Hello

I have a question and am looking for an answer or opinions.

Why does brand new brass give approximately 50fps faster velocities versus Older brass fired many times?

Thanks
Mark

First thought are either case capacity or neck tension. Old brass gets work hardened and may not generate initial pressure like new brass; or you new brass just happens to have a little less capacity.

Been loading for 40 years and can't say I have seen that. New brass or old the brass will simply expand to fill the chamber. The chamber determines the combustion space not the brass. As I typed that it struck me that case thickness impacts it as well. Thus different brands different thickness different pressure.

I guess as old brass has flowed forward and trimmed there would be a very slight decrease in thickness resulting in a slight increase in combustion space reducing pressure.

While I have seen impact of different brands causing different pressure never simply by older brass.

That is the only thought that comes to mind.

quote:

Picture of ramrod340

posted 10 November 2014 23:33 Hide Post
Been loading for 40 years and can't say I have seen that.

me2

me 3. If it is the same load, then the "newness" of the brass is a moot point. Now if you were talking a factory vs a hand load, that is another story altogether.

For me, if I see any velocity difference at all, new brass will be a little slower. I attribute that to the energy expended by the gas column in having to expand the new brass to the dimensions of the chamber. When I resize I bump the shoulder only .001 to .002, so my fired brass is very close to chamber size and thus more of the energy is used to propell the bullet. However, that is just a guess on my part as I have done no controlled testing.

On a tight chambered custom rifle I often see no velocity difference between new and fired. On a factory chamber, especially with a belted case, I am not surprised to see a velocity increase with fired brass.

Now I usually don't fire cases more than six times and if I did I would anneal, so I don't what happens velocity wise after six firings. I have seen neck tension change after a few firings, and while that can affect accuracy in a 1K BR rifle, I don't know if it affects velocity.

PAGE 29 http://www.dtic.mil/dtic/tr/fulltext/u2/a456635.pdf New less capacity. Fired + 4%

Since I never use a chronograph to work up a load, I wouldn't know if the velocity is higher but I had a recent experience that might shed some light on the subject.

I've been working up some 308 Winchester loads and had started with once fired Lake City (i.e., military brass). Everything was going fine until I used the same load in some brand new nickel plated Federal cases. On the first shot, I had a blown primer indicating a significant overload. I believe the reason was decreased case capacity as alluded to by 243winxb. I've since reduced the load by a couple of grains and no more blown primers.

quote:

Originally posted by Grumulkin:

I've been working up some 308 Winchester loads and had started with once fired Lake City (i.e., military brass). Everything was going fine until I used the same load in some brand new nickel plated Federal cases. On the first shot, I had a blown primer indicating a significant overload. I believe the reason was decreased case capacity as alluded to by 243winxb. I've since reduced the load by a couple of grains and no more blown primers.

Different brass could, and does constitute a reduction in capacity because of a difference in thickness. But using the same brass twice is not the same comparison. By the time the pressure peaks with new brass, the case will have been expanded firmly against the chamber walls just like it would the 2nd time around thus yielding an identical capacity. IE; there will be no difference.. The only difference would be from the gradual flow and thinning of the brass which would not likely be enough to see on a chronograph..

quote:

Originally posted by Grumulkin:

I've been working up some 308 Winchester loads and had started with once fired Lake City (i.e., military brass). Everything was going fine until I used the same load in some brand new nickel plated Federal cases. On the first shot, I had a blown primer indicating a significant overload. I believe the reason was decreased case capacity as alluded to by 243winxb. I've since reduced the load by a couple of grains and no more blown primers.

The way I'm reading this you change a component of the load and didnt work it back-up.

Weigh the cases and see what you get.

Here's a couple examples of what different cases can do.

Load #1
200 gr Nosler Partition
C.O.L. 3,07”
Norma 203-B
Case: Headstamp; Winchester 8x57 Headstamp. Case weight 160.1 grains
Primer: WLR

46.0 2395fps
47.0 2442fps
48.0 2508fps
49.0 2557fps (no pressure signs.)


Load #2 (Note that a different case was used)
200 gr Nosler Partition
C.O.L. 3,07”
Norma 203-B (same lot)
Case: Headstamp; WW 8mm Mauser Headstamp. Case weight 178 grains
Primer: WLR (same lot)

46.5 2495fps
46.8 2510fps (my settled on load.)
47.5 2563fps (max with pressure signs.)


150gr Speer, IMR 4895, 3.02 OAL, CCI200 Primer, XXX Case

48gr 2578fps Winchester 8x57 Head stamp 160.1 case weight
48gr 2642fps WW 8mm Mauser Head stamp 177.0 case weight


150gr Hornady, H 4895, 2.95 OAL, WLR Primer, XXX Case

48gr 2678fps RP 8mm/8x57 Head stamp 174.8
48gr 2732fps PMC 8mm Mauser Head stamp 187.9


Ruger #3 30-40 (Not for grandpappy's krag. No charges listed.)
Load #1
150 gr Sierra BT
C.O.L. 3,08”
Big Game
Case: Winchester Case weight 170.1 grains
Primer: WLR

XX.X 2720fps

Load #2
150 gr Sierra BT
C.O.L. 3,08”
Big Game
Case: Remington Case weight 160.8 grains
Primer: WLR

XX.X 2660fps

quote:

Originally posted by Wstrnhuntr:
Different brass could, and does constitute a reduction in capacity because of a difference in thickness.

A big hell yes.