7MM 08 40' Improved

[Westerner2]

I am re-barreling a Mod 7 from 243W to 7MM 08.If I do it in 40'Imp.Could I get it up 280 Rem numbers?And is it worth it??

Westerner2

[Mike Moss]

Westerner2,

In general the so called 'improved' chambers are really just a hobby. I have tried them in rimless, rimmed and belted rounds and now I am stuck with the odd chambers.

I even met Lysle Kilborn who invented the concept with the .22 K Hornet. He was an employee of Lymans.

For a 7mm-08 'Improved' chamber to be done right the headspace should be set to be a contact fit with the standard 7-08's neck shoulder junction. This is to make sure that the expansion web on the standard round does not get stretched making the side walls fail. This of course limits the chambers flexibility.

Not only all that but I doubt that you will get near 280 Rem ballistics with safe pressures. Keep in mind that there is little of any data for the subject round.

A common sense way around this is to keep or sell the 243 as it is and buy another rifle in 7mm.

[Larryjk]

Mike Moss, I don't understand your response to Westerner2.
(1) Your first paragraph is a IMHO. This will always be disputed.
(2) Irrelevant. I met P.O.Ackley once and that is irrelevant in this case.
(3) Ackley Improved chambers are 0.004 shorter in headspace than the parent chamber so the case web doesn't get stretched during the fire-forming process. This in no way "limits the chamber flexibility". If you think so, please explain your reasoning.
All chambers are specific to the chambered cartridge and minimal headspace is always what is desired; flexibility be damned.
(4) I basically agree with what you say in this paragraph and the next. However, I might add that there is more data all the time on the .280 AI. Unfortunately, most of it is gathered without the pressure being considered. Of course, anyone who takes an "excursion" beyond the strict limits of the data in a loading manual is doing the same thing. Remember, each barrel is a separate entity because they are not identical. An average of five different barrels with the same ammunition only gives you the average of five barrels. The next five barrels tested may very well give a different average.

[Rocky Raab]

So-called "Improving" of rifle cases was a passably good idea when most rounds were long, skinny and sharply tapered. Improving the .25-35 worked wonders for it.

But all that abruptly changed when cases started coming from the factory with fat bodies, little taper and reasonable sharp shoulders. The 7-08 fits that description and is already "improved" just as it comes.

If you try to "improve" it even more, you run into possible feeding problems with very steep shoulders, you spend double or triple on loading dies and gain...well, let's examine that.

There's a long standing and very well proven formula that says you will gain or lose velocity by one fourth the percentage of case volume change. In this instance, a 7-08 case holds about 50 grains of water by weight (the usual standard). If you blow the case out and sharpen the shoulders as much as possible, you might be able to add four grains of water to that.

Now, 54 compared to 50 is an eight percent increase. One fourth of that is two percent. If your un-improved 7-08 got 2800 fps with a given bullet, then all your expensive dies, re-chamber job and fireforming of cases gains you an extra (drumroll here) 56 feet per second. That's about what you'd see in the variation between two shots of a UNmodified 7-08.

Worth it? Not to me.

[Catfish]

I am a wildcat nut and have several of them, but what Rocky said about your increase in velocity is absolute correct. Another thing to consider is that wildcat rifle bring far less than one chambered in factory round if you sell it. If you plan on shooting out the barrel yourself that makes no difference though. In any event your gain in velocity with that round will be very small on paper and unnoticable in the field.

[BILLY D.]

I concur with what Larry, Rocky and Catfish about Ackley Improving rounds.

They are not going to turn the parent round of any particular rifle into a Hamburger Helper rifle.

However they do prevent case stretching and are easier on brass. If you do a tremendous amount of shooting you might have a use for them.

I have never had a Deer that I shot turn around and say, "Gee I just got hit by a 243 AI", flop.

I have several Improved cartridges, 19 Calhoon Hornet, 19 Badger, 19-223, 223, 22-250, 243 and 6,5x68. I like them all.

Then there is the inherent "snob" effect of the rounds also. I got something you don't.

Some claim the Ackley rounds are more accurate than the factory versions. My 2 22-250's and 243 were plenty accurate with the factory rounds, the only reason I went Ackley was for the reasons stated about brass life and I had shot out the barrels of the rifle. Time for somethin' new.

