High pressure signs include ANY of the following:
1) A "puckering" of the primer metal around the firing pin indentation on the primer's "face", but this "sign" can also be caused by an enlarged firing pin hole in the bolt-face or softer-than-normal metal in the primer face. Some "lots" of primers in the SAME brand... and some brands of primers (in general) have slightly softer or harder metal in the primer face than others. But any time you see "puckering", take a "hard look" at your load.
2) A "blown" primer, i.e., the firing pin indentation becomes a "hole" in the primer face, but this "sign" can also be caused by a "soft" primer material or too long a firing pin It is very unusual for a firing pin to be "too long", but it CAN happen. If you're loading less than "maximum" loads and get this "sign", lower your powder amounts, change primer brands and "work up" the load again. If the new primers also have the same thing happen, then the problem is probably too "hot" a lot, back off on the amount of powder you're using or change the type/brand of powder you're using and start working up your load all over again.
3) An inverse firing pin "indentation", i.e., instead of the primer's face having a "dent", extremely high chamber pressure forces the primer material INTO the firing pin hole in the bolt face which, in turn, causes the firing pin "dent" to become an upraised protrusion. THIS INDICATES EXTREMELY DANGEROUS, HIGH PRESSURE! DO NOT FIRE ANOTHER ROUND OF THIS LOAD!
4) Case extraction is much more difficult than normal. Very high chamber pressure causes the cartridge case walls to dramatically expand against the inside of the gun's chamber causing the case wall to "stick" to the chamber's wall. A chamber with rough inside walls can cause the same problem even at relatively low pressure. But if you've fired factory rounds and never had extraction problems, then it's a "sign" your loads are too "hot". Back off the powder load.
This problem can also be caused by the overall cartridge length being too long. Measure the overall cartridge length to insure your cartridge isn't too long. A bullet, which is seated too far out causing it to engage the barrel's lans & grooves when the action is closed, can cause high chamber pressures, too.
5) The primer hole enlarges and won't hold the new primers tight enough. This is almost always a SURE "high pressure" sign... back off your powder load! Discard the case(s)... they're ruined.
6) A slight "bulge" in the diameter of your cartridge case, just above the "head" (the heaviest part of the base of the case just above the case's rim) is also a high-pressure sign. Discard the case(s)... they're ruined.
These are some of the most "common" high-pressure signs. There are possibly I few other's I've forgotten or that are extremely rare, but the above are the most common. If your reloads have one or several of the above "high pressure signs", then you need to "back off" and/or change components to lower your chamber pressures.
In my opinion & experience (based on over 40 years of reloading), IMR4320 rifle powder is a bit too "slow" (too slow a burning rate) for best use with a 150 grain bullet in a .300 Savage cartridge. You are AT "maximum load" (43.5 grains of IMR4320) at this time... and due to the amount of powder, you ARE experiencing a fair amount of what is called a "compressed load" which means you're CRUSHING powder grains when you seat the bullet. In the case of IMR4320, you're crushing quite a few of the powder granules.
Crushing the powder granules CHANGES (tends to increase the powder's burning rate) which, in turn, increases chamber pressure. Many rifle powder's granules are coated with graphite to retard the powder's speed-of-burn (burning rate). When you crush a powder granule, you break it up, increasing the amount of the powder's surface which is NOT coated with graphite... thus INCREASING the "rate-of-burn" and, thus, increasing chamber pressure.
I suggest you "work up" 150 grain bullet loads using IMR4895, IMR 4064 or IMR3031... powders well-suited for such a load in the .300 Savage caliber. You'll probably get slightly "compressed load" at the maximum load of IMR4895 (41.5 grains) as well, but it is BARELY a "compressed load" and you aren't crushing very much of the powder IF you are using Winchester brass which tends to have a slightly greater powder capacity than other brands of brass (thus lowering the internal cartridge pressure thus lowering the chamber pressure for a given amount of powder).
