AI?

10-96 · September 9, 2017, 04:49 PM

Not to hijack Bbarn's threat, his question did lead me to a question of my own.

I recently picked up a CZ 527 in 7.62x39. I've only made it to the range with it once so far, so I can't really say how I feel about it yet. But anyway, I got to wondering if anyone here has seen, done, or looked at the numbers from a 7.62x39 AI?

I know, it sounds silly to me too, but ya gotta admit, there's not much new under the sun, and if nothing else- it would make for some interesting Ken Waters style reading.

Geezerbiker · September 9, 2017, 04:57 PM

It sounds interesting to apply the Ackley treatment to the 7.62x39 for a bolt gun. So far I've not seen nor heard of anything like that. It would be expensive since the chamber reamer and dies would both be special order items...

Tony

Scorch · September 9, 2017, 05:52 PM

In PO Ackley's book, he says that the cartridges that benefit the most from "improving" are cartridges with a lot of taper to the case and shallow shoulder angle. I think the 7.62X39 fits into that category pretty well. For a bolt gun, an increase in pressure is not an issue (within reason), so you could even hot-rod it a little bit. Give it a try and do a write-up of before/after velocity and accuracy.

HiBC · September 9, 2017, 06:09 PM

You might look into the PPC series of cartridges and the .30 Walker.
They may not fall exactly into the 7.62 x 39 AI pattern,but its a derivative of x39 brass ,30 deg shoulder and straightened body.

Reamers,dies,etc will be much easier.

ThomasT · September 9, 2017, 09:15 PM

If you are looking for more power than the 7.62-39 you might just jump to a 300 savage or 308. You will never get enough extra powder in that case to come close to matching those rounds. Why not just enjoy the round for what it is?

If you need an AI chamber to make your round of choice an effective hunting round then you are way undergunned to start with.

10-96 · September 9, 2017, 09:23 PM

Naw, I wouldn't have the means or ability to do a x39 AI. And, I suppose it would put in the .300 Savage ballpark, but it was just fanciful thinking. But on the other hand- it would juice up my CZ 527 a bit and be something to give my buds a few "Ooohs and Ahhhs". But I would like to see what it's capable of...

old roper · September 9, 2017, 09:50 PM

You could AI the case. I, AI the 35 Whelen and you have more shoulders on the 7.62x39 than the 35 Whelen.

I build 7.62x39 using a 30 cal barrel and shot BIB 30 cal with 1/15 twist barrel.

BIB got those 112gr/118gr 30 cal for 1/17 twist barrels.

Look at this case

http://bulletin.accurateshooter.com/...ve-shot-group/

std7mag · September 9, 2017, 10:23 PM

Chamber reamers are chamber reamers. Meaning that if you call Pacific Tool and Guage the price for a custom reamer isn't extreme.

Custom dies however...

Option is to get die blanks ($20) and have reamers made for them. Saves you about $400 or more.

If you want to do 7.62x39AI, i say go for it!
Let use know how it works out. I may be interestef in one too.

Stats Shooter · September 10, 2017, 01:09 AM

I say go for it!

Unremarkable results are still results. I mean, if you find that all you have done is made an expensive .308, then you can write it up. Research is often it's own reward. Also, models and extrapolation are good guides, but not a substitute for real world results.

As others have said, a custom reamer can be machined for. 7.62x39 as easily as any other reamer. Then, you can get a gun Smith to ream a die blank for you with the same reamer.

One big upside is that you would have a bunch of cheap brass to Ackley up. And you would have the only one I have ever heard of.

HiBC · September 10, 2017, 02:50 AM

I'm sure if the OP wanted to carry a 308 rifle ,he could.
I think the point is the CZ rifle. It won't hold a 308.
The 6.5 Grendel is a worthwhile cartridge based on the x39.Case taper is straightened out and it has a little sharper shoulder.
Same with the very successful PPC cartridges.Based on the .220 Russian,which is essentially an Ackley'd x39 case,maybe with a slightly less sharp shoulder.
This has all been done.
There is a cartridge called the 30 Walker.Its a 30 cal PPC.
This link will get you an article about a 30 cal version of the 6.5 Grendel.
Is it worth it?Thats up to the OP.
I think I saw 2500 fps with a 150 gr Sierra boat tail in the article.Standard 7.62x39 is about 2400 with a 123 gr bullet.

