280ai vs 7mm rem mag?

[MudRunner2005]

oh sorry i misunderstood ...the way you were talking about how the 280 Sherman eliminates the gap on the 7mag with the heavy bullets I thought you had all the stuff personally have shot them side by side! My bad ill see what i can get going

Nope, I've just spent years independently studying cartridge mechanics and designs, burn rates, shoulder angles and flame patterns, along with case design efficiency and how the designs affect burn pattern and gas flow. Knowing all this stuff will help you be able to know in your mind, virtually how a cartridge will perform without ever bringing it to reality...But in reality, there are external factors that affect performance, so there is no way to truly know exactly how a cartridge will perform until it is produced...But you can get a really good idea if you do the math.

I know how the Shermans are designed, and that they are an excellent design, because I designed nearly the exact same cartridge as Rich Sherman did, without knowing he had already designed it first. So, after posting up a picture of it here on the forum, and after finding out how similar they were, he and I discussed it (which he was ok with it, being that it was coincidence), but out of professional courtesy I chose to delete my designs, because I like being an original, and Rich had already had some reamers cut and such, so out of respect for him, I dropped my designs.

And if you don't believe that story, maybe he'll chime-in and verify it.

 

[Bfmine]

Soooooooooo. What it comes down to is a 150ish fps difference between the two when using the same weight bullet? Are there any bullets that the 7rm can shoot that the 280ai can't?

 

[MudRunner2005]

Are there any bullets that the 7rm can shoot that the 280ai can't?

No. Any .284" bore can shoot any .284 bullet. The only outside factor that would differentiate would be the barrel's twist rate. As long as the barrel has the proper twist rate, any modern 7mm should be able to shoot any modern 7mm bullet.

And yes, basically +/-100 fps difference (with the same weight bullet) between the .280 AI and 7mm RemMag with equal barrel lengths and twist rates.

And with the .280 Sherman vs. the 7mmRM there is maybe at most 30 FPS difference, if any at all, between the two.

 

[elkaholic]

Soooooooooo. What it comes down to is a 150ish fps difference between the two when using the same weight bullet? Are there any bullets that the 7rm can shoot that the 280ai can't?

There won't be 150' difference between an A.I. and the RM! It will be considerably less! The shorter the barrels get, the closer they will be. I would be willing to bet that with a 7RM with a saami reamer, and a Sherman, there wouldn't be more than 30'! AND, with the capacity difference and non belted case, the A.I. and Sherman are pretty darn competitive! There is no doubt that the 7 RM is one of the most popular all time and for good reason. Largely because it was first, well established, chambered by everyone, and it works.

 

[nmbarta]

I have a 280ai that shoots the 162 eld-x at 2920 out of a 25" lilja.
I have a 7rm that shoots the 175 eld-x at 3050 out of a 27" brux.
Not an exact comparison, the barrel on the 7rm gives it a bit of an edge, but they really aren't that close anyway.
With these two guns, you can see that the 7rm is running a 175 over 100fps faster than the my 280ai is running a 162. Both are throated to maximize standard remington magazine length.
The 7rm puts a pretty good spanking on the 280ai in terms of power.
If i had it to do over, I'd skip the 280ai and just build a 7rm.

 

[Tidus56]

The truly impressive thing is that the 280 Sherman and 280 AI are on a standard bolt face. So a guy with an old 270, like the OP, can swap a new barrel on and have close to 7 RM speeds. If I had a magnum bolt face the 7 RM wouldn't even be a consideration for me. So I guess its how you look at it. I am very impressed with what the Sherman and 280 AI accomplish on a standard bolt face.

 

[elkaholic]

I have a 280ai that shoots the 162 eld-x at 2920 out of a 25" lilja.
I have a 7rm that shoots the 175 eld-x at 3050 out of a 27" brux.
Not an exact comparison, the barrel on the 7rm gives it a bit of an edge, but they really aren't that close anyway.
With these two guns, you can see that the 7rm is running a 175 over 100fps faster than the my 280ai is running a 162. Both are throated to maximize standard remington magazine length.
The 7rm puts a pretty good spanking on the 280ai in terms of power.
If i had it to do over, I'd skip the 280ai and just build a 7rm.

I can guarantee you that a 280 A.I. is better than 2920 with a 162 out of MOST barrels! Not discounting that's what yours does......rich
For the record, the Sherman will run a 180 Berger at 3050' all day long without destroying cases.

 

[7magcreedmoor]

My 280 runs pretty close to my old 7RM. Both barrels 26 inch, 8 twist. Mag with 168 berger, 3050. Ack, 3015. Mag with 180, 2905. Ack 2875. Why did I switch? Built the 280 myself, and wanted something I didn't already have...

 

[Edd]

If you have a 7mm rifle, you choose the cartridge, shooting a 180 gr bullet at 2800fps, how much will the velocity change with a 10,000 psi change in pressure?

 

[gohring3006]

If you have a 7mm rifle, you choose the cartridge, shooting a 180 gr bullet at 2800fps, how much will the velocity change with a 10,000 psi change in pressure?

I thought about that before, but pressure is only one factor. A 30-06 running 60,000 psi won't have the same velocity as a Win mag running 60k with same bullet weights.

 

[nmbarta]

Velocity is exactly what the the gunsmith said it would do.
I could push it harder for sure, I could push the 7rm harder as well, but I don't care to run any of them at their breaking point. I just buy bigger guns when I want to go faster, no point in trying to make something into something it's not.
The 280ai is not a 7rm.
If your getting close to the same speeds, your running different pressures.
both are efficient cartridges, neither is over bore.
The 7rm has 8-10 gr more capacity.
It's a bigger gun, it goes faster on the same level as any other cartridge with 8-10 gr more capacity than any other cartridge of similar size.
There's no magic in any of them, at least no magic that that I buy.

 

[Edd]

I thought about that before, but pressure is only one factor. A 30-06 running 60,000 psi won't have the same velocity as a Win mag running 60k with same bullet weights.

That's true, a 30-06 running 60,000 psi will have about the same velocity as 300 Win Mag will have running 50,000 psi.

 

[Bfmine]

No. Any .284" bore can shoot any .284 bullet. The only outside factor that would differentiate would be the barrel's twist rate. As long as the barrel has the proper twist rate, any modern 7mm should be able to shoot any modern 7mm bullet.

I know that part. Was just curious if the 7rm can shoot a heavier bullet where the Ai won't be able to maximize its performance. Like any bullets the rm can shoot that are too heavy for the Ai. Thanks for the help

 

[MudRunner2005]

I know that part. Was just curious if the 7rm can shoot a heavier bullet where the Ai won't be able to maximize its performance. Like any bullets the rm can shoot that are too heavy for the Ai. Thanks for the help

No. It's all in what you are looking for, but you have to accept pro's and con's of each direction you head. If you shoot light bullets (120-150), they're faster, but lose energy VERY quickly. Mid-weight bullets (160-175) are about the best mix of velocity and performance. Heavies, like the 180-195's will have slower MV's, but will maintain velocity and energy much better at distance.

Personally, I shoot 168's in my 7mmRM, 1) because I don't hunt over 500 yards with that particular rifle (sporter barrel, lightweight, low-power scope, etc...), and it's just not built to shoot LR, although I'm sure it would have no problems doing so, if I needed it to. 2) At the time I had it built, the 168 was the only Berger available that would work in that twist rate. And 3) is because it only has a 1:9.25" twist barrel. I plan on trying some of the new Berger 175 Elite Hunters before next hunting season to see how well I can get them to shoot.