Reamer input

[Justice1327]

Hello, please see attached. Looking for. Reamer inputs, for my two AI cartridges.
One attachment is the SAAMI print and the other is my reamer print. Just want to make sure the .200 datum line is ok and the body/neck junction isnt too large. Any other input or suggestions is appreciated.

Lapua 6.5x55 brass measures
.200 datum: .473
Body/neck: .430

Win 7x57 brass measures
.200 datum: .464
Body/neck: .424

 

[Tac-O]

So it looks like they're improved cartridges but not AI since you're increasing headspace for your reamers, right?

For 0.200 line, I'd go 0.004ish larger than your brass. The magnum cases reamers that have a 0.200 dimension that prevents sticky extraction after multiple reloads is generally 0.005 bigger than the case, but those are generally harder to resize than standard size cases due to size. So depending on how hot you're going to load and how many reloads you want to be able to get, I'd do 0.003-0.004 on yours. And of course, you want to make sure your resize die diameter at 0.200 is small enough to get enough sizing to prevent sticky extractions, which generally works well at 0.001 smaller than virgin brass.

For shoulder width, I can't speak to blowing it out as much as you're going to. It seems most people try to stick to a body TPI of 0.010 per inch. You can get away with less if the case is shorter. Yours might be fine with those cases but I don't know.

You didn't ask, but I thought I'd comment on the freebore width. It is more common now to have a freebore that is 0.001 over bullet size which helps prevent pressure issues from carbon buildup and it does not affect accuracy, per Alex Wheeler. I think in some of his more recent reamer prints he's used 0.0012 over bullet diameter.

 

[Mikecr]

For the 6.5x55, SAAMI is already grossly too big for the brass, and you went even worse..
When clearance at/near webs is excessive, the brass yields like crazy there. THIS is a contributor to difficult extraction.

People commonly think that more clearance solves what excess clearance already causes..
And it works like gas to put out a fire

 

[Justice1327]

So it looks like they're improved cartridges but not AI since you're increasing headspace for your reamers, right?

For 0.200 line, I'd go 0.004ish larger than your brass. The magnum cases reamers that have a 0.200 dimension that prevents sticky extraction after multiple reloads is generally 0.005 bigger than the case, but those are generally harder to resize than standard size cases due to size. So depending on how hot you're going to load and how many reloads you want to be able to get, I'd do 0.003-0.004 on yours. And of course, you want to make sure your resize die diameter at 0.200 is small enough to get enough sizing to prevent sticky extractions, which generally works well at 0.001 smaller than virgin brass.

For shoulder width, I can't speak to blowing it out as much as you're going to. It seems most people try to stick to a body TPI of 0.010 per inch. You can get away with less if the case is shorter. Yours might be fine with those cases but I don't know.

You didn't ask, but I thought I'd comment on the freebore width. It is more common now to have a freebore that is 0.001 over bullet size which helps prevent pressure issues from carbon buildup and it does not affect accuracy, per Alex Wheeler. I think in some of his more recent reamer prints he's used 0.0012 over bullet diameter.

Thank you for your input.
These are supposed to be Ackley improved cartridges
Can you tell me how I change the headspace by changing the shoulder angle to 40° and increasing the body neck junction diameter.
What would you change the free bore to for each of these cartridges?

 

[Tac-O]

Thank you for your input.
These are supposed to be Ackley improved cartridges
Can you tell me how I change the headspace by changing the shoulder angle to 40° and increasing the body neck junction diameter.
What would you change the free bore to for each of these cartridges?

Unless I read the prints wrong, it looks like your headspace is longer than saami. For an Ackley improved chamber, the headspace is supposed to be 0.004 less than the saami minimum headspace gauge, that way when you chamber a round it is a slight crush fit for fire forming.

The shoulder angle is changed to 40*. I'm not sure, but I believe that PO ackleys general body taper was about 0.010/inch, but he may have had some that were a bit more or less. It is a good place to start. Calculate your new shoulder diameter based on the diameter of and length from 0.200 line.

If you talk to JGS, I recommend just telling them you want to AI those cartridges and they'll make a print and reamer that is spot on for the body dimensions.