This may not be exotic enough for full custom die and reamer prices. You might be able to conjure up a seating die with a chamber finish reamer,but not a sizing die. Obviously you can't resize cases by chambering them. It takes a separate reamer. Now,PTG or equiv can take a dull chamber reamer and regrind it to a sizing die reamer. You will still have a soft die .

A conversation with Redding or Forster customer service MIGHT produce something as simple as a 6.5 Grendel bushing die with a 30 cal bushing.
A Wilson type straight line seater might work out.

For myself,a CZ in 6.5 Grendel would be sweet,but that is a re-barrel.
Brownells handles a Howa small bbl'd action in 6.5 Grendel for more or less $500.

http://bulletin.accurateshooter.com/...beats-300-blk/

Mobuck · September 10, 2017, 06:53 AM

I see a few reasons this is fools' play.
The AI "concept" involved the capability to use factory standard chamber ammo in the AI chamber. How's that going to work with steel case ammo?
The x39 design is purposely tapered to facilitate chambering and extraction in military weapons. Expanding the shoulder area to the extent that most AI designs use would likely split even brass case.
In the old days, rechambering to an AI design was a CHEAP alternative to buying a different rifle or barrel. Current gunsmithing costs virtually negate this cost savings. Why not just choose a cartridge that suits your needs?

HiBC · September 10, 2017, 08:30 AM

I'm not particularly advocating for the project.
I'm advocating having some respect for folks with ideas different than what I might do.
I'd like to think we can discuss our ideas and priorities without some arrogant rude disrespectful person calling us a fool.
What seems ignorant is the assumption anyone would consider fireforming or reloading steel cases.
Split the brass case? Ackley himself said the best cases to AI have substantial taper.Regardless,Lapua and Norma,and maybe Hornady brass is available in the PPC and 6.5 Grendel configurations which are of minimal taper.
I bought 500 .257 R virgin cases to feed my 257 R AI.Never was my plan to buy factory .257 R to shoot in my rifle.I never have.
Mobuck ,you seem to think the 6.8 SPC is a reasonable option to fit a deer cartridge into an AR receiver. OK. Enjoy.I'm not going to rain on your parade.
Why is it so hard to get that someone might want to boost the performance of the slick,small bolt action CZ?
A 150 gr Sierra at 2500 fps ought to be fine for 250 yds or so.
I'm sure our OP can get a $ estimate together and make his own decisions about 30 grs more bullet,a better BC and 100fps.

I'm not going to build one. I would not build a 6.8 SPC,either. But I don't feel at all compelled to put down folks who enjoy their 6.8.
In the mean time,I can treat his ideas with respect.
As ARX Enterprises explains in the article,you just neckup Lapua 6.5 Grendel brass. ARX Enterprises sells dies. HMMM. I bet they could even chamber a CZ barrel.No need to buy the reamer.

T. O'Heir · September 10, 2017, 12:23 PM

Sounds like lipstick on a pig to me. As mentioned, you won't see much 'improvement'.
"...The AI "concept" involved the capability to use factory..." Just for fire forming. Steel cased ammo is low end stuff anyway. If you're going to play with modifying a rifle and cartridge to AI, you're not likely to be using low end ammo.
.220 Russian(5.56 x 39) is just a necked down 7.62 x 39. Allegedly for deer hunting .

Mobuck · September 10, 2017, 09:09 PM

"Mobuck ,you seem to think the 6.8 SPC is a reasonable option to fit a deer cartridge into an AR receiver. OK. Enjoy.I'm not going to rain on your parade.
Why is it so hard to get that someone might want to boost the performance of the slick,small bolt action CZ?"
No problem, just choose a starting point with at least minimal chance for success(like having the action re-barrelled to 6.5 Grendel or one of the numerous wildcats based on the x39 case). The 6.8 is "plug and play" with a proven level of success.
"Split the brass case? Ackley himself said the best cases to AI have substantial taper"
Most likely Ackley was referring to the advantages of cases with more taper vs cases that already have minimal taper. The ability to fire factory ammo in an AI chamber was touted a a "big advantage" in case your AI ammo got lost, damaged, or forgotten on some long distance trip-not just as a way to fireform cases.

stagpanther · September 10, 2017, 10:40 PM

Quote:

The 6.5 Grendel is a worthwhile cartridge based on the x39.Case taper is straightened out and it has a little sharper shoulder.
Same with the very successful PPC cartridges.Based on the .220 Russian,which is essentially an Ackley'd x39 case,maybe with a slightly less sharp shoulder.
This has all been done.