And then there is the old, "Well shucks you can always shoot a Factory produced cartridge in a Ackley chamber", true but it's not a factory sized case any more.

It's a personal thing,some folks such as me like them, others don't.

Best wishes, Bill

[Rocky Raab]

Billy is right that a custom barrel with a hand-cut chamber, installed by a good gunsmith is often more accurate than a factory barrel. But that's hardly surprising no matter WHAT it's chambered in, is it?

[Westerner2]

Thank for the Info.I did look up 7mm 08 Dies and they are $160 for a set.

Westerner2

[Evan03]

why not run get 280 rem and blow it out and run with the 7mag while burning less powder.


i dont see anyreason feeding would be concern .

if it were the wsm wssm blown out 284 cases 6 brs and the like wouldnt work as hunting rounds because they be reduced to single feeding. this is not the case.

unless for some reason the 308 case is already feeding poorly from short actions. i d dont think it is .


just thinkn.

why not rechamber to 284. this case is almost identical to the 280 cases volume while running in a short action. but bullets might be seated into the shoulder. theres on reason not to.


the 7mm08 is great case left alone. itl work at close and long range when fed the right bullets. itl also work on very large game wwhile chewing on the heavy 175s.

while not being flashy about the 708 just does it all very well.

[Barlow]

If you read the Ackley Handbooks you will find that Mr. Ackley was absolutely honest in is opinions on his many improved cartridges, or wildcat cartidges. If a cartridge did not show improvement, or little improvement, he said so. If it did gain in velocity to his satisfaction, he also noted that. P.O. Ackley was not an uneducated gunsmith. His knowledge of firearms, and all things related IMHO will probably never be duplicated again. Get his books and read them to get the full story.

[Ridge Runner]

one of the main misconceptions of the AI rounds and other improvements is that you can gain alot of velocity with less pressure, this is just not right, rocky is right about 2% gain at the same pressures with the same length barrel is the norm.
now most custom barrels are normaly a bit faster than a production one with the same loads due to the barrel being smother, and more consistant. you'll normaly see about a 100-125 fps increase with a custom barrel/min spec chamber over a production one.

Now you take a case and improve it, take out most body taper, put a 40 degree shoulder on it and polish the chamber to a mirror finish. So now you have brass that fits the chamber exactly, doesn't adhere to the chamber before pressures peak, and a min taper case not pushing back against the boltface like a backwards wedge. So you won't see your typical pressure signs, like ejector pin marks or heavy bolt lift until your pressures are way beyond what they normaly run in the parent case. so unless you have pressure testing equipment you have no idea what pressure your running in your AI chamber but must assume if your running greater than 2% increase in MV that you are running higher pressures. is this safe? not for me to say, but I know its not good for case life.
I have custom wildcats which show no pressure signs at all till the primer pocket won't hold a primer. So I experiment till I'm satisfied with the performance and case life and thats my max load.
RR

[8X56MS]

My experience with Ackley Improved cartridges is limited to just two.

.30-30 AI and 7x57 Mauser, AI.

Both of these show a marked improvment, but then they are not already fat with little taper.
I have been very impressed with the speed and accuracy of my old FN Mauser with the Shilen barrel, Canjar trigger and 7x57 AI chamber.
Wildcats have traditionally been done for reasons other than just strict practicality .

[Larryjk]

Ridge Runner, I agree with most of what you said, except you were 100% wrong on polishing the chamber. If a reamer is sharp, you will get the best finish in a chamber relative to what happens in there when yu pull the trigger. You absolutely do not want a glassy, shiny chamber. Then the pressures have to be peaked before the case expands enough to grasp the chamber walls. The case has been pushing back against the bolt face, and in turn the lugs with all of the chamber thrust of the case. Don't get the chamber too smooth and you will be doing your gun a favor. If you polish, no smoother than about 220 grit cloth.

[Larryjk]

Most custom chambers are as tight as the gunsmith can hold the reamer during lathe reaming. Tight chambers do not show pressure signs as early as a "loose" chamber because many of the pressure signs you are used to seeing are masked by a tight chamber.

[Ridge Runner]

I wasn't wrong larry, the info I stated was told to me by not 1, but 2 different gunsmiths, one of them has built several rifles for members of the pa 1000 yard benchrest club.
RR