243 AI headspace
- Thread starter gaintwist
- Start date
H
hecksf
Guest
Well
When Mr Ackley designed the Ackley Improved line of cartridges he did so in a manner that factory cartridges would headspace properly in the Improved chamber so that the brass could be fire formed properly and it would allow the shooter to use standard factory ammunition as a back up.
SO I guess the answer is yes.
Ted
When Mr Ackley designed the Ackley Improved line of cartridges he did so in a manner that factory cartridges would headspace properly in the Improved chamber so that the brass could be fire formed properly and it would allow the shooter to use standard factory ammunition as a back up.
SO I guess the answer is yes.
Ted
D
Dennis Sorensen
Guest
Actually the headspace gauge for an AI is shorter than the standard gauge...
A factory cartridge/brass should be hard to close the bolt on in an AI chamber. The shoulder of the factory standard case should be contacting the chamber very hard.
A factory cartridge/brass should be hard to close the bolt on in an AI chamber. The shoulder of the factory standard case should be contacting the chamber very hard.
Last edited by a moderator:
M
mike in co
Guest
how can this be ?
the ai is based on converting a stock 234 to ai. how can the headspace/chamber get shorter ?
thanks
mike
The .243AI headspace must be set at least .006 SHORTER than the GO gauge allows.
Mike, YES the cartridge must headspace on factory brass but it does so clear down at the corner of the neck/shoulder junction instead of at the datum line. As Dennis says, to work properly the factory brass must jam firmly into the chamber for a crush-fit on the shoulder, only it's NOT the actual shoulder....... so there's the problem. IMO it's fitting to set the chamber of an AI 10-12thou under te .243 GO gauge. And in the event that it's too much it's a simple matter to just tickle the shoulders with a sizer to get them to crush-fit.
I've spent years with the .243AI, 5 different reamers.
al
Mike, YES the cartridge must headspace on factory brass but it does so clear down at the corner of the neck/shoulder junction instead of at the datum line. As Dennis says, to work properly the factory brass must jam firmly into the chamber for a crush-fit on the shoulder, only it's NOT the actual shoulder....... so there's the problem. IMO it's fitting to set the chamber of an AI 10-12thou under te .243 GO gauge. And in the event that it's too much it's a simple matter to just tickle the shoulders with a sizer to get them to crush-fit.
I've spent years with the .243AI, 5 different reamers.
al
D
Dennis Sorensen
Guest
When a stock 243 is chambered to AI the barrel must be set back to do this correctly. I am sure many, many chambers were not done correctly and brass life suffered because of it.... but the truth should be spoken.
C
Cheechako
Guest
Mike
The headspace gets shorter because a properly fitted AI is done by setting the barrel back one full turn before chambering.
Some guys will use the 243W Go gauge as No-go. But unforunately, if the bolt closes on the Go you may have already gone too far. I use the brass I intend to shoot in the rifle and cut the chamber until I get a good crush fit on several empty cases.
Ray
M
mike in co
Guest
thanks guys...learn something new every day on these boards.
mike in co
mike in co
AI Headspace
I had a gunsmith friend (now sadly deceased) that really liked the .257AI and .280AI. When he rechambered the barrels he would never take the time to set them back. He had case separation problems in every rifle due to excessive case stretching (headspace). When he did a .22/250AI and .244AI for me I bought the proper AI headspace gauges and insisted he use them. I never had a case separation problem with those rifles. The headspace was 0.004" shorter, AI v standard. In hindsight, 0.006 shorter might have been even better. Vic
I had a gunsmith friend (now sadly deceased) that really liked the .257AI and .280AI. When he rechambered the barrels he would never take the time to set them back. He had case separation problems in every rifle due to excessive case stretching (headspace). When he did a .22/250AI and .244AI for me I bought the proper AI headspace gauges and insisted he use them. I never had a case separation problem with those rifles. The headspace was 0.004" shorter, AI v standard. In hindsight, 0.006 shorter might have been even better. Vic
Dave Tooley
Active member
Here's something to add to the mix.
If you are using a std 243 gage on an Ackley chamber the headspace will vary with different neck diameters. The std gage touches the chamber at the juction of the neck and shoulder. Different diameter neck, different headspace. I started out using a shortened 243 gage and had 3 different 243 Ack reamers. A customer would change neck diameters and his brass might not fit because the headspace changed from barrel to barrel. A head space change means shoulders in a different place and the FL die has to adjusted for every barrel. That violated rule #1, I got a 243 Ack 40 degree gage now they're all the same. The phone doesn't ring as much now.
Dave
If you are using a std 243 gage on an Ackley chamber the headspace will vary with different neck diameters. The std gage touches the chamber at the juction of the neck and shoulder. Different diameter neck, different headspace. I started out using a shortened 243 gage and had 3 different 243 Ack reamers. A customer would change neck diameters and his brass might not fit because the headspace changed from barrel to barrel. A head space change means shoulders in a different place and the FL die has to adjusted for every barrel. That violated rule #1, I got a 243 Ack 40 degree gage now they're all the same. The phone doesn't ring as much now.
