Polished brass. Can it be too smooth?

[Dusty Stevens]

Proof loads. Plain old proof loads.

Hope some readers don't feel ok shooting their stuff at that level.

We shoot matches with proof loads then

 

[ireload2]

Expecting your brass to stick to the chamber and act as a mechanical brake to reduce the load on the action is all wrong.

Varmint Al's site has a fairly extensive coverage of the subject of chamber finish including Finite Element Analysis of the effect of chamber surface texture.
http://www.varmintal.com/a243z.htm

If your action cannot take the small extra thrust you probably need to reduce your loads or use a stronger action.

A number of machine gun and auto cannon designs make use of lubricated ammo to insure reliable functioning.

I have lightly lubed cases being fire formed and being fired the first time for years with 100% satisfactory results.

Surface texture of the brass should be smooth enough to avoid stress concentrators from nicks and scratches and other surface defects. Other than that brass is going to take on the surface texture of the chamber when fired.

 

[KenOath]

A couple of years ago at a match, it was raining a fine misty rain. The wind was blowing toward the firing line and my shells were sitting in a loading block. The sighters went ok and the farther down the record string I got, the more stiff bolt lift I had. I know the cases got wetter the longer they sat there. By the last record round, I could hardly open the bolt. I figured the water took up room in the chamber and hydraulically built pressure. Those cases were ruined and the expansion on the case heads were great. It also happened to another shooter and we talked about it. His cases were also over expanded and he also got the hard sticky bolt. Matt

Yes i trashed 8 or so cases also...

 

[RW]

P.O Ackley when "Improving" cartridge chambers found that cases and chambers with less taper had less pressure rearward thrust that cartridges that chamber dimensions had less tapper and there is Improved cartridges that use this engineering, I don't know about the cross hatch or roughage grit

 

[ireload2]

I am not aware of any bolt thrust measuring equipment used by Ackley. Many people accept that statement but I don't really think Ackley had any way to prove it other than sticky extraction.

I for one would like to know how such a slight angle change would make a SIGNIFICANT DIFFERENCE in bolt thrust.

Regardless of bolt thrust when primer pockets and case heads expand your brass is going to fail. If you used the right action bolt thrust should not matter.

P.O Ackley when "Improving" cartridge chambers found that cases and chambers with less taper had less pressure rearward thrust that cartridges that chamber dimensions had less tapper and there is Improved cartridges that use this engineering, I don't know about the cross hatch or roughage grit

 

[RW]

Ackley, in his first book I believe fired a 30-30 ackley imp in I believe a Mod 94 with out the locking lug to check the rearward thrust theory I know that this was pretty crude but a hot load and no rearward thrust. RW

 

[BoydAllen]

Expecting your brass to stick to the chamber and act as a mechanical brake to reduce the load on the action is all wrong.

Varmint Al's site has a fairly extensive coverage of the subject of chamber finish including Finite Element Analysis of the effect of chamber surface texture.
http://www.varmintal.com/a243z.htm

If your action cannot take the small extra thrust you probably need to reduce your loads or use a stronger action.

A number of machine gun and auto cannon designs make use of lubricated ammo to insure reliable functioning.

I have lightly lubed cases being fire formed and being fired the first time for years with 100% satisfactory results.

Surface texture of the brass should be smooth enough to avoid stress concentrators from nicks and scratches and other surface defects. Other than that brass is going to take on the surface texture of the chamber when fired.

I have great respect for Varmint Al's work...but in this one case I will have to disagree with his conclusion.

A friend was seeing pressure signs in the form of ejector marks on his case heads, the first shot or so after cleaning. It turned out that he had not been drying his chamber, the bore but not the chamber. With the chamber dried after cleaning, there were no marks. One can do all sorts of test and create all sorts of simulations, but unless they actually duplicate the situation in question there can be "slippage". IMO in this case there was. The rifle was a slow twist 6BR varmint rifle, with a polished chamber.

