I hope you know that a SDMR(squad designated marksman rifle), is pretty much just a rifle in the hands of a skilled marksman... In the Army they may/may not give someone an accurized rifle, same goes for any other branch.
A DMR is a sniper rifle that was designed too shoot at a much higher ROF. Ie, a M21 or M1a thats accurized and tuned by the Army's marksmanship unit armorers. These guns are designated sniper weapons and only issued to trained DM's or Snipers. They are never issued with anything that would not be beneficial on the rifle(ie, M203's, red dots, etc etc). They are usually issued with a scope of some magnification, including ACOG's, as well as a PEQ(IR laser) of some sort, and a bi-pod if they have extra's in stock... Thats all that goes on the rifle. Why carry a M203 when you wont get issued 40mm grenades?
IMO it sounds like you are just trying to make an accurate rifle, with a few attachments... Which is alright, its just not a DMR though.... Nothing is wrong with stopping every once in awhile and providing long range support with a rifle, it doesn't have to be a DMR and I bet if you head to a MilSim game right now people will be doing just that. Performing precision rifle fire with a normal assualt rifle style replica. I talked with someone who did DMR "work" with an almost stock PTW, this specific PTW also only had a 10in barrel. He was covering people who were using M16's to clear an airfield at our local place. He did a great job of it too!
point being, you are probably not making a DMR, but that doesn't mean that you cannot perform the role of a DM with a normal rifle.
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