[pittspilot]

From CDNN's latest catalog. (399.00)

Would this be a good first step to building an AR?

What else will I need? and how much?

[Harry Tuttle]

thats gonna have a 1/12 twist

http://www.ammo-oracle.com/

http://www.ammo-oracle.com/body.htm#twists
Q. OK, what is all this stuff about rifle twists and different ammo?


Rounds in flight spin for stability because of the rifling on the inside of the barrel.? Depending on how much they spin, they are more or less stable in their flight and therefore more or less accurate.? The earliest AR15s from the early 1960s had a twist rate of 1 complete twist every 14", or 1:14.? This was increased to a twist rate of 1 turn in 12" for the M16, XM16E1, M16A1, and later rifles and carbines.? The current M16A2s and up and the M4 carbines have a much faster twist rate, 1 turn in 7".? The reason for the 1:7 twist is mainly to stabilize the M856 tracer bullet, which is much longer than other bullets.? You will recall from above that the M856 was designed to provide 800 meters of trace out of the SAW.


While the slow 1 in 12" twist is adequate to stabilize the 55 grain M193, it will not stabilize the 62 grain M855.? As a result, the newer M855 ammo will group 1-2 feet at 100 yards, with bullets flying through the air sideways, instead of shooting to about 2" at 100 yards, like military ammo should.

[NMshooter]

If you are looking for a clone of the original M-16/AR-15 it is a good start. If you are looking to build an AR on the cheap, I would keep looking. Unless you really want a carry handle, a flattop upper receiver is the best choice. Used parts are a good thing to avoid if it is a defensive rifle.

[BigG]

The SP1 rifle is my favorite version of the venerable AR15. That said, the upper has a larger front hole that takes a hinge pin differnet than the standard military 1/4" push pins. It is no problem as offset screws are available for about $5 to mate SP1 uppers to std pin lowers. Just thought you should know.

Also, the SP1 does not have the fabled forward assist. I like NOT having it but some think a forward assist is a good thing.

The 1:12 twist is far better than the quicker twists on later models, imho. 55 grain ammo is still standard and you can buy a ton if you want to stock up. Good luck!

[cabinetman]

I wanted an honest-to-God SP1 as close to identical as the original M16 that was first issued, right down to the three-prong flash hider. I was lucky. I found one on eBay last February and paid $289 for it, shipped to my door. According to what I can determine, my upper was one of the first 15,000 made. These first Colt SP1s had no forward assist and were called a "slab side". It fit the bill. It also had the "big hole" in the front pin which is military. So, I had to find an "eccentric" bushing to make it work with the aftermarket, commercial lower receiver with a small hole. You will too. Without it, the rifle would not function properly having too much slop between the mating surfaces and allowing the rear plunger to move too far forward and shear off the little spring loaded pin in the buttstock. Ask me how I know!

The upper also had the black plastic triangular handgards. I even found an original pistol grip in the original bakelight material. So, other than the pre-ban EA receiver which is semi-auto only, everything else on my AR15/M16 clone is 100% original.

Out of the box, it shot so amazingly accurately that I only had to make minor adjustments. I was really surprised. All the vets who have seen it and fired it say it is as close to what they all remember so I'm very pleased with it.

I collect WWII semi-autos but wanted an "original" AR15/M16 to add to my collection. Having an EBR "space gun" with all that bling bling hanging off of it with folding stocks and shortened barrels don't interest me in the least. Original was the only way I wanted to go and I was fortunate to have been successful. A lot of guys like the "tactical" look, however, so to each his own.

So, if that's what you're looking to build, make sure there is no forward assist and make sure you find the eccentric bushing to make the new lower work with the military upper. Bushmaster sells them, btw. All up, I assembled my rifle in one morning from start to finish once I had all the parts. I was in the field with it that afternoon. This type of build is easily attainable by anyone with basic mechanical skills and some knowledge of firearms. No special tools are needed, but good instructions for the lower internals are important.

I've seen CDNN and others selling what they are calling SP1s but I've seen the forward assist on them. I don't know if the nomenclature changed with the added forward assist but if you're looking for ultimate authentic, no forward assist SP1 is what you're looking for.

Rome

[mototard]

I got one and put it on a RRA lower. Very cheap build and a great little rifle. I shoot the Winchester XP2 through it and its very accurate

Basically
$400 upper (actually traded a used DPMS Lo-Pro 16" classic upper for it)
$115 Bolt and carrier (Del-ton)
$ 53 Lower receiver kit (Del-ton)
$120 RRA bare lower (local)
$ 90 Sp1 Colt NIB buttstock assembly (Gunbroker) Get cheaper elsewhere
$ 25 ended up with w /phantom yhm-28 on it

I had the 16" DPMS upper for awhile and ended up with about $450 total in a SP1 build not counting the trade. Built it for my boy. Currently has a cheap 4 position stock on it. His arms are a tad short and the middle notch is the perfect length for him. Cant wait until the sp1 stock gets put on. Great looking light weight rifle and I love the slab side upper. Whish I had an original SP1 lower to go on it.

