M69 Trainer Headspace Fix

Discussion in 'The Powder Keg' started by Joshua M. Smith, Jan 24, 2008.

  1. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    M69 Trainer Headspace Fix​
    In cold weather, I was experiencing some spitting of hot gasses onto my shooting glasses when firing my M69 trainer. The problem was especially bad in the cold, or with hot ammo like Velocitors. Combined, the rifle wasn’t pleasant to shoot for this left-hander. (I doubt right-handers would even notice the problem.)

    It was suggested by a couple people on a couple different boards that the headspace tolerance was out of spec. While I couldn’t disagree, I couldn’t find a headspace specification for this particular rifle. One gent gave me a rough measurement – two pieces of Scotch tape on the rear of an empty shell should make a “no-go” gauge.

    By this measurement, my trainer was just in spec at room temperature. This could partially explain why it only acted up when it was cold out – the tolerances grew as the metal contracted. I decided to shim it up.

    The first step, after checking headspace, was to disassemble the bolt. Excellent instructions exist on the Web on how to do this, and so I didn’t repeat them. The instructions are located here: Collecting and Shooting the Romanian Trainer - Bolt Disassembly and Reassembly

    Before starting, you should be sure to have shim material in .010”, .020”, etc an a means to cut it to size. Their will have to be a center hole approximately .50” in diameter. I did not measure the outside, but rather waited until I put the bolt back together to get the outside diameter. It gave me a much cleaner look.

    [​IMG]
    This is the finished piece. Notice the shim is hardly visible. However, it’s effective.

    I got lucky. The first shim I tried worked well. Disassembling this bolts is not a fun task, and believe it when you’re told you need a vice or a c-clamp.

    I used a .020” shim on the first (and only) pass. It locks up tightly now – tighter than most production rimfires, and as tightly as several target rimfires I’ve tried.

    I am pushed for time right now, and therefore don’t have time to properly test it in the cold. However, upon firing some Velocitors out the back door on my old shooting range, I experienced no spitting whatsoever, and those did vent in this rifle even in warm temperatures. Tomorrow I’ll have to do some cold shooting and add an addendum to this report.

    Some have suggested that this rifle was not made for hot loads. I assure you, it was. The receiver is all steel – in fact, I’ve not been able to find anything on this rifle that is not steel or wood – and some have gone so far as to convert their M69 trainers from .22 long rifle to .22 magnum. While I don’t hold with this practice, they report absolutely no problems, save for necessarily reduced capacity of one round.

    I’ll report back once I’ve fired in the cold.

    Josh <><

    Follow these instructions at your own risk. Neither the author nor this board will be held liable for any damages due to faulty workmanship, defective materials, or accidents or injuries of any sort whatsoever.
  2. lefty o

    lefty o G&G Enthusiast

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    stop right now. you cannot use scotch tape and a fired case to measure headspace. where these geniuses come up with this is beyond me. headspace guages are made for a reason, not so someone can half a$$ed a measurement, and never truly know where the headspace is, or whether it is safe or not.
  3. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    While I agree in theory, it has a strange way of working.

    I'm not doing this alone... I have a gunsmith I refer to who has 25 years of experience and has gauges which I borrow if I need them, and when the redneck method agrees with the gauges, well, I tend to believe them. It worked for a Mosin and a shotgun, so I figure I'll test it for sure tomorrow when I grab a gauge, but hey, if it works for the masses, why not?

    I believe half the gunsmithing stuff out there was developed to make money for someone.

    Josh <><
    Last edited: Jan 24, 2008
  4. lefty o

    lefty o G&G Enthusiast

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    alot of the gunsmithing equipment that is available , is there so they can do a quality job. the problem is there are a lot of hack gunsmiths out there that use crap like tape stuck to the back of a case to measure headspace. the fact is, if you write this up on the internet, and recommend this method, then some idiot follows your bad advice, your liable. now ive seen your write up on this, and the one on your homemosin trigger job, and have to say if you've learned this stuff from this gunsmith, you need to find a new mentor.
  5. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    He only encourages me to find ways of doing things - think around the problems.

    I'm not telling anyone to do this - I'm just saying that this is what I did, proceed at your own risk.

    I still am at a loss to see why polishing the faces of the trigger and sear linkages is unsafe, if you don't change angles.

    Maybe I'm doing a bad job of writing this stuff up, because I take safety very seriously.

    Josh <><
  6. lefty o

    lefty o G&G Enthusiast

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    from your write ups on your trigger, you did more than just polish parts.
    now back to this headspace issue. your talking a rimfire in this instance, you want to use an empty case, did you measure the rim thickness, did you measure the tape thickness, and did you measure the thickness of the rim with the tape stuck to it? if no to any of these questions, you didnt measure anything. secondly closing the bolt on an empty case with tape on it proves nothing because the tape can move, or compress. the rim of the rimfire case itself is not strong enough to not compress either. in short you have not checked anything, and made changes to your rifle based on this lack of measrements. thankfully its a rimfire and it most likely will cause you no harm. now attempting do do this on a centerfire could cause serious harm to the gun and yourself. im sorry, but when dealing with very high/explosive pressures inches from your face, there is only one way to do things, and that is the right way. the eyesight you save may be your own.
  7. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    Yes, yes and yes.
    PM me with where I said I did anything more than polish the parts on the Mosin.
    Josh <><

    Something I forgot to add, for everyone who reads this:

    All tolerances were checked with proper gauges. The fact that the tape on the spent cartridge trick worked in my particular instance does not necessarily mean it will work for you. Headspace should be correlated with a proper set of headspace gauges even if you use the spent cartridge method.
    Last edited: Jan 25, 2008
  8. Mooseman684

    Mooseman684 G&G Newbie

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    Hot gasses spitting back is also an indication of a very worn chamber in the barrel, allowing gas seepage around the brass case. Headspace should be set to specification that allows the brass to swell and then contract upon firing.If your chamber is worn, gasses will continue to erode the chamber around the Casing, and all you have accomplished is forcing the rim of the cartridge to act like a seal between the bolt face and barrel. If you are compressing the rim of the cartridge, you NOW have the possibility of a round firing when you close the bolt, resulting in a dangerously UNSAFE condition! It really Irks me that people won't utilize a trained, experienced Gunsmith when necessary...Some things are NOT DIY !
    Rich
  9. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    Mooseman,

    The ammo I used was not experiencing good combustion at the temps I was shooting, and therefore wasn't sealing the chamber due to low pressures.

