PDA

View Full Version : SP1 fix


munchoman
December 16, 2017, 09:25
I've had to move the rear site, way to the right, to get it my SP1 sighted in.
I pulled the barrel, and found that the barrel locating pin has about .005 slop between it and the notch in the receiver.
What would be the fix for this?

hueyville
December 16, 2017, 10:37
Know history of rifle? From what your describing barrel is off axis and front sight tower is leaning a bit. 90+% of time I see this is when kitchen table builders install front sight tower off center but since you say slot has play assume your issue is there. Is it a parts mix rifle or all original? Without accurate measurement of notch and then determining if centered would be my first diagnosis. At some point could have been put together with loose barrel nut then as barrel twisted on could have worn the notch seeing it's steel on aluminum. Say multiple swaps of muzzle device with loose barrel nut or just lots of use with loose nut or could have come from factory like that but never seen such with an unmolested Pony gun.

Your problem may be best solved with simple small shim and a prayer or tolerate sight alignment looking odd. Can't count the number of home built and bargain factory guns have seen with rear sight cranked as far to one side as possible. Some have been like that for years. I would no tolerate it but have boxes of NIB uppers can swap but not piles of original Colt uppers so repair might become my solution.

Have taken in quite a few uppers with messed up threads and pin notches. Luckily my part time welder is an artist with a TIG and has nuclear pressure vessel rating. Have had him weld up stripped thread areas and then chased threads and welded up pin slots and recut on mill. Accurate measuring and locating is key. Usually let my part time machinist do these type tasks as he is full time machinist through the week and can be done in same time I am still trying to get parts centered. If slot is still dead center could remove pin, redrill hole to proper size and install oversize pin. Of course you now have an out of spec barrel extension and pin if we're to ever be moved to different upper.

Highly caution anyone welding up an upper receiver. I would not do unless it's very small area and have my guy who usually sits over a TIG 60 hours per week. And full time machinist finish the work. If all threads are stripped when an upper is brought in it becomes a paper weight. If first few turns are cross threaded then have my guy run a bead and then rethread. If don't have more than 50% of original threads don't try this either. Have several rifles built on welded uppers that have seen abuse without failure.

Another option is coat barrel extension in locktite, insert in upper and use multiple machinist levels or other devices to ensure barrel/front sight tower is 100% installed dead vertical, let thread lock harden then torque barrel nut to spec and see if barrel/FSB stayed straight. Still have to worry about future slipping. Anytime try fixing or fixing an upper usually have more time in labor than its value except with an original Colt.

MAINER
December 16, 2017, 11:08
https://www.rockriverarms.com/?fuseaction=category.display&category_id=277

AR0015 15 - Barrel indexing pin $2.00

Is your index pin loose or too small? I haven't had a problem with Index pins so don't know much about them except that they are tapered and a press-fit to the Barrel Extension.

mikeuniform
December 16, 2017, 11:08
I've had to move the rear site, way to the right, to get it my SP1 sighted in.
I pulled the barrel, and found that the barrel locating pin has about .005 slop between it and the notch in the receiver.
What would be the fix for this?

Before adjustment, POI was to the left, correct?

Is this new to you rifle/upper or it suddenly started shooting crooked?

With the slop in the notch you are describing, when tightening the barrel nut, it should be rotating barrel/FSB towards the left side of the target.
Seems it is canted to the right, interesting.

IMHO, your FSB is canted.

munchoman
December 16, 2017, 11:19
all original Colt SP1, bought it used 35? years ago, and changed barrels then, and now replacing that barrel, with the original barrel it came with.
I have not shot the rifle in 30 years, so Iam kind of vague on the details

lockjaw
December 16, 2017, 14:11
If you can successfully zero the rifle, and you still have room for adjustment in either direction, there isn't anything wrong with your upper..... it is likely how it shipped from the factory.

V guy
December 18, 2017, 18:29
When torquing the bbl nut, it is dragging the bbl to the left, to the limit of the slot.
How does the gas tube line up?

