Sanity Check from the Hide's reloading Gurus.

[MetroJethro]

I have been loading for a few years know (mostly for pistols), and I think I know just enough to get myself in trouble. I would appreciate any help from anyone (most of you, if not all) who knows more than I do.

I just received my AI AE MKIII .308 from Mile high this week. This is my first AI and so far I am pretty happy with the rifle. During my first two sessions I began working up my hand loads while also shooting a variety of factory ammunition to familiarize myself with the weapon.

This evening I used my RCBS Precision Mic to help fine tune my resizing die. Using 168g Federal Gold Match I measured the spent cartridges from today versus the unfired cartridges remaining in the same box. There was only .001inch difference in the fired and unfired measurement. I also measured the brass from my hand loads. Using Lapua brass, the fired cartridge is .004 inch larger that brass sized with my current set up.

First Question: .001 difference between fired and unfired seems really low to me. Is this typical for AIs? I am assuming that this is a really tight chamber.

Second Question: Based on my .004 difference on the fired/unfired Lapua, I was going to sent my die up .002 so that I am only bumping the shoulder by .002. Is this correct?

The group sizes aren't to bad. With 150g SMKBT, 43.0g Varget the average group is .564, the 168g SMKBT opens up a little to and average size of .847 and the 175g SMKBT a tad smaller at .753.

Thank you in advance for any suggestions/advice.

 

[jdonovan]

First Question: .001 difference between fired and unfired seems really low to me. Is this typical for AIs? I am assuming that this is a really tight chamber.

Second Question: Based on my .004 difference on the fired/unfired Lapua, I was going to sent my die up .002 so that I am only bumping the shoulder by .002. Is this correct?

So SAAMI has a range of dimensions that are acceptable for ammo to be within... your FGM might have had brass that was a bit to the larger side of spec, and didn't expand as much.

Your Lapua brass might have been closer to minimum size specs, and therefore could stretch more.

Also:
The metallurgy of the brass will determine the 'spring back' after firing.
The pressure levels of the load will have some effect on the springback as well.

I've heard anecdotal evidence that says FGM is fairly soft/springy brass, and that might explain why it sprang back.
Lapua brass is known for being one of the thicker/harder cases on the market and could explain its more significant stretch.

If you are putting the brass back into the same gun, and trying for max accuracy. I'd try re-chambering a few pieces of brass, and make sure they will chamber. If so, I'd only neck size them until they stop fitting the chamber well. Then I'd body size, and bump the shoulder back 1-2 thou. Repeat. There will need to be some trimming/annealing in there as the brass ages.

Interesting question. Whats the shoulder difference between the fired Lapua and FGM. If they are in the same place that might tell you something.

 

[MetroJethro]

Thank you for the info. Makes sense. Comparing the FGM and Lapua, there is a .001-.002 difference in the shoulders (measured 5 of each). So it looks like the FGM springs back further than the Lapua.

 

[JGorski]

I have been loading for a few years know (mostly for pistols), and I think I know just enough to get myself in trouble. I would appreciate any help from anyone (most of you, if not all) who knows more than I do.

I just received my AI AE MKIII .308 from Mile high this week. This is my first AI and so far I am pretty happy with the rifle. During my first two sessions I began working up my hand loads while also shooting a variety of factory ammunition to familiarize myself with the weapon.

This evening I used my RCBS Precision Mic to help fine tune my resizing die. Using 168g Federal Gold Match I measured the spent cartridges from today versus the unfired cartridges remaining in the same box. There was only .001inch difference in the fired and unfired measurement. I also measured the brass from my hand loads. Using Lapua brass, the fired cartridge is .004 inch larger that brass sized with my current set up.

First Question: .001 difference between fired and unfired seems really low to me. Is this typical for AIs? I am assuming that this is a really tight chamber.

Second Question: Based on my .004 difference on the fired/unfired Lapua, I was going to sent my die up .002 so that I am only bumping the shoulder by .002. Is this correct?

The group sizes aren't to bad. With 150g SMKBT, 43.0g Varget the average group is .564, the 168g SMKBT opens up a little to and average size of .847 and the 175g SMKBT a tad smaller at .753.

Thank you in advance for any suggestions/advice.

If you're measuring .001" difference at the neck, yeah, that's pretty tight, usually that kinda measurement is reserved for Benchrest rifles.
What is the measurement after firing, btw? I'd like to compare it to my 308s.

 

[HodgdonExtreme]

If you're measuring .001" difference at the neck, yeah, that's pretty tight, usually that kinda measurement is reserved for Benchrest rifles.
What is the measurement after firing, btw? I'd like to compare it to my 308s.

He wasn't talking about neck diameters, hence the RCBS precision mic reference.

OP, you've received good advice and guidance above.

 

[bigedp51]

1. You have a British manufactured rifle and they are not governed by U.S. SAAMI guidelines.
2. The headspace for the British 7.62 L42A1 sniper rifle is 1.628 GO and 1.635 NO-GO.
3. The headspace for the British L1A1 7.62 battle rifle is 1.6325 GO and 1.643 NO-GO.
4. The headspace for the American SAAMI .308 is 1.630 GO and 1.634 NO-GO
5. The headspace for the American military M14 7.62 rifle is 1.6355 GO and 1.6385 NO-GO
6. The headspace for the AR-10 A2 7.62 rifle is 1.633 GO and 1.636 NO-GO
7. The headspace for the AR-10T 7.62 rifle is 1.631 GO and 1.633 NO-GO
8. The RCBS Precision Mic is not calibrated and is a comparator gauge only, my .308 Precision Mic reads -.003 with a 1.630 headspace gauge. Meaning the Precision Mic reads 1.627 with a 1.630 headspace being measured. Or "zero" on my Precision Mic is 1.633.

Below, a Colt 5.56 FIELD GAUGE 1.4736

And a Hornady cartridge headspace gauge can be calibrated to read true headspace. My Precision Mic and Wilson case gauges have been retired.

 

[bigedp51]

Thank you for the info. Makes sense. Comparing the FGM and Lapua, there is a .001-.002 difference in the shoulders (measured 5 of each). So it looks like the FGM springs back further than the Lapua.

Pause at the top of your reloading presses ram stroke for thee seconds, lower the ram and rotate the case 180 and repeat sizing operation with pause at the top. Pausing at the top of the ram stroke tells the brass to "hold still" and not spring back. Rotating the case 180 degrees and sizing the second time reduces neck runout and reminds the brass to "hold still" and "be straight" .

If you pay that much for a rifle you need to let the brass know who's the boss.

 

[MetroJethro]

Thank you for the info.

 

[FLIGHT762]

Pause at the top of your reloading presses ram stroke for thee seconds, lower the ram and rotate the case 180 and repeat sizing operation with pause at the top. Pausing at the top of the ram stroke tells the brass to "hold still" and not spring back. Rotating the case 180 degrees and sizing the second time reduces neck runout and reminds the brass to "hold still" and "be straight" .

If you pay that much for a rifle you need to let the brass know who's the boss.

I have tested this ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ and it works. Being consistent and using the correct amount of case lube can make a difference in your shoulder bumping numbers also. Not using enough lube can throw your numbers off.

 

[MetroJethro]

I have tested this ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ and it works. Being consistent and using the correct amount of case lube can make a difference in your shoulder bumping numbers also. Not using enough lube can throw your numbers off.

I will definitely try bigedp51's suggestion. I currently use imperial sizing wax. Should I consider alternatives?

 

[FLIGHT762]

I will definitely try bigedp51's suggestion. I currently use imperial sizing wax. Should I consider alternatives?

Your Imperial wax will do fine. I use Imperial. Recently, I tried a suggestion from another reloader to try Mobil 1 Synthetic oil as a case lube. A Friend of mine had some extra 20-50 Mobil 1 and gave me a few ounces to try. It works very well, as good a Imperial.

 

[JGorski]

Your Imperial wax will do fine. I use Imperial. Recently, I tried a suggestion from another reloader to try Mobil 1 Synthetic oil as a case lube. A Friend of mine had some extra 20-50 Mobil 1 and gave me a few ounces to try. It works very well, as good a Imperial.

I did almost 100pcs of LC brass with 100% canola oil cooking spray last night. Worked very well, also.