fit and I would have to change the hammer pin,Add the external slide release and the bolt stop assembly that pivots on the trigger pin. I might be missing something since I didn't have time to detail strip both guns and I haven't took one apart to that extent for a while. Maybe a difference in the width of the trigger where the pin goes through? I was planning on putting a MKII upper on the gun if that makes a difference. I see the grip panels would also have to be changed. Is this doable with either the original upper or the newer MKII upper. What year did they actually start putting MKI on the receiver? Mine doesn't have it.

[Bullseye]

It has been done before with the A-100 frame. One thing you left out, and possibly the most difficult part, is drilling the frame for the bolt stop return plunger and spring. The underside of the receiver will also need a slot cut to allow the bolt stop to fit. You can see this cut by inspecting the underside of a Mark II/III receiver.

R,
Bullseye

[Bullseye]

I didn't have time to post this earlier.



Here is a close-up of how the top of the slot should look. In the previous picture you can see a squared off milled hole for the bolt stop button.



This is the tougher one to drill. The spring and plunger are necessary to cause the bolt stop to drop out of the way when the bolt is pulled rearward.



You'll also need to use a Mark II trigger with the relief milled on top for clearance for the bolt stop plunger. A Mark I trigger is straight all the way across.

Hope this helps.

R,
Bullseye

[xtratoy]

Thanks for the info and excellent pictures. Since I have a couple MKII uppers to choose from the biggest issue would be the spring and plunger hole. I think I will keep this gun as shipped from the factory for now. I have enough projects for the time being. I will have to remember to count to nine when I shoot this one.

[Bullseye]

You asked if it can be done. It certainly can with that frame. I just wanted to let you see what the job entailed. This way you can formulate a plan if you should decide to take on the task.

R,
Bullseye

[greener]

Thanks for the info and excellent pictures. Since I have a couple MKII uppers to choose from the biggest issue would be the spring and plunger hole. I think I will keep this gun as shipped from the factory for now. I have enough projects for the time being. I will have to remember to count to nine when I shoot this one.

Use your MKII mags and count to 10

[Bullseye]

Or you can make a hold open follower for your magazine. http://www.guntalk-online.com/forum/viewtopic.php?t=10 I've used many materials to make these over the years. Originally I used aluminum, but over the years I've used Delrin and UHMW Plastic too. All this follower does is catch the bolt after the last shot is fired. The trade off is one round of magazine capacity. Once the last round is fired you have to manually retract the bolt and set the safety switch to remove the magazine.

R,
Bulleye

[gunsmither]

http://www.rimfirecentral.com/forums/sh ... p?t=144208

The link is to an old thread on Rimfire Central explaining how to do the conversion. One section shows how I did a MK1 using a simple wire method instead of drilling the frame to hold the spring and plunger.

Hope this helps someone. Joe

[Bullseye]

Thanks Joe, that was a really old posting you dug up from RFC. I remember back when it was active. I haven't done many frame conversions, but I have made several hold-open followers over the years for bullseye shooters still using their old Mark I/Standards for local competitions.

R,
Bullseye