Bolt Thrust Pressure

[Savvy Jack]

Back about 2010 there was discussion and tests run, testing the theory by some, that there is not much if any pressure pushing the case into the bolt with low pressure cartridges such as the 44-40. There was a video made in 2013 by using an early sn# Colt Lightning were the bolt does not lock-up. By Nov. 26th, 2013...John Kort did the final test. Here is an insert from that discussion.


by w30wcf » Wed Nov 06, 2013 10:14 pm

Ok, finally had a chance to test the .44-40 ....... a few days later than anticipated. Life gets in the way sometimes .......

Anyway, the test indicates that the case head did not make contact with the bolt.

I used 2 cases with thinned rims (front) allowing for .015" headspace.

I seated the primers to stand .012" proud of the base of the case then applied 2 small clay pads on either side of the primer to the same .012" thickness.

Cases were loaded with 6.5 / Trail Boss / 215 gr cast bullet. Pressure 13,000 CUP or thereabouts.

Result:

Primer protruding .010" . Clay pads the same. No evidence that the case head touched the bolt since the small clay pads were not distorted as they would have been if the case head touched the bolt face.

I will say that the cases used were not full length sized. Just neck sized as I do all my .44-40's with a special die.

I'll post a pic in the next day or so.



by w30wcf » Mon Nov 11, 2013 11:59 am

I had added a piece of scotch tape over the case head to keep the clay from possible sticking to the bolt face.

I would expect that as pressures would increase, the case head would eventually overcome the primer thrust and reseat the primer but this is specifically a test of low / standard SAMMI pressure for the .44-40......

Later my testing of 6.4gr of Trail Boss only produced 7,224 psi, rather than 10,000 psi (12,000ish cup) and 9.4gr produced 15,182 psi (18,000ish cup).


More info and discussion links here;
https://sites.google.com/view/44winchester/contributors/john-kort/bolt-thrust-pressure?authuser=0

[Savvy Jack]

If you think your 73' has been exposed to covid...err...I mean Over Pressures, there is a simple way to check for stretched toggles....or even worn out toggles from wear.



There is a quick test you can perform to check your 73's bolt if you suspect the toggles are getting worn or stretched due to wear or over pressures. The obvious is to check the toggles themselves for excessive play. The other is to check the Case head Clearance. (see photos and video)

1. measure the case length of an empty resized case.

2. Finger start a spent primer

3. Insert case into rifle chamber and close bolt. This will push (seat) the primer into the primer pocket. The primer should not seat fully into the primer pocket.

4. Remove and remeasure case length with the primer seated by the bolt

5. Do the math

The goal is have a difference of only .006", my Ubert 73' is .007" and my Marlin is .006"...no change since I got both over ten years ago.

For photos and a video: https://sites.google.com/view/44winchester/contributors/john-kort/bolt-thrust-pressure

[Savvy Jack]

Tonight I tested 4gr of Unique and a 220gr 43-214A bullet.

For details, click here: https://sites.google.com/view/44winchester/contributors/john-kort/bolt-thrust-pressure

Slow Motion video, skip to about the :27 mark


https://www.youtube.com/watch?v=i3a15DELim8

[BobInAus]

Savvy Jack, I did the test to check on toggle wear / thrust-pressure and on closing the bolt, the primer seated flush with the base of the case. It did not sit out from the base of the case. I do not know what that indicates. Any information would be helpful.

Bob

[Savvy Jack]

Savvy Jack, I did the test to check on toggle wear / thrust-pressure and on closing the bolt, the primer seated flush with the base of the case. It did not sit out from the base of the case. I do not know what that indicates. Any information would be helpful.

Bob

Just to clarify you did this with an empty case and a spent primer, with the primer being seated with the bolt?

[Savvy Jack]

Today I tested 6.4gr of trailboss. Forgive me for not posting here, I am tired so I will just post a link to the videos and photos. Scroll to the bottom of the page at the following link: https://sites.google.com/view/44winchester/handloading/bolt-thrust-pressure

[popper]

Sounds like a good head space test.

[Savvy Jack]

Sounds like a good head space test.

That could be a bad thing!!!

[BobInAus]

Savvy Jack, yes empty case, full length resize , spent primer and seated with the bolt.

Bob.

[Savvy Jack]

Savvy Jack, yes empty case, full length resize , spent primer and seated with the bolt.

Bob.

Sounds like there is no headspace. Could be the barrel is set a tad too close but not necessarily a bad thing. You certainly don't want too much gap.

[Hootmix]

I like this method of testing head space better than any I have read yet ,, keep up the good work , ya'll .

coffee's ready ,, Hootmix.

[BobInAus]

Savvy Jack, thanks for that. I checked the few fired cases I have and the primers didn't seat any further into the case. So I guess Ill go with no headspace.

Bob