Questions:

So factory loads must be pretty weak, just in case?

Treat each rifle independently don't shoot same loads in multiple rifles unless really conservatively loaded?

Barrel and or chamber specs all over the place causing this issue?




I've always read this about the 7 mag and I thoroughly trust the author so would probably be very diligent to segregate ammo if owned multiples.




Thoughts?





Mike

I have five 7mm Rem mags. I load 64 grains of IMR 4350 with a 140 Ballistic Tip for all of them. I need to get a chronograph to check velocities for the heck of it. This has made me curious. Two 700’s, two Sako’s, and a Kleinguenther K-15.

I have a Rem. 7mm magnum purchased around 1992. I have always found it necessary to go 3 to 4 grains over book maximums in order to come close to the velocities forecast in the loading manuals. Brass always lasted for many reloadings, no other problems experienced.

Jim

It wouldn't be so odd to me if it wasn't only ever mentioned about this particular round.

Mike

243 gets some mention.

Never had any issue with either, but I have only loaded for 2 or 3 rifles in
each.

69 grains of Reloader 26 under a 162 eldx gives less than 10 FPS difference between two Tikkas.

I've never really wanted a 7 mag but know where there is a fairly nice, push feed model 70 with the plastic stock appears 24 or 26" barrel for a price of what the action alone is worth.

Kinda peaked my interest.


Mike

I always suspected some of this was due to when factory loads were loaded with 7828 powder the same for the 243. I have never had any verification of this other than anecdotal experiences of others. Of course chamber differences and throat wear are additional causes. I have shot out one 7RM and probably didn't shoot more than a couple boxes of factory loads in it so almost no testing on my part with factory fodder. If it was case geometry then the 264 Win. should show the same variation, but the only inconsistency I have heard of with the 264 was due to two diameter bullets when compared to conventional single diameter bullets.

Load data for the 243 Win. and 7mm Rem. magnum being more conservative than in the past isn't because of differences between individual rifles.

I had a Savage 7 mag for a long time that was a hammer. I was using original Barnes X at the time. I had the 160 loaded to around 2900. I bought another Savage and that barrel/chamber? was so much tighter, that I had to back off the load by five grains to quit seeing pressure signs. I went back to Interlocks and Partitions, with the load tailored to the newer rifle and never had another issue.

The best eye opener for me regrding the 7 mm Rem Mag was Ken Water's Pet Loads from January 1981. He referenced a couple of things that he thought were common to the cartridge that affected it round a lot. This was the first round I loaded for back in 1973, and had me scratching my head for quite some time. I have had several rifles (five if memory serves) and they have all been unique from the others. According to Waters there were (as I saw it) a couple of things that affected it. One he pointed to a wide variation in case capacities of different headstamps of brass, secondly he indicated a wide variation in chamber dimensions, as the critical headspace dimension was the belt, there seemed to be less regard for tolerances at the shoulder. Whether or not any of this still holds true, I don't know, but every time I load for a different 7 mm RM, I use a box of factory ammo and my chronograph as a reference point, along with loading notes and good data sources. So I took from that that if you had a particular 7 RM with an oversize chamber and a case with greater internal dimension than another 7 RM, they might be considered a "wildcat" each to the other.

Along similar lines... I bought my first 7mm Remington Magnum, a new Sendero, a few years ago when there were shortages of many components. The only new brass I could find was PPU, a brand I was not familiar with. As things turned out, I eventually found some new Winchester brass. The PPU brass averaged 14% greater weight than did the Winchester brass; enough weight difference that I had to increase powder charges by about 1.5 grains with the Winchester brass to get the same velocity as I was getting with PPU brass using a 140 grain bullet.

Nothing wrong with the PPU cases, but I don't recall running into a weight disparity that great with any other brass.

The 7mmRM exhibits a lot of pressure variation (AKA pressure spikes) from shot to shot even in SAAMI pressure bbls. That is why twice in the 1970's Remington lowered the powder charge--and consequently the advertised MV--in their ammunition.