Kinda what I've always thought--it's spawned some worthwhile children--ya never know...

Geezerbiker · September 11, 2017, 03:35 AM

That .30 ARX is an interesting looking caliber that would make a good round in a lightweight deer rifle. That is if the dies can be found. A quick search failed to turn any up.

Tony

HiBC · September 11, 2017, 04:03 AM

Geezer,the article said ARX has them for sale

Geezerbiker · September 11, 2017, 04:55 PM

The ARX website says the dies are available but I wasn't able to find them on their site... The dies they do have are expensive at $225 for a set. So you'd really have to be sure you want it before making the decision.

Tony

stagpanther · September 11, 2017, 05:14 PM

I'm not interested in the 30 ARX--but already have a grendel redding bushing die that I use to make 6mm predator--can you simply use a bushing for the 308 neck-up and an expander?

HiBC · September 11, 2017, 06:53 PM

Quote:

I'm not interested in the 30 ARX--but already have a grendel redding bushing die that I use to make 6mm predator--can you simply use a bushing for the 308 neck-up and an expander?

That concept went through my head.I would guess talking to a Redding (or other) customer service rep would be the best plan.I don't have the bushing dies and I don't know how the shoulder transition works out.
Good thinking!
Lee might be able to assemble components to make a collet type die,too.
Its possible if they see potential dollar signs in a new product they'd give a little support.
If you know someone with an EDM machine,you can alter the hardest dies to work.
For a bolt rifle,I'd just blow the necks out like I would making 35 Whelens or 40 basic out of 303.

Geezerbiker · September 11, 2017, 09:58 PM

As interesting as the .30 ATK sounds, I don't think it offers enough performance increase over the 7.62x39 to justify the cost. There are now several bolt action rifles in this caliber to choose from and I'm thinking about a Ruger ranch rifle in 7.62x39 for my next gun purchase. The Howa is tempting too...

Tony

stagpanther · September 12, 2017, 12:42 AM

Quote:

I don't know how the shoulder transition works out.

The redding die arrangement has what amounts to two bushings--the actual neck size change and one on top of it on the stem, there is a bit of a "float" to allow for self-centering concentricity--when you set the die you do a 1/16 turn out. My guess is that worse case scenario is that you might have to fire-form the brass once to "sharpen" the shoulder to neck transition. I'm thinking of eventually trying out a .257 in the grendel case (which is going the other way in a neck-down, but the .243 predator was pretty straight-forward so I don't see that being a problem).

kraigwy · September 12, 2017, 06:24 AM

Wouldnt a 7.62X39 AI be something along the lines of a 7.62X54R.

Or would that be a AI on steroids?

Mobuck · September 12, 2017, 06:47 AM

"Wouldnt a 7.62X39 AI be something along the lines of a 7.62X54R."
Basically completely different cartridges.
The thing with the 7.62x39 is the significant taper starting at the head of the case. The typical AI chamber is nearly cylindrical. Firing a standard case in the AI chamber would leave a large amount of the case unsupported during the fireforming process. This scenario would be less than optimum even if the case didn't just split. With so much room to expand , there would be a good chance the brass would come out lopsided or uneven (thick on one side/thin on the other).

oldscot3 · September 12, 2017, 10:55 PM

Years ago my brother and I played around with Ackleys and Gibbs improved cartridges. My 6.5 Gibbs didn't pan out at all; when velocity gains over, say your basic 270 Winchester, were realized, they were accompanied by serious over-pressure symptoms like blown primers and sticky bolt lift. I had the rifle to the gunsmith several times and tried everything I could think of to get even a percentage of the benefits touted by the wildcat faithful. No dice; after much expense and frustration the LGS I acquired it from bought it back from me.
My brother still has a couple he had made, a 257 Roberts improved and a 6.5 Swede improved. Ackley never did the Swede but he had a custom reamer made following Ackley's principles. He gets a very modest gain, but I'm suspicious that he's exceeding prudent pressures a little bit.
My experiences changed my thinking from, "velocity is king" to, "there is nothing more effective than putting a good bullet were its supposed to go" (even if it's 100 fps slower when it arrives).

The 7.62x39 is such a small case with a 30 cal bullet, I doubt if anything measurable would result from "improvement".