 

[Laurie]

I have great respect for Varmint Al's work...but in this one case I will have to disagree with his conclusion.

A friend was seeing pressure signs in the form of ejector marks on his case heads, the first shot or so after cleaning. It turned out that he had not been drying his chamber, the bore but not the chamber. With the chamber dried after cleaning, there were no marks. One can do all sorts of test and create all sorts of simulations, but unless they actually duplicate the situation in question there can be "slippage". IMO in this case there was. The rifle was a slow twist 6BR varmint rifle, with a polished chamber.

I saw those results too with my first 6BR -I'd forgotten about it until your post. I'd been using Wipeout foam from a pressurised can and hadn't noticed a slight build-up in the chamber which rodding it out of the bore didn't touch. The surplus Wipeout lubricated the chamber walls enough to see the rifle shoot weirdly and the first few cases after cleaning show ejector marks slowly diminishing in the order of firing as the chamber dried a bit.

 

[alinwa]

Ackley, in his first book I believe fired a 30-30 ackley imp in I believe a Mod 94 with out the locking lug to check the rearward thrust theory I know that this was pretty crude but a hot load and no rearward thrust. RW

He sure did

I guess one "proof" is that he didn't lose his fingers.

I've done this sort of thing quite a bit, including firing a round without an action attached....... and a few other "proofs" are that you can make a slamfire shotgun from steel pipe and that nearly everyone who's paid attention has noticed instances where the primers are left protruding from the casehead.

'MUR'CA! right here......

 

[alinwa]

A couple more opinions.....

Having tested it rawther extensively I don't believe the finish on the brass cases has any effect on bolt thrust.

Water on the other hand, even trace amounts has 'YUGE effect,

And I've never placed much stock in any of Varmint Al's analyses. Sorry VA but all computer modeling is based on input/output and GIGO applies. I've experienced dozens, nay hunnerds of instances of computer modeling (and/or engineered specs) do not illustrate/explain real life.

 

[dcali]

And I've never placed much stock in any of Varmint Al's analyses. Sorry VA but all computer modeling is based on input/output and GIGO applies. I've experienced dozens, nay hunnerds of instances of computer modeling (and/or engineered specs) do not illustrate/explain real life.

I used to do those for a living. And you're correct, especially for complex analyses involving friction or any kind of joint, for that matter. My old boss used to have a saying - "we analyze for insights, not for numbers". They can be very helpful in figuring out "what" is going on, but are only pretty good at figuring out "how much".

 

[alinwa]

I used to do those for a living. And you're correct, especially for complex analyses involving friction or any kind of joint, for that matter. My old boss used to have a saying - "we analyze for insights, not for numbers". They can be very helpful in figuring out "what" is going on, but are only pretty good at figuring out "how much".

Your old boss was a smart man

I think I might steal that

 

[dave@aDave]

http://varmintal.com/a243z.htm

Rifle Chamber Finish & Friction Effects
on Bolt Load and Case Head Thinning.
FEA Calculations done with LS-DYNA

http://varmintal.com/afric.htm

Friction Coefficient Tests of 416 Stainless Steel on Cartridge Brass

from Varmit Al, 2015

 

[alinwa]

http://varmintal.com/a243z.htm

Rifle Chamber Finish & Friction Effects
on Bolt Load and Case Head Thinning.
FEA Calculations done with LS-DYNA

from Varmit Al, 2015

As I said........

Same Planet, Different World.

I'm and end user, a builder of stuff. In my world we go with the stuff that WORKS not with what "the math" says will work...... Facts trump computer models.

EVERY time.

This was specifically one of the completely meaningless "tests" I argued with Al on back when it was done.... 1 of about 5.

GIGO

I've done tests IN THE GUN that show completely different results VS sliding blocks on tables. In a completely repeatable fashion.

