Bolt Thrust Pressure

[Bryan Austin]

The late John Kort, author of "My 44-40 Black Powder Journey" performed a test back in 2013 on low pressure case/bolt contact when fired. Heck, I'll just let you read it.

Full story with several related links: https://sites.google.com/view/44winchester/contributors/john-kort/bolt-thrust-pressure

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......

[Dirty Dick]

Would a lightly oiled chamber or cartridge case with case lube make any difference?

[Bryan Austin]

Would a lightly oiled chamber or cartridge case with case lube make any difference?

I think I saw in one of the replies, forget which topic link,  where that was talked about but I forget the result. I don't think it was tested but seems to have merit. I will try find it and post a link or a quote.

[Professor Marvel]

Thanks Bryan -
that is absolutely fascinating because it avoids all the "arguments" and gets right down to testing the question!

makes one wonder..

yhs
prof marvel

[greyhawk]

Thanks Bryan -
that is absolutely fascinating because it avoids all the "arguments" and gets right down to testing the question!

makes one wonder..

yhs
prof marvel

There would be a heck of a lot of variables at play in this - oily round, rough finish on the chamber, neat chamber versus sloppy chamber ........................

[Bryan Austin]

Thanks Bryan -
that is absolutely fascinating because it avoids all the "arguments" and gets right down to testing the question!

makes one wonder..

yhs
prof marvel

It does indeed. These things continue to bust certain myths. When I tested 6.5gr and 9.3gr of Trail Boss with only a 200gr lead bullet.....first let me say these bullets were the popular hard cast ACME "Magma" design much like the Laser Cast, the "Desperado", and the "Cowboy" that so may CAS shooters use. I sized mine to .429 and shot them through the PressureTrace II strain gauge system and recorded the following

1 1/4" diameter MGM barrel with .429" bore and 1:20" twist
Starlin Brass
CCI-300 Primers
200gr ACME of the Magma Engineering design
10 shot avg. each

Test #12 - 6.4gr @ 7,224 psi at only 1,000 fps
Test #19 - 9.3gr @ 15,182 psi at only 1,250 fps

Most if not all "Cowboy" factory loads barely hit 1,000fps from a rifle.

-----------------------------------------------------------------------------------------------------------------------------------------------------------
On a side note!!!

Test #1 - Buffalo Bore "Heavy" se to 11,300 psi (SAAMI MPLM) as my "Control"
Test #1A - Magtech 976 fps @ 6,000 psi (6,000 psi is rock bottom in order to make a reading on the gauge)
Test #2 - Winchester Super-X Hunting, 1,025 fps @ 6,6594 psi
Test #3 - Winchester Super-X Hunting, 1,025 fps @ 6,762 psi
I never did test Winchester Cowboy Loads
Test #15 - 10gr Unique, 200gr ACME Magma 1,419 fps @ 14,007 psi (John Taffin load from Guns Magazine 2005)
Test #26 - 10.5gr Unique, 200gr Speer SJHP, 14,753 psi [maybe 18,000 cup] (Lyman 49th max load Group II, 1,282fps @ 19,600 cup)
Test #28 -18.5gr IMR4227, 200gr Speer SJHP, 1,097fps @ 9,205 psi (Lyman 49th max load Group I @ 11,600 cup)
Test #29 - 10.5gr Unique 205gr 427098, 1,469fps @ 17,837 psi [21,500 cup](Lyman 49th max load Group II 19,700 cup)
Test #37 - 26.5gr Reloder 7, 210gr 427098, 1,432fps @ 11,373psi
Test #43 - 40gr/W Swiss FFg, 210gr 427098, 1,337fps @ 14,285psi (Original pre-1884 unheadstamped cases)
Test #47 - 26.5gr Reloder 7, 217gr 43-215C, 13,048psi (no chrono)
Test #53 - 40gr/W Goex FFFg, 210gr 427098, 1,272fps @ 11,001psi (WLP's WRA semi-balloonhead cases)
Test #54 - 40gr/W Goex FFFg, 210gr 427098, 1,248fps @ 10,037 psi (WLP's REM-UMC semi-balloonhead cases)
Test #55 - 40gr/W Goex FFFg, 210gr 43-210B, 1,235fps @ 8,305 psi
Test #71 - 40gr/W Goex FFFg, 210gr 427098, 1,356fps @ 12,649 psi (small and large primer WESTRN semi-balloonhead cases)


All 84 tests can be seen here: https://docs.google.com/spreadsheets/d/1cZyKKXVyHq9as9uFJiko5yReJ9a-ER32YsENTgJGJs4/edit#gid=651705900 Make sure to click each "powder" tab at the bottom.

