Gunsmith with Ackley......
- Thread starter deerslayer
- Start date
The rifle is a Rem 700 mtn , 280 rem ,22 inch slim barrel with a custom KDF , detach clip was installed a few years back , trigger job , Rem after market composite stock , rifle bought new in 1992. Would like to do 280 Ackley improved conversion , I would beleive all that needs to be done is a re-chamber job. If anyone has done this to one of their rifles let me know how it turned out
Deerslayer,
I have owned three 280 Ackleys over the years. The first was a rechambered Model 77 Ruger. It would get 160s to 3000 fps in the 22" barrel with good case life. An RCMP member bought it from me and is still using it up here for sheep and caribou.
The next was rebarrelled Mauser 98 that I only had for a few weeks and a friend of mine just had to have it. It had a 24" barrel and would get about the same velocity.
The last one was also a Model 77. It had a 25" Shilen barrel and would get a bit over 3000 fps with the same weight bullets. Bronco Mudder has that one now, and I'm pretty sure he is not letting it go anywhere.
The 280 Ackley is a great cartridge. There should be more of them.
Ted
I have owned three 280 Ackleys over the years. The first was a rechambered Model 77 Ruger. It would get 160s to 3000 fps in the 22" barrel with good case life. An RCMP member bought it from me and is still using it up here for sheep and caribou.
The next was rebarrelled Mauser 98 that I only had for a few weeks and a friend of mine just had to have it. It had a 24" barrel and would get about the same velocity.
The last one was also a Model 77. It had a 25" Shilen barrel and would get a bit over 3000 fps with the same weight bullets. Bronco Mudder has that one now, and I'm pretty sure he is not letting it go anywhere.
The 280 Ackley is a great cartridge. There should be more of them.
Ted
David Henry
CGN Regular
- Location
- West of the big road
Ackley
True Ackley chambers require a bit more than just the reamer run into the old chamber, doing this ends up with a bastard chamber.
For correct headspacing the barrel should be set back as the new chamber is .004" shorter at the datum line than the parent case, most important for fireforming and saftey.
This of course is not the case with rimmed cases like the 30-30 Ackley which only require modification with the improved reamer.
The 280 is a great case and gains about 200 fps when improved via the 40 degree Ackley method, I also have this reamer. Regards David.
True Ackley chambers require a bit more than just the reamer run into the old chamber, doing this ends up with a bastard chamber.
For correct headspacing the barrel should be set back as the new chamber is .004" shorter at the datum line than the parent case, most important for fireforming and saftey.
This of course is not the case with rimmed cases like the 30-30 Ackley which only require modification with the improved reamer.
The 280 is a great case and gains about 200 fps when improved via the 40 degree Ackley method, I also have this reamer. Regards David.
I believe that is the midpoint of the shoulder. - dan
"Datum" line is a reference point on the shoulder of the case... it may vary depending on the case... I know for instance with a 270 or 30-06 case the datum line is where a 3/8 inch diameter hole would contact the shoulder. Datum lines specs are not required by a gunsmith unless he is making reamers... I rely on the fine reamer maker we have to make it right... the same for gauges...
Any Ackley Improved rimless case should be headspaced so a factory case can be felt firmly when closing the bolt. This is a crush fit on the shoulder and insures proper firerforming and case strength. It also means when chambering a correctly headspaced factory chamber to an A.I. chamber, the barrel requires setting back at least 5 or 6 thou... if sights are involved, then one turn, so it can be correctly headspaced.
Any Ackley Improved rimless case should be headspaced so a factory case can be felt firmly when closing the bolt. This is a crush fit on the shoulder and insures proper firerforming and case strength. It also means when chambering a correctly headspaced factory chamber to an A.I. chamber, the barrel requires setting back at least 5 or 6 thou... if sights are involved, then one turn, so it can be correctly headspaced.
David Henry
CGN Regular
- Location
- West of the big road
Datum line
Just like Dennis said, that should sum it up. David.
Just like Dennis said, that should sum it up. David.
The .004" difference in the AI chambers and the factory chamber is not at the datum line; It is at the juncture of neck and shoulder. This since the factory cartridge headspaces at this point in the improved chamber. It has always been standard practice by the toolmakers to make AI headspace gauges by grinding standard guages .004" short.
When a factory cartridge is fired in an improved chamber, the datum line actually moves forward while the neck/shoulder juncture moves back (by .004).
So, all AI cartridges based on the '06 case, for instance, end up with the datum line in a different place. This is necessary in order for the capability of the AI chamber to shoot factory ammunition to be realized.
Ackley's drawings for the 30/06 AI do show the datum line moved back by .004". I believe this was simply a mistake on his part. This is borne out by the fact that all reamer/guage makers have continued to make headspace guages based on a standard "go" guage shortened by .004". So the reamers are made on one concept (datum line -.004"), while the guages are built according to another (neck/shoulder juncture -.004").
In the end, the imprortant thing is that all AI chambers must be slightly shorter than the factory chamber so a "set-back" is required. As Dennis pointed out, this "set-back" may be only enough to assure proper headspacing or it may have to be a full turn to accomodate open sights or an extractor cut. Regards, Bill.
When a factory cartridge is fired in an improved chamber, the datum line actually moves forward while the neck/shoulder juncture moves back (by .004).
So, all AI cartridges based on the '06 case, for instance, end up with the datum line in a different place. This is necessary in order for the capability of the AI chamber to shoot factory ammunition to be realized.
Ackley's drawings for the 30/06 AI do show the datum line moved back by .004". I believe this was simply a mistake on his part. This is borne out by the fact that all reamer/guage makers have continued to make headspace guages based on a standard "go" guage shortened by .004". So the reamers are made on one concept (datum line -.004"), while the guages are built according to another (neck/shoulder juncture -.004").
In the end, the imprortant thing is that all AI chambers must be slightly shorter than the factory chamber so a "set-back" is required. As Dennis pointed out, this "set-back" may be only enough to assure proper headspacing or it may have to be a full turn to accomodate open sights or an extractor cut. Regards, Bill.
David Henry
CGN Regular
- Location
- West of the big road
Ackley
Your absolutly right Bill thats a better explaination than mine. David.
Your absolutly right Bill thats a better explaination than mine. David.
