ElmerThud
Handloader
- Jul 16, 2011
- 809
- 119
I wanted to find an exact chamber measurement to determine 'Go' and 'No Go' dimensions when setting up my re-sizing dies and a lady (Julie) from a Scottish gunsmith company made the following reply.
The method as I understand it can be used to determine the correct 'Go' / No Go' measurement in any rifle. I think it may be helpful to some of you guys out there. ATB ET. She states the following:
Chamber/Breech Head space Measuring
HS gauges for the 6.5x55 SE are not available as a series, only the usual g/ng/f
The only sets of which generally available, are for the 308/7.62 series and derivatives.
This for two reasons:
1. The rather obvious 308 vs 7.62 head space difference - so OK to use 7.62 in a 308 chamber but not 308 ammo in a 7.62 gun etc
2. Traditionally the custom target rifles tend to be based on 308 cases, so if you built a custom rifle, you would head space down to the bottom end of the acceptable range – hence why 308/7.62 HS gauges can be obtained in a series.
This second point also guides you on the approximate HS your gun will have. If the rifle is a custom target version, it will usually be head spaced around the bottom end, so typically, a little over the ‘Go’ gauge (1.7794) – say 1.780 – 1.781. If however it is a general or stalking rifle, it would be head spaced towards the ‘No Go’ (1.785) to ensure it’s “less fussy about ammo or cases” – say 1.783 being a Sauer and 1.785 if it was Ruger etc.
Of course this is when new. After manufacture when it has been used a lot, most guns head space well above the ‘No Go’ guage, which is OK as long as it is below field (1.789)
This will depend on the gun and usage/age.
These days custom target rifles don’t tend to be based on 308 cases anymore and are usually some wildcat derivative – in which case we use a different technique for head space measurement – which you may use.
Basically it is usual when building a custom target rifle in some odd wildcat based cartridge, to only have the ‘Go’ gauge manufactured. Therefore, when chambering just ensure it ‘Goes’.
Then, for the ‘No Go’ just add packing.
Rizla paper comes in various thicknesses, so if you use the Rizla ‘Silver’ it is around 0.8 mill thick – about 0.02mm – so using two ‘Silver’ Rizla papers on the head of the head space gauge will change the 6.5 x 55 go (1.7794) to 1.781!
Method: Use a tight(ish) case then add packing. (Draw the paper over your jumper/trousers so that it will receive enough static to stick to the case head) Adding pieces of paper until you generate a situation where the cartridge Will/Won’t ‘Go’.
e.g., three papers will ‘Go’, but four won’t, then use your current measuring method (I assume you are using the Hornady Cart HS kit) – which will give you the range as say 1.7832 will ‘Go’ whilst 1.784 won’t.
Unfortunately there are a few downsides here.
First, the Hornady kit is designed to be used with a Vernier or digital calliper and the digital’s aren’t too accurate. Only accurate to 1-2 mill or so and although verniers are much more accurate, they are very expensive. The usual ones available are generally not suitable in my view, so you do need to use a micrometer to correctly measure with great accuracy.
Second, be careful about the paper. The paper may stick to the bolt face. (When you measure it you miss a couple of thicknesses) You fold the paper over and miss a thickness, or you can compress the paper with the bolt – therefore it’s a good idea to limit the number of papers to 3 or 4.
Whatever you do, use care to arrive at the correct measurement and the data will be useful as an aid to consistent reloading of your ammunition when full-length re-sizing cartridge cases.
Julie
The method as I understand it can be used to determine the correct 'Go' / No Go' measurement in any rifle. I think it may be helpful to some of you guys out there. ATB ET. She states the following:
Chamber/Breech Head space Measuring
HS gauges for the 6.5x55 SE are not available as a series, only the usual g/ng/f
The only sets of which generally available, are for the 308/7.62 series and derivatives.
This for two reasons:
1. The rather obvious 308 vs 7.62 head space difference - so OK to use 7.62 in a 308 chamber but not 308 ammo in a 7.62 gun etc
2. Traditionally the custom target rifles tend to be based on 308 cases, so if you built a custom rifle, you would head space down to the bottom end of the acceptable range – hence why 308/7.62 HS gauges can be obtained in a series.
This second point also guides you on the approximate HS your gun will have. If the rifle is a custom target version, it will usually be head spaced around the bottom end, so typically, a little over the ‘Go’ gauge (1.7794) – say 1.780 – 1.781. If however it is a general or stalking rifle, it would be head spaced towards the ‘No Go’ (1.785) to ensure it’s “less fussy about ammo or cases” – say 1.783 being a Sauer and 1.785 if it was Ruger etc.
Of course this is when new. After manufacture when it has been used a lot, most guns head space well above the ‘No Go’ guage, which is OK as long as it is below field (1.789)
This will depend on the gun and usage/age.
These days custom target rifles don’t tend to be based on 308 cases anymore and are usually some wildcat derivative – in which case we use a different technique for head space measurement – which you may use.
Basically it is usual when building a custom target rifle in some odd wildcat based cartridge, to only have the ‘Go’ gauge manufactured. Therefore, when chambering just ensure it ‘Goes’.
Then, for the ‘No Go’ just add packing.
Rizla paper comes in various thicknesses, so if you use the Rizla ‘Silver’ it is around 0.8 mill thick – about 0.02mm – so using two ‘Silver’ Rizla papers on the head of the head space gauge will change the 6.5 x 55 go (1.7794) to 1.781!
Method: Use a tight(ish) case then add packing. (Draw the paper over your jumper/trousers so that it will receive enough static to stick to the case head) Adding pieces of paper until you generate a situation where the cartridge Will/Won’t ‘Go’.
e.g., three papers will ‘Go’, but four won’t, then use your current measuring method (I assume you are using the Hornady Cart HS kit) – which will give you the range as say 1.7832 will ‘Go’ whilst 1.784 won’t.
Unfortunately there are a few downsides here.
First, the Hornady kit is designed to be used with a Vernier or digital calliper and the digital’s aren’t too accurate. Only accurate to 1-2 mill or so and although verniers are much more accurate, they are very expensive. The usual ones available are generally not suitable in my view, so you do need to use a micrometer to correctly measure with great accuracy.
Second, be careful about the paper. The paper may stick to the bolt face. (When you measure it you miss a couple of thicknesses) You fold the paper over and miss a thickness, or you can compress the paper with the bolt – therefore it’s a good idea to limit the number of papers to 3 or 4.
Whatever you do, use care to arrive at the correct measurement and the data will be useful as an aid to consistent reloading of your ammunition when full-length re-sizing cartridge cases.
Julie