My "GO TO" loads are here, with a powder test "flow chart" that lead to my "go to" load choices.
https://drive.google.com/file/d/1L4CrfgL59_4nBSq-FzUgyMuCc_oylycZ/view?ths=true

[Bryan Austin]

There would be a heck of a lot of variables at play in this - oily round, rough finish on the chamber, neat chamber versus sloppy chamber ........................

Yes, but that is not necessarily the point.

Revolvers are a great example. 44-40 case primers, and even 45 Colt case primers get pushed out at low pressures because the case expands and locks against the cylinder walls at and below X amount of pressure. When that pressure is exceeded, the case releases and is pushed back against the blast plate and reseats the primer...etc etc etc. Many variables yes...........

[Trailrider]

Would a lightly oiled chamber or cartridge case with case lube make any difference?

While there are a lot of variables, when there is enough pressure against the inside of the cartridge case to press it against the chamber wall so that it adheres to the wall by friction, the backthrust on the inside of the case would have to exceed the yield strength of the brass, which, depending on the hardness of the brass (yield strength is proportional to hardness).  So the cartridge itself will not stretch rearward if the pressure isn't anywhere from 13,000 psi to 35,000 psi. When the pressure drops low enough that the sides of the case don't adhere to the chamber wall, the cartridge MAY then move rearward. But, if the pressure drops quickly enough, there may not be sufficient pressure left to move the case at all. 

Obviously, an oily chamber will decrease or eliminate the adhesion of the case to the chamber wall. Certain automatic or semi-auto guns that used the delayed blowback principle depended on either the cartridges or the chamber being lubricated to allow backthrust on the bolt.

[Bryan Austin]

While there are a lot of variables, when there is enough pressure against the inside of the cartridge case to press it against the chamber wall so that it adheres to the wall by friction, the backthrust on the inside of the case would have to exceed the yield strength of the brass, which, depending on the hardness of the brass (yield strength is proportional to hardness).  So the cartridge itself will not stretch rearward if the pressure isn't anywhere from 13,000 psi to 35,000 psi. When the pressure drops low enough that the sides of the case don't adhere to the chamber wall, the cartridge MAY then move rearward. But, if the pressure drops quickly enough, there may not be sufficient pressure left to move the case at all. 

Obviously, an oily chamber will decrease or eliminate the adhesion of the case to the chamber wall. Certain automatic or semi-auto guns that used the delayed blowback principle depended on either the cartridges or the chamber being lubricated to allow backthrust on the bolt.

I like that explanation better 

If the cartridge stretches rearward, is this what then is the need to trim the case?

[Bryan Austin]

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

[Dirty Dick]

Bryan, it would be interesting to test your RX7 loads for bolt thrust as well? A comparison with other heavier loads as well?

[Bryan Austin]

Bryan, it would be interesting to test your RX7 loads for bolt thrust as well? A comparison with other heavier loads as well?

I am thinking the same thing, slower burning vs faster burning....wonder if this affects case release?

Anyhow, I have a contraption made, just need the time and a place to go tests these things.


This is exaggerated, barrel being placed further forward than for future powder charge tests.
Primer blast test -

[greyhawk]

I like that explanation better 

If the cartridge stretches rearward, is this what then is the need to trim the case?

I started out with a worn original 92 in 32/20, good clean bore and it shot well, sloppy action and excessive headspace - didnt know much about either in those early days - I got it when I was 15 and just went to work having fun - first reloads were shotgun ballistite - got the local pharmacy man to weigh me out the correct charge that I took home carefully in a gel capsule and used that to cut a scoop measure. We graduated to Nobels Revolver no1 - I never trimmed a case - didnt know of such things but case head separations were a regular part of life with that 92 - until I sold it to a collector - If I still had it I would pull the barrel, turn a thread off it, recut the chamber and have a good safe shooter. Have no idea what pressure we were running we just tuned our load so we had the same point of impact we got with bought ammo (not the HV stuff)
So we had enough pressure for the case to grip the chamber walls but also enough to then drive the base rearwards in contact with the bolt face - stretching it and thinning it at the solid head - and we got that classic lopsided swelling that comes from a resized case lying at the bottom of a fat chamber - and we needed to resize because we had stretched the brass in that fat chamber.

Had a lot of fun with that old rifle - wasted a lot of ammo - lived on a 4000acre bush block those days - could let one go anywhere you liked - we played with aerial shooting -started on half housebricks and beancans - one guy threw it the other shot - then two by two wood blocks - we got to about 50/50 on those - the end game was throw a penny up with your right hand - gun empty - rack the action and shoot - I still have the one I hit in my gun room - probably my favourite trophy - once to prove it was possible, never tried it again - our pre decimal penny was an inch and a quarter diameter so it was a chance - the US penny would have been a fluke though I  saw a movie of Lionel Bibby shooting airborne 22 short cases (3 from 5).     

