How to Measure CETME Bolt Gap

 

CETME Bolt Gap
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First off let me say, I am not a gunsmith.  I am even less an expert on delayed roller blowback (DRB) rifles like the CETME or an HK 93. However, let me say that this post from military firearms.com does an OUTSTANDING job of describing what is going on inside your rifle.

If you’re not interested in knowing how it works and just want to know how shoot, my article will tell you what you need to know to ensure your CETME or G3 has proper bolt gap.

However, I would highly recommend you read the military firearm post by bladeworks123, because the more you know about your rifle the easier you will be able to keep it running.

Bolt Gap is Not Headspace

You need to know that there is a difference in bolt gap and headspace. Headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge to the face of the bolt. This is important.  If the headspace is incorrect, ammunition will not chamber correctly.  Alternatively, it may rupture and cause damage to the firearm or the shooter.

In locked bolt guns like an AR-15 you can buy gauges that are machined to look like cartridges.  The gun should lock up on a “go gauge” and fail to lock up on a “no-go” gauge. When a DRB rifle barrel is pressed into the receiver, it is not pressed to the face of the bolt.  It is pushed even further so that the rollers in the bolt head are pushed against the locking piece.  The locking piece is putting pressure on the bolt carrier creating a gap the bolt head and the bolt carrier.

Bolt Gap is Critical

This gap is critical.  It is the point that the action is about to open.  Consequently, it is the measurement that allows the rifle to function correctly. If the barrel is pushed in too far the action will open too soon. Alternatively, if the barrel is not pressed in far enough, the rollers will have to travel too far to unlock the gun.  Since the back pressure from the gun’s firing may not last the full trip the gun probably won’t cycle. If it is extremely short than then portions of the neck of the cartridge will be unsupported and may rupture.

In a DRB a go or no-go gauge will both seat in the firearm. There is no true way to measure headspace in a rifle such as this, but the bolt gap measurement achieves the same result and is a more accurate measure of what you are trying to check.

Here is the procedure:

  • First, remove any magazine and check that the chamber is empty.
  • Perform the HK slap by pulling the charging handle to the rear and locking it. Then, slap the charging handle down with the palm of your hand sending the charging handle forward using spring pressure only. This is important to get a true measurement.  Riding the handle forward may cause it to bind at the end of the cycle.
  • Pull the trigger so the hammer is down.
  • Invert the firearm so the empty magazine well is pointing up.
  • Next, open the feeler gauge up to .5mm.  Try to slide it into the very slight gap between the rear surface of the bolt head and the front surface of the bolt carrier.
  • The .5mm measurement is the maximum the gap should be.
  • Open the feeler gauges to the .25mm leaf and try to fit that between the bolt head and carrier. The feeler gauge should fit without forcing it.  Additionally, if the gap is smaller than .25mm the likelihood is that the gun will have problems with extraction / ejection.  In fact, it may not run at all.

Buy the Right Gauges

You should buy a feeler gauge set that has several leaf sizes between .25mm and .5mm.  This will let you get a good idea of the bolt gap. Checking this measurement regularly will let you track accurately the bolt group wear.

If the bolt gap is not between .25mm and .5mm, there are oversize and undersize rollers manufactured.  Next, you can swap them with the stock rollers to either increase or decrease the bolt gap. Finally, if the gap is substantially out of spec, changing the barrel or reinstalling the barrel either further in or out may be required.

As a side note (I am not paid to say this)

I buy my rollers from RTG International Surplus Parts in Arizona

And for barrel work, I use wither Dave’s Gun Shop in Cookeville TN (I’ve been in firearms classes with Terry their gunsmith – great bunch of guys)

Or Lock Stock and Barrel in Franklin TN (sorry no website)

She don't like guns

She don’t like guns – Steve Lee

She don't like guns - Steve Lee
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I love Steve Lee love songs…  My favorite is I like guns, but this one is pretty good.  I share it because I think many of us are in the same place.  We like guns, and we love out partners, but she don’t like guns.

Luckily while my wife isn’t a gun person, she loves me.  Because of this she puts up with my personality and the guns that keep appearing in the house.