Now, when VA or anyone else steps up and slides blocks around under 40,000-50,000 or 75,000psi I'll perk up and reassess for relevance. But in the meantime, it's kinda' like the statement above regarding "proof".....ie "no real proof"...."tools for bolt thrust measurement" and "except for sticky extraction" makes my point. There's a large segment of the population who'll accept a mathematical "proof" over facts.

I'm not in that camp.

I read both SF and Fantasy........one to EXPLORE reality, and one to ESCAPE reality.


al-keepin'itreal-inwa

 

[rammac]

As others have said, there are so many variables for every situation that it's hard to come up with a perfect computer model (global warming?), unfortunately there are people that have their own version of reality and you'll never make them see that their either they are wrong or the circumstances are different.

A perfect example was that I was ready to disagree with an earlier post which claimed that reloading dies are finished to the same surface roughness as resizing dies but after I thought about my response I realized that it might be true, it's not the way I'd finish my chambers or dies but some people might do it that way. I was ready to challenge this assertion because my experience is that my chambers are all rougher than my resizing dies but I suspect that it's not true for everyone.

I will point out that I've never seen one fact mentioned in any of these conversations about surface roughness and that is that the surface roughness of the chamber is more important than the surface finish of the brass (in so far as the general fit and performance of the cartridge case inside the chamber goes). I suspect that a polished case could cause cartridge case slippage in the chamber under a very slim range of situations but in most situations I doubt if the case finish will cause much change at all. Most chambers are purposely finished to some degree of roughness so that the case will stick in the chamber during obturation but I suspect that the perfect storm of conditions would be a highly polished chamber, a highly polished cartridge case, and some lubricant, in that situation I'm sure that just about any powder charge would cause the case to move back in to the bolt face and produce maximum pressure on the bolt lugs. You'd get cracked bolt lugs eventually but your cases would last for a long time.

 

[dickn52]

OP, No it can't be too shiny or too clean.

 

[dolek]

OP, No it can't be too shiny or too clean.

+1

 

[msinc]

I am not aware of any bolt thrust measuring equipment used by Ackley. Many people accept that statement but I don't really think Ackley had any way to prove it other than sticky extraction.

I for one would like to know how such a slight angle change would make a SIGNIFICANT DIFFERENCE in bolt thrust.

Regardless of bolt thrust when primer pockets and case heads expand your brass is going to fail. If you used the right action bolt thrust should not matter.

I don't know that he ever claimed it was "significant" but it is less. It's funny, there are those that believe in the existence of bolt thrust and there are those that do not. I mentioned it in a post on here years ago and got jumped on by several "non-believers". They maintained that recoil was the result of the weight of the bullet leaving the barrel and the gas blowing out behind it, period. When I asked what made blow back actions work and why does everything else have a locking lug they dried up and went away.
P.O. Ackley took the locking block completely out of a Winchester 94 and successfully fired a 30-30 AI round {if I remember right it was an overloaded round at that} out of the rifle with no damage to the gun or himself to demonstrate the concept. I don't believe he had the rifle on his shoulder when he fired it and I get that there was no "measuring device" present, but that is proof enough for me. By the same token, cartridges with long tapers seem to recoil more for their capabilities, e.g. the 300 H&H.
As to the original question, I have tried cases, bullets, chambers and bores every thing from as rough as I could find or make them to as polished and smooth as I could make them. About the only thing I can say is that when the bore itself is polished really fine and you really "put dat shine on it" it will positively copper foul worse.
This will make a few fanboys sieze up and bawl like a fat dog, but I do not use Iosso or Flitz polish or JB Bore Brite because they are a polish and can/will make the bore too fine. JB Bore Cleaner does not. There might be some bores and bullet combos that might maybe work better, but I haven't seen any of them yet. Polish the bore too much and it will copper foul.
Case wise, no difference, bullet wise, nope. Chamber is a little different...on a bolt gun no change, but some automatics are more reliable to extract if the chamber is a little bit smooth. I use Brush Research Manufacturing brand chamber "flex hones" to polish some chambers and have had several AR-10's and Garands/M1A's that needed it to stop jams. I have had several bolt guns with what looked like a rough chamber make the bolt click on extraction, but I was always able to find a small galled spot in the chamber that proved to be the cause and not the general way it was finish machined.

