[Bruce Hamlin]

Hi guys,

I did not need it, but found a "very" good deal on a Poly today at a gun show. It made it to my collection. I am in the process of outfitting it with USGI parts and have a few questions.

I can not get the rear sight aperature out, or the elevation and windage knobs to come off. I have taken many off of M1A's, but these will not come off. The aperature will run all the way up, but it hangs there as though something is blocking it from coming totally off. The windage knob will not screw off either. Any tricks to these?

I have a unitized gas cylinder, a GI Op Rod, GI trigger group, GI FS etc.. Am I right that I will need to re-use the Poly castle nut and cylinder lock?

Just how bad is the Poly bolt supposed to be? This rifle is in very good shape and I would rather not have to send it off right now to have a GI bolt installed.

Is there any market for all those Poly parts that I am taking off? I am only using the receiver, barrel and bolt. I even found the new in wrap cleaning kit neatly installed in the Poly stock.

I would already had this rifle refitted if I could get the sights off. Thanks in advance.

 

[Quagmire]

1. Unscrew the little nut in the center of the windage knob. This will release the elevation pinion from the windage knob.
2. Unscrew the windage knob from the rear sight base.
3. Pull the elevation pinion out of the rear sight base.
4. With the aperture @ half way up, apply forward pressure on the rear side of the aperture with your thumb. This will pop the spring clip out of the groove in the receiver & will allow you to remove the rear sight base.

AFAIK, unless you've ground on the base of the aperture, it should not just come out of the base while the elevation pinion is installed.

Yes, you will need the poly castle nut & gas cylinder lock. A USGI castle nut will usually work, but the threads are different. Better to use the chinese one.

 

[Bruce Hamlin]

Quagmire,

I have tried that method a dozen times, this thing will not come off. The pinion will not seperate from the windage and the windage knob will move the sight base from side to side, then it just free spins. Any other methods other than a well placed hammer blow?

Bruce

 

[Bruce Hamlin]

Hey,

I got it apart. Had to take a punch and tap the end of the pinion shaft, by coming through the screw hole on the windage nut. She would not pull aprt, but just a gentle tap did it. Thanks again Quagmire.

 

[Fred Smith]

I picked up a NIB poly a month back and have fired about 400 round through it and the headspace is fine. You need to check it to make sure it right to start with. I have heard of some having out of spec. headspace. If you do shoot it a lot keep your eye on the bolt some say they are not as good as USGI bolts. And they are headspaced for 7.62 ammo so stay with surplus ammo mine likes port the best.

 

[thomjb]

Got a new to me Preban Poly a month or so ago, it swallowed the Field gauge

 

[Quagmire]

Got a new to me Preban Poly a month or so ago, it swallowed the Field gauge

If your field gauge was a Forster, then you're probably good to go.

Forster
GO: 1.630
NOGO: 1.634
FIELD: 1.638

NATO
GO: 1.6355
NOGO: 1.6405
FIELD: 1.6455

Pretty sure these numbers are correct. As you can see, the Forster FIELD gauge is less than the NATO NOGO. The chinese rifles are chambered to the 7.62 NATO spec, not the commercial .308 SAMMI spec.

 

[Bruce Hamlin]

Quagmire,

Please explain the gauges to me again. I have read the information before, but my mind has not accepted the practice yet.

If go means good and no-go means bad, what does field mean? What reading do I need to have in order to shoot .308 commercial ammunition? Thanks.

 

[cw]

This is a very complex topic. You might want to check out Fulton's detailed explanation at: http://www.fulton-armory.com/headspace.htm with diagram at http://www.fultonarmory.com/JPGs/Chamber2.jpg

Actually, you can find a lot of good reading there at http://www.fulton-armory.com/FAQ.htm#General and
http://www.fulton-armory.com/FAQ.htm#M14R

-- cw

 

[Bruce Hamlin]

OK, I understand that portion. What is the relationship of the go, no-go and field guages? In others words, what is good, bad or optimum?

 

[Quagmire]

Anything in between go & field is OK. NOGO supposedly only applies with a new barrel.

 

[pmhayden]

Optimum for the broadest range of ammo?

New from the factory rifles are normally chambered between Go and No Go. This is "spec" for a new rifle. (I had a Ruger that would close on a No Go guage, and my tightest rifle is a factory Sako.)

Field is the safety standard. If it will close on a Field guage, it probably is not safe to shoot, by conservative standards. This does not mean that you will experience catastrophic failure of the receiver. But brass will start to fail sooner, etc. And you will not be getting optimum accuaracy. In general, a shorter chamber is more accurate than a longer chamber.