More importantly, she understands where I am coming from and is supportive as I share the American gun culture with our son.

Obviously you can love someone that is not a clone of yourself, people disagree, and my wife believes things that I don’t.  But a mutual respect allows those disagreements to be dealt with in a postivie manner.

For us, Genny goes shooting with me, and she enjoyed it, but she does not love it, so after she learned the basics of firearm safety she gradually stopped going to the range.

That’s fine, because I did the same with trips to her mothers…  All joking aside.  The song She don’t like gun’s celebrates mutual respect and how a person can live with someone they don’t always agree with as long as the base is their.

You Have to Practice Your Plan

Prepper Precepts #25 You Have to Practice Your Plan

 

52 Unique Techniques for Stocking Food for Prepper
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You have to practice your plan, thinking is not the same as talking, and talking is not the same as doing.

Practice helps you find gaps, practice makes perfect, practice is much better than talking and never doing.  In this world actions are much more powerful than words.  Don’t talk about your plans for preparedness talk about what you did.  Get out and get it done.

This prepper precept has payback.  I promise you that the more you do the better you will become at doing.  Be a doer and not a talker – your life will be richer and so will your wallet.

Rules of Civility: The 110 Precepts that Guided Our First President in War and Peace

These precepts are my creed, and having prepper precepts guides me when I face tough choices.  A wise man once told me that when facing a moral problem, the right choice is usually the action you don’t want to take.

I am not a pollyanna person that is wishy washy or blindly follows rules, heck I have a little rebellious streak and love to know the WHY of rules, but I do respect and understand the need for law and know how vital it is for a society to have a moral code.

By knowing what I believe in you can know how I will act. This is very important in times of stress.  If you don’t want to read east prepper precept individually, the completed list can be found here: Completed 27 Prepper Precepts.

Ayoob on Continuing Training

Ayoob on Continuing Training

Ayoob on Continuing Training
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Continuing training is vital to continued skill.  If you want to carry a gun for self protection, you have to invest in good training and time spent keeping that training up to date.

According to Wikipedia Massad Ayoob is an internationally known firearms and self-defense instructor. He has taught police techniques and civilian self-defense to both law enforcement officers and private citizens since 1974.

He was the director of the Lethal Force Institute (LFI) in Concord, New Hampshire from 1981 to 2009.  Ayoob now directs the Massad Ayoob Group (MAG).

Additionally, Mr. Ayoob writes some of the best firearm books on the subject of the legal aftermath of a self defense shooting.

Furthermore, I widely quote his work in my classes,  and recommend his books courses and videos to my students.

With many things I learn a skill, try it out, have fun with it, and then put it on the shelf until I need it.  The concept works well for basic skills that are rarely used and have low consequence for failure.   In contrast, this does not work when failure is not an option.  With skills like the defensive use of a firearm continuing training is vital.  Finally, shooting is a perishable skill, shooing for self defense is complicated and has extreme penalties for failure.

Handgun Scenario #1 Bank Robbery

 

Handgun Scenario #1
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This video is a clip of a Handgun Scenario from the old TN handgun permit video, it is being used under the fair use doctrine.

This video will show a brief encounter that a legally armed citizen will face.

Please watch it and then think about what you would do in this situation.

An armed citizen generally has an extremely compressed window in a use of force situation. If you have not spent some time seriously considering what would cause you to use force and the implications (Physical, Legal, Moral, Psychological, and Sociological) then you are setting yourself up for failure.

Consider your gut reaction and what you immediately think you should do. Then think about the implications of those actions and see if it changes your mind on what you should do.

Answer these two questions:

  • Would I have taken same action as the armed citizen in the video?
  • If I had, would it have been legal?

Tomorrow we will discuss the “legal” response…  I have several of these handgun scenarios that I hope you find useful.

I think this kind of what would you do training is invaluable to preparing a person to carry a gun for self defense.  If you never work on handgun scenarios you will have to work through the situation when it occurs – this will waste precous seconds and may cause you to do the wrong thing.  Please look at the post on OODA loop for more information.

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