Home Forums Hunting & Shooting Ask The Gunwriters 280 Ackley SAAMI vs. 280 Improv 40 deg pre-SAAMI

I'm quick to mention die setup any time I'm talking with a newbie handloader.

Put a Nosler SAAMI 280 AI in the original Ackley and it's loose and rattles - is that minutia?

Sorry, this is sore subject with me - these days anyone can take someone else's non-SAAMI design, change it around a little and "hijack" it as their own to SAAMI. I've heard all the "reasoning" behind Nosler's decision, and I still don't think there was a legitimate reason to change the original Ackley dimensions.

Put a minimum SAAMI-spec ,30-06 round in a maximum SAAMI-spec .30-06 chamber, and the "loose" headspace is exactly the same as the difference between the Ackley and Nosler .280 AI rounds.

Yes, I understand what you're saying, but in my experience it isn't the end of civilization as we know it.

John:

I don't want to hijack this thread, but this question is related. Just about everything I read says that the .280 is downloaded, or at least has a lower SAAMI-spec PSI limit, than the AI. I've also read that if the .280 is loaded to the same pressure limit as the AI, i.e., 65k, that there really isn't very much gained by going the AI route. So here's my question: You have a nice target-velocity schedule, based on bullet weight, for the 7x57 since that data has historically been all over the board. Do you have something similar for the .280? In other words, how much velocity should one expect by loading the .280 to the same AI pressure level?

I don't know if what I'm asking makes any sense, but there it is.

Thanks

I just did a bit of figuring with Hodgdon's 280 data for a 140 grain Partition.

H4350 is reported in CUP, so I extrapolated to 54000 CUP which is a usual pressure for 300 Weatherby. This gave an estimate of 3054 fps for the extrapolated max in the 280.

A similar calc for IMR4451 at 65000 PSI estimates 3059 fps.

Of course grain of salt and Danger Will Robinson, yadda yadda.

Glad you asked that question. I was just thinking about the same thing.

Mule Deer:

Just out of curiosity, how much of a velocity difference did you find with the .280 AI over the standard .280?

I've only ever owned two rifles chambered for an "improved" cartridge. The first was a .218 Mashburn Bee, the second (which I still have) a .219 Improved Zipper. Both of the parent cartridges for those are quite tapered and the improved versions show a marked increase in case capacity.

I own a .280 (a Remington Model 725 - which I think to be perhaps the handsomest regular production rifle Remington ever produced, but that's just an opinion and worth whatever someone will pay for it) and I don't see that there's much room for increasing case capacity by blowing out a .280.

Thanks.

Rem

According to one basic rule of internal ballistics, loading the standard .280 (SAAMI Maximum Average Pressure of 60,000 PSI) to 65,000 PSI (AAMI MAP for the Nosler .280 AI) will gain around 60-65 fps in velocity with loads in the 3000 fps range.

The .280's gain in powder capacity over the standard .280 isn't all that much, about 4 grains, which according to another rule, means a similar gain in velocity when loaded to the same pressure. So about half the .280 AI's gain comes from the higher pressure. Add the powder capacity to the pressure and the AI's gain is around 120-130 fps, in an equal-length barrel.

My first .280 was a custom rifle made by the late Dave Gentry, and I handloaded it warmer than the SAAMI specs, using both the old "pressure signs" familiar to most handloaders, and a computation of what should be possible when loaded to .270 Winchester pressures (also a 65,000 SAAMI MAP). It had a 23" barrel, and at first I used two different loads that shot to the same place, a "deer" load with the 139 Hornady Spire Point at around 3100 fps, and the 160 Nosler Partition at around 2900. The Hornady load shot very well, but the Partition load wasn't quite so accurate, though it killed everything I pointed it at, including one of my two biggest caribou bulls, shot at just under 400 yards. The first shot landed in the right place, but the bull (as caribou sometimes do) locked up and stood there, so I shot again. The second landed within two inches of the first, and the bull fell over. So it didn't really matter that the 160 didn't shoot quite as well as the 139.

I eventually was reminded by the late Chub Eastman, who worked as the writer-relations guy at Nosler for many years, that Nosler also made a 150-grain Partition, which in his experience tended to shoot better. Eventually I settled on it as an all-around load at just about 3000 fps, which shot and worked great. Of course, that was back before super-high BC bullets became absolutely necessary for killing big game.

Have owned two other .280s, and three .280 AIs, and never could tell any difference in killing power or accuracy between them, given the same bullets--these days often with much higher BCs. But then I always handloaded the standard .280 to what was probably around 65,000 PSI.

BTW, if you have an "old" chamber and "new" (SAAMI) FL sizing die, Redding makes one of their "Competition" shellholders which is +.014" (to prevent pushing the shoulder back that .014" with die body touching the shellholder). This can obviously also be achieved by backing out the die as mentioned previously.

This Nosler FAQ from 2013 confused me. Based on the first paragraph, I got myself halfway believing a rifle set back a thread and chambered would meet the SAAMI standard. Called Nosler and they said "Nope. .014" headspace." They're right; proved it today on the rifle I mentioned at the beginning--shuts on a SAAMI-standard no-go gauge.

That said, I think this FAQ could be a little clearer......

Good timing... I just purchased a barrel chambered in 280 RCBS with dies marked 280 Improved 30 deg.

It's a shouldered barrel I need to install on a Rem 700 LA. How would i go about head spacing it correctly? also, can I fire form 280 Rem brass with it then reload with the dies?


Thanks

Not answering your questions, but do you have fired cases from it? A friend has a 1937 M70 Super Grade with "7mm" marked on the barrel. It was originally a 7x57 but had been wildcatted probably in the 50's or 60's. Our best guess based on a lot of research was 7-06 RCBS Improved (30 deg shoulder). If you're not positive, consider doing a chamber mold with Cerrosafe, etc. https://www.brownells.com/gunsmith-...osafe-chamber-casting-alloy-prod384.aspx

I do not have any from the previous owner. I'll check out the mold idea. Thanks

If, when you chamber a 280 cartridge, you can feel some slight resistance, it is perfect. If there is any clearance, it is not. It may be that factory 280AI will headspace at the corner of the shoulder quite well since the outside corner of the shoulder is further forward on a 40 degree than on a 30. GD

Getting back to the question of using Nosler factory brass in an 280 Rem Ack. Imp. 40 degree (pre SAAMI chamber). In an adundance of caution I always size new Nosler factory brass up to .308 cal. and size back down to .284 cal. leaving a false shoulder. This results in a loaded round that gives slight but noticeable resistance when closing the bolt. I have never experienced and problems with excessive headspace using this method. It adds a couple of steps to the process but gives me confidence that my loaded rounds are safe. I use Redding dies marked 280 Rem. Ack. Imp. 40 degree which were made around 1993. I have never fired Nosler 280 Ack. Imp. factory rounds in either of my rifles so I cannot comment on how that works.

I've never used factory brass in this chambering.
I have both RCBS .280 Remington Dies and RCBS .280 Rem IMP 40 dies.
I start with once fired .30/06 brass, resize with the standard 280 dies to create the false shoulder and then load seat using the IMP dies thereafter. Never had an issue.

My rifle is a Winchester Featherweight XTR in 7x57 which was re-chambered to the Ackley chambering. It is a nice hunting rifle and quite the looker. Best performance from the 22" barrel comes from 140 grain bullets which reach 3200fps with relative ease. Lighter bullets suffer from the shorter barrel and the 175's will hover in the 2800-2850fps range,

Probly always will be.