Help me look for pressure signs (7mm-08)

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Next up are 160 grain Nosler Partitions over 45-47 grains of Big Game, in 0.5 grain increments (Left to Right in the image). 46 seemed to be the plateau (2725 fps) with 46.5 and 47 grains actually decreasing in velocity (2710, 2715).

160 NPT 45-47g BG.JPG
 
Third are 160 Partitions over 47, 47.5 and 48 grains (L to R) of H4350, giving me 2688, 2699 and 2721 fps.

160 NPT 45-47g H4350.JPG
 
160 NPT 47g IMR 4350.JPG Finally, I stuffed 47 grains of IMR 4350 into a case (nearly to the mouth) and dropped a 160 Partition in just because. I have a tiny amount of IMR 4350 on hand, and wanted to check velocity vs. the H4350. The 47 grains of IMR 4350 gave me about 30 fps. more velocity than the H4350, and Hodgdon's load data does show faster speeds from the IMR.
 
So far, Big Game is acting a lot like H4350 in my rifles. I had read that Big Game is outstanding in 7mm-08 under 120-grain NBT's. This is what I got out of 120-grain Sierra Pro Hunters today at 3000 fps.

IMG_0742.JPG
 
I'm seeing what appears to be some slight ejector marks on the heads of a few, not all. 3rd 160's middle one between the stars. This is one of the first indications that your getting up in pressure. Need to look closely with better light and see if it's present on all. Noticed it on the first group too, first row, 3rd one. Primers still look good, starting to flatten but nothing to worry about. May need to back off just a touch 0.1-0.2 gr and it may clear since it's not showing up on all.

Shooting at those loads my shorten the life of the brass a little.
 
Blue, thanks. I noticed the same and have backed off a bit from that load. Shot for groups this evening and it appears that (no surprise) H4350 is the winner both in pressure and accuracy.
 
Just a little FYI.....you can't tell much about a load's performance based on one shot. Granted a severe overload may let you know in one shot but regarding velocity or pressure signs in the normal range you need an average based on several rounds. It isn't at all unusual to get a higher velocity from a lower charge as you did. Averages and level of uniformity tell a truer tale.
 
I have some pretty old reloading manuals where the data is measured in CUP, then some of the latest data that was developed with strain gauge measurement and pretty much without fail the later data is milder than the older versions. Problem with CUP is it kind of averages out the pressure being applied to the measuring slug and can miss rapid spikes that the strain gauge will see. So if you are interested in pushing things...getting strain gauge data would seem to be important.

Plus add in the fact that many of the published loads are NOT maximum and were limited to where they stopped for other reasons. Accuracy rapidly dropping is one, as well as velocity consistency where adding more powder starts to make things get flaky so they stop. So max pressure could very well not be involved with the data at hand...only way to know is to read what the developers report as to how they came to the numbers.

A load that shows CUP pressures to be within limits could have pressure excursions well above the maximum which will normally not instantly blow up the gun, but repeated firing could very well do damage to the chamber. The strain gauge measures how much the chamber expands...so if the number is too high you can pretty much bet that the chamber is experiencing something that is not good for it and in time could cause problems.

Being older and hopefully wiser now, I'd stay within published strain gauge numbers and if they're not available.....the equipment isn't all that horribly expensive and would be the way to go if you decide to push beyond published data. With the myriad of variables available in both the rifle and ammo it's pretty near impossible to exactly duplicate what the load developers did and hopefully they added in a bit of fudge-factor just for safety sake. If the rifle is accurate...50 fps at 400 yards won't make much difference at all and is questionable whether the risk/reward of pushing it harder worth the effort IMHO. Good shooting and cautious loading...well done.:)
 
Thanks Stumper. I realize that but it was all the IMR 4350 I had left so I figured I'd at least try it.

If the rifle is accurate...50 fps at 400 yards won't make much difference at all and is questionable whether the risk/reward of pushing it harder worth the effort IMHO.

I agree. Was hoping to achieve 2000 fps. at 400 yards because it's a number I can easily recall when I'm out of breath at 10K feet and need to make a split second decision. I know that under stress, your brain needs simple go, no-go guidelines that require little to no thinking. Having said that, I'm pretty darn sure a 160-grain Partition traveling 1950 fps. will still put a number on an elk so long as it's put in the right spot. ;)
 
It looks good. I believe could even push a bit more for hunting loads but brass will not last as long.
So around that pickup what groups best and test again when it gets warmer to see if you need to backout
specially with big game. ...just the normal consideration to get the spreads with temperature variances.

So pickup the most accurate and forget about a few fps up or down. I mean, taking other individual circumstances
in consideration obviously.

As I told you and you can see max charges from books and manuals are a good reference but they are all over the place. There are so many variables and it looks many loads are written by lawyers and not engineers.

There is no substitute for a good process, close observation and taking notes. Also your caliber and micrometer are your best friends and we assume nothing.

You know, we follow Murphy's law at all times.

Great job man!.
 
I'm seeing what appears to be some slight ejector marks on the heads of a few, not all. 3rd 160's middle one between the stars. This is one of the first indications that your getting up in pressure. Need to look closely with better light and see if it's present on all. Noticed it on the first group too, first row, 3rd one. Primers still look good, starting to flatten but nothing to worry about. May need to back off just a touch 0.1-0.2 gr and it may clear since it's not showing up on all.

Shooting at those loads my shorten the life of the brass a little.


Any sign of head stamping on any cartridge in that load lot is a fortunate warning to back down and work from there. For that partial moon to appear, the brass has to have reached a temperature adequate to allow/cause the brass to flow as a liquid.
 
Are you getting any case stretching? Check the interior of your case wall near the web; fashion an "L" with a wire and see if you can detect a groove or ring inside the lower 1/4 of the case wall.
 
Any sign of head stamping on any cartridge in that load lot is a fortunate warning to back down and work from there. For that partial moon to appear, the brass has to have reached a temperature adequate to allow/cause the brass to flow as a liquid.

Hi,
One can get extrusion and swipe marks in the brass and not be necessarily related to dangerous pressures.
Even factory ammo might show this and could be more a condition of the gun and/or bolt than anything else.
For example if the ejector plunger hole has not been properly chamfered or the chamber doesn't provide all the support the brass needs like a polished chamber that is a mistake
or a combination of these two and other factors.
This results in a high impact (obviously) and things get imprinted in the brass but no other signs that might indicate dangerous pressure is present.
It is not unusual for brand new service ammo to show plunger marks specially auto-loaders.

Lake city ammo even slightly flattened that is found many times with service ammo.

upload_2018-1-21_20-28-43.png


Again if there is trouble the signs normally come in twos or threes at the time.
If one has blow by or extreme extrusions or even blown primers that is a big NO NO.
I had brand new Hornady factory match ammo blow the primers on me and we know that is a huge problem.

My point is that we need to look at the whole picture and including brass, primers and the gun too / cambering situation too.

Only the OP can get close and inspect with care taking everything into consideration. So far I have not seen anything crazy
but only him can know paying a lot of attention to the detail. Measuring the base of the brass with the micrometer is a great
way to see if in fact there is deformation at the base like I believe you are suggesting as a possibility. Bras will always give a few
thousands through its serviceable life but because the base is compromise normally the pockets go first or incipient head situation
if one is over stretching the brass.
That is why I always headspace my bolt guns with the brass produced with my dies and the ammo I normally shoot.
For those who do not have a choice on selecting head-space, one can adjust dies and neck size only too obviously.
 
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