CIP Headspace Gauges ?
- Thread starter waltk
- Start date
Walt Krafft
Gold $$ Contributor
Headspace tolerance is cartridge specific. There is no standard.
waltk
Gold $$ Contributor
Really?
WSnyder
Silver $$ Contributor
In general a lot of (maybe most?) SAAMI chambers from min to max shoulder datum is .010" difference but not all. As he said you need to look at the particular SAAMI cartridge to see what min max is. Are you confusing the various go, no go, field gauges and their dimensions?
dellet
Gold $$ Contributor
CIP and SAAMI chambers for the same cartridge are not always the same. I know of one person who sent a rifle to Europe and it could not pass Proof testing for this reason without a lot of extra time and expense.
If you look at CIP spec prints they do not have a “headspace” measurement. The distances from base to body to shoulder junction and base to shoulder to neck are defined along with the angle. No base to shoulder datum measurement. CIP, like SAMMI has a minimum chamber with both length and diameter maximum allowable variation.
What is interesting is that those lengths are basically the same, but in a SAAMI chamber +.002” length allowance somehow translates into .010” headspace variation. More than combining diameter and length would seem to cause.
If you look at reamer prints you can find 30.06 Springfield in both SAAMI and CIP versions and they differ in measurements, more than converting inches to millimeters. Also worth noting that the CIP reamer print does include a reference or datum line on the shoulder with a tighter tolerance and that point is at a different diameter on the shoulder than the SAAMI reamer.
Good for Forster for filling a gap.
If you look at CIP spec prints they do not have a “headspace” measurement. The distances from base to body to shoulder junction and base to shoulder to neck are defined along with the angle. No base to shoulder datum measurement. CIP, like SAMMI has a minimum chamber with both length and diameter maximum allowable variation.
What is interesting is that those lengths are basically the same, but in a SAAMI chamber +.002” length allowance somehow translates into .010” headspace variation. More than combining diameter and length would seem to cause.
If you look at reamer prints you can find 30.06 Springfield in both SAAMI and CIP versions and they differ in measurements, more than converting inches to millimeters. Also worth noting that the CIP reamer print does include a reference or datum line on the shoulder with a tighter tolerance and that point is at a different diameter on the shoulder than the SAAMI reamer.
Good for Forster for filling a gap.
jareese
Gold $$ Contributor
When none of them can agree on a standard for WHERE the actual Datum line is, that makes things a little more less standard. I've seen a few seperate HS gauges for the same cartridge, from same manufacturer, vary by 4-6 thou... I don't buy cheap the ones.
Is there any more thoughts on these cip Forster gauges with the .004 clearance between min and max? Was thinking about a set for the 6BR Norma and didn’t know if you did anything different on the max guage(ie: add a piece of tape?), these being different from the .010 regular go-no go gauges.https://www.forsterproducts.com/product/cip-dimensioned-headspace-gages-rimless/
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The nogo gauge is a gunsmith's tool. SAAMI/CIP has nothing to do with it. All of my old Remington barrels would cheerfully swallow a +0.004" nogo gauge. Go +0.004" is common, Manson does Go +0.006" as their default nogo gauge. As mentioned earlier, they'll make it whatever length you want if it's custom ordered.
Max SAAMI chamber length is determined with a Field gauge. Often, that's 0.010" over minimum (Go).
A typical full SAAMI spec would be +10 on the chamber, -10 on the case, tested at 20% over pressure. I wouldn't plan on reusing that piece of brass but it's within the standard.
Setting up a prefit barrel using just a go gauge isn't much of a trick. If you have a bump gauge, it's easy enough to figure out what the tape adds to the length. Don't use a thick piece of mushy tape. The gauges are discounted when you buy them with a reamer and I'll buy both. Fooling around with tape isn't worth my time. Even with gauges in 0.001" increments, there would still be a feel and judgement component to using them. For a novice, anything within 0.002" either side of a given gauge would be a pretty good first effort. On bolt guns, I don't bother stripping the bolt, but I do check that the ejector will go below flush.
I use the Hornady bump gauge to compare a case fired at full pressure with the go gauge I set the barrel up with. If there is 0.001" difference, I hang my head in a moment of silent shame and move on.
If I receive a new batch of brass and it's within 0.006" of the go gauge, I'll fire it. By 0.008", I'll open the neck up at least 0.020" and put a false shoulder on it. I've had batches of brass from boutique manufacturers that were 0.016" under the go gauge. 0.012" under isn't uncommon enough for bulk brass. This is a brass life issue, not a safety one. If there is too much of a change in length on the first shot, the brass will concentrate that change on a short section. The necking it produces will focus both the loss of thickness and decrease in ductility on that spot, shortening the case life significantly. With factory barrels, the brass length criteria should be adjusted for the chamber dimensions indicated by a piece of fired brass. I'll throw a piece in the die box after the gun is fired for the first time.
If you set up a prefit, you're outsmarting yourself if you sell the go gauge when you're done.
Max SAAMI chamber length is determined with a Field gauge. Often, that's 0.010" over minimum (Go).
A typical full SAAMI spec would be +10 on the chamber, -10 on the case, tested at 20% over pressure. I wouldn't plan on reusing that piece of brass but it's within the standard.
Setting up a prefit barrel using just a go gauge isn't much of a trick. If you have a bump gauge, it's easy enough to figure out what the tape adds to the length. Don't use a thick piece of mushy tape. The gauges are discounted when you buy them with a reamer and I'll buy both. Fooling around with tape isn't worth my time. Even with gauges in 0.001" increments, there would still be a feel and judgement component to using them. For a novice, anything within 0.002" either side of a given gauge would be a pretty good first effort. On bolt guns, I don't bother stripping the bolt, but I do check that the ejector will go below flush.
I use the Hornady bump gauge to compare a case fired at full pressure with the go gauge I set the barrel up with. If there is 0.001" difference, I hang my head in a moment of silent shame and move on.
If I receive a new batch of brass and it's within 0.006" of the go gauge, I'll fire it. By 0.008", I'll open the neck up at least 0.020" and put a false shoulder on it. I've had batches of brass from boutique manufacturers that were 0.016" under the go gauge. 0.012" under isn't uncommon enough for bulk brass. This is a brass life issue, not a safety one. If there is too much of a change in length on the first shot, the brass will concentrate that change on a short section. The necking it produces will focus both the loss of thickness and decrease in ductility on that spot, shortening the case life significantly. With factory barrels, the brass length criteria should be adjusted for the chamber dimensions indicated by a piece of fired brass. I'll throw a piece in the die box after the gun is fired for the first time.
If you set up a prefit, you're outsmarting yourself if you sell the go gauge when you're done.
Thank You. That is a great explanation!
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