It's been my experience that the best suited powder (most accurate, highest velocity) for any load is the powder that fills the case up to the base of the bullet while maintaining SAFE chamber pressures.
As other posts have wisely advised, if you change even ONE component in a "load", then you need to "start over"... or if you're using the same powder that you're already loaded to "maximum load", I'd recommend you LOWER the amount of powder you're using by at least 5% or two full grains, which ever is greater.
Lowering the amount of powder by 10% has always been the "rule" in handloading when ANY component is changed, but I believe lowering it 10% is excessive when working with a powder you've aleady loaded to maximum with other components while working with the larger amounts of powder such as one often does in center-fire, big game hunting cartridges.
This is NOT to suggest your "starting load" (when trying out a totally new powder) should only be 5% lower than the "maximum load". You should ALWAYS start out 10% below the "maximum listed load" and work up when using a NEW POWDER. But at the lowest levels, you can add .4 or evern .5 of a grain amounts of powder for the next incremental load level until you get within a couple of grains of the "maximum load of that powder. THEN you should lower the amount of incremental change (increase) in your powder loads and limit the increase to .1 or .2 grains of powder per incremental increase until you reach the "maximum listed load" OR until you begin to see "high pressure signs"... which ever comes FIRST.
If you use only a .1 or .2 of a grain incremental increase in the amount of powder you use at the "starting load" level, you're just wasting powder, primers and bullets... as well as your time.
In the above scenario, you're already reached the "maximum" powder load using one specific bullet. Therefore, you've proven that a near-maximim or maximum load is "safe" in your rifle. I'm all for "safety", but I'm also reasonably "frugal" with my components and time.
Changing the load's projectile (aka "bullet") will normally not cause EXTREME differences in chamber pressure, but it can cause SOME changes (increases or decreases) in chamber pressure depending on the how much of the new bullet's body-length is in contact with the rifle's lans & grooves. Generally, the longer the length of the bullet body's contact with the lans and grooves, the greater the chamber pressure because there is greater bullet resistance to moving down and out the rifle's barrel.
Some changes in chamber pressure can also be caused by the make up of the bullet's metal. Generally, the "harder" the bullet's outside metal, the more the bullet resists it's outside diameter from being "grooved" by the barrel's lans. Therefore, a "hard" bullet with a long bearing surface would tend to cause somewhat higher chamber pressures than a "softer" bullet with a shorter bearing surface.
This is why changing the bullet CAN and often does cause some change in the chamber pressure. Chamber pressure is also effected by the brand of brass, the lot # of the brass, the brand and type of primer (magnum or non-magnum) and, as we've just discussed, the brand, weight and type of bullet used.
Even the day's temperature (when you're at the range) can and does cause changes in chamber pressure. A "maximum load" developed on a cool day may be a dangerous over-load on a very hot day, especially if you leave your cartridge laying on the shooting bench in the direct sun where they are heated up by the sunlight.
If in doubt, decrease the amount of powder by TEN PERCENT less than the "maximum" indicated load in your reloading book... and "work" the load back "up" SLOWLY, watching for high pressure signs. This is especially true for a "newbie" reloader. Get some YEARS of experience and/or get with a careful, experienced reloader-buddy before you "go outside the 9 dots" (change any of the "ultra-safe reloading rules").
While not always the case, I've generally found that maximum accuracy occurs at slightly less than the maximum powder load (as in my "hunting load" listed below) IF... IF... if you're chosen the most appropriate, best-suited powder for that specific load (i.e., for the specific bullet (brand, weight & seating depth), powder (type and amt.).
I worked up a deer-hunting load for my Model 99 in .300 Savage caliber that consistently put 3 shots into ¾ of an inch (or less) at 100 yards from a solid bench rest.
My test loads consisted of 4 different powders - IMR-3031, IMR-4064, IMR-4895 and Varget
4 different standard (not magnum) large rifle primers - Winchester, CCI, Remington and Federal
and 3 different brands of 150 grain, .308 caliber bullets - Hornadys, Sierras and Nosler Ballistic Tips
all loaded in once-fired Winchester brass.
