AI Confusion...

[std7mag]

I bought a used Stevens 200 in 7mm-08. Shoots well, especially with my hand loads. Bought it to hunt, and possible silhouette shoots.

I want to do the Ackley Improved to it. Got the reamer, go gauge. No-go gauge just arrived today.

Have not reamed it yet.

Put go gauge in and bolt closes.

Put no-go gauge in and bolt closes...

I'm at a loss as to where to go now....

Reamer and gauges are new from Pacific Tool and Gauge.

Any help would be greatly appreciated!!!
(although I suspect I know what you are going to tell me)

Std7mag

 

[James K]

I don't understand that. Either your gauges are not for the AI or the rifle has already been rechambered. Maybe there is something I don't know, but I don't see how you could even get the bolt closed on an AI gauge in a standard chamber. I think you need to do a lot of checking before going any further.

Jim

 

[Lucas McCain]

You say that it shoots well, look at your empties and see how they match up with your reamer and your gauges.
I am aware that there is a 243 AI and a 243 Win IMP, and they are different, I do not know if that is true with the 7MM-08 and you have the wrong stuff.

 

[std7mag]

I did check my hand loads(from that gun) to factory Federal cartridges.
Nothing visibly different.

Going to take gauges to local gun shop after work and see if the same happens to one of their guns. Then will know if it's the gauges or the gun.

 

[std7mag]

Ok, took both gauges to local gun shop.

Tried the no-go gauge in a Ruger American in .308, and a Savage Axis in .308.
Bolt closes on both guns.

Called Pacific Tool and Gauge. Was told that an "Ackley" no go is the same as a go gauge for standard .308, 7mm-08.

Also told that I now need a "standard" 7mm-08 no-go gauge.

Doesn't make any sense to me!!!

Please help me understand...


Std7mag

 

[Jim Watson]

What do you mean, "The bolt closes?"
Headspace is properly checked with a stripped bolt and fingertip pressure.
You don't load the gauge like your last cartridge with a charging buffalo.

 

[Brian Pfleuger]

The go gauge for the parent becomes the no go for the AI. As such, the AI go gauge will be "shorter", so it will close in a standard chamber.

The "no go" gauge is a slight misnomer. It's not unusual for a factory rifle to close on a no-go. You need a field gauge to check to see if it's out of spec. No go is more like a "maybe".

Not sure why you'd need a standard no-go.

 

[Bart B.]

I think you need to get a chamber cast then measure it to see what case it's made for.

 

[Sierra280]

This all makes sense, most Ackley chamberings are meant to have a 'crush' (~.003) on the headspace. So a factory go gauge would in effect become a no go.

 

[James K]

The GO/NO-GO gauges are used at factories or gunshops when a barrel is chambered. The whole business is best understood when put this way:

Mass produced ammunition is made to plus/minus tolerances. If all cartridges were made to a set of specs and perfectly made, there would be no problem, but they are not. So gauges ensure that a given rifle will accept and fire without danger all cartridges that are within set tolerances.

A GO gauge ensures that the longest cartridge that is within specs will chamber and fire. A NO-GO gauge ensures that the shortest cartridge that is within specs will not stretch beyond a certain limit when fired.

A FIELD gauge ensures that the shortest cartridge that is within specs will not stretch enough to tear apart when fired, thus disabling the gun.

So, a NO-GO gauge is a nice-to-have, but the real test comes with a FIELD gauge. Almost any rifle that has seen extended service will fail a NO-GO test, but that is not very important. Some will contend that any rifle that fails a NO-GO test must be rebarreled or scrapped; that is absurd. It is like the tread depth on a tire. To say that any tire with a tread depth less than that of the factory spec must be replaced is nonsense; tires with ten miles on them would be scrapped under that idea.

Jim

 

[Bart B.]

Almost any rifle that has seen extended service will fail a NO-GO test

What's "extended service?"

If that's true, how many .30-06 rounds does an action need to have its bolt face set back more than .010" from the receiver face? That's the difference between a GO and NO GO headspace gauge for it.

Some folks rebarreled their M1903 Springfields every year with a new $4.00 barrel from the DCM back in the early 1900's. After 20 years and 20 barrels (2000 to 3000 or so rounds each), the same receiver and bolt headspaced safely on all of them. Evidence to me the bolt face setback over some 40,000+ rounds was insignificant.

And tire spec'd tread depth is the minimum recommended before replacing, not the new, maximum tread depth.

 

[Clark]

In 2002 I chambered a rifle in 257 Roberts Ackley Improved with a new piece of 257 Roberts brass as the go gauge. I could just barely feel the brass as I closed the bolt.

That did not work out well. The firing pin pushes the case forward and the base of the chamber neck cuts into the base of the case neck. This allows the case to move too far forward, ~0.004". Then the powder goes off, the case walls grab the chamber walls, the case head is pushed back and thus the case stretches. The case cracks behind the shoulder. See attached pic. I have tried ~100 things for form the case. The easiest I have found is 10 gr pistol powder covered with Cream of Wheat and high pressure lube on the outside of the case. This forms half a shoulder. That brass can take full 257 RAI loads and get the same 0.5 moa accuracy that fully formed shoulders can.

What does it all mean?
Ackley chambers should be headspaced .004" shorter than the brass. When brass is put in the chamber, the base of the chamber neck should dig into the base of the case neck by .004".

 

[Jimro]

std7mag,

You have a Stevens.

Loosen the barrel nut and then adjust the barrel onto the "go" guage until it stops. Tighten the barrel nut, this will set headspace.

Now rechamber to AI. Repeat the headspace setting excercise after.

Jimro

 

[old roper]

STD7Mag.

This is from Dave Manson Manson Reamer on the Ackley

http://www.mansonreamers.com/Instructions/Ackley Gaging.pdf

 

[mete]

Hatcher's Notebook has an interesting discussion about this . When the bolt is closed fast and forcefully as you might in a wartime situation , the shoulder is pushed back noticably !!

 

[Bart B.]

mete, most folks have no idea how much low angled rimless case shoulders set back from slamming bolts chambering them; especially when external extractors press hard on case rims as it slides over them. And firing pin impact can do the same thing.

All of which why Holland & Holland's rimless cases made from rimmed ones (used in double rifles) with very low shoulder angles had to have a belt added so they would maintain headspace in bolt action rifles. This happened about a century ago.

 

[Jimro]

Bart B.,

The bolt action rifles Holland and Holland was working with were controlled round feed Mauser actions.

The non-rotating claw extractors holds the brass against the bolt face, no shoulder slamming involved at all which is why the 7x57, 8x57, 30-06, and even 30-40 Krag could get by with shallow shoulder angles.

This is one of the reasons why controlled round feed actions such as the 1903 Springfield, 1917 Enfield, and M98 had no problem with the very shallow shoulders of the 35 Whelen cartridge or even 400 Whelen, while push round feed actions like the Rem700 and Rem670 pump actions had headspacing issues.

So your explanation of why Holland and Holland put the belt on those doesn't fit the facts of the matter. Never could figure out a good structural reason myself, other than the belt gives a handy lip for the fingers to grab when trying to stuff ammo back into a rifle in a hurry.

Jimro

 

[Clark]

Jimro,
I can see what the belts are for, by looking at them. They are to stand up to firing pins that push the cartridge forward.

 

[Bart B.]

No Mauser style non-rotating claw extractor based rifle I've shot held the case head against the bolt face when the primer fired. They all had enough claw to bolt face clearance to let shoulders set back from firing pin impact. Tested .300 & .375 H&H mags, .308 Win and. .30-06 based cartridges with primed cases measuring case shoulder headspace before and after firing those primed cases.

Actions used in my tests were German M98 and FN Mausers, M1903, M1917, Win 70 classic, a magnum Mauser (.375 H&H) and one or two others.

All of them had the claw pushed forward upon case ejection to gave plenty of space between it and the bolt face to easily let rounds from the magazine slip their rims in behind the extractor claw lip. Even saw some extractors move forward on firing; proof to me they didn't hold the case head against the bolt face but got pushed forward with the case from firing pin impact.

All such extractors I know of have no force in/on them to pull them back after a round's chambered. And I think its a good idea to not let firing pins drive case rims hard against extractor claws. It's good to have the case stop against its headspace point instead of the extractor. Extractors last much longer so designed. Besides, cartridges would be pushed crooked in the chamber with their rim stopped against the claw misaligning the bullet with the bore; not good for accuracy if they fired so chambered.

As H&H made rimless cases made from rimmed ones as rimmed ones didn't load into and feed reliable ftom bolt action box magazines, that belt gave reliable headspacing in double rifles as well as use in box magazines. Hunters could have a bolt action and double chambered for the same cartridge.

History on that belt:

http://www.chuckhawks.com/great_cartridge_families.htm

 

[Clark]

When I convert a 98 Mauser to belted magnum, I have to open the bolt face and relieve the extractor.

That is easy. 223 conversion is hard.