M5 RAS Dissipater


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Using a M5 RAS on a Bushmaster Dissipater Upper

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M5 RAS on Dissipator by compuvette of AR15.com forums:

I purchased an Knight's M-5 (full length) RAS and installed it on a Bushmaster Dissipator A3 upper.  The RAS fit pretty tight on the HBAR barrel, but everything works fine.  The Bushmaster Barrel actually measures 0.75" which is significantly smaller than the 0.84" that is ideal for the M5 RAS.

The Dissipator upper utilizes a functioning gas block with shaved front sight in the normal carbine position (covered by the full length rifle handguards), adding a "dummy" gas block/front sight assembly further out on the barrel at the rifle length position. The functioning shaved gas block did contact the inner surface of the RAS at the four corners of the shaved top surface of the gas block.  Minor dremel tool modification to the inner portion of the RAS at the contact points provided complete clearance of the gas block.

The weight feels fine, not really different then the stock hand guards.  I have a GGG A2 flip-up on the flattop upper receiver and an Eotech 501 mounted about two slots up on the RAS and an Insight M-3 light mounted on the right side of the RAS mounted all the way forward. 

O'DubhGhaill, another member of AR15.com advised he has also done this and has the following advise:

I would suggest that anyone using the M5 on a Dissipator, clearly not a milspec barrel assembly, check the gas block corners to inner RAS surface clearance, as the integrity of the RAS's perfectly straight rail properties might be compromised whilst the RAS clamp is tightened and the rail is compressed over the shaved gas block interference. (note: my RAS returned to its originally perfectly straight condition after the mod.) Realizing that the M5 is designed and manufactured for use on 20" milspec barrel assemblies, I am very happy I could make the M5 work on my Dissy with such minor modification, a mod not all Dissies might require of the M5. I am completely satisfied with the exceptional quality and performance of the M5 and am thoroughly enjoying the vast real estate the M5 provides on my 16" Dissy!


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This site was last updated 01/07/04