22 ARC SAMMI specs show headspace specs as 1.220 - .007. Fired factory Hornady brass measures 1.224. New barrel from Rainer Arms. Thinking chamber is to long by .004. Checked with a few others on FB group and most were getting 1.217 after firing. Unfired Hornady brass is 1.215. This increase is to much, correct. Have emailed Rainer Arms concerning this. Am I on the right track or am I making a mountain out of a mole hill.
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22 ARC headspace concern
- Thread starter rick539
- Start date
Are you using something like the Area419 .350 or SAC .350 (specifically the .350 from sac, not their shoulder insert) ?
If not, what datum gauge specifically are you using to measure your fired brass?
Also, you're quoting SAAMI spec for the cartridge. It can be as short as 1.213.....which your Hornady starts out inside. Min chamber length is 1.220 and max chamber is 1.2301.....which your fired brass is inside of.
In theory, you could have a chamber at 1.2301 and a cartridge at 1.213 which would be the difference of .017.
So, basically, your chamber is within SAAMI based on your measurements so far. In fact, if your brass doesn't grow more than 1.220 and you're using an .350 datum gauge, your chamber is actually cut the minimum SAAMI spec.
(actual headspace is spec'd on the chamber print, not the cartridge)
In theory, you could have a chamber at 1.2301 and a cartridge at 1.213 which would be the difference of .017.
So, basically, your chamber is within SAAMI based on your measurements so far. In fact, if your brass doesn't grow more than 1.220 and you're using an .350 datum gauge, your chamber is actually cut the minimum SAAMI spec.
(actual headspace is spec'd on the chamber print, not the cartridge)
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Thank you. I had the cartridge sammi spec on one page and failed to look at the chamber spec sheet. Thank you for pointing this out. Guess I need to email Rainer and say….never mind.
Most all Comparator Datum measurements DO NOT agree with SAAMI measurements.
I believe the only one may be the .350" SAC insert that may show real measurements that Rio Precision pointed out.
I went through this years ago thinking my Hornady Datum comparator gave me real SAAMI measurements. I learned that the inserts have a chamfer on the edge. I have two .400 inserts. I used a 308 1.630" Go gauge and measured it with both inserts. One insert measured 1.611" which shows a .019" chamfer and the other one measured 1.622", which showed a .008" chamfer.
You can't compare your Datum insert measurements with anyone else as their measurements will most likely be different than yours.
I believe the only one may be the .350" SAC insert that may show real measurements that Rio Precision pointed out.
I went through this years ago thinking my Hornady Datum comparator gave me real SAAMI measurements. I learned that the inserts have a chamfer on the edge. I have two .400 inserts. I used a 308 1.630" Go gauge and measured it with both inserts. One insert measured 1.611" which shows a .019" chamfer and the other one measured 1.622", which showed a .008" chamfer.
You can't compare your Datum insert measurements with anyone else as their measurements will most likely be different than yours.
Area419 set and the datum insert from SAC should work for getting absolute measurements. Or any insert that is custom made with the proper size hole that isn't chamfered or any other such alteration to the datum hole.
What does it matter if you're reloading? Set your sizing die to bump 2 - 3 thou and call it good. When reloading that's all that really matters.