[DMK]

It also had the "big hole" in the front pin which is military. So, I had to find an "eccentric" bushing to make it work with the aftermarket, commercial lower receiver with a small hole. Actually the large hole isn't a Military thing, it's a Colt Commercial thing. I believe only commercial SP1s had the large hole. The Military "A1" M16 uppers had a small hole. I have an Air Force M16A1 upper(no deflector or forward assist) that swaps perfectly on my Rock River lower.

[Samuel_Hoggson]

These uppers are actually M-16 take-offs. They are 1:12 twist, chrome bore and chamber barrels on A1 uppers with forward assist. They have autosear cutouts, and are small pin uppers.

Thus, they are not really SP1 uppers, but will work with a conversion pin if you happen to have a large pin AR or SP1.

Sam

[mototard]

Mine is a slab side with no forward assist. It is mil spec pin size. It did have the recess for the .250 screw not pin in the forward hole. Pins will work on it. As long as it is 1/4" not 5/16" diam hole. I thought only Colts civilian models got the large front screw/pin?
Also what are you talking about auto sear cutouts? I thought that was only on the civilian lowers are did Colt do something else to the civilian uppers to?

[ftierson]

What Samuel Hoggson says...

[borderguy]

If you check the EE Board at AR15.com, there is someone selling early AR15 SP1 type uppers for $259.99. They are small pin uppers and will go on your lower.

Sarco has a kit for $386.00 that everything but the lower reciever.

In addition to the upper, you'll need a Bolt Carrier Group, Charging Handle, Lower Reciever & Parts, Buttstock and Grip.

[Samuel_Hoggson]

If you can get a copy of Black Rifle II you'll find a side by side comparison pic of the undersurface of SP1 and M-16 uppers. Anyway, the autosear cutout is located on this surface towards the rear of the upper receiver. It is a shallow relief and accomodates the autosear located in the corresponding position on a M-16 lower receiver. An SP1 upper does not have this cutout (well, for all I know b/c I don't own an SP1).

I can't see why having the cutout would cause problems when used on a SP1 lower...........obviously, you have to deal with the front pin size.

The ones CDNN sells are small front pin, forward assisted, A1 uppers.........unless they're selling both types???

Sam

[mototard]

Got it.
My upper is susposed to be an SP1(well I thought so) it is small pin and has the auto sear cutout, pencil barrel (C MP) triangle HG and flat delta ring along with 3 prong FH. So does my A2 upper 11.5" heavy barrel and is small pin, Colt. What years did Colt start all the civilian mods (non milspec) on their AR's? (another reason to stay away from Colts) :banghead: Where can I get a copy of this Black Rifle II?

[Samuel_Hoggson]

http://www.collectorgrade.com.

The saga of Colt's multiple iterations of "full-auto-proofing" politically correct BS is almost as interesting as the M-16 saga itself.........and more confusing (large pin, small pin, offset pin, sear block(s), fire control pin sizes, carrier mods, eieio..........). To be fair to Colt they were in the unenviable position of having to break ground with the feds concerning modifications for civilian sales. The second volume has most of the stuff you want concerning this matter.

Also, http://www.biggerhammer.net has a FAQ on ARs and M-16s that has more data than you'll want to digest.

Sam

[mototard]

I've got 2 wks off for christmas maybe I can really confuse myself.
Thanks

[zach13168]

I bought one of the SP-1 uppers for my Bushmaster lower and its great. I added everything that was needed to make it an A1 issue. The upper was in great shape the only issue was the old grease but with simple green it came off great. personally after having an H-bar before I have a great appreacation for the A1.

Zach

[DMK]

personally after having an H-bar before I have a great appreacation for the A1. Yea, they are very light. I can even feel a big difference between my A1 upper and my A2 upper with the Govt. profile under the handguards.

[1911user]

DMK,

Have you noticed much difference between shooting the A1 vs govt. profile A2?

I'm thinking seriously about an AR with a 20 inch barrel and don't want it to weigh too much since my kids will use it some. But, I don't want to handicap myself with too light of a barrel since it will be shot occassionally in local 3-gun matches and small amounts of rapid-fire. I do understand the 1x9 vs. 1x12 barrel differences and how that affects ammo selection. thanks

[NMshooter]

Bushmaster makes a 20" A2 profile barrel with a 1/9 twist.

Probably the best compromise out there.

I am very happy with mine.

[DMK]

DMK, Have you noticed much difference between shooting the A1 vs govt. profile A2? Well, I really can't say. My A1 upper is dedicated to exclusively shooting .22LR with a Ciener kit. I've never shot .223 though it. I do need to try it one day though.

[1911user]

I'll most likely end up with an A2 type barrel in pre-ban config.

I looked at the bushmaster site, but only found a post-ban 20 inch, govt. profile A2 barrel. It'd be nice to find one that's chrome-lined and govt. profile without having to pay extra to get the muzzle threaded.

[DMK]

I looked at the bushmaster site, but only found a post-ban 20 inch, govt. profile A2 barrel. It'd be nice to find one that's chrome-lined and govt. profile without having to pay extra to get the muzzle threaded.
They have the unneutered A2 Govt. barrel here:
http://www.bushmaster.com/shopping/barrel-assemblies/abbl-20a2.asp

Or did you want a complete upper? If so, give them a call. I'll bet they'll assemble one for you.

[1911user]

DMK, That's exactly what I was looking for. I'm not sure how I missed it, but obviously did. Thanks for the help.