308 Reloading Questions

[MotoFlier]

Good evening all,
Brand new to reloading with a question, figure there will be some more as I get rolling so I left the title generic. 1st I will say I been reading the stickies and threads in this forum and the information is amazing, its given me the confidence to pull the sheet off the press I bought a few years back and give this a serious effort. Decided to build a test rig so I pieced together a Savage model 10 in 308 with KRG Alpha stock 18" barrel & VG6 brake with 3-15 SWFA scope as a budget entry level rifle to learn with.
Where I am at now is I fired 20rds of off the shelf Winchester Super X 150g through it to get my starting brass now I'm at step 1 determining headspace. I'm using an RCBS precision micrometer and getting right at 0 for every case. If I understand correctly the micrometer is set to zero at SAAMI minimum which for .308 is 1.6300/1.6400 so that means i'm already at 1.6300 minimum length before sizing. So when sized it will be at 1.6270/1.6280 I have read some information that says SAAMI is a recommendation and the measurement can be LONGER limited by the ability to feed the round but nothing that has said you can go SHORTER. My concern is if I push the headspace smaller I will actually increase the pressure in the case even at the recommended minimum starting loads. One idea I had was to try reinstalling the barrel with a lighter feel on the headspace gauge to try and get a few extra thousandths headspace? Would I be safe to just decrease the minimum charge by a few grