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.308 Reamer with 7.62 Headspace?

2K views 5 replies 2 participants last post by  M14xman 
#1 ·
I've just discovered that my other semi-auto M14 has a longer leade than my Springfield Scout. Specifically, it's 0.012" longer.

This rifle's headspace is supposedly 1.632-1.6325", so it's in between .308 Winchester and 7.62 Nato.

One of the guys who made the rifle told me that they use a .308 Winchester reamer. Would that explain the longer leade? My thinking is that COAL is the same for both cartridges, but headspace is shorter for .308. Therefore, the space forward of the case shoulder would be longer for a .308 reamer.

Does that make any sense?

FWIW Springfield marks their M1As as 7.62 Nato. Their tag says my M1A has headspace of 1.6315.

PLEASE let me know if it makes more sense for this thread to be in the "Ammunition" section.
 
#2 ·
it is not between 308 and 762.

7.62 minimum is 1.6355, so your 1.632 reading is .0035 shorter than 7.62 minimum. 3 1/2 thousandths is a lot when talking about highpower rifle cartridges headspace. you should be ok for both with that reading if you do not run across any extra long nato mil-surp stuff. winchester white box is all over the place with their WCC nato mil-surp and i would not shoot it in my rifles until i checked each cartridge for overall length first. same goes for any mil-surp i shoot in my 308 chambers. yah, i know springfield says its ok for both but they also say that they do not go by milspec, they go by "their specs" when building rifles. qoute from phone conversation i had with them.
trust only your measurements and common sense. nobody else's. i believe a lot of extraction and failure problems associated with sai m1a's is due to people shooting many country's mil-surp in chambers cut for commercial at 1.631
 
#4 ·
I've just discovered that my other semi-auto M14 has a longer leade than my Springfield Scout. Specifically, it's 0.012" longer.

This rifle's headspace is supposedly 1.632-1.6325", so it's in between .308 Winchester and 7.62 Nato.

Does that make any sense?

FWIW Springfield marks their M1As as 7.62 Nato. Their tag says my M1A has headspace of 1.6315.

PLEASE let me know if it makes more sense for this thread to be in the "Ammunition" section.
Other Rifle headspace---------- 1.6325
SAI Scout headspace----------- 1.6315
difference--- 0.0010
this is one thousandths difference, not twelve thousandths.

"I've just discovered that my other semi-auto M14 has a longer leade than my Springfield Scout. Specifically, it's 0.012" longer."

if it were twelve thousandths difference, it would be 1.6435 and be two thousandths from failing nato field reject at 1.6455.

still ok for nato mil-surp shooting but if you reload, you would have to adjust your dies accordingly to get any life out of the brass to keep from over stretching it each time you fire it, especially if you bump the brass back to s.a.a.m.i. specs like factory new brass. if you just shoot and leave your brass lay on the ground, and have good accuracy, do not worry about it. i hope this helps.
 
#5 ·
M14xman - The LEADE is .012" different, not the headspace.

IOW with a 168 gr SMK loaded to COAL of 2.82", the bullet jump before it hits the lands is about .030" for the SAI and over .040 for the other rifle. AFAICT that's a pretty big jump in terms of accuracy.

I'm shooting for headspace of 1.627" when reloading as .003 to .005" is the recommended difference between headspace for chamber and cartridges in semi-autos. Should work with either rifle.
 
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