View Full Version : Bolt pressure

06-27-2010, 10:14 PM
Here is my question. If the chamber pressure of a round ( 6ppc ) is in the neighbor hood of 60,000 psi and every thing is working properly, what would be the actual pressure against the bolt face?

Bob Ford
06-27-2010, 10:40 PM
Close to 7140 pounds thrust. Inside diameter of case X inside diameter of case X .785 X 60,000. Stuart Otteson's The Bolt Action volume 1 Page 275. The thrust might be a little high as I do not have inside diameter.

.223 at 60,000 would be 4800. .225 Win would be 6300. 30-06 would be 7560.


06-27-2010, 10:48 PM
Thanks. That helps a lot.

06-28-2010, 01:36 PM
Well not exactly. While I'm not questioning the math, the actual bolt thrust is less due to the grip the brass takes on the chamber walls. How must grip? Don't know if there is an actual value, but it does happen.

Bob Ford
06-28-2010, 02:35 PM
The case does definitely grip the walls. Otherwise we would not get case separation. Problem is each chamber and case is different. I do the calculations like the case and chamber was oiled. That is worse case scenario. If you do otherwise you risk failure.

06-28-2010, 05:45 PM
Bob: Just adding what I am sure you meant to. Cases should never be oiled. Gary P. hansen

06-28-2010, 06:24 PM

You are correct to disregard the case grip when calculating bolt thrust, when one is designing a bolt/action for strength. The grip is icing on the cake.

And, you're right, each chamber/case will be different.

06-28-2010, 08:41 PM
Well here is what i did, i made a mock up of the bolt head and receiver lugs. I then made a press adapter to fit the bolt face and put them in our press at work. I used an aluminum tube with 3/4" wall thickness as a shield and applied pressure to the bolt against the lugs of the receiver. Well my press adapter failed at about 8 1/2 tuns and i applied a little more to stop at 10 tuns. The press adapter swagged out into the bolt face and i had to pry them apart. I will next heat treat the press adapter and see what king of pressure the bolt and receiver lugs can take before failure. So far i am happy with the results, should be somewhere in the neighbor Hood of 3 times normal bolt face pressure, yes?

Bob Ford
06-29-2010, 09:48 AM
like your idea for testing locking lugs, but it is flawed. You are not duplicating the force between barrel threads and action. In effect you are setting the action on end and pushing against the lugs. It is the threads for the barrel and the metal between them and the lugs that usually fail.


06-29-2010, 01:21 PM
Dan Lilja did some testing of a few actions. He didn't do many, I think he started getting complaints from the action makers, so he quit.

But what he did was analyze the size and shape of the locking lugs and see how much yield there was given a certain amount of pressure.

Remember, when shooting hot loads (which is done commonly in benchrest and with the PPC) when you get a stiff bolt rise, you have set back somewhere. The bolt is giving some, the brass is expanding and taking up that space. Usually, it is a matter of something being out of square or not making even contact. Locking lugs not bearing evenly, boltface not perfectly square with the case/bore, then you may get to the point the bolt is yielding.

In theory, you should be able to trash the brass case before any problem with the bolt can be felt, if everything is locked up right.

06-29-2010, 09:53 PM
Thanks for the input it is much appreciated. This is a challenging project for me. I want to make a bench rest action and for some insane reason im hung up on titanium. The material is Ti-17. I could have gone with traditional materials such as 17-4 but just wanted to break from the pack. While this may be an unconventional test it is one of the few i can do. I would gladly listen to any ideas on how to test the strength of the receiver threads. The material is suppose to be around 40 Rc and is listed as having adequate strength. I have been thinking of a barrel block gun.

Bob Ford
06-29-2010, 11:15 PM
If you are building a action 1.5 in diameter or larger you should have adequate size and strength in front of the locking lugs. Make the barrel threads not less than 1 with 14 -16 threads per inch with at least .75 inches engagement. The area between the threads and lugs keep the wall thickness at least
3/16 inches thick and no sharp corners to start a tear.. I have no experience with Titanium.

For a thread and front of lugs test make a piece shaped like a top hat. The body of the hat 1.5 in diameter. The brim 2 by .5 thick. Bore and cut threads in the top. Bore the area behind to 1.125.
Thread a piece for the barrel and screw in place. Make a push rod to rest on the threaded plug and long enough to reach out the back. Place in press using the brim of the hat to hold the part. Apply pressure to the push rod until failure or you are satisfied.


06-30-2010, 10:27 AM

Ask your self this question, are there any commercially available actions in titanium? I remember reading something about titanium not being a good choice for an action. Titanium work hardens quickly, that may make it unsuitable for an action. Gary P. Hansen

06-30-2010, 08:42 PM
Actually Remington made a 700 titanium action for awhile and also torus makes a revolver out of titanium

J. Randall
06-30-2010, 11:06 PM
I think there is a guy that posts over on the AR forum some, that will make you a Mauser clone from titanium. I think his name might be Satterlee, they say his work is excellent, but the wait might be pretty long.

07-01-2010, 06:44 AM
Thanks J. Randall, heck i already have a rem 700 in a bench rest configuration and a Hall action in a heavy bench rest configuration. I would love to have a Bat action. But since i have most of the tooling i would like to give it a try, the biggest challenge will be the cutting the race ways for the lugs.

07-02-2010, 04:57 PM
I believe titanium for actions is okay, but there have been problems using it for barrels. I heard there was a problem with galling and rifling stripping out when using copper jackets. They seem to be okay in revolvers due to lead bullets and short barrel length. Others have tried lining titanium barrels with steel, but that was a problem due to the expansion rate difference.

07-06-2010, 10:22 AM

Here is a link that may help with the broaching. No affiliation at all, I just saw it some time ago and saved it.


07-06-2010, 08:18 PM
Thanks RWS, i think i have that saved, or the links anyway, on a cd. I did my stress test the other day and the bolt held 20 tones before it failed. Time for a little thinking on my part and will have to study up on some math and use Dan lilja's bolt strength formula and see where i'm at.

08-30-2010, 09:42 PM
Ok, so here is what i did for a test. I made a mock up of the bolt head and the receiver out of titanium, Ti-17. I made some adapters to go into the press at work witch has a pressure Gage on it, probably not the most accurate thing in the world but all i have at hand. I have some .750" wall thickness aluminum tube that i used for a shield, stuck the bolt head on top of the receiver and applied pressure to the failure point. It made it to 21 tons or 42,000 psi and then kapow. So, any experts out there that can tell me if this is a good test or not. Will this be strong enough to hold the pressures of a 6PPC?

J. R. Williams
08-30-2010, 10:24 PM
Check out "Hatcher's Note Book" as I seem to recall he performed similar experiments on the old "Springfield" rifle actions.