[Bryan Austin]

I started out with a worn original 92 in 32/20, good clean bore and it shot well, sloppy action and excessive headspace - didnt know much about either in those early days - I got it when I was 15 and just went to work having fun - first reloads were shotgun ballistite - got the local pharmacy man to weigh me out the correct charge that I took home carefully in a gel capsule and used that to cut a scoop measure. We graduated to Nobels Revolver no1 - I never trimmed a case - didnt know of such things but case head separations were a regular part of life with that 92 - until I sold it to a collector - If I still had it I would pull the barrel, turn a thread off it, recut the chamber and have a good safe shooter. Have no idea what pressure we were running we just tuned our load so we had the same point of impact we got with bought ammo (not the HV stuff)
So we had enough pressure for the case to grip the chamber walls but also enough to then drive the base rearwards in contact with the bolt face - stretching it and thinning it at the solid head - and we got that classic lopsided swelling that comes from a resized case lying at the bottom of a fat chamber - and we needed to resize because we had stretched the brass in that fat chamber.

Had a lot of fun with that old rifle - wasted a lot of ammo - lived on a 4000acre bush block those days - could let one go anywhere you liked - we played with aerial shooting -started on half housebricks and beancans - one guy threw it the other shot - then two by two wood blocks - we got to about 50/50 on those - the end game was throw a penny up with your right hand - gun empty - rack the action and shoot - I still have the one I hit in my gun room - probably my favourite trophy - once to prove it was possible, never tried it again - our pre decimal penny was an inch and a quarter diameter so it was a chance - the US penny would have been a fluke though I  saw a movie of Lionel Bibby shooting airborne 22 short cases (3 from 5).     

Sounded like a lot of fun!!


to continue....
I know most here have never trimmed a 44-40 case, never a need to with such low pressures. However, with higher pressure loads, I have trimmed many cases. Let me try to explain in a question format!!!

I don't exactly know where cases do stretch whether it be a 30-06, .308 or whatever. I guess the case would stretch in one of maybe two places. Maybe the first place being all areas between the case mouth and the neck, maybe along the crimped area as it seems to be the thinnest on the 44-40.. Another would be along the base where headspace could be an issue. If there is .006" between the base and the bolt, I guess if pressure are high enough, some stretch could be from there.

If my cases are 1.300" and eventually I get 1.310" when using higher pressures...12,000psi and higher....there is some stretching going on somewhere and the case is certainly getting weaker somewhere. I have had new cases range from 1.292" to 1.300". Those also stretch to 1.298" to 1.306". I then trim back to 1.300". I have yet had a case failure but at this rate, it could soon happen. The only case mouth splits I have had is when using the LFCD and greater than .428" bullets.

Your thoughts?

[Slamfire]

  This is a " GREAT " write up ,,I have a 92 Rossi w/ 24" oct. barrel ,, I have been  loading to 73 specs , I also use H-4198 ( would like a test for it ) my 427098's avg. 215-217 gr. and so far my shot groups are about the same as you have posted ,, I thank you ( all ) for your time and dedication to a " GREAT " cartridge .


  coffee's ready ,, Hootmix.

[greyhawk]

Sounded like a lot of fun!!


to continue....
I know most here have never trimmed a 44-40 case, never a need to with such low pressures. However, with higher pressure loads, I have trimmed many cases. Let me try to explain in a question format!!!

I don't exactly know where cases do stretch whether it be a 30-06, .308 or whatever. I guess the case would stretch in one of maybe two places. Maybe the first place being all areas between the case mouth and the neck, maybe along the crimped area as it seems to be the thinnest on the 44-40.. Another would be along the base where headspace could be an issue. If there is .006" between the base and the bolt, I guess if pressure are high enough, some stretch could be from there.

If my cases are 1.300" and eventually I get 1.310" when using higher pressures...12,000psi and higher....there is some stretching going on somewhere and the case is certainly getting weaker somewhere. I have had new cases range from 1.292" to 1.300". Those also stretch to 1.298" to 1.306". I then trim back to 1.300". I have yet had a case failure but at this rate, it could soon happen. The only case mouth splits I have had is when using the LFCD and greater than .428" bullets.

Your thoughts?