The point of Quagmire's specs is that the Nato/7.62 (mil surplus) Go guage starts at the upper end of the .308 No Go guage. In other words, if the rifle will "just close" on a .308 No Go guage, you are at the tight end of the 7.62 chambering. This is probably "optimum" for plinker/battle rifle - where the safe range for .308 overlaps with headspacing for 7.62. You can still safely shoot .308, and have about as tight a chamber as you want for 7.62 in a semi-auto rifle. You will probably get your best accuracy with 7.62 Nato. This is probably what a new GI barrel should be at, in the best of all worlds. I think it is "optimum".

.308/7.62 is a hotter cartridge than older .30-06, 8mm Mauser, etc. It builds higher pressures. It is probably a good idea to buy a set of head space guages - at least the .308 Field guage. Also, it makes you really appreciate .30-06.

I don't reload. But I have rebarreled a lot of old Mausers, some to .308. I don't think the older (pre-1930) 98 actions can really take repetative magnum-like chamber pressures of hot .308 hunting loads without stretching. Accordingly, the repect for what repetative shooting does to a bolt and receiver transfers over to other actions, such as M-14. And it makes one appreciate Remington 700 (and other modern bolt) actions.

If you are only shooting custom loads for accuracy in a match barrel, .308 specs are probably best. However, if you have a chrome-lined standard barrel for fun shooting of surplus ammo, 7.62 specs are best.

 

[Bruce Hamlin]

OK, this is beginning to make some sense to me. I will mostly shoot military surplus, but I do hunt with my rifles - thereby requiring commercial rounds. Two of them are SA's and the third is the Poly. Now, if I purchase the military guages and everything is between go and field - can I safely shoot commercial rounds? If I purchase commercial guages and everything is between go and field - can I shoot military rounds? I do not reload or shoot reloads.

If memory serves me correct, both of my SA's came from the factory with the tag that said 1.632. I have no idea what the Poly is. Now, what type of instrument do they use to get that measurement? Is it worth worrying about with the Poly?

The only thing left to change out on the Poly is the bolt. Everything else is pure GI now, except the receiver and barrel. I am still not sure if the current bolt is OK, or if I should go ahead and replace it. It came to me with very few rounds fired through it. The current bolt shows no abnormal signs of wear or fatique, but again I don't think it was ever fired that much. I have seen some posts that say the bolts are soft and some that say they are OK.

Thanks for the information so far.

 

[Cheetahman]

These guys have been giving you good information. I've got 5 chinese bolts in my collection now, and 1 shows signs of excessive wear and it measures pretty soft. I keep it for reference but I'll probably drill a hole in it so it doesn't find it's way back into service. You need to get the head space checked, for your peace of mind and to be 100% safe. Then the soft bolt issue is this: Once you establish the head space is in the safe range, if the bolt is softer, the rate at which the head space will lengthen is quicker. Softer bolts wear faster. However if the head space is good now, and if you don't shoot a lot, even say 50 rounds a month, you could be good for quite a while. The key I think is to know where you are now, via a competent gunsmith. Then you shoot a couple or three hundred and see if the head space has changed. This determines if the rate of wear is abnormal or not. This is what you are trying to find out! If it has worn detectably in 200 to 300, or even 500, then you know you'll need a new bolt sooner than later. If it doesn't change, most likely you are going to be good for a normal shooting life of 15,000 or more. Some guys don't want to do this, they don't even want to be thinking about it, so they spend the money up front, and convert. In the end it's what you are comfortable with. Good Luck!!

 

[pmhayden]

1. Get a set of Forster guages for .308 (Go, No Go, and Field). These are essential if you change bolts around.

2. Use the .308 No Go and Field in lieu of the 7.62 Go and No Go guages. In other words, as long as you don't close on a .308 Field, you are probably good to go. But check every 500 rounds or so. If your bolt begins to close on a .308 Field, replace the Chinese bolt. (Note that a GI bolt may not drop in with a Poly barrel.)

The 7.62 Field guage is too long for .308 ammo. The .308 Go guage is technically too short for 7.62. (Slamfire problem is possible, though not likely with most ammo. You can use a new 7.62 cartridge in lieu of a 7.62 Go guage - test several cartridges. If your bolt closes easily on a cartridge your headspace is not too short.)

Note that hunting ammo can result in different pressures than military ball. In particular, .308 comes in heavier bullets, and "light magnums". If you shoot .308, shoot only ammo comparable to military ball. You can close the gas cylinder valve, but you will only have a single-shot rifle, and the extra pressure still goes somewhere. Or you can get a after-market gas cylinder nut with a valve to regulate the gas pressure. Beware of 180 gr. bullets and "light magnums".

If you are not sure about the hunting ammo, use a bolt action. They are better at handling all types of ammo than a semi-auto rifle