September 9, 2017, 04:49 PM	#1
10-96 Senior Member Join Date: October 19, 2005 Location: Tx Panhandle Territory Posts: 4,160	AI? Not to hijack Bbarn's threat, his question did lead me to a question of my own. I recently picked up a CZ 527 in 7.62x39. I've only made it to the range with it once so far, so I can't really say how I feel about it yet. But anyway, I got to wondering if anyone here has seen, done, or looked at the numbers from a 7.62x39 AI? I know, it sounds silly to me too, but ya gotta admit, there's not much new under the sun, and if nothing else- it would make for some interesting Ken Waters style reading. __________________ Rednecks... Keeping the woods critter-free since March 2, 1836. (TX Independence Day) I suspect a thing or two... because I've seen a thing or two.

September 9, 2017, 05:52 PM	#3
Scorch Senior Member Join Date: February 13, 2006 Location: Washington state Posts: 15,248	In PO Ackley's book, he says that the cartridges that benefit the most from "improving" are cartridges with a lot of taper to the case and shallow shoulder angle. I think the 7.62X39 fits into that category pretty well. For a bolt gun, an increase in pressure is not an issue (within reason), so you could even hot-rod it a little bit. Give it a try and do a write-up of before/after velocity and accuracy. __________________ Never try to educate someone who resists knowledge at all costs. But what do I know? Summit Arms Services

September 9, 2017, 09:23 PM	#6
10-96 Senior Member Join Date: October 19, 2005 Location: Tx Panhandle Territory Posts: 4,160	Naw, I wouldn't have the means or ability to do a x39 AI. And, I suppose it would put in the .300 Savage ballpark, but it was just fanciful thinking. But on the other hand- it would juice up my CZ 527 a bit and be something to give my buds a few "Ooohs and Ahhhs". But I would like to see what it's capable of... __________________ Rednecks... Keeping the woods critter-free since March 2, 1836. (TX Independence Day) I suspect a thing or two... because I've seen a thing or two.

September 9, 2017, 09:50 PM	#7
old roper Senior Member Join Date: June 11, 2007 Posts: 2,155	You could AI the case. I, AI the 35 Whelen and you have more shoulders on the 7.62x39 than the 35 Whelen. I build 7.62x39 using a 30 cal barrel and shot BIB 30 cal with 1/15 twist barrel. BIB got those 112gr/118gr 30 cal for 1/17 twist barrels. Look at this case http://bulletin.accurateshooter.com/...ve-shot-group/ __________________ Semper Fi Vietnam 1965 VFW Life member NRA Life Member

September 10, 2017, 02:50 AM	#10
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,287	I'm sure if the OP wanted to carry a 308 rifle ,he could. I think the point is the CZ rifle. It won't hold a 308. The 6.5 Grendel is a worthwhile cartridge based on the x39.Case taper is straightened out and it has a little sharper shoulder. Same with the very successful PPC cartridges.Based on the .220 Russian,which is essentially an Ackley'd x39 case,maybe with a slightly less sharp shoulder. This has all been done. There is a cartridge called the 30 Walker.Its a 30 cal PPC. This link will get you an article about a 30 cal version of the 6.5 Grendel. Is it worth it?Thats up to the OP. I think I saw 2500 fps with a 150 gr Sierra boat tail in the article.Standard 7.62x39 is about 2400 with a 123 gr bullet. This may not be exotic enough for full custom die and reamer prices. You might be able to conjure up a seating die with a chamber finish reamer,but not a sizing die. Obviously you can't resize cases by chambering them. It takes a separate reamer. Now,PTG or equiv can take a dull chamber reamer and regrind it to a sizing die reamer. You will still have a soft die . A conversation with Redding or Forster customer service MIGHT produce something as simple as a 6.5 Grendel bushing die with a 30 cal bushing. A Wilson type straight line seater might work out. For myself,a CZ in 6.5 Grendel would be sweet,but that is a re-barrel. Brownells handles a Howa small bbl'd action in 6.5 Grendel for more or less $500. http://bulletin.accurateshooter.com/...beats-300-blk/ Last edited by HiBC; September 10, 2017 at 03:04 AM.

