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

We have several calibers on the same case.

.264 Win Mag
7mm Rem Mag (with pressure spikes)
.308 Norma Mag
.338 Win Mag
.358 Norma Mag

So does anyone know what specifcally is the reason for spikes in only the 7 mm and not the others?

Because perfection only occurs in UNBELTED cases . . . . .

Actually, the same applies to the 308 (very stable) and the 243 (not so much). Oddly, the 243AI avoids the pressure spikes.

Go figure . . . . .

BMT

BTW-Dr. Howell may have an explanation. But, I understand that generally, no one knows--they just measure 'em and then avoid 'em.

BMT

I think it has something to do the throat length of different manufacturers. There doesn't seem to be a definate throat length set for the 7 MMmag.

A rifle with a short or no throat will give much higher pressures in a rifle with a short or no throat that one that is throated properly.

Using loads that are perfectly safe and normal in a long throated chamber will show much higher pressure in a non-throated rifle.

From the experience I have had with them, using a slow burning powder that fills or almost fills the case, such as 4350 or 4831 seems to produce consistant results.

Rifle to rifle variance is not the subject.

So the 243 spikes too. I'm just getting ready to do a 243 8 twist for long range varminting.

Bb

I dunno....I've handloaded the 264,the 7RM,and the 338.Of the 3 the 264 was clearly the "touchiest"; I have blown two primers in my life and one was with a 338.....so.......if I'm getting these pressure spikes with the 7RM(which I've been loading for since the 70's,and in maybe 15 rifles(just a guess),I have not been able to detect it.......it does not make sense that the 7mmWeatherby is not known for this behaviour,and the 7RM is,especially since the two cases have virtually identical capacity.....so it can only be the variations in throating of various 7RM rifles,or the shorter neck somehow playing a part...mnaybe both.....who knows, and personally I am starting on building another 7RM

I have had several 7 RM rifles and loaded for my brothers's as well, and have never had obvious pressure signs.

I was wondering if there could be inconsistencies in the belted head space? If that was or is the problem, then it would not be a problem with once fired cases head spaced off of the shoulder.

On the other hand I did have a used .270 Wby. Mag that would knock at least 4 or 5 primers out of the pocket from a box of 20 Wby factory loads. But I had that rifle re barreled.

I've loaded for several different 7 rem mags and found them to be about as handloader friendly as any cartridge out there . I don't own one at present but still load for 3 different ones I sold .

I think it is the best one rifle choice a man can make .Glad I don't have to !

Lotsa stuff reported that I ain't seen yet .That shouldn't mean nuthin' to nobody but me .

It's already been established [ on another thread ] to some folk's satisfaction that Weatherby ammo kills at both ends .

Reckon I'm just lucky with mine .

I have only experienced one pressure spike and that was using a Mark V rifle in .270 Weatherby Magnum. The bolt froze and required a serious belt with a hammer to open, the primer blew and the velocity broke 3500fps with seemingly little recoil and a reduction in blast. Don't have the load data with me.

I hand weigh all rifle charges.

JW.

Is it possible that modern rifles are strong enough that not everyone is aware when they have a pressure spike? Some shooters might not pay much attention to a slightly sticky bolt lift.

Also, do the competition shooters who use the 22-250 case necked up to .243, do so to avoid the .243 pressure spikes?

AussieGunWriter,

Do they still make Melbourne Bitter beer? It was my favorite while visiting Australia. Unfortunately, it's never been available here.

the spikes with the 7 RM and 7 STW are well known. Sometimes it takes a bit longer of a range to see them and more particular shooters. Read that competition types. Its well known the 7mm is a very LD bullet, BUT its also known that at 1000 especially where it SHOULD shine, it has fliers here and there that loose matches and have NO explanation whatsoever other than that they are out.

Funny enough, when you move down the 7mm scale to say the 284 and less, it becomes very reliable as a projectile even at exteneded distances.

Jeff

I believe so. Victorian Bitter (VB) is the most popular beer there now but it changes every few years.

John

HMMM... That's really bad. Does the 7mm WSM have similar problems in long range matches?

I had a somewhat similar experience with the 7mm RM. The rifle was a Browning A-Bolt, Norma cases, Fed 215 primers and some original H-4831, mostly to check to see if the powder was OK. I was using some Nosler BT 150's. I do not remember the charge, but I was working from the Nosler manual. I was trying to match the 3,150 fps of some Winchester factory ammo. I had cautiously worked my way to that point. I had ten cases left, so I decided to run a final ten shot string to keep the number of firings the same in that bunch of cases. The first five were running right at 3,140, which I thought was close enough to where I wanted to be, and was within the upper limit of the manual data. On shot six, the rifle bellowed and kicked like an angry mule. My first thought was "wow, I better be more careful about how I hold the rifle for the rest of these!". I then looked at the Chrony screen and got a sick feeling in my stomach. It said 3,290 fps. I needed a rubber mallet to open the action. The case came out in one piece, but the primer was blown. The remaining four rounds were broken down and the charge was right where it should have been. I had been using a new RCBS electronic scale, but the weights checked on my balance scale. I have no idea what was maybe wrong with that one round, but I can't say for sure something did not get screwed up with the charge. I do not think so, as I charge the case, visually inspect the powder level in the case and then seat the bullet. I was also weighing each charge.

I have not gone back to the original H 4831. I have always put that down to one of the pressure spikes I had heard about. I was very careful about that powder and the rounds I fired previously with the 150 BT's and what I had fired in the workups did not show any thing abnormal. Except of course for that one round. I will always wonder about that old powder, even though it still looks and smells just fine. I alway figured if it was something with that old powder it would have showed up faster than it did (this was probably about the 20th round), but I really don't know.

IIRC on the below -

A long time ago, when the fire was smaller, Charlie Sisk used to do a bunch of testing with his equipment and pick brains here.

I believe he said he can create it in various calibers/cartridges. He blew off the end of a 338 screwing around with it once. Read this - GREAT thread.

Good Find Teal!

I note that pressure spikes were NOT a problem with heavy for caliber boolits.

This may be why Montana Marine can move a 208 grain A-MAX though a 20.5" 308 at pretty high speeds.

Justa thunk . . . . .

BMT

I've re-read that thread probably 1500 times. Good head scratching stuff there and I knew it was either go thru 10,000 of my posts or 1700 of Charlie's... I went thru his this afternoon to find it.