I have a colt late 60's SP1 (don't see the twist number on barrel)

and a Colt m16a1 upper, just says C MP C.

wanted to know what rate of tists are in each so I know what grain weight ammunition to buy.

Also what would be the best recommendations for each twist?

-mark

both are 1/12.

Stick to 55gr or under. 62gr and higher will fly out like wounded ducks.

Quoted: I have a colt late 60's SP1 (don't see the twist number on barrel)

Like the others said, 1/12.  Am curious what markings your SP1 barrel has though.

Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks.

so it would actually be more accurate with lighter grained bullets than 55gr?  I've never really seen anything below 55gr.

Quoted: Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks. so it would actually be more accurate with lighter grained bullets than 55gr?  I've never really seen anything below 55gr.

Winchester has some 45gr Varmint loads at Wal-Mart that are supposed to be pushing 3600fps out of a 24" barrel.

I've heard that these are super accurate out of the 1/12 barrels.

WIZZO

Quoted: Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks. so it would actually be more accurate with lighter grained bullets than 55gr?  I've never really seen anything below 55gr.

If you handload, you can set up loads w/bullets from 40 grains up.  You don't find them that light in factory loads, because most of the lighter bullets, which were created for lower velocity cartridges like the .22 Hornet thru .222 Remington, would tend to come apart at the velocities you could get w/the .223. Basically, 52-55 grain bullets are what work best in the 1in12 barrels.  Sierra does, or did, make a 62 grain flat base bullet, semi pointed, that always gave me excellent accuracy, and reasonably good velocity, out of the 1 in 12s. Used to load them back when 1 in 12 was the ONLY twist you could get an AR15 barrel in.

well, thanks for the help, I'll try a box of the winchester varmint ammo (although I heard for self-defense it's like shooting someone with a pellet gun lol).  

I just ordered 1000 rounds of XM193 (not PD) 55gr.  Never shot that I believe, I'll see how it does.

thanks again.

-mark

Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks.

WHAT?

Have you ever shot 62gr bullets from a 1/12 barrel?

Or did you just read it on the cowpath to misinformation "net?"

Quoted: Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks. WHAT? Have you ever shot 62gr bullets from a 1/12 barrel? Or did you just read it on the cowpath to misinformation "net?"

I know some 63 grain bullets that shoot FINE in a 1:12" twist rate.  Sierra SMP's but that is a handload proposition.

It all boils down to the Greenhill formula.  Nowhere in it is there any reference to bullet weight, only length.  You see, if M855 bullets were solid lead core instead of steel/lead, they would weigh about 72 grains.  They are some LONG bullets.  And M856 would be 100 grains if they didn't have a bunch of flare material in the rear.

Quoted: well, thanks for the help, I'll try a box of the winchester varmint ammo (although I heard for self-defense it's like shooting someone with a pellet gun lol).   I just ordered 1000 rounds of XM193 (not PD) 55gr.  Never shot that I believe, I'll see how it does. thanks again. -mark

gave you some awhile back to try along with the q3131a and the federal ae.




if the wally world varmit ammo works out cheaper per round that is the way i would go for your 1x12

oh, might meet up some fellow arfcomers this weekend at Hot wells



gonna bring the 'wulf out

Quoted: oh, might meet up some fellow arfcomers this weekend at Hot wells gonna bring the 'wulf out

saturday or sunday?

also not even sure if varmint will load in my ARs, they wouldn't load one round in my BM.

totally sucks though, wally is out completely of Q31.....whatever.  Can't find it any of them, only the Remington UMC 55gr, which is actually just as good in my opinion.  It gave me the same groups at 100 yards with my BM scoped.

-mark

Quoted: Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks. WHAT? Have you ever shot 62gr bullets from a 1/12 barrel? Or did you just read it on the cowpath to misinformation "net?"

FM 23-9, military tests show that 62 grain M855 ammunition shot from a 1/12 barrel shoots like shit.

Quoted: Quoted: Quoted: Stick to 55gr or under. 62gr and higher will fly out like wounded ducks. WHAT? Have you ever shot 62gr bullets from a 1/12 barrel? Or did you just read it on the cowpath to misinformation "net?" FM 23-9, military tests show that 62 grain M855 ammunition shot from a 1/12 barrel shoots like shit.

That's cool.

My own personal tests show that 62gr Federal XM855 shoots nicely throug a 1:12 barrel.

Bought an SP1/M-15 upper (Colt, no assist, no deflector, 3-prong hider- an OLD mother) and B/C/CH assembly for my brother this past Christmas, so he'd actually have a complete rifle instead of 2 lowers.

We put it on his Bushmaster A2 lower, swapped out the A2 buttstock and PG for the A1 that came with the upper, and took it and my two Bushmaster AR's out to the rock pit we shoot at.

This particular pit has about 90 yards from where we setup the bowling pins to where we shoot from.

For reference, my two Bushies are an A2 HBAR and an M4gery, both with 1:9 twist barrels.  The A2 HBAR has an A2 hider, the M4gery has a Gemtech Bi-Lock.

When we left the house, I had grabbed a bag with a dozen or so loaded 30rd mags.  When we got to the pit, I realized that they were all loaded with XM855.

First thought through my head was "crap, my brother's rifle is going to shoot like shit..."

Well, we setup the pins, and started plinking.

I'm not the greatest of shots - my way of thinking is that if I can empty a 30rd mag at an 8.5"x11" sheet of paper at 100 yds and put 15+ rounds on the paper with iron sights, I'm doing good - I'm not match shooting, and the rifle was designed to shoot people, not paper, so a 50% hit rate with crappily aimed fire is pretty damned good in my book.

My brother started playing with his new rifle, while I dinked around with my two.  After a few seconds, I stopped and watched him nail every single target he aimed at, where I was still missing.

Thinking he's just a better shot than me, but wanting to make sure, I borrowed his rifle, loaded a new mag, and proceeded to shoot like an Olympic Marksman.

That 20" 1:12 barrel with 62gr XM855 kicks all kinds of ass - it's a freakin' tack driver if I've ever shot one!

Every round I fired out of that hit it's target - this rifle made my other two AR's look like the AK's in my collection!

Saying that a 1:12 barrel is useless for the heavier ammo (at least up to 62gr) is a fallacy and a half.

It not a fallacy, many of us here have tried it.  My old A1 would keyhole at 100 yards with M855 some will, and some won't.  Couple things are factors here that effect gyrostability, one being temperature, and the other being that just because a barrel is supposed to be 1/12 don't mean that it is.  On top of that, just because yours worked yesterday, don't mean it will work this December at 600 yards with a 15 miles cross wind, go ahead and try.  Military testing includes more then one barrel, one load, and one condition.