September 9, 2017, 04:57 PM	#2
Geezerbiker Senior Member Join Date: March 20, 2011 Location: Willamina, OR Posts: 1,908	It sounds interesting to apply the Ackley treatment to the 7.62x39 for a bolt gun. So far I've not seen nor heard of anything like that. It would be expensive since the chamber reamer and dies would both be special order items... Tony

September 9, 2017, 06:09 PM	#4
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,287	You might look into the PPC series of cartridges and the .30 Walker. They may not fall exactly into the 7.62 x 39 AI pattern,but its a derivative of x39 brass ,30 deg shoulder and straightened body. Reamers,dies,etc will be much easier.

September 9, 2017, 09:15 PM	#5
ThomasT Senior Member Join Date: January 22, 2009 Location: Texas Posts: 2,753	If you are looking for more power than the 7.62-39 you might just jump to a 300 savage or 308. You will never get enough extra powder in that case to come close to matching those rounds. Why not just enjoy the round for what it is? If you need an AI chamber to make your round of choice an effective hunting round then you are way undergunned to start with.

September 9, 2017, 10:23 PM	#8
std7mag Senior Member Join Date: June 23, 2013 Location: Central Taxylvania.. Posts: 3,609	Chamber reamers are chamber reamers. Meaning that if you call Pacific Tool and Guage the price for a custom reamer isn't extreme. Custom dies however... Option is to get die blanks ($20) and have reamers made for them. Saves you about $400 or more. If you want to do 7.62x39AI, i say go for it! Let use know how it works out. I may be interestef in one too.

September 10, 2017, 01:09 AM	#9
Stats Shooter Senior Member Join Date: August 26, 2016 Location: North Dakota Posts: 1,636	I say go for it! Unremarkable results are still results. I mean, if you find that all you have done is made an expensive .308, then you can write it up. Research is often it's own reward. Also, models and extrapolation are good guides, but not a substitute for real world results. As others have said, a custom reamer can be machined for. 7.62x39 as easily as any other reamer. Then, you can get a gun Smith to ream a die blank for you with the same reamer. One big upside is that you would have a bunch of cheap brass to Ackley up. And you would have the only one I have ever heard of.

September 10, 2017, 06:53 AM	#11
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	I see a few reasons this is fools' play. The AI "concept" involved the capability to use factory standard chamber ammo in the AI chamber. How's that going to work with steel case ammo? The x39 design is purposely tapered to facilitate chambering and extraction in military weapons. Expanding the shoulder area to the extent that most AI designs use would likely split even brass case. In the old days, rechambering to an AI design was a CHEAP alternative to buying a different rifle or barrel. Current gunsmithing costs virtually negate this cost savings. Why not just choose a cartridge that suits your needs?

September 10, 2017, 08:30 AM	#12
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,287	I'm not particularly advocating for the project. I'm advocating having some respect for folks with ideas different than what I might do. I'd like to think we can discuss our ideas and priorities without some arrogant rude disrespectful person calling us a fool. What seems ignorant is the assumption anyone would consider fireforming or reloading steel cases. Split the brass case? Ackley himself said the best cases to AI have substantial taper.Regardless,Lapua and Norma,and maybe Hornady brass is available in the PPC and 6.5 Grendel configurations which are of minimal taper. I bought 500 .257 R virgin cases to feed my 257 R AI.Never was my plan to buy factory .257 R to shoot in my rifle.I never have. Mobuck ,you seem to think the 6.8 SPC is a reasonable option to fit a deer cartridge into an AR receiver. OK. Enjoy.I'm not going to rain on your parade. Why is it so hard to get that someone might want to boost the performance of the slick,small bolt action CZ? A 150 gr Sierra at 2500 fps ought to be fine for 250 yds or so. I'm sure our OP can get a $ estimate together and make his own decisions about 30 grs more bullet,a better BC and 100fps. I'm not going to build one. I would not build a 6.8 SPC,either. But I don't feel at all compelled to put down folks who enjoy their 6.8. In the mean time,I can treat his ideas with respect. As ARX Enterprises explains in the article,you just neckup Lapua 6.5 Grendel brass. ARX Enterprises sells dies. HMMM. I bet they could even chamber a CZ barrel.No need to buy the reamer. Last edited by HiBC; September 10, 2017 at 08:52 AM.

September 10, 2017, 12:23 PM	#13
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	Sounds like lipstick on a pig to me. As mentioned, you won't see much 'improvement'. "...The AI "concept" involved the capability to use factory..." Just for fire forming. Steel cased ammo is low end stuff anyway. If you're going to play with modifying a rifle and cartridge to AI, you're not likely to be using low end ammo. .220 Russian(5.56 x 39) is just a necked down 7.62 x 39. Allegedly for deer hunting . __________________ Spelling and grammar count!

