Rifle cases and pressures

[big rifle man]

Dr. Mike, A question that you might be able to shed some light on. I'm using Norma cases for my .300WSM and after about four firings I start getting bright marks (pressure signs) on the case heads. The load is the same and nothing else is changed. I purchased a Hornady case annealer unit and after annealing the cases I fired them again and the pressure signs disappeared. The most obvious answer would be a change in neck tension but I'd like to hear your thoughts.

 

[DrMike]

BRM,

Without examining the cases, it is impossible to make a definitive statement, but perhaps some on the forum can make an educated guess. Perhaps you could shed some light on the question by responding to the following questions.

Are the bright marks concentric (or partially so) or a smear emanating outward from the primer pocket?

Is there a bright, concentric ring at or near the web of the cartridge?

Are you aware of any pressure signs other than these bright marks (flattened primers, soot in the primer pocket, sticky bolt lift)?

How many times has the brass been trimmed before you anneal?

Is case stretch measurable and significant with each firing?

In what rifle are you firing these cartridges? Is this a custom rifle or a stock rifle? Who was the manufacturer?

Early chambers for the WSMs were cut in such a way that they allowed for excessive stretch that left a fair amount of brass deposits on the bolt face of many rifles. I do occasionally see this same condition even on newly manufactured rifles.

I have observed concentric rings with Norma brass after a few firings, more so in my 300 WSM than in my 270 WSM. I see similar marks on other brass in the WSMs (especially Remington brass in the 270 WSM and in the 300 WSM); generally, it is more an interesting observation than a serious concern. I have related this phenomenon to work hardening of the brass.

 

[rick smith]

Neck sizing, FL or PFL?Rick.

 

[big rifle man]

Rick, partial resizing. Doc, I am seeing ejector marks on the head. There are no rings and the rifle is a five year old Kimber Montana. Accuracy with the load is excellent. I trim after each shot and the case stretches no more than 2-3 thousands. The load is 1 1/2 grains below max. I notice after 4-5 shots the trimming is more difficult (work hardened brass?). I tried new Winchester brass (fired twice so far) and didn't have a problem. I realize case capacity may also be a factor.

 

[DrMike]

BRM,

It certainly sounds as if the brass is quickly work hardened. If you worked up your load in the Norma brass, you should have already demonstrated that case capacity is not a problem. If you simply selected a charge, it may be beneficial to work up to the charge you are using as case capacity can indeed vary between different manufactured brass and even between different lots. I'm inclined to avoid trimming as frequently as you indicate, especially when you say that the case stretches no more than 2-3 thousandths. I note that you mention that the neck becomes difficult after 4-5 shots and the extractor marks appear after 4 shots. Everything does point to work hardened brass. Annealing will address this issue. In the interim, you may want to ensure that you are not over charging the case by working up a load if you haven't already done so.

 

[rick smith]

Agree with DrMike on this. After I do an initial prep to new brass I fire the brass, neck size and fire again. Keep check on trim length and trim only when the brass reaches max length. PFL only when the cases start to get snug to bolt closure. Depending on chamber/load I normally get five or more firings before a trim or PFL is necessary.Rick.

 

[Scott Spencer]

I fire the brass, neck size and fire again. Keep check on trim length and trim only when the brass reaches max length.

I do the exact same thing as Rick. Maybe I am lucky but I don't have to do a whole of trimming on my cases.

 

[DrMike]

Unless the chamber is grossly out of spec, it should not be necessary to trim until after three or more firings, depending on the cartridge and/or load. I either PFL size or neck size, which means that I need to set the should back after three or so firings.

 

[big rifle man]

Guys, I try to stay away from neck sizing as this rifle is strictly for hunting and I want to insure 100% chambering.
I went to the range yesterday and fired the 10 winchester cases for the fifth time. I found no signs of pressure and the brass still seems very workable. Doc, I worked up the IMR4831 load this past winter when temps were in the 60s-70s. The present temps are in the high 80's low 90's. I realize heat could be a factor but again the winchester cases work fine. I did notice that after the fifth partial resizing on the Norma cases bolt closure is becoming tighter. I'm beginning to think its the make up of the Norma brass. which is doing something to change dimensions and therefore pressure. I guess the easy answer is to use the winchester brass but Norma is supposed to make high quality brass which was my initial reason for using it. In regards to the need for trimming I guess I'm a bit fussy in that respect and like to see everything the same length.

