Author Topic: Lock Down That Bolt - Or Else!  (Read 317 times)


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Lock Down That Bolt - Or Else!
« on: November 16, 2019, 10:09:09 AM »
One of the things that is sometimes neglected, and seldom talked about, in Big Bore airguns, particularly ones that have been modified from smaller calibers, is the safety of the bolt locking mechanism.... Now it is obvious that the bolt must be strong enough to withstand the backwards force on it from firing, and should be designed with a safety margin of at least 3X that force.... What isn't often thought of, is what would happen if the gun was fired with the bolt closed, but not locked into place.... Usually that locking mechanism is the handle, pushed downwards into a slot.... Have you ever thought what might happen if you forgot to do that, or you bumped it upwards before firing?....

Once the bolt is not locked in place, when you fire the gun, it gets accelerated backwards at the same time the bullet is heading towards the muzzle.... It doesn't reach anything like the velocity of the bullet, but it does pick up significant energy, and the larger the caliber and the higher the pressure, the greater the FPE that ends up in the bolt.... If it comes to a sudden stop by hitting the back of the cocking slot, the forces on it are MUCH higher than you might ever imagine.... Lloyd Sikes has done some testing on this, and produced a series of three excellent videos to enlighten you.... I strongly suggest that you watch this series.... It will open your eyes as to what could happen if you forget than one simple thing.... to push the handle down to lock the bolt....

Here is a link to the thread on the GTA that Lloyd started.... followed by links to the three videos.... and a chart of just how much energy the bolt will have if you forget to lock it down....


Lloyd put a lot of work into the testing and videos.... They are very educational and I hope you will take a half hour to view them.... It could just save your life !!!


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Re: Lock Down That Bolt - Or Else!
« Reply #1 on: November 16, 2019, 11:16:08 AM »
We had few incidents a cam did fail in the Netherlands.
Not a pretty sight.
So i believe in a closed upper like XP for example.
So when something fails, it will be catched by the upper itself.

We had a tuning project last year.
Upgrading a 100 joule .30 pellet sidelever rifle into a solid shooting 308.

We did succeed.
Finished with a 320 joule rifle, intern regulated and a sub moa garanty.
We just ended hour project with the words
Upgrade the upper.
We included blueprints for it, plug and play for cnc machine.

High pressures will not have mercy when the mechanics fail.
« Last Edit: November 16, 2019, 11:18:42 AM by Nicesurprice »
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Re: Lock Down That Bolt - Or Else!
« Reply #2 on: November 17, 2019, 03:04:21 PM »
I exchanged a few emails with Lloyd after his first post on the subject. I have two experiences with this and I developed a serious twitch that Kevin can testify to. High pressure air makes me twitch period.

The first bolt blow back I will blame on myself. The second I’m not so sure, though I admit that my twitch may have caused me to unconsciously lift my hand and bump the bolt out of place simultaneously as I squeezed the trigger, and the rifle fired. I even stuck a GoPro camera next to me to catch any shenanigans on my part. Of course this was after the second blowback.

After the second bolt blowback I ordered stainless steel rod and cut off a suitable length and threaded both ends. Instead of the small stainless ball that the builder used I bought double size and way heavier stainless ball. I thought that perhaps the bolt detent was not keeping the bolt handle in place, and thought more leverage and mass would make it more reliable. So far the rifle has not done another blowback. Knock on wood.

Somewhere on the web I’d found another similar rifle with a leather strap set up that locked the bolt down. I almost went that route.

I greatly appreciate Lloyd’s article and testing.
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