Need Help: .308 FTF

[Hoser]

If I'm understanding correctly, this is your point, right ?

Yup.

[james_bond_007]

Yup.

Thanks for "learnin' me" .

[james_bond_007]

Any comments on my questions in post #54 ?
http://www.ar-15.co/forums/showpost....7&postcount=54

[james_bond_007]

I typically learn more if I can research things and "make a stab at it".
So, as is my nature, here's "a stab at" answering one of my own questions. Please understand that I'm not trying to "teach", but sort of regurgitating my research findings:

• C: If SAAMI indicates headspace of 1.627" to 1.634"

1. What value should I strive for? 1.627" ? 1.634" or something in between?
2. If I KNEW my chamber headspace, what value of cartridge headspace would I strive for ?

Answer is Headspace should allow :
a) about 0.002" shorter cartridge than chamber for bolt rifles
(and there are subtly different opinions on this)
and
b) about 0.004" to 0.005" shorter cartridge than chamber for semi/gas guns.
(and there are subtly different opinions on this)

The question of whether the chamber is within SAAMI specs is a different issue.

Measuring the chamber headspace (distance from the chamber datum point to the boltface) can be tough to do with semis/gas guns.

[james_bond_007]

So what are the recommended methods for measuring chamber headspace on a semi/gas gun?

1) Call the manufacturer - I've read (and cannot attest by any other means) that Springfield Arms measured all the chambers and provided them with the rifle. As I bought mine used, I have no such document. I HAVE sent an email to SA to request the info. This is, of course, providing the bolt is the original bolt shipped when new.

2) Use Go/No-Go gauges - I've read that (and cannot attest by any other means) one can check to see if the bolt DOES close on a GO gauge or DOES NOT close on NO-GO gauge. This will tell you that you are in the range of SAMMI or NATO measurements for said gauges, respectively.

• SAMMI 308
  
  • Go = 1.6300"
  • NoGo = 1.6340"
  • Field = 1.6380"
  • Reject= 1.640"
  
  

• NATO 7.62 x 51
  
  • Go = 1.6355"
  • NoGo = 1.6405"
  • Field (reject) = 1.6455"
  
  

3) Use Resized Test Brass - I've read (and cannot attest by any other means) that one can resize some brass, chamber it , and try it like a GO/NOGO gauge. There seems to be some issues with the accuracy of this method, such that when the brass is a bit long, the shoulder may get crushed and shortened when closing the bolt. It was suggested to measure the brass after testing. Also, it was indicated that if one tries to mark and save a "golden standard", be cautious to remeasure the piece after every test, as it could get crushed and change with each trial.

4) Measure a Spent Case - I've read (and cannot attest by any other means) that a spent case will be fire-formed to the chamber dimensions. While this can be true for bolt guns, it was indicated that it MAY not work well for semis/gas guns. Seems that the bolt may begin to extract the cartridge while pressure in the chamber is still sufficiently high, causing the cartridge to continue expanding while being extracted.

5) Feeler Gauge - I've read (and cannot attest by any other means) that if one removes the ejector and extractor, a feeler gauge can be placed between the cartridge and boltface to measure headspace. This method received a lot of criticism on the forums which I found it presented. The concern was that when the feeler gauge was inserted, it sort of twisted the bolt, causing inaccurate measurements

6) Cast the Chamber - I've read (and cannot attest by any other means) that casting the chamber could give the requested measurement. the method was to "overcast" the chamber with the bolt out (have the casting material "domed". Then replace the bolt and start shaving the dome down until the bolt locks. This method also received some criticism regarding accuracy.


NOTE: Again, I'm a reporter, not a teacher. The above is what I gathered, not what I profess. I can only hope that the experienced guys will "demystify" things I listed that are wrong or confusing.

[Hoser]

You could buy a go and a no-go gauge.

However I will bet $$$ that you just need to bump your shoulder back a touch and just be sure the base of the case gets fully resized. I only say that as I have seen people have the same fits with gas guns before.

The offer to use my body die and case gauge still stands. Or, PM your address and I will send you some GI brass that I have run through my 1050.

[james_bond_007]

The offer to use my body die and case gauge still stands. Or, PM your address and I will send you some GI brass that I have run through my 1050.

I mentioned that I bought a Redding FL SB die (#91355).

What would the Body die do differently than the SB FL die ?

[jerrymrc]

However I will bet $$$ that you just need to bump your shoulder back a touch and just be sure the base of the case gets fully resized. I only say that as I have seen people have the same fits with gas guns before.

This. I am not an M1/M14 person but have a few miles with the Fal's. Seen it before.

[Hoser]

What would the Body die do differently than the SB FL die ?

You can use a body die on loaded ammo.

[Hoser]

So did you get it figured out yet?