 

[DrMike]

FWIW, I don't use brass more than three times (virgin and twice resized) for hunting rounds. After that, regardless of how good the brass appears, I relegate it to load development. The hunt is too important to risk a problem in the field. The temps you mention should not give you significant pressure problems. Had you developed your load at 0 and were now shooting at 90, I would say that you could have a problem, but it would be unusual to have a significant pressure differential given the scenario you describe. Again, if Norma brass is available, I use it almost exclusively for hunting (270 WSM, 280, 7mm RM, 300 WSM). I have only recently begun using Nosler brass, which I understand to be made by Norma. Norma brass has served me quite well heretofore. The reason you had difficulty closing the bolt after the fifth partial resizing is likely that you needed to set the shoulder back a couple of thousandths. You will eventually observe the same problem with Winchester brass if you fail to set the shoulder back after a few instances of partial resizing. Since you are using these rounds strictly for hunting, you might wish to full length size every time, relegating the brass to load development after a couple of times sizing it. Consequently, I've had very good success in my 300 WSM (and in a number of others) with IMR4831. It has a good burn rate for that cartridge.

 

[rick smith]

Having hunted with my reloads for over 30years and having used the sizing method I described above, never had a problem with chambering. By going to the range almost every weekend from Jan through August, I know each rifle and exactly the condition of the brass for that rifle. If the brass is getting snug to bolt opening/closure, then I put a note in the box to PFL on next loading. All my rifles are for hunting so they have to be ready. I have used brass for over ten loads in several rifles and never a chambering problem. You absolutely do not have to FL or PFL on each loading just to be sure they will chamber.Rick.

 

[big rifle man]

Thanks Doc and Rick, I think I will err on the side of caution and use either new or once fired brass for my hunting loads. With a $4000.00 trip coming up the last thing I need is ammo problems in the field. I did full length resize the Norma brass and found that all bolt closure problems were eliminated. As I mentioned previously the annealing process did eliminate what I thought were pressure signs. Thanks again guys.

 

[sithlord6512]

Unless the chamber is grossly out of spec, it should not be necessary to trim until after three or more firings, depending on the cartridge and/or load. I either PFL size or neck size, which means that I need to set the should back after three or so firings.

Do you PFL resize or neck size your .300 WSM brass for hunting loads and/or your brass for reloads? I have read a number of posts that suggests FL resizing in not always necessary for the .300 WSM (and other calibers), whereas, the general advice in popular magazine articles is to FL resize your hunting brass.

If I neck size my brass for hunting rounds (I plan on following your practice of limiting my hunting brass to those fired 3 times), is it enough to chamber the neck-sized empty brass and see if the bolt closes easily to determine whether or not I need to FL resize my hunting rounds? It seems that for best accuracy, I should neck-size only if I can, but of course, I would rather want be 100% sure my hunting rounds will chamber when needed.

 

[DrMike]

I use a Forster Neck Sizing Die to neck size my once fired brass, although I have used both RCBS and Redding Full Length Die to partial neck size once fire brass in the past. I do use virgin Norma brass on which I true the necks with a Sinclair expander mandrel. I do recommend to people who ask to full length size hunting ammunition, simply because if it should fail to chamber, or chamber with resistance, it is possible to miss the only opportunity at trophy game. I do cycle my loaded ammunition to ensure that it works in my rifle, however.

 

[Divernhunter]

I am a firm believer in new brass only for hunting loads(big game) and quality first run bullets. Heck that is the cheapest cost of the hunt even if it were several dollars per round. I use fired brass for range work or fun shooting. I also get so use to picking up my brass that I find myself doing so when I am hunting which can be a bad thing.