Home Forums Hunting & Shooting Ask The Gunwriters 7 RM and PRESSURE SPIKES

7wsm held the mile record group and may still, I have a link to some of that info somewhere if its still valid.
It would be my choice if using a 7mm for long shots for matches. That being said I was stubborn and just had a 7x300 wtby built to test the waters. So far its been a headache with 2/1 and 4/1 groups.... 2 good one way out.... but in fairness it had a crummy stock to start with, first run was with e tips which I found AFTER the fact had headaches of their own...but I'm still going to play with... and now has the correct stock BUT have not had time to bed it. It shot a couple of 1.5 inch groups today at 200 but thats not good groups...

Jeff

Teal,
Thanks for posting that old thread, I'll probably read every word of it because I would really like to understand this.

I was probably lucky I didn't blow myself up back in the 1970's. I was maxing out the old Hornady loading manual with 139 grainers in front of 73 grains of the old H4831.

Amazing the number of threads I've read here since '03 and I can recall that one.

I still am thinking that the fact he could punish that brass so hard and not have it fail before the barrel - the 2nd spike was saving his action/face IMO.

Am not brave enough to wonder if there is a connection to the WBY "issue" breached on the fire not so long ago....

Seems to be that light for caliber with high load density = second spike, regardless of caliber/cartridge. (If I did the math correct)

Also considering the short amount of time a bullet is actually in a barrel - it's amazing we measure anything at all or that it can swing up and down like that in 22 inches...

rost: Back in th 80's I was talking to Butch Searcy and asked how come 7mm is not more popular as a match caliber...he said 7mm's throw flyers at long distances...now he never mentioned what you did about the smaller cases behaving better,just made that observation FWIW.

The pressure you experienced was NOT due case design or caliber. I have shot thousands and thousands of rounds through all matter of custom and factory 7mm mags. Yes, it does spike, but not to the level you experienced. There has been a lot of testing and experimenting with this round and it does spike, but is far from dangerous in any way. The "spikes" just don't go that high. Generally a chronograph is the only way to see the spikes. Most spikes run about 15-35 fps. or 500 to 1,000 PSI. Not catastrophic by any stretch and precious few people would ever notice. It has more to do with the type of powder, ambient temperatures, load density, primer and bullet then anything. Even changing primers can and will cause spikes in non magnum cartridges, but show more drastic pressures in belted cases. What typically causes pressure spikes is the brass. Weigh your brass and you will see what I mean. We worry about 1/10 of a grain variations in our powder charges, but 5-10 grain variances in brass are VERY common. That variance increases or decreases powder load density, which causes pressures to go up and down accordingly. You can't visually detect case capacity or case weight. Every brand is completely different lot to lot. Load a Winchester case with xx grains of your favorite powder, then a Remington case with the same charge and same bullet. Velocities will vary greatly. I have seen 75 fps differences in simply changing cases and nothing else. Mix one case accidentally with a brand of less case capacity and pressures go up quick, often blowing primers, especially if you are already on the ragged edge of supposedly "safe" loads. There are SOOO many variables that can't be seen. Perhaps you had some crud in the seater die that pushed the bullet deeper into the case, or didn't allow it to seat deep enough and it was touching the lands, which makes pressure climb FAST! Perhaps the chamber was warm from shooting a 10 shot string (more like burn your fingers hot). Chamber and or shell temperature can cause catastrophic pressure spikes. Perhaps the primer wasn't seated correctly or flush. Who knows, but stuff happens when you load. To say the .243 and 7mm are splikey is true, but not nearly to the level that anyone would ever be able to detect. So go forth and love them both. Both are absolutely superbly accurate, fun and SAFE! Flinch

Flinch - Charlie was seeing an initial pressure reading of the neighborhood of 60k with secondary spike of over 90k. 12 fps deviation.

IIRC. Based on Charlies experience, I would simply run heavy for caliber and be happy. (something I prefer anyway)

There was a WHOLE lot more to his equation than just case design and pressure spikes. The brake DEFINITELY had something do do with it, since that is what blew off. I would say the unburnt powder or part of it was acting like a bomb in the recessed brake area. Perhaps copper was shearing off the bullet in the break area. Too tough to call, since I wasn't there, but the test was too simple and basic to quantify good data. If it were simply physics of case design, no Mfg. would be loading such a dangerous round. 30,000 PSI would cause a lot or rifles to "nuke". I take his findings with a grain of salt. That isnt' to say he didn't know what he was doing, but there isn't enough data to work off of. Flinch

For me - the fact he can do it with about any cartridge by loading high density and light for caliber - regardless of that one 338 tells me there is something more. It's not strictly case design but interior ballistics and some voodoo with properties of hot gasses. IMO. Plus a secondary pressure spike in the barrel of the 7mm Rem Mag is one of those "worse kept secrets". Not all of them have a brake.

Really wish he would chime in and let us know what else went on - after.