 

[VinceMule]

I would measure the inside dia of your full length sizer, you can not use calipers.

 

[KRP]

Unless I read the prints wrong, it looks like your headspace is longer than saami. For an Ackley improved chamber, the headspace is supposed to be 0.004 less than the saami minimum headspace gauge, that way when you chamber a round it is a slight crush fit for fire forming.

The shoulder angle is changed to 40*. I'm not sure, but I believe that PO ackleys general body taper was about 0.010/inch, but he may have had some that were a bit more or less. It is a good place to start. Calculate your new shoulder diameter based on the diameter of and length from 0.200 line.

If you talk to JGS, I recommend just telling them you want to AI those cartridges and they'll make a print and reamer that is spot on for the body dimensions.

An Ackley cartridge's headspace is longer than the parent cartridge.

Without a specific gauge with the proper shoulder angle and dimension the parent cartridge go gauge -.004 is how it is typically set just as directed on those prints.

The parent cartridge, or gauge, should make contact at the neck/shoulder junction in an Ackley chamber, you'll notice that dimension is a few thousandths shorter, and is where the "crush fit" comes from.

 

[VinceMule]

KRP, you are correct in your explanation, but the AI is Shorter than the parent case, which may confuse some. I measure the headspace of the new brass I have on hand, then headspace .004-.006 on the shortest piece. I want firm contact on closing the bolt, and I keep the lugs lubed every 25 rounds or so, fire forming with bullseye and cream of wheat.

Dies are made on SAAMI spec dimensions. If you reduce the reamer print too much, then your full length sizer is worthless. This was an expensive lesson to learn. At that point, you have the choice of ordering a die reamer which is .010 smaller than your reamer, set the barrel back and re chamber with SAAMI spec reamer, or cut the chamber to a new caliber if you have enough barrel shank to do so.

I have a custom 6.5x55 on a Rem long action, 26" Pac Nor barrel, #6 contour. I shoot 130s at 3150 with R#26 and cci 250 primers in Lapua brass. This is a safe working max load for my barrel and chamber, but I started seeing increases bolt lift on .5g Hotter.

 

[Tac-O]

An Ackley cartridge's headspace is longer than the parent cartridge.

Without a specific gauge with the proper shoulder angle and dimension the parent cartridge go gauge -.004 is how it is typically set just as directed on those prints.

The parent cartridge, or gauge, should make contact at the neck/shoulder junction in an Ackley chamber, you'll notice that dimension is a few thousandths shorter, and is where the "crush fit" comes from.

Yep, you're right! I did a poor job of explaining that. Thanks for the correction.

 

[Justice1327]

I would measure the inside dia of your full length sizer, you can not use calipers.

I don’t have any dies yet. I wait till I fire the Brass three times then have them made.

 

[KRP]

KRP, you are correct in your explanation, but the AI is Shorter than the parent case, which may confuse some. I measure the headspace of the new brass I have on hand, then headspace .004-.006 on the shortest piece. I want firm contact on closing the bolt, and I keep the lugs lubed every 25 rounds or so, fire forming with bullseye and cream of wheat.

Dies are made on SAAMI spec dimensions. If you reduce the reamer print too much, then your full length sizer is worthless. This was an expensive lesson to learn. At that point, you have the choice of ordering a die reamer which is .010 smaller than your reamer, set the barrel back and re chamber with SAAMI spec reamer, or cut the chamber to a new caliber if you have enough barrel shank to do so.

I have a custom 6.5x55 on a Rem long action, 26" Pac Nor barrel, #6 contour. I shoot 130s at 3150 with R#26 and cci 250 primers in Lapua brass. This is a safe working max load for my barrel and chamber, but I started seeing increases bolt lift on .5g Hotter.

What's shorter?

 

[VinceMule]

AI of course has the shorter headspace. I like a crush fit, so -.006 is more to my liking.

 

[Tac-O]

AI has longer headspace, headspace being measurement from base to 0.365 datum line on shoulder. But AI has a shorter measurement from base to neck/shoulder junction.

 

[Justice1327]

I am confused now.