Cut an old case - one that you have trimmed a couple times - section it lengthways - the brass you trimmed from the front end has likely gone missing from the area where the case walls join the solid head right at the point where a case stops swelling in the chamber . Seems a bit contrary to logic but thats what happens - often its quite a distinct little ring of thinner brass
So needs enough pressure to glue the case wall to the chamber and to stretch the case back against the bolt face - needs headspace or spring in the action enough to let it move.
Does the whole case stretch? or does it just move in that small area ? debateable but I go for the small area being responsible for most of the movement - guys talk about brass "flowing" forward. I dont think that happens, the case stretches near the base and then its longer than it was before, full length size it and you speed up the process by about five times over, shoot the fireformed brass - its got a lot less room to move - last a lot longer - if it wont chamber just a little kiss with an appropriate die till it will fit.  I make those dies on the lathe. sometimes only needs a tiny nudge where the case has swelled at the rear.
     
Lots of variables - I Shot a 22/250 till it quit from throat erosion (some over 4000 we think) - or its lost that fine edge it had - full factory velocity loads - never trimmed a case - never full length sized a case - a winchester model 70 with a really neat chamber (a credit to winchester really) the only fired brass we ever found that would go back in that rifle was its own and the brass from another similar vintage rifle a mate of mine owned .

Had a 30/30 I could not use unless I sized the brass after every firing - didnt matter 30/30 brass is not dear.

Straight wall cases like a 44/40 or 45/70 are gonna behave differently than a bottleneck one too.   

[Bryan Austin]

Cut an old case - one that you have trimmed a couple times - section it lengthways - the brass you trimmed from the front end has likely gone missing from the area where the case walls join the solid head right at the point where a case stops swelling in the chamber . Seems a bit contrary to logic but thats what happens - often its quite a distinct little ring of thinner brass
So needs enough pressure to glue the case wall to the chamber and to stretch the case back against the bolt face - needs headspace or spring in the action enough to let it move.
Does the whole case stretch? or does it just move in that small area ? debateable but I go for the small area being responsible for most of the movement - guys talk about brass "flowing" forward. I dont think that happens, the case stretches near the base and then its longer than it was before, full length size it and you speed up the process by about five times over, shoot the fireformed brass - its got a lot less room to move - last a lot longer - if it wont chamber just a little kiss with an appropriate die till it will fit.  I make those dies on the lathe. sometimes only needs a tiny nudge where the case has swelled at the rear.
     
Lots of variables - I Shot a 22/250 till it quit from throat erosion (some over 4000 we think) - or its lost that fine edge it had - full factory velocity loads - never trimmed a case - never full length sized a case - a winchester model 70 with a really neat chamber (a credit to winchester really) the only fired brass we ever found that would go back in that rifle was its own and the brass from another similar vintage rifle a mate of mine owned .

Had a 30/30 I could not use unless I sized the brass after every firing - didnt matter 30/30 brass is not dear.

Straight wall cases like a 44/40 or 45/70 are gonna behave differently than a bottleneck one too.

Yeap, certainly what I have seen. I would think the "solid" area of the case at the head certainly doesn't "give" any while the area right above it is the weak spot for stretching. Thanks for the clarification. This must certainly be why Winchester warned against re-loading their factory high velocity offerings. The case heads back then were still of the semi-balloonhead design and would certainly be very weak at that location.

[Dirty Dick]

A mystery to me, why does .45 ACP brass get SHORTER the more times it is reloaded? Back in the day when I shot IPSC I shot about 40K of .45 ACP reloads a year, H&G 200gr swc over 5 grs. of Bullseye. Some cases were used so much the caliber and maker stamping on the case head was gone, the rims frazzled, primer pockets were SHALLOWER, the extractor groove got thinner until the case web ahead of the extractor groove expanded preventing chambering. Never had a .45 ACP case head separation, but lost many  to longitudinal splits , usually from the case mouth, sometimes from the web almost to the case mouth. This was much less when using a barrel with a tighter match chamber.  Wanted to find out what would happen if they were reloaded again, if they would chamber, sometimes with help on the rear of the slide, they fired just fine, split was a lot longer but nothing else untoward was noticed.  When we switched to .38 Super loaded to at least twice the psi of the .45 I did not notice the same thing happen in regards to the cases getting shorter. 

PS...........The point of this diatribe was I was wondering if .45 ACP brass in an 1873 rifle conversion would react the same as in the 1911, sorry I forgot to state as such above. Perhaps with the necessity of using a roll crimp on the ACP case in the '73 the brass would grow longer? They say the first thing to go is the memory, I forgot what second thing is. Gotta remember to take my senility/ED meds if I could only find them.

[Bryan Austin]

Today I tried 4gr of Unique with a 220gr 43-214A

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

SLOW MOTION at about :27

[Professor Marvel]

My Dear Bryan

Firstly, you are now my Ballistic Sciences hero.

Second, would you please be so good as to describe what we are watching in slo-mo? I clearly see the rim of a shell,apparently in a test barrel,
some sort of flame, and then the large rectangular thingy is moving... towards the test barrel?

thanks very much, please keep up the good work!!

your admirer
prof marvel