[art luppino]

There are several types of Guides now available for the M1A. The difference is in length and quality of fit, to both the barrel and the Opt Rod. When you buy a Guide, take your Opt Rod and Barrel, if possible, with you, so you can check for a smooth slip fit to both.

The purpose of the Guide is to stabilize and guide the Opt Rod during the rear and forward travel when the rifle is fired. Also, to align the forward end of the Rod with the end of the Piston Stem, if you do not have one of my Alignment Fixtures, you should, which protrudes out the rear of the Gas Cylinder and is in contact under some pressure from the recoil spring..There must be some pressure between the end of the Opt Rod and the end of the Piston. Both of these requirements are equally important for function and absolute for Accuracy.

The following is a personal opinion on how to best mount an Opt Rod Guide, this method applies to the USGI Guide and all others. It is not a mandate.

The USGI Barrel has a raised Collar to accommodate the USGI Opt Rod Guide, also the USGI Barrel has a slot on the underside to accommodate the Guide Pin which helps to hold the Guide to the Barrel and to prevent rotation or front or rear movement. Some Commercial Barrels have this Collar some do not, some have the Pin slot some do not. The mounting surface on the Commercial Barrel is machined longer to offer the longer purchase area of a longer Commercial Guide, and usually a little oversize in relation to the passage in the Commercial Guide for a tight fit.

Which ever type of Barrel or Guide is to be used, except for a long Commercial Guide on a USGI Barrel, which I have not as yet seen, the fit between the two parts can be achieved in a number of different ways, The most common way is a DRIVE on fit, this requires the use of a hammer of some sort and a tool to place against the Guide to prevent damage to the Guide and to force the Guide on and over the Barrel or Barrel shoulder. This has been the standard method of installing the Guides for many years. Barrels that have a mounting surface or Collar that is too small, wherein the Guide to be used is too loose, can be knurled or stippled to raise up the mounting Barrel surface to take up the slack is a common practice, and a good one.

I prefer to do it differently, I do not want any possibilities of any constrictions on the Barrel.
Also, I do NOT want to to install anything on the Barrel that requires a hammer to get it on. That sentence is the essence of this Thread. This is not the method I was taught originally, but in my experience, in search of Accuracy, another mounting choice, exactly the opposite resulted.

This is what I call the Slip Fit Method, used between the Guide and the Barrel. If necessary, I remove metal from either, or both, the Barrel or the inside of the Barrel mounting hole in the Guide to get a Slip on fit of the Guide over the Barrel. This means, when the Guide is selected, I fine one that is as close to the Slip on fit as possible, or a second choice of, selecting a Guide just a little too large, but not sloppy. The second choice requires a thin strip of brass shimming material placed at 12;00 o'clock on the Barrel when I epoxy the Guide on. It is unusual for me to use a Guide Pin at all.

Is this time consuming, yes it is, is it necessary, I think so, does it improve accuracy? What does not improve accuracy is not taking enough time when doing a installation, that on the surface, it appears simple.. Art

 

[ripsaw]

Is this time consuming, yes it is, is it necessary, I think so, does it improve accuracy? What does not improve accuracy is not taking enough time when doing a installation, ............................. Art

Haa,.....I love it !! So true....

 

[82nd ABN]

Art (cactus comet) I remember speaking to you on the phone not to long ago on this subject. Using the barrels I do and the size of the op rod guide I always have to hammer them on. I do however remove some material from half of the guide with a dermal tool and a drum bit. I make it so they are just snug enough that they wont move when I put the assembly in a drill press to drill the hole for the pins. WOuld you consider this an acceptable squeeze on the barrel. I would imagine a shoulder is a shoulder is a shoulder all day long even though the Kriegers are twice as wide. I have not seen any degradation in accuracy on any of the builds, is this something that will occur over a long period of time? I don't feel any bubbles or humps when I pass the jag through either. Any thoughts. Are heavy barrels an exception to the rule?

 

[art luppino]

Guide Instillation

Hey Warren K,. To answer your question: Is hammering the Guide going to interfere with Accuracy. The answer is found elsewhere in my mind, with serious Bench Rest Shooters I have talked to. "They go to great extents to ensure Nothing is touching the barrel."

Will things attached to the M1A barrels cause constrictions, probable not as I use mine, which is slow fire. This Platform is Titled , Accuracy Unlimited, the word Unlimited to me, I started this Platform by the way, means, "How accurate can I make my M1A shoot five shot groups off the bench at 100 yds.. Not to include rapid fire in any form. Rapid fire, is required in NRA Across the Course Matches.. It is during this rapid fire stages that the barrel heats up. Heat cause expansion, anything tight surrounding and attached to the barrel may cause constrictions, I think it is safe to say, will cause constrictions. I avoid that possibility as much as possible when mounting the Guide.

I will send you a Bolt Roller Retaining Clip, there are a box of them here somewhere. Maybe awhile, the PO is a long way off.

As you know I use all USGI parts, except the receiver, on my rifles, therefore much of what I Preach may or may not be applicable to rifles that are built using whatever. art

 

[NEastgunner]

Hi Art,

Just a thought, wouldn't the guide heat up also? Meaning the rate of expansion would be similar to the barrel's expansion rate. This is also assuming they are of the same or very similar material (metal).
I think how close the working pieces are to the heat will also effect this. Not sure if anything I wrote above is true, just thinking out loud and asking.

2nd, When you are referencing using pins, are you driving a pin through a press fit hole in the guide that makes a press fit on the barrel. Not sure if I was following you guys on that. Is it similar to "Dutching" or "dutchmen" pinning.?

 

[art luppino]

Heatiing up

Hi Art,

Just a thought, wouldn't the guide heat up also? Meaning the rate of expansion would be similar to the barrel's expansion rate. This is also assuming they are of the same or very similar material (metal).
I think how close the working pieces are to the heat will also effect this. Not sure if anything I wrote above is true, just thinking out loud and asking.

2nd, When you are referencing using pins, are you driving a pin through a press fit hole in the guide that makes a press fit on the barrel. Not sure if I was following you guys on that. Is it similar to "Dutching" or "dutchmen" pinning.?

The Guide will heat up, you hit it on the Head with, "Similarly".

The Guide is most often used with a rollpin, or split pin, and it is a drive fit that contacts the bottom of the barrel, The USGI M14's used this to secure the Guides, many have always thought it was one of the weak points in the rifle. in including me. Semi auto fire it held up OK, but on auto, it was often a problem.

Press fit is correct. I have never hear the Dutchman term.. art

 

[MemphisMachinists]

This topic came up while I was building the last one and I my OP rod guide to barrel fit was .005" inteference. Art suggested to me that this was too much. The shape of the guide makes it a little tricky to hold on to, but with some vise jaw stops and angle parrellels I was able to clamp it in a vice. Indicated the hole in and bored it out untill it was a metal to metal fit. (ID and OD the same). It sounds like a lot of trouble, but it really took less than 1 hr. I put one together without doing this. I thought it was supposed to "spring" out to clamp the barrel. Putting it together sure feels better when your not driving it on. Tapping is nuch easier on the nerves.
I wonder how they do it at the barrel manufacturer?

 

[lefty o]

to my uneducated mind, a interference fit of about .0001" would get the guide on snug without constricting the barrel. how would the average guy get that kind of fit, i dont know.