September 10, 2017, 09:09 PM	#14
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	"Mobuck ,you seem to think the 6.8 SPC is a reasonable option to fit a deer cartridge into an AR receiver. OK. Enjoy.I'm not going to rain on your parade. Why is it so hard to get that someone might want to boost the performance of the slick,small bolt action CZ?" No problem, just choose a starting point with at least minimal chance for success(like having the action re-barrelled to 6.5 Grendel or one of the numerous wildcats based on the x39 case). The 6.8 is "plug and play" with a proven level of success. "Split the brass case? Ackley himself said the best cases to AI have substantial taper" Most likely Ackley was referring to the advantages of cases with more taper vs cases that already have minimal taper. The ability to fire factory ammo in an AI chamber was touted a a "big advantage" in case your AI ammo got lost, damaged, or forgotten on some long distance trip-not just as a way to fireform cases.

September 11, 2017, 03:35 AM	#16
Geezerbiker Senior Member Join Date: March 20, 2011 Location: Willamina, OR Posts: 1,908	That .30 ARX is an interesting looking caliber that would make a good round in a lightweight deer rifle. That is if the dies can be found. A quick search failed to turn any up. Tony

September 11, 2017, 04:03 AM	#17
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,287	Geezer,the article said ARX has them for sale

September 11, 2017, 04:55 PM	#18
Geezerbiker Senior Member Join Date: March 20, 2011 Location: Willamina, OR Posts: 1,908	The ARX website says the dies are available but I wasn't able to find them on their site... The dies they do have are expensive at $225 for a set. So you'd really have to be sure you want it before making the decision. Tony

September 11, 2017, 05:14 PM	#19
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,789	I'm not interested in the 30 ARX--but already have a grendel redding bushing die that I use to make 6mm predator--can you simply use a bushing for the 308 neck-up and an expander? __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!*

September 11, 2017, 09:58 PM	#21
Geezerbiker Senior Member Join Date: March 20, 2011 Location: Willamina, OR Posts: 1,908	As interesting as the .30 ATK sounds, I don't think it offers enough performance increase over the 7.62x39 to justify the cost. There are now several bolt action rifles in this caliber to choose from and I'm thinking about a Ruger ranch rifle in 7.62x39 for my next gun purchase. The Howa is tempting too... Tony

September 12, 2017, 06:24 AM	#23
kraigwy Senior Member Join Date: June 16, 2008 Location: Wyoming Posts: 11,061	Wouldnt a 7.62X39 AI be something along the lines of a 7.62X54R. Or would that be a AI on steroids? __________________ Kraig Stuart CPT USAR Ret USAMU Sniper School Distinguished Rifle Badge 1071

September 12, 2017, 06:47 AM	#24
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	"Wouldnt a 7.62X39 AI be something along the lines of a 7.62X54R." Basically completely different cartridges. The thing with the 7.62x39 is the significant taper starting at the head of the case. The typical AI chamber is nearly cylindrical. Firing a standard case in the AI chamber would leave a large amount of the case unsupported during the fireforming process. This scenario would be less than optimum even if the case didn't just split. With so much room to expand , there would be a good chance the brass would come out lopsided or uneven (thick on one side/thin on the other).

September 12, 2017, 10:55 PM	#25
oldscot3 Senior Member Join Date: July 1, 2007 Location: texas Posts: 997	Years ago my brother and I played around with Ackleys and Gibbs improved cartridges. My 6.5 Gibbs didn't pan out at all; when velocity gains over, say your basic 270 Winchester, were realized, they were accompanied by serious over-pressure symptoms like blown primers and sticky bolt lift. I had the rifle to the gunsmith several times and tried everything I could think of to get even a percentage of the benefits touted by the wildcat faithful. No dice; after much expense and frustration the LGS I acquired it from bought it back from me. My brother still has a couple he had made, a 257 Roberts improved and a 6.5 Swede improved. Ackley never did the Swede but he had a custom reamer made following Ackley's principles. He gets a very modest gain, but I'm suspicious that he's exceeding prudent pressures a little bit. My experiences changed my thinking from, "velocity is king" to, "there is nothing more effective than putting a good bullet were its supposed to go" (even if it's 100 fps slower when it arrives). The 7.62x39 is such a small case with a 30 cal bullet, I doubt if anything measurable would result from "improvement".