A few facts have always bothered me about this report and many
of those following it. Why did the muzzle break blow off when the
pressure spike was measured at the breech?.
The pressure spikes are read with a strain gauge, barrel bending
moment looks the same ( read "Vaughns Rifle Accuracy Facts").
Is there any data taken with a Piezo pressure transducer ?.
Good luck!

I just don't understand how a 7RM is noted for this,and many other small bore magnums that push light bullets at high velocity are not....I've pushed 120 TTSX from a 7mmDakota at 3550,and 130TSX from a 300 Win Mag at over 3600.You never hear anything about them.......can't figure how a 7 RM gets singled out.

Am I missing something here?

Whether or not it is yet explainable, with modern equipment it is measurable. Same for the 243 but not the 308 from whence it came.

Interesting that the 7mm STW and 7mm UM are both SAAMI pressure limited to 65K. You would think any issue with pressure spikes in a RM would be multiplied several times over in these two cartridges.

I have had two dozen Rem 700 7 Mags since the 70's, reloaded for all of them, I have three custom 7 STW's right now.

I have shot 120's, 140's, some 150's and 160's mostly in the 7 Mags, and the 120's and 140's in the 7 STW's.

Something must be wrong with me, I have not had pressure spikes. I shot R#22 with the 120's, IMR 4350 with the 140's, R#25 and 4350 with the 150's, and IMR 4831 and 4350 with the 160's.

In the 7 STW's, I shoot R#22 and IMR 7828 with the 140's, and R#22 with the 120's.

I have been shooting the 7 Mag since 1978 and the 7 STW since 1990.

I don't think that pressure spikes are applicable to the powders and bullet weights that I have shot. Spikes must have something to do with heavy bullets and slow powders.

I did some testing a few years ago on brass hardness. I noticed that some bullets seated much harder than others in the bullet seating operation. One of those things that make you go, Humm......

So, other than the obvious that the brass needs annealing, wazz up with brand new brass when one bullet seats harder than the next. I kept up with the bullets that had a firmer grip on the bullets, and those bullets ended up being flyers out of the group.

Next was to have new brass Rockwell tested, Federal, Remington, Winchester, PMC, and Weatherby. Brass had quite a variation in hardness within the same brand and about a 12% average swing between the brands from softest to hardest. PMC brass was the hardest, Winchester, Rem, then Federal, then Weatherby.

I kinda' like BMT's answers the best.....

Despite the incredible amount of knowledge on these handloading sites, pressure spikes are rarely written about--but yet it is allegedly one of the most important factors when SAAMI determines max pressure for a cartridge.

Interestingly, many (but not all) of the 7mm's exhibit moderate to large pressure spikes--but it's not likely to have anything to do with caliber.

Remington reduced the powder charge in their ammo in the late 70's and again in the early 80's. A good family friend used to own a tool and die manufacturing company in Illinois, and his primary customer was Remington. He was a gun enthusiast, and a fan of the 7mmRM and M700's. He had access to the Remington ballistic labs and indoor shooting range. He said the engineers finally described the spike phenomena as "inexplicable" in the 7mmRM.

In the mid-90's, a couple friends and I had access to a pair of Oehler Ballistic Labs, and we glued strain gauges to a bunch of rifles (we bought gauges by the carton!). We weren't entirely aware of the whole pressure spike thing, and when we saw spikes on our graphs, we initially chalked up to our handloading techniques. Eventualy we learned more about pressure spikes, and some cartridges certainly showed more spikes. Of course, some loads undoubtedly were probably more prone to spikes than others.

For example, a couple of 280R's we had hooked up to the M43 showed a fair amount of pressure "spiking" with a variety of loads--which is why I kinda' cringe when the 280 fans want to load to 65k psi.....I think there is good reason for the SAAMI max pressure.

This could be a interesting thread.

Casey

A 280 spikes but the 270 and 25/06 don't. Doesn't seem to be related how overbore a cartridge is.

Someone mentioned that the 243 spikes, maybe it is any even metric caliber that has this problem, anyone know if the 8mm RM spikes? lol

Does rifling twist have something to do with it? The 6mm (or 244 I think) was introduced with a slow twist, was Remington trying to solve a perceivable problem the 243 had?

After reading the thread regarding Charlie Sisk's testing that was posted on this thread by Teal, I think you are right about it not likely having anything to do with caliber.
Charlie was getting secondary spikes with various calibers by using small for caliber bullets with slow case filling powders.

I am still not clear on one point, given that spikes can occur in many calibers, are they more likely in the 7 RM or was the 7 RM perhaps the caliber some lab technician was using when they first started discovering these spikes?

I'm having the impression that the 7 RM would be spike free using a 160 bullet.

Does anyone know or remember who or what was the source of the original rumor in regards to the 7 RM pressure spikes?

