OK...

I am about to go and place an order for my first custom rifle.
It will be based on a Rem 700 long action with an extended wyatt's mag box. It will have a 24" lilja #2 barrel, 1:8" 7mm.

Now, I am wavering between the boring old 7mm rem mag, or the 280 ackley.

I am having the chamber throated for long, heavy 7mm bullets, also hence the fast twist and extended box. I am looking also at the 172gr "absolute hammer" from hammer bullets, a 1.62" projectile.

Now, I want to understand if there will be a significant performance gain with the 7 rem mag over the 280ai when going custom.

I understand that in factory length chambers, there isn't much performance difference between the two. I have a 7RM currently and just sold my 280ai.

However, to my pea brain, if i can get either cartridge OAL to somewhere around 3.6", I will not take up as much room in either case with the longer bullets, and as a % gain I should gain more case capacity for powder in the 7RM... and since it comes with more capacity in the first place, would I gain a larger % increase in capability with the 7RM over the 280?

I've never had a custom chamber/throat done like this, so I'm trying to understand what I may or may not gain by doing this.

Bottom line, with the custom chamber will the 7RM really shine over the ackley? Or will they still be pretty similar in performance, and go for the ackley to take less ass-whoopin at the back end?

Purpose of the rifle: 6.5 - 6.75 lb mountain deer/elk rifle. Looking at a mcmillan game hunter, mesa altitude, or manners eh2 stock to hold everything together.

Thank you

I have, and have built, both 7RM and 280 Ack; both are about the same.
Now, if you want to do a maximum throat in each, and seat bullets only a minimum amount (I routinely seat at .1 inch in my 257 roberts with long throat). you will get more from each.
How much more? You can answer that yourself; take one of each case and fill it with water; insert bullets as deep as you want; then weigh them. Oh, weigh them without the water first.
See what the difference is, and that will translate to power capacity.
Or just fill each with powder and see, too.
Do not consider recoil; if you do, then just use a 7x57.
Make sure your mag length will handle your bullet and seating depth.
Making a longer throat is child's play.

The 280 AI will fall 150 fps short of the 7mm Rem unless the RM is loaded down and the 280 is loaded to the nuts. I did this comparison, in the same barrel, 40 years ago.
Throat length gains you some capacity but not a huge amount.
More freebore lets you use more powder to attain the same velocity.
If you drive a 175 grain bullet at 2950 (possible in the mag but not in the AI), it will result in a certain amount of recoil, regardless of the headstamp.
The AI, loaded hot, might be able to push the 175 to 2800 (2750 is more likely) and it will recoil slightly less. Load the 7 mag down to that level and recoil will be about the same. Regards, Bill

my question would be, are you going for accuracy or velocity?

if both, go 7rm, but don't make the throat any longer than you need .. so it may be long for a stock 7rm, but perfect for your choice bullet...

most cannelured bullets, in caliber, as the same length from the groove to the tip -- so if you want tp crimp on the groove, they usually wind up OAL

Since you have enough magazine and velocity seems to be your goal, then you should simply opt for a 7mm STW.

quote:

Originally posted by Stonecreek:
Since you have enough magazine and velocity seems to be your goal, then you should simply opt for a 7mm STW.

Well, there is that -- GREAT idea

Then go for the 7 RUM.

Take Wyatt mag box length, subtract case length for the cartridge you want. That is the longest bullet ogive length you can use (unless you want to single load). If you want to use bullets with a longer olive you will need to move to a shorter case.

I like the 7mm RUM but for long ogive bullets the 28 Nosler might be a better choice.

I looked hard at the 28 nosler. I will inherit a 7RUM one of these days. My choice...I ended up going 7 RM for a variety of reasons. One, it'll always be around (IMHO), I have dies, brass, powders, bullets for it, though I will need more bullets as this gun is designed for the longer heavier 7mms. I think

What i ended up going with..

rem700
lilja #3 fluted
mcmillan game scout
plus some bells and whistles Richie at High Tech Customs can do.

Should end up 6.25-6.5 lbs I think. The scopes I'm looking at are generally 20-22oz; so should be just around 7-3/4 scoped and loaded. If only mcmillan wouldn't take 6 months to get the stock shipped...