Using an upper receiver vice block and a method of holding the bbl/ft sight to the middle of the slot while torquing, might do it.

The bbl nut and receiver are metal to metal, and that upper receiver is thin; I suppose the upper could have bent/sprung while over torquing in the past.
It ain't a cylinder head bolt, or even an FAL bbl. EZ peazy does it.

The bbl nut should not allow the nut to loosen, as the tube is a close fit in those slots.

lockjaw
December 18, 2017, 20:11
It is not uncommon to see minute amounts of movement between the pin and recess (personal experience as an Army armorer).

Use your gas tube for timing while tightening the barrel nut.

Even so, with a Colt 604 type receiver (SP1 is the civilian variant) where the actual manufacture of the receiver itself may contribute to significant windage adjustments for zero, as well as the machining of the FSB itself. These receivers were not designed for windage adjustments on the fly (such as an A2 or A4). As long as the rifle could be zeroed for battle, it was within spec.

I have more than a few vintage Colt SP type rifles in the safe, and retro clones built on factory USGI uppers. Extreme right or left windage adjustments are not uncommon.

John A
December 18, 2017, 20:30
all original Colt SP1, bought it used 35? years ago, and changed barrels then, and now replacing that barrel, with the original barrel it came with.
I have not shot the rifle in 30 years, so Iam kind of vague on the details

:?

It's been so long now, it's doubtful that you'll remember whether that barrel shot that way when you took it off then or not.

But as has been said, if it adjusts out, it's within spec.

I have a couple of guns that the windage is nearly maxed out on.

munchoman
December 18, 2017, 20:59
:?

It's been so long now, it's doubtful that you'll remember whether that barrel shot that way when you took it off then or not.

But as has been said, if it adjusts out, it's within spec.


Ya, your probably right, I think Ill put the barrel back on, and call it a day.
And to all that replied, thanks for the help

lockjaw
December 18, 2017, 22:17
Ya, your probably right, I think Ill put the barrel back on, and call it a day.
And to all that replied, thanks for the help

.... and congrats on the old SP1. I am anal retentive about small details, it have learned to look past some of the "flaws" on these goats. They are a pleasure to shoot and the nastalgia cannot be beat. Anytime a buddy shoots one of mine, they get a big goofy smile on their face... much more so than when shooting any of the modern fanboy flavor of the month tacti-cool crap flooding the market today.

cwikjr
December 19, 2017, 06:33
I have installed a couple AR barrels that have a little slop in the index pin groove... When torqued down they have shot either to the left or right and the rear sight has to be moved excessively to compensate...

So what I've done is mount a optic on a co-witness goose neck mount (fixed carry handle AR) zero the rifle with the optic then loosen the barrel and center the rear sight and line up the front sight with the optic and torque the barrel nut down... The sights will be dead on and centered...

It takes two people to do this one to torque the barrel and the other to twist the the upper and eyeball the the sights and optic so they are all centered...

TenTea
December 19, 2017, 07:22
Unfortunately no longer made by ArmaLite, but they formerly manufactured an affordable clamp-on .750" FSB (2 ea. socket head cap screws) which allowed easy windage alignment with a centered rear sight.

Every once in awhile I used their suggestion to set the rifle, sights down on a hard and square surface like a countertop, and make the minor adjustment by canting the front sight a wee bit.

As a sidebar, JP makes such an item today which is also an adjustable gas block, but not SP1 material and fairly spendy...they look well made, though.

https://www.jprifles.com/buy.php?item=JPGS-2FS

hueyville
December 19, 2017, 08:09
Dribe pins out of front sight tower. Put receiver in vice, level with machinists level then level front sight tower. Much easier with two levels. Clamp front sight tower in place (I use padded vice grips with curved jaws) use tapered pin reamer and just lightly ream a small tad, drive pins back in and front sight tower is now square with upper receiver and problem fixed. Don't even have to loosen barrel nut.