Totally in the dark on "bolt thrust" .

[350JR]

Ok. I know what bolt thrust IS......but I'm obviously looking at the whole shebang from an incorrect angle or..........something.

The MAIN factors I keep reading about are the size of the case and rim diameter.

It would SEEM (to me) that the larger diameter of the case body AND longer lengths, therefore having more surface contact with the chamber, would help LOWER the bolt thrust BUT, do understand that super high capacity rounds have more recoil and the "for every action there is an equal and opposite" thing is understood, so that energy has to go SOMEWHERE.

Case in point, that has me WAY off in left field is comparing two big boys the 378 Weatherby and the 416 Rigby. Both require the .590 bolt face but the chamber pressures of these two rounds are dramatically different but BOTH are quoted as having "very high bolt thrust" numbers.

I'm obviously missing something and have read articles online for most of an entire day.

The SINGLE most quoted factor that "increases bolt thrust" LISTED in these articles is the size of the rim diameter.........and very little else gets mentioned (OR I missed them).

I'm trying to wrap my head around WHY. The chamber pressure all else are the same, or similar, but if it has a larger rim diameter it has more bolt thrust? .... and two rounds roughly the same capacity both have high bolt thrust numbers EVEN THOUGH they aren't close in chamber pressure?

Where am I messing up?

Important? Nope...I just can't stand not understanding something like this.

HELP!!

God Bless

 

[SJB358]

Can't help, but man, I am interested in the answer....

 

[350JR]

Not knowing me personally, guys........you have NO idea how FRUSTRATED this makes me!!

:shock:

Lilja barrels don't recommend 700 actions for the 378 ( or that ilk)......but Remington made one.

Bolt thrust on the 416 Rigby is "immense" (even though a very moderate chamber pressure round?) but they make a barrel for Encores???

Hmmmmmmm.

Edit:

SOME of the answer is here:

http://en.wikipedia.org/wiki/Bolt_thrus ... olt_thrust

where down the page it shows calculations for such but only mentions the friction of the case and wall of the chamber but DOES mention that oiling the cartridge / chamber was used at one time as "test loads" and IMHO dramatically PROVES that case friction is more than a little bit of a factor affecting bolt thrust.

Unless I'm again, lost on their calculations, even a lower recoiling, lower capacity round "with the same chamber pressure and rim" is going to have the same bolt thrust.......EVEN THOUGH the recoil would NOT be equal??

My head hurts LOL!

 

[SJB358]

I have thought the same thing. I heard the 338 Lapua was too much (same for Rigby rounds) for Remington and Winchester actions. Again, great topic.

I believe the Norma (300 and 338) rounds are two that produce more bolt thrust than the Rem and Winchester type actions can handle.

 

[Vince]

Don't mind me, I'll just stand in the corner by the punch bowl.

I honestly have no idea what this conversation is about but I'll practice my Administrator skills my nodding my head at infrequent intervals and looking sagely. I'm not an Administrator and ain't likely to ever be one but I can acquire the skill set.

Now I want to learn what bolt thrust is. Can someone explain it in a manner that makes sense to a mechanically challenged individual?

 

[350JR]

So I don't get in trouble running my yap, Vince.........click the link I have a couple posts up that is on wikipedia. Pretty much it's simply the pressure on the bolt face caused by the expanding gasses shoving the cartridge case AT YOU.

It CAN damage your bolt lugs if they are not "adequate".

Until one gets into the super big boys with larger than "magnum" rim sizes it doesn't seem to come up much.

God Bless

 

[Vince]

:?:
Thank you but as you can see I'm still cornfuzzled. Not to worry that's my usual state. :grin:

 

[350JR]

Thinking "online" as it were so I'll either confuse the issue more or clarify it some (for myself).

With the area OF the part of the case pushing rearward being circular, this same area will increase radically as the diameter of the rim (or bottom of the case body under pressure) increases.

Only as a reference, comparing the area of a .532 rim (all the belted mags) is 0.22228652979739943 sq inches. The area of a .590 rim is 0.27339710067865175 sq inches. In increase of the area the pressure is shoving against of ROUGHLY 23 percent.

With the pressure inside the chamber being universally equal and pushing against the inside uniformly, I understand where multiplying the chamber pressure x the surface area against the bolt DOES increase bolt thrust radically as the rim diameter grows in size.........however:

With the chamber pressure of the 416 Rigby (depending on where you look) being ROUGHLY 50,000 psi this is 21 percent less than the 63K psi of some (most) of the belted mags using the .532 rim.

Even with the larger rim diameter this pressure reduces the amount back against the bolt to levels near standard bolt face mags. (.532 rim and 63000psi calculates out = 14004 and using the .590 area and 50000psi = 136670)

So HERE is where I am lost. WHY does then the lower case pressure, .590 rimmed 416 Rigby considered to have a "high bolt thrust" since by calculation is has roughly the same, if not less than a standard belted mag round? (This is only accurate in numbers considering that the friction of the brass/chamber to be equal).