In 1970 MV with a 150gr factory load was advertised at 3260 fps,, by 1978 was advertised at 3110 fps.

I wouldn't describe the broader pressure probability distribution as pressure spikes.

My understanding, from more than one major pressure lab, is that the 7mm RM shows a wider spread in pressures than most other cartridges of the same class, both high and low. Which is why the SAAMI Maximum Average Pressure (MAP) was set at around 60,000 PSI when piezo-electronic pressure-testing became standard.

Some other rounds have a SAAMI MAP of 65,000 PSI, which is as high as SAAMI will go, but they also have standard for what the highest-pressure round in a string measures, to allow a safety margin.

Which is why I used the word "variation". There will always be some degree of shot variation in the same firearm, and of course in different rifles or loads when compared to one another. But I'm talking about the same load in the same SAAMI spec pressure bbl.

Last I knew there has been no definitive reason discovered why the 7mmRM displays such a large shot to shot variation. And when Remington couldn't figure it out they lowered the powder charge in the 70's.

With the added a/k/a pressure spikes, which was the bone I picked.

Ok, I understand

I've owned a few 7 Rem Mags.....I don't care a lot for them as they turn out to be just another .270 wannabe. But of the few I've owned, I've never encountered anything like the things claimed in this thread. It's not that I don't believe it....it's just that I've not experienced it.

The 7RM and 300 Win. cases do seem to vary more than most. I use one lot of brass for each rifle and after the first firing no issues. I have not been able to detect any pressure excursions with my rifles. Maybe if I shot more long range targets I would but I am not much of a target shooter.

The same thing is reported with the 243 Winchester if I remember correctly?

Those are the two that you hear about anyway.

Yep, but in the .243 the pressure variation apparently doesn't occur with bullets under about 100 grains.

One problem with both rounds (again, info from pressure labs) is the short neck and shoulder angle. The combination results in relatively quick throat erosion, which in its early stages can also result in erratic pressure. Once the erosion extends farther down the barrel, pressures tend to decrease.

vapodog,

Do you have pressure-testing equipment?

Thanks for the response. Wonder why you don't see the same thing in a 300 Win Mag despite a short neck and similar shoulder angle?

My hunting load is 11 grains over max published by Hodgdon, but it with a moly bullet and 3.34" OAL, so it is more like 10 gr over max equivalent. There is still good safety margin to stay below extractor groove growth.

I have hunted with 3 bolt action 7mmRM rifles that I rebarreled, re stocked, re triggered, pillar bedded, rescoped, etc , and one Ruger #1 and one Browning 1885 that have original barrels.
I headspace at 0.215" to the belt, not the 0.220" minimum called out by SAAMI.

Curious what velocity and what bullet your using if you don’t mind

140 gr NBT 3400 fps

Clark

I don’t doubt your results.

My oldest 7 Mag is a 700 from the late 80s, don’t remember exact yr.
it now is my Son’s but in my house.

I’ve shot pounds of the same powder and hundreds of 139s at 3300 FPS and
have had long case life - NO blown primers - no case head scrapes, etc.
The load is/was in a bullet manufacturer manual and in a book published
by a hunter, shooter, tester etc.
I shot that load for years in the SAME rifle so NO ONE can say it’s unsafe.
Any failures WOULD have shown up in SO many rounds fired.

ATST 3300 was my chosen velocity object and I did NOT attempt to push it
any harder or faster.

BTW it was very accurate too.

Jerry

All these tales of Uber Velocity and staying within SAAMI safe pressure limits makes me glad I have a couple of long necked 7mm Weatherby Magnums! LOL! Happy Trails

One item to be duly noted is that the Remington factory ammo in 150 & 175 gr PSP Corelokts are Dual diameter bullets just like the 140 gr .264 by Remington used in their 264 Win Mag loads and their 140 gr 6.5 Creedmoor ammo. So from from cannelure back its groove dia and bore riding forward of the cannelure. MB