Advice needed ... bolt opens on firing!

[gewehrsniper]

I have a no4 mk1 rifle that does the same thing. When id fire it the bolt hangke would kick up about a centimeter. Also the take down gap on the bolt head track had the corners worn off...and I never could find out what the screw on the left center of the receiver was for but I replaced it and tightened it (not too tight) to where the action feels brand new. The bolt body/handle no longer kicks up and the bolt head hasnt once came off track since I fixed it. I'm guessing the screw on the side of the receivee is just to adjust the tightness of the action...

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[5thBatt]

Give me 5 Min guys, just got to nip out & get some popcorn & a drink.

[Son]

Thank you Parashooter, for going into the mechanics of the of the reaction. I only hope it isn't lost on those not technically trained or technically minded.
To anyone who cannot get your head around it, try stripping out a bolt and go back through it with the parts in your hands creating all the scenarios that together make up the cycle of action. Understanding what is going on is vital to working out what is going wrong. Plenty of great help here...

[Peter Laidler]

We're wayyyyyyyyy off the subject now, but I believe that it'a all down to the fact that you can compress steel (and air) and it WILL react as opposed to a liquid that you cannot compress and it won't react. Get a poly bag or baloon of water, empty it of air and tie it up. Drop it onto a surface plate or something similar and see what happens. It'll just deform and lay there like a wet fart.

Get a ball, fill it with air and do the same thing. It'll bounce to a set drop to bounce ratio

Get a ball of steel, like a ball bearing (or even a hammer head, ring spanner, the harder the steel the better......) and do the same. It will bounce. Don't believe me, take a look! Once again, to a set drop to bounce ratio. This is in effect just what you are doing to the bolt when you hit the bolt head, which is attached to the bolt. If I had a 40 minute physics lesson I'd explain it better but that's about it. There is no secret or black magic there.

Forgot to say. You can easily and simply eliminate the striker spring torque theory by taking it out and firing the cocked cocking piece/striker forwards with a catapault (or something similar) contraption. Yep....... the bolt still rotates slightly.

There is a word for this physical property but I forget what it is. JM...., help!

I know Muffer thinks that I'm getting cranky but I don't suffer fools any better or worse that the rest of you. I'm wise enough to answer the questions - just so long as you don't keep changing the questions or even worse.......... I won't go on!

[5thBatt]

There is a word for this physical property but I forget what it is. JM...., help!

Harmonics maybe??
The two parts being of different masses will "ring" at different frequencies & repel each other, not trying to be technical as thats not my field (I'm a spray painter) but thats the best way i can explain it.

[303Guy]

Thanks all. I've noticed this bolt jump on dry firing, now that I'm reminded. I don't like to dry fire - not sure if it wears the working bits or not and besides, pulling the trigger is serious business! I expect it to go bang. I don't recall bolt lift on firing maybe because it doesn't happen. Would y'all say 5thBatt has nailed it? Makes sense to me.

[jmoore]

I've noticed this bolt jump on dry firing, now that I'm reminded

And there's the likely culprit. If the bolt handle touches the socket whilst cocked and the bolt has lots of vertical play, then it's not hard to see how the "unwinding" of the bolt occurs. Pressure from the sear will keep the bolt in it's most upward position until the striker is released. As the pressure is relieved, the bolt moves downward and the hanle, having nowhere else to go, starts rotating. Rearward thust from the cartridge will keep things energetic!

BTW, I assume the 0.015" gap you mentioned is with the striker down and with nothing in the chamber. Since there's no real forward postioning control, the bolt often will move forward until the extractor hits the breech cutout or the LH lug contacts something. Otherwise you might get upwards of 0.060" free motion!

ETA: This reminds me of a thread from 2009-2010, maybe. But I'm thinking that there may be a cure for the vertical slop in the raceway. Need to round up some scrap actions at the shop and do scary things...

[WarPig1976]

Gentleman, I've followed this thread and I'm convinced that nothing is happening to this rifle that can not be solved by the use of duct tape and some superglue...

[spentprimer]

Don't you think that would be a bit tacky? i mean, with the tape residue and all.

[Peter Laidler]

I know warpig was a bit tongue in cheek but the fact remains that you could not manually lift the bolt fast enough to cause a dangerous situation. End of problem!