    It works fine with other ammo.

    However, I figured I'd increase headspace a bit since I had a mismatched bolt that was never mated to the receiver.

    It was shown that the bolt face was square to the chamber, and only length need be adjusted.

    I consult with a real time gunsmith, a friend, who has done this stuff for 25 or more years.

    The only thing I'm guilty of is that I try to find ways that the average joe can measure and say there may be a problem with tools on hand, rather than keeping a stockpile of gunsmithing stuff on had that will maybe be used once.

    Measure the thing, and if you're competent, get gauges. If not, take it to a qualified gunsmith.

    That's all I'm saying.

    Josh <><

    That said, I'm done with this post. People are not stupid. They can judge for themselves whether they're qualified to do a particular piece of work, and if they are, they'll know how to go about it.

    This was only one person's fix.

    I'm out.

    Josh <><
    Last edited: Jan 25, 2008
  10. Mooseman684

    Mooseman684 G&G Newbie

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    Joshua,
    If the bullet was exiting the barrel, there was more than enough pressure( thousands of Pounds)
    Regardless of Temperature, to seal the chamber...Your statement lacks Validity. I shoot in Sub zero Temps with very little velocity loss using frozen ammo...I have currently been testing at -22 degrees ,both gun and ammo frozen to test Dogoil for Dogolden, using .22 LR ammo.
    You evidently experienced High Pressure close to normal or you would not have had hot gasses spitting in your face.
    Rich
  11. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    As I said, I'm done with this issue.

    Take it up with the gents on Rimfire Central and Rimfiire Shooting. They seem to agree with me, and take this stuff very seriously.

    There are a lot of opinions flying around about rimfire, but very little fact that I've found. You cast your lot I guess.

    I'm not getting stuck in between. This is already starting to go around in circles.

    Again, I invite you to Rimfire Central or Rimfire Shooting. I'll continue there.

    I'm on 20 or so boards and just don't have time to keep coming back to argue this.

    Plus, I need to go shoot and test the thing.

    Josh <><
  12. lefty o

    lefty o G&G Enthusiast

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    the fact is josh, people are stupid. the fact that your using unsafe techniques proves this. you are advocating using potentially dangerous ways of guesstimating headspace, and than writing about it on the internet, and defending it. now what makes you think someone else wont try this, and end up injuring themselves? 99% of people of any firearms internet discussion forum are in no way shape or form qualified to discuss headspace, how to measure it, and how to set it. the fact is probably 50% of "professional" gunsmiths arent qualified.
  13. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    Lefty O,

    I cannot believe that you just called people, as a whole, since you didn't specify, "stupid."

    Your credence just went totally out the window with me.

    You sound like you think you're better (or maybe smarter?) than us mere mortals. So be it.

    Once again, I'm dumb... er... DONE.

    Josh <><
  14. lefty o

    lefty o G&G Enthusiast

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    josh, yes when it comes to guns im smarter than the vast majority. and yes people as a whole are typically stupid, lacking common sense and knowledge . ever heard the term SHEEPLE. the fact that you've put disclaimers after your posts, and state that even using the tape method you then need to use guages tell me that you are CYA- you know what you've posted is a bad idea. the fact that you need to check your tape method a second time with guages negates doing the half assed hack job of putting tape on a case in the first place. sorry josh, you can post all kids of crazy off the wall stuff and i wouldnt care, but the instant you advocate doing potentially dangerous stuff, i will climb all over you. it really doesnt matter to me if i have credence with you, the only thing that matters is that some other idiot doesnt try what you did and not get lucky and injure themselves.
  15. samuel

    samuel G&G Newbie

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    Your type must get a real bang figuring how they can post something that may maim or kill someone not informed or dumb enough to try it.I wish there were some way to keep dangerous posts,made by sadists like you off the forum. sam.
  16. SwedeSteve

    SwedeSteve Freedom Zealot Forum Contributor

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    Ditto to Moose, Lefty, and Sam!
  17. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    It must make you feel special to feel so superior to the average person.

    Good for you.

    Josh <><

    You realize that, with the recess in the bolt, it's near impossible for the round to discharge even if the bolt were mashed against the breech face on one of these, right?
    Last edited: Jan 25, 2008
  18. lefty o

    lefty o G&G Enthusiast

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    the recess in the bolt face is your headspace!
  19. Joshua M. Smith

    Joshua M. Smith G&G Enthusiast

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    Riiiiight... that's what I'm getting at.

    I think we may just have a major miscommunication here, Lefty.

    Let's step back, both of us cool off (I know I need to) and regroup.

    I'll take some additional pictures later and we'll see where we stand.

    This is my olive branch.

    Josh <><
  20. lefty o

    lefty o G&G Enthusiast

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    there is no miscommunication on my part. you have advocated checking headspace with an empty cartridge and tape, i have said it is potentially dangerous to check or set headspace in such a manner. no miscommunication.
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