To MY "pea brain".....this don't compute so asking for what I am missing.

God Bless

 

[IdahoCTD]

Pressure is psi (pounds per square inch) as you increase the area (ie the larger bolt face size) it applies more thrust to the bolt face and lugs. If you were to turn the rim size down to standard magnum .532, from .590", the same cases would apply less "thrust" to the bolt. That is why many don't like using Remington and Winchester actions for the .590" bolt face size. Many people have measured the lug set back from using a standard Remington action and it amounts to several thousandth's over the course of a few hundred rounds. It seems the chromoly actions are stronger than stainless. I intend to build a .30-.338 Norma Mag (.590" bolt face) on a chromoly Remington with a PTG bolt but I'm going to have the action nitrided.

Defiance actually builds a Lapua based action on the same dimensions as a Remington with a .750" bolt body diameter so the lugs are actually shorter height wise. I have a buddy that had 2 of them and they worked perfectly even with really large cases (.460 Weatherby, .500 Weatherby). I think their action material is much better than the average Remington though.

 

[350JR]

I was adding to my above post as you posted Idaho.....please read my addition.

 

[IdahoCTD]

Most people load the Rigby hotter today than they use to. The brass is made accordingly as well. The low pressure stuff is for hot temps in Africa to maintain reliability. The Rigby loaded at 50k is barely more potent than a .416 Rem. despite the much larger capacity. Loaded to it's potential it's knocking on the .416 Weatherby.

I'm sure if you kept your pressure reasonable it would be fine. Remington makes a factory 338 Lapua and I have a .30-378 Imp. I built 15+ years ago on a Remington that has never given me fits. People get carried away with the good brass made today and tend to exceed the SAAMI pressure specs. That is when things start to go south.

 

[350JR]

Thank you much! I do appreciate it.
God Bless

 

[Oldtrader3]

To get the correct results of the case friction in the chamber, you need to calculate the area of exterior case friction on the outside surface of the case and know what the "coefficient of fiction" is for the particular hardness of your brass case times the coefficient of friction of that material on the chamber steel. Having oil or and other material coating the chamber or case exterior changes this coefficient to make calculating it pretty empirical.

 

[Hegland]

To get the correct results of the case friction in the chamber, you need to calculate the area of exterior case friction on the outside surface of the case and know what the "coefficient of fiction" is for the particular hardness of your brass case times the coefficient of friction of that material on the chamber steel. Having oil or and other material coating the chamber or case exterior changes this coefficient to make calculating it pretty empirical.

Read my mind, sir, and as the diameter of the rim (and along with it, the diameter of the case body) increases, the body surface area of the case increases substantially as well.

Charlie, you should write a textbook. This is so much better than the blocks and inclined planes in the books I had!

 

[Oldtrader3]

Justin, I used to train out of school, management candidate, engineers and manage their integration into the real corporate world of manufacturing. Part of that effort was to get them to express them selves in plain English.

I have no desire to write a text and people such as my PhD, Professor, daughter would tear me a new one because I don't have PhD "rights" with just an MBA. That is a major source of their income and they can be snobs! Plus, I was also confused by those same texts that you refer to.

 

[350JR]

All very helpful and informative.

The chamber pressures of the 416 do vary a lot online in reports and I had read the cordite and Africa temps had lots to do with the CP quoted back then. I am, however, little surprised someone hasn't hooked a few modern rifles with modern components up to a gauge of choice and ran some tests.

The Oct Handloader issue has an article from John Barsness on "Both thrust and Other Myths" that I want to get my hands on........just for chits and giggles. It has a 416R article too.

The online (partial) pdf has the article on the 416 and quotes the 52K PSI from SAAMI being the peak pressure. PLENTY but again.......makes me scratch my head a bit if this IS max BUT, never fear......I think that would be quite enough for my desires.
Not having a strain gauge or experience using one, it's my brass that tells me what is too much like most reloaders. What it actually IS.....is just info.

It was the bolt thrust issue that had me tilting my head.

Cant have too much info........( I think. LOL!) On another tangent, my brain has more questions yet unanswered but I try to not make myself too much of a nuisance. The whole "moderate pressure, high capacity case vs lower capacity, higher pressure" discussion could have me chin scratching on which I'd prefer (given a choice)..........for weeks. Efficiency is good but so is less brass, throat etc etc abuse (that's as far as I've got on that.)

This is like hunting it seems. The PLANNING stages is a huge part of the fun!!

The entire bolt thrust of the .590 rimmed rounds being lumped into one similar "HIGH" category just had me shaking my head going "NO NO NO.....that can't be right" Chamber pressure, surface contact with chamber.....etc..... has to be involved there........so off I went with the calculator.

Thank you all.
God Bless