When life gives you lemons... converting my AR15 A3 to a DMR

[RostokMcSpoons]

I've got 4 rifles at the moment, only one of which is truly healthy. 
I've got 2 which aren't feeding well on full auto.  It might just be they need a new nozzle fitted, or maybe getting new hop units / bucking, but while I've got my Classic Army AR15 shooting just fine on semi, maybe "when life gives you lemons, make lemonade" I should just go with the flow and convert it to a DMR build, so it can justify a space in the back of my car at the next skirmish. 

 

It's got a nice long barrel and when I've got the outer barrel shimmed well, it even shoots quite straight   And it looks the part when it has a scope on it.

 

I'm happy enough to bung in a chunky spring to get close to the 450fps limit at SpecOps, but I have no idea on how to lock it to semi auto mode.   I could just drill a hole into the lower receiver, and block the selector lever with a bolt... but is there a better way to meddle with the internals?

 

Are there any gotchas?  The occasions when my guns have needed a short burst of full auto to clear a semi lock-up spring to mind, not that I think the AR15 has done that

Edited February 16, 2022 by RostokMcSpoons

[Fatboy40]

33 minutes ago, RostokMcSpoons said:

.... but I have no idea on how to lock it to semi auto mode.   I could just drill a hole into the lower receiver, and block the selector lever with a bolt...

 

Which I what I did, along with some Loctite 270 which you can only weaken with heat, and all the sites I've been to so far have been happy with this (I really didn't want to hack the selector plate about etc.).

 

34 minutes ago, RostokMcSpoons said:

Are there any gotchas?  The occasions when my guns have needed a short burst of full auto to clear a semi lock-up spring to mind, not that I think the AR15 has done that

 

This was the No.1 reason why I waited until I had the cash and used a Double Eagle M908A as the base for a DMR, cycle control with the Falcon Controller so no worries about potentials jams on semi. Only other thing I'd add is factor in potentially replacing your cylinder, trying a few different ones, as my DMR wasn't up to scratch until I went with a 4/5 (and probably a full / closed one would have been better).

[Lozart]

42 minutes ago, RostokMcSpoons said:

I've got 4 rifles at the moment, only one of which is truly healthy. 
I've got 2 which aren't feeding well on full auto.  It might just be they need a new nozzle fitted, or maybe getting new hop units / bucking, but while I've got my Classic Army AR15 shooting just fine on semi, maybe "when life gives you lemons, make lemonade" I should just go with the flow and convert it to a DMR build, so it can justify a space in the back of my car at the next skirmish. 

 

It's got a nice long barrel and when I've got the outer barrel shimmed well, it even shoots quite straight   And it looks the part when it has a scope on it.

 

I'm happy enough to bung in a chunky spring to get close to the 450fps limit at SpecOps, but I have no idea on how to lock it to semi auto mode.   I could just drill a hole into the lower receiver, and block the selector lever with a bolt... but is there a better way to meddle with the internals?

 

Are there any gotchas?  The occasions when my guns have needed a short burst of full auto to clear a semi lock-up spring to mind, not that I think the AR15 has done that

 

There's easy - trim the selector plate, there's slightly less easy but arguably better - drill and tap the receiver and put a screw in to block the selector lever (as you suggested) or there's the expensive way - fit a Gate Titan/Aster/Perun and set the auto position to semi (assuming your site allows electronically locked AEGs as DMRs)

[RostokMcSpoons]

Yeah, I like the idea of tapping the receiver, so a screw in there can be removed with some fiddling to do the full auto thing if I have to.   

Doing stuff to the tappet plate is a bit irreversible and I'm doing this on a budget so the Mosfet is going to be a basic one if I do that at all.  (I'm happy enough to run an 11.1v on it without a 'Fet, as it's going to get used pretty infrequently, and I accept the contacts will burn out or need scraping eventually.)

[Iceni]

Keep it simple.

Buy a second selector plate, Remove a little plastic.

With that modification you have a gun that can only select semi. Yes you can move the selector to auto, but it'll still only shoot semi. When you want to go back to a normal Rifle you just put a regular selector plate in and change the main spring. I would used a mosfet with absolutely no features. As a 3rnd burst will still work on a semi only gun.

 

Doing anything more than that is pointless. If you need full auto to clear a trigger jam all you do is split the upper and hold back the COL with a screwdriver.

 

Edited February 16, 2022 by Iceni