I have yet to hear a good explanation for pressure spikes--my info (although it's been a while) suggests pressure spikes haven't been adequately explained.

It's important to note that spikes don't always occur frequently for a given cartridge or load.

In your Dakota, the spikes may be infrequent, may not go over 70k psi, and you may have a more robust action and barrel, or the spikes may be very small and not important to begin with. I doubt the Dakota cartridges have been subject to the same scrutiny as the 7mmRM.

Some BR shooters running the 22PPC's have demonstrated their loads may be running 70K psi or more! But they are running very large diameter actions and large diameter barrels, so they may not be "over pressure" for there firearm and cartridge, and consistent pressure curves are one their main goals.


Casey

The SAMMI pressure for the 8 mm Rem is 66K psi. So using the spike logic, that deductively says that the 8 mm Rem doesn't spike with regularity. It is only loaded with 200 gr. and up bullets by Rem. and I believe they are the only ammo. supplier and they under load it to about 62 K psi.

I have only loaded for 2 big 7's and only with 160 and 175 gr. bullets and case full powders. I really think that light bullets cause some sort of "fluffing" in the powder charge because they accelerate quickly and disrupt the flame front/burn pattern.

As the powder burns the powder mass also moves in the case. I could see a situation where the flame front would develop a cloud and a hole in the powder mass that would suddenly get a lot of surface area and burn too fast, ie. gas spike, because of the increased surface area.

The real problem is that to really understand the phenonema one would need to film at very high speed the burn process like they do in engine combustion chambers. The pressure in the chamber makes that almost impossible. There has been a lot of burn work done in engine combustion chamber/fuel system design that would be applicable here if the pressures weren't so high.

From another thread, this relevant comment on the current question by Mule Deer:
"Some comments on the latest batch of comments:

1) Actually the .243 Win. and 7mm Rem. Magnum do not exhibit pressure "spikes," at least not often. What they do generally show in pressure labs is wider pressure variations--both high and low from average--than most other cartridges. These might amount to a total of 12,000 psi, or plus-or-minus 6000 from average, rather plus or minus 3000 in some other rounds.

These variations aren't enough to be noticed by the home handloader. But these wider pressure variations are well known among lab ballisticians.

2) I once had a Rem. 700 rebarreled to .270 with a 26" barrel, just to see what would happen. With the fairly standard load of 60 H4831SC and the 130 Hornady Spire Point, this rifle got 3350 fps or so at the muzzle, with very fine accuracy. If I subbed Nosler Partitions with the same powder charge, the velocity dropped 100 fps or so. Why I dunno, but that is still pretty darn fast. It was easy to get 3150+ with several 140s. So the old '06 Improved does pretty well in a longer barrel. Granted the 6.5mm bullets have better BC's, but as Mark pointed out, with dots and/or turrets, so what? Out to 500 or so the minor differences don't matter much at all. Now if I were building a 1000-yard target rifle, it would definitely be a 6.5, because of wind drift.

3) Somebody mentioned switching to a .25-06 after years of shooting a .264 and .270, and killing a deer real sudden at 200 yards. Well, gee, I have done the same thing at 200 yards or so with a .257 Roberts, s .243, and a .220 Swift. And all three kick even less than a .25-06! Amazing what we discover when we try different rounds.

I have killed various deer and antelope and similar-sized game out to 350-450 yards with the following cartridges: .257 Roberts, .25-06, .257 Weatherby, 6.5x55, .264 Win., .270 Win., 7x57, .280 Rem., .280 Remington AI, 7mm SAUM, .308 Win., .30-06 and .300 WSM. Have also killed a pile of deer and antelope, not quite so far away, with a list of cartridges about as long. Hsve also killed a few larger animals, including caribou, elk, moose, and various African beasts, but only with cartridges down to 6.5mm.

What I have noticed is that when I shot them right, the animals died pretty darn quickly, regardless of which cartridge was used. There were slight differences in trajectory, but with about the same muzzle velocities not so much that it made any real difference as long as I was aware of them. In other words, the cartridge didn't make nearly as much difference as all the advocates of this or that would like to believe. Neither did the bullet, within reason--and for sure the make of the bullet has a lot more to do with penetration than any differences in sectional density.

4) What does make a difference to a lot of shooters is whether they can buy ammo at a reasonable price, since not everybody is a cutting-edge handloader with time to argue about such tiny differences in everything. And I have never been in any store on the several continents I've hunted where .270 ammo wasn't available. Even if they only stocked a dozen kinds of ammo, .270 was always on the shelf, even in Alaska and Africa."

There is another comment below the above here:
http://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/2604501/6

BE CAREFUL - the above is on page 6 of 7 in a hotly debated thread about infinitesmal gack that happened almost a year ago, so watch that you don't get sucked into it.

Another and perhaps more relevant response.

https://www.24hourcampfire.com/ubbth.../true/Re_I_d_Like_Some_Proof#Post1952472