Radio
10 Years on the Files
FALaholic # 263
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I agree, it's not as hard as many folks might worry it is. I'll try to cover as many bases for you here as I can think of.
1.630" Forster GO
1.630" Winchester .308 minimum
1.6315" NATO 7.62 minimum
1.632" Clymer GO
1.634" Forster NO-GO
1.636" Clymer NO-GO
1.638" Forster FIELD
1.638" Winchester .308 maximum
1.640" Clymer FIELD
1.640" NATO 7.62 maximum
Factoring in SETBACK will make your initial pin gage/sizing rod thickness GROW by .001" because the locking shoulder will move away from the chamber, "set back," and thus require a thicker gage/rod (or locking shoulder) to return to the same headspace dimension you started with.
(People who are smarter than me seem to think that introducing firing pressure into a just-assembled rifle, in addition to affecting the locking shoulder, also seats the threaded barrel into the receiver. It usually all adds up to about .001" anyway.)
* Your bolt closes with two-thumbs pressure on a .262" pin/rod
* To account for "setback" ADD .001"
* Correct pin/rod will now be .263"
* This is true regardless of which brand of headspace gauges you are using.
CLYMER GAUGES: Clymer GO is 1.632"; add the .001" for setback and you're done, the rifle's headspace is set at 1.632".
FORSTER GAUGES: Forster GO is 1.630"; in this case, add your .001" setback compensation THEN SUBTRACT .002" to set the rifle's headspace at 1.632".
If for some reason you want to resist conventional wisdom and set your rifle's headspace larger than 1.632", take the difference between your target figure and whatever gauge you're using and SUBTRACT from your nominal pin gage/sizing rod/locking shoulder reading, again after first ADDING .001" for setback.
EXAMPLE:
* Your bolt closes on two-thumbs pressure on a .260" pin/rod
* ADD .001" for setback, equals .261"
* You are using a Forster GO gauge, 1.630"
* You'd like a 1.634" headspace
* SUBTRACT .004" from .261", equals .257" locking shoulder.
Probably more people use the Forster set than the Clymer. What perhaps contributes to confusion is that +.001 -.002 = -.001, so builders are constantly trying to remember if that's PLUS .001 or MINUS .001 to get where they're trying to go. If you do it the long way, you'll always get it right. SETBACK GROWS THE LOCKING SHOULDER READING BY .001".
I didn't know about Lockstock back in "olden times;" I paid $16.95 each for my Forster gauges at Bushmaster. My Clymer gauge, of course, cost a lot more and I have yet to see a good deal on those.
--Radio
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"Very damaged. Zathras can never have anything nice." --Zathras, Babylon 5
Status: Offline | Posts: 9876 | Registered: Jul 2000 | Marketplace Rating: (0) | IP: Logged | Report this post to a Moderator
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May 22, 2002 00:11
Thanks for saving me some time!!! I'll be putting in my order for some tomorrow. Check that... They are on order NOW!!! Was super easy having the part numbers from the link you posted.