All bullets were seated to give the maximum overall length (with bullet) of 2.60 inches, the "book" suggested maximun length.
Working up SLOWLY once I was within 2.0 grains of the maximum load listed in my reloading manuals, I used an incremental increase of 2/10ths of a grain of powder at each new powder load level until I reached the maximum (listed) load... carefully watching for high pressure signs.
My best (most accurate with the highest velocity) hunting load yielded a 3-shot group that had an average muzzle velocity of 2680 fps and measured .191 inches @ 50 yards (and averaged ¾ of an inch @ 100 yards) using a 150 grain Nosler Ballistic Tip, boat-tailed bullet in front of 41.5 grains (a MAXIMUM load) of IMR4895 sparked by a standard large rifle Winchester primer in Winchester cases. This load had a maximum velocity deviation of 19 fps (+9 fps / -10 fps).
My absolute BEST group @ 50 yards measured .112 inches and consisted of a 150 grain Nosler Ballistic Tip bullet with a muzzle velocity that averaged 2647 fps in front of 41.1 grains of IMR4895 sparked by a standard large rifle Winchester primer in Winchester cases. This load had a maximum velocity deviation of just 13 fps (+6 fps / -7 fps). I didnt try shooting this group at 100 yards, but Im sure it would yield an excellent group at that range.
I was extremely disappointed in the performance (or lack thereof) of Varget rifle powder. Since Varget was specifically developed for use in the .308 Winchester and the .308 was developed from the .300 Savage cartridge, logic dictated that Varget might be "THE" perfect powder for reloading the .300 Savage cartridge. However, in "real world" use, Varget never came close to attaining the promised "2740 fps" with a 150 grain Nosler Ballistic Tip bullet. While accuracy was just "ok", the best I could chronograph using a maximum listed charge of Varget behind a 150 grain Nosler Ballistic Tip bullet sparked by Winchester standard large rifle primers in Winchester cases was 2615 fps... far below the 2740 fps reportedly attained by the ballisticians of a popular reloading manual.
Groups were fired using my 3x-9x by 40mm variable scope set on 9x at both 50 and 100 yards.
Incidentally, these groups were fired & these muzzle velocities attained from my 1953 late EG Savage Model 99 lever-action rifle with a 24-inch barrel using a rifle rest and sandbags off a very solid bench-rest on a 78ºF to an 85ºF day (11 AM til 3:30 PM) with very little wind on June 24, 2002.
The final chronographed IMR4895 loads (averaging 2680 fps) consisting of 41.5 grains of IMR4895 were fired when the temperature was estimated to be 84ºF to 85ºF.
Earlier tests in May @ cooler temperatures (73ºF) yielded an average muzzle velocity of 2664 fps using 41.5 grains of IMR4895 with all other components the same as the above hunting load.
I hope this gives you some insight into what you might try in your rifle. Approach maximum loads with caution. The above load (41.5 grains of IMR4895) is listed in my reloading book as a MAXIMUM load. It is also a very slightly compressed load, but did not show any high pressure signs in my rifle.
The Savage Model 99, with its massive breech block, is an extremely strong lever action and is quite capable of handling "maximum loads". Of course, you must realize that "maximum loads" in a .300 Savage cartridge have relatively LOW chamber pressures compared to many other cartridges in the same class.
The SAAMI Average Pressure for the .300 Savage cartridge is only 46,000 C.U.P. (Copper Units of Pressure) compared to similar cartridges like the .308 Winchester (developed FROM the .300 Savage) which consistently use chamber pressures in the 52,000 to 53,000 CUP range. Later Model 99's were chambered for not only the .308 Winchester, but the "hot" .284 Winchester as well.
Good luck with your loads... and "think" SAFETY at all times. :wink:
Strength & Honor
Ron T.
