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AR-15 advise
marek13
Member Posts: 209 ✭✭✭
Hello I am planning to build an Ar15 and I was looking at:
1) A DPMS 24" SS barrel assembly 1/9 twist
2) A silver or black Diamond series lower assembly (with 2 stage trigger)
Now what do you think of this configuration. The barrel assembly cost me 350(with bolt and charging handle). Now how much do the diamond series receivers assy go for? I saw one for 400. Is this good?
And I guess my question is;are the diamond receivers good or should I go with the Bushmaster lower that I can but for 300
1) A DPMS 24" SS barrel assembly 1/9 twist
2) A silver or black Diamond series lower assembly (with 2 stage trigger)
Now what do you think of this configuration. The barrel assembly cost me 350(with bolt and charging handle). Now how much do the diamond series receivers assy go for? I saw one for 400. Is this good?
And I guess my question is;are the diamond receivers good or should I go with the Bushmaster lower that I can but for 300
Comments
Greg
That's the 1st I've heard of a black diamond receiver. Looks like there is one for sale here on GB for like you said, around $400. My only thoughts might be, you could save a few $$ by going with a Rock River lower with a national match trigger. For example:
http://www.gunbroker.com/auction/ViewItem.asp?Item=9187627
Regards,
Fort knox hit the nail on the head with the twists. I worked on / built M16's for uncle Sam for 9 years. The bullet you want to shoot should determine your twist 1/12=55gr 1/9=62gr and 1/7=69gr. Have seen some 1/10 twists that do a fair job as a happy medium, but to tweek out subMOA with them you almost have to reload. As far as Barrel material; we found black bores the most accurate, chrome lined the most durable and stainless to be the happy medium (I like stainless too). Just make sure you go with a reputable manufacturer. DPMS is fine and so is Bushmaster. Different lowers had very little effect on accuracy - tried large pin, small pin, Colt, DPMS, Bushmaster, Bohica and others - Tight is nice and usually more desirable, but had some real shooters that rattled around like a BB in a boxcar. It was the upper and barrel that made the difference in the end. If it were me, and it has been in the past, I'd save the money on the lower and put it into the Barrel, and a good match trigger. You won't be disappointed
B-Man308 - Former USAF Combat Arms Instructor, NRA Life member
thanks again Mark[:D][:D][:D]
The stuff I posted was from some resources I referred to at that time and took as said...w/o a scientific explanation. I think "www.AR-15.com" may have had some specifications posted regarding bullet weight and barrel twist...and some other resources I don't recall at the moment. Anyway, you got me thinking about it some more...so I did a search on two or three topics.
There is a formula called the "Greenhill Formula" that is used to determine "ideal" twist rates for different bullet weights/types and other conditions that are pertinent to accuracy and stability. Three things determine "bullet stability": 1.) "It must be statically stable" 2.) "It must be dynamically stable" 3.) "It has to be tractable."
The "Tractable" component appears to apply to the phenomenon of "over-stabilization." Quote: "Over-stabilization means that the bullet rotates too fast and becomes incapable of following the bending trajectory, as it's longitudinal axis tends to keep it's direction in space. This effect is often observed for high-angle shooting, but is of minor interest in normal shooting situations." You can find this and an abundance of other information regarding this at: "http://www.nennstiel-ruprecht.de/bullfly/stab.htm"
Also, just do a search on "Barrel Twist" and "Over-Stabilization"... these two got me to the site I referred to in short order. Thanks for the inspiration! Take care.
This is what I have come to understand about the over stabilization phenom. It is also my understanding that the overstabilization phenom will have its greatest effect on accuracy at extreme distances. For the .223 this would be beyond 500 to 600 meters.
The 1-9 twist is probably the best compromise for most bullet weights commercially available. If you are going to use heavy bullets (80 grainers), you will not only be hand loading them, you will also have to hand feed them into the rifle due to their length. The 1-7 / 1-8 twist barrels are best for this weight bullet.
Boomer
"Success is to be measured not so much by the position that one has reached in life as it is by the obstacles which one has overcome while trying to succeed."
NRA Life Member
B-Man308 - Former USAF Combat Arms Instructor, NRA Life member