Edit: I just remembered I have an AR-15 made by LaRue. It's an OBR. It has this thing they call "Xtraxn"...some kind of alteration to the chamber that they make big claims about. The rifle is very accurate, but then most AR's are. It has never jammed, but then most AR's don't. Is it a gimmick...I cant say. You can read what they have to say about it here: https://www.larue.com/page/xtraxn-technology-larue-tactical/

 

[ireload2]

Some people also believe in the grassy knoll too.
If you think you need to use the cartridge case for a brake you are using the wrong action.
Rather than reciting the old M94 BS story why don't you get one and fire it from your shoulder with no locking lugs. Locking lugs are there for a reason.
Blow back actions work with wimpy cartridges up to about the .380 in handguns. Why would you even mention a blow back you basically prove the point because there are NO high pressure rifles with blow back actions.

I don't know that he ever claimed it was "significant" but it is less. It's funny, there are those that believe in the existence of bolt thrust and there are those that do not. I mentioned it in a post on here years ago and got jumped on by several "non-believers". They maintained that recoil was the result of the weight of the bullet leaving the barrel and the gas blowing out behind it, period. When I asked what made blow back actions work and why does everything else have a locking lug they dried up and went away.
P.O. Ackley took the locking block completely out of a Winchester 94 and successfully fired a 30-30 AI round {if I remember right it was an overloaded round at that} out of the rifle with no damage to the gun or himself to demonstrate the concept. I don't believe he had the rifle on his shoulder when he fired it and I get that there was no "measuring device" present, but that is proof enough for me. By the same token, cartridges with long tapers seem to recoil more for their capabilities, e.g. the 300 H&H.
As to the original question, I have tried cases, bullets, chambers and bores every thing from as rough as I could find or make them to as polished and smooth as I could make them. About the only thing I can say is that when the bore itself is polished really fine and you really "put dat shine on it" it will positively copper foul worse.
This will make a few fanboys sieze up and bawl like a fat dog, but I do not use Iosso or Flitz polish or JB Bore Brite because they are a polish and can/will make the bore too fine. JB Bore Cleaner does not. There might be some bores and bullet combos that might maybe work better, but I haven't seen any of them yet. Polish the bore too much and it will copper foul.
Case wise, no difference, bullet wise, nope. Chamber is a little different...on a bolt gun no change, but some automatics are more reliable to extract if the chamber is a little bit smooth. I use Brush Research Manufacturing brand chamber "flex hones" to polish some chambers and have had several AR-10's and Garands/M1A's that needed it to stop jams. I have had several bolt guns with what looked like a rough chamber make the bolt click on extraction, but I was always able to find a small galled spot in the chamber that proved to be the cause and not the general way it was finish machined.

Edit: I just remembered I have an AR-15 made by LaRue. It's an OBR. It has this thing they call "Xtraxn"...some kind of alteration to the chamber that they make big claims about. The rifle is very accurate, but then most AR's are. It has never jammed, but then most AR's don't. Is it a gimmick...I cant say. You can read what they have to say about it here: https://www.larue.com/page/xtraxn-technology-larue-tactical/

 

[alinwa]

Some people also believe in the grassy knoll too.
If you think you need to use the cartridge case for a brake you are using the wrong action.
Rather than reciting the old M94 BS story why don't you get one and fire it from your shoulder with no locking lugs. Locking lugs are there for a reason.
Blow back actions work with wimpy cartridges up to about the .380 in handguns. Why would you even mention a blow back you basically prove the point because there are NO high pressure rifles with blow back actions.

Not QUITE true..... a certain 30-06 machine gun comes to mind..... but to make it work you had to use the greased steel cases right out of the ammo can.

Which does help support your point