Strange but VERY welcome AR-15 accuracy increase!

[PSE]

I suspect you are right on the first part beltfed. As for the second part, that would make sense, but it would only be a small amount. I am not a really high level shooter, but I am fairly proficient and the bit of extra recoil on this rifle won't effect me enough for what is being observed. its like softball or at best baseball sized groups vs loonie/toonie sized groups.

I'd say if your modification is working for you (and it sounds like it is) than keep it and rejoice. From baseball to toonie sized groups is huge - seems like you hit the accuracy jackpot.

 

[thump_rrr]

Rifle springs have 41 to 43 coils and are approximately 12.75″ when new.
Carbine springs have 37 to 39 coils and are approximately 10.5" when new.
They will shorten with use.
If it shrinks by 1/2" or more it is time to replace it.

 

[JR Hartman]

Yea, I saw those numbers in my AR-15 book (Patrick Sweeny) as well.

 

[recce]

Don't remember where I got this pic.