CAR 15 Upper?

[TooTaxed]

I have an early Colt SP-1 CAR-15, 1:14" twist, and would like to get an upper that would allow me to use bullets heavier than 55-gr.

Are there any pitfalls in getting a Rock River A4 kit for this early collapsable stock lower? I assume I would need an adapter pin...

Any appreciable difference between 18" and 20" bbl lengths? Chrome-moly HBAR and air-guaged stainless steel?

 

[rbernie]

Why not just get a replacement barrel? It'll save ya a bunch of money and would let you keep the rest of the rifle intact.

 

[Jeff White]

Well, according to Colt no SP1 was ever made with a 1/14 barrel. I bet your barrel is 1/12 twist.

You will need and adapter pin for the small hole replacement upper to fit your lower. There are so many combinations out there to choose from. It would help if you told us what you intend to use the carbine for.

Jeff

 

[TooTaxed]

Jeff, could be...I've been told it's 1:14, but I haven't measured. I can slowly run a tight patch through the bore and measure the distance required for one revolution...but both are pretty well limited to the 55-gr bullets. Mine doesn't do well with 62-gr...

 

[TooTaxed]

Sorry...I will use the rifle mostly for range shooting to 360-yd (& over?). If I like the combo, I may eventually try target or combat competitions on an informal basis.

 

[Jeff White]

It's the length of the projectile, not the weight you need to worry about. IIRC, Hornady makes a 60 gr varmint bullet that is short enough to use in a 1/12 twist.

For the shooting you plan on doing, I'd recommend a 10" especially if you're going to start competing.

Jeff