Dave
Bill Leeper
New member
First, we all know the Ackley headspace is based on the factory minimum minus .004. Headspace gauges were made which were simply factory gauges ground ,004" inches short. Within the last few years, some reamer makers have decided to establish a datum measurement for the AI cartridges and make gauges with the appropriate shoulder angle for the cartridge. This is not as easily done as it is said because of errors in Ackley's drawings. The 30/06 is a classic example. Ackley mistakenly drew the print with the headspace set on the same datum line as the standard cartridge (- .001"). This resulted in the juncture of the neck and shoulder being moved back almost .034" in relation to the parent cartridge. Interestingly, all reamer makers have faollowed this print from the beginning and continue to do so. This means the neck of the reamer is .034" too long. At least the 30/06 AI shooter will never have to trim!
Anyway, AI chambers have always been and will continue to be problematic for gunsmiths and chambering to fit the brass might be the best answer. Regards, Bill.
Anyway, AI chambers have always been and will continue to be problematic for gunsmiths and chambering to fit the brass might be the best answer. Regards, Bill.
I have come to the belief that the AI's and the 308 for LR or any chamber should be cut with a select few cases and this normally winds up to be about .004 to .005 short regardless of the shoulder angle this will make the brass last.
I'll support both Bill and Al on the case use for headspace
Lige what the hell are you building???
Clarence
I'll support both Bill and Al on the case use for headspace
Lige what the hell are you building???
Clarence
Hi Clarence,
Thanks for your input. I am pretty much set on headspacing with std gage and setting back .006 plus making sure my brass (new Lapua) will be tight. Can also make my dies shorter if needed. This is part of annual winter project rifle. Hopefully to shoot in your neighborhood this Feb.
I am going to Amarillo this weekend for metric regional, will give them your regards.
cheers,
-lige
Thanks for your input. I am pretty much set on headspacing with std gage and setting back .006 plus making sure my brass (new Lapua) will be tight. Can also make my dies shorter if needed. This is part of annual winter project rifle. Hopefully to shoot in your neighborhood this Feb.
I am going to Amarillo this weekend for metric regional, will give them your regards.
cheers,
-lige
ultramagmed
JKM
Newbie Question Dennis, Dave and others
If the chamber was AI without setting the barrel back, once the brass was fire formed wouldn't the excessive headspace be corrected as long as the brass wasn't full length sized thereafter? Or do the cases separate on initial fire forming? Newbie here, am I missing something?
If the chamber was AI without setting the barrel back, once the brass was fire formed wouldn't the excessive headspace be corrected as long as the brass wasn't full length sized thereafter? Or do the cases separate on initial fire forming? Newbie here, am I missing something?
C
Cheechako
Guest
ultra
No, you're not missing anything. If you can hold the case head solidly against the bolt face, the fire-forming will result in an AI case that fits the chamber perfectly with no possibility of a later seperation.
The problem lies in holding the cartridge solidly against the bolt face. Some will rely on the extractor to do that, others will seat a bullet long and let the throat push the bullet deeper into the case. Both methods have worked, and both methods have not worked.
My concern lies with that rifle after I'm gone. Say it eventually ends up with my great-grandson. The barrel is marked 243 Ackley Improved. That means that a factory 243 Winchester can be fired in it and out comes a perfect AI case. So he does just that. But, assuming that he only has a couple of hang-fires or mis-fires, those cases are going to stretch and will definitely be prone to seperation. That's not something I want to leave for him.
JMHO
Ray
No, you're not missing anything. If you can hold the case head solidly against the bolt face, the fire-forming will result in an AI case that fits the chamber perfectly with no possibility of a later seperation.
The problem lies in holding the cartridge solidly against the bolt face. Some will rely on the extractor to do that, others will seat a bullet long and let the throat push the bullet deeper into the case. Both methods have worked, and both methods have not worked.
My concern lies with that rifle after I'm gone. Say it eventually ends up with my great-grandson. The barrel is marked 243 Ackley Improved. That means that a factory 243 Winchester can be fired in it and out comes a perfect AI case. So he does just that. But, assuming that he only has a couple of hang-fires or mis-fires, those cases are going to stretch and will definitely be prone to seperation. That's not something I want to leave for him.
JMHO
Ray
D
Dennis Sorensen
Guest
The brass will fire form if the pressure is high enough but the brass will stretch just ahead of the web of the case and be greatly weakened.
What happen is when the firing pin hits the primer with the heavy force that is has, the case is driven as far forward in the chamber as it can until the shoulder contacts the chamber and it is now held there.
Bullets seated out into the rifling will not hold a case against the boltface. They bullet will simply be jammed into the rifling farther or the case will be driven onto the bullet farther.
So now that the case is held against the shoulder and the pressure build up, the case expands against the chamber wall and forms a seal... the pressure builds up higher and the thinner parts of the case remains stuck to the chamber walls and eventually just ahead of the wed area (the web is very thick and does not expand like the thinner areas and is not fully supported by the chamber) the case will stretch as the case head is forced back to the bolt face.
This result is a weaker case than one that is held hard against the bolt face and blows the shoulder area out on firing, rather than stretching in the web area.
I like to chamber using the correct steel go gauge but I always check several factory brass/ammo after to confirm the bolt closes quite hard on a factory round.
ultramagmed
JKM
Thanks Ray and Dennis...............
Great explanations from both of you guys, that clarifies exactly what I was wondering. I have been working on the building I'm going to put my lathe in, so I haven't had time to check to see if anyone posted an answer to my question until now. Thanks for sharing your knowledge, as always I appreciate it.
JKM
Great explanations from both of you guys, that clarifies exactly what I was wondering. I have been working on the building I'm going to put my lathe in, so I haven't had time to check to see if anyone posted an answer to my question until now. Thanks for sharing your knowledge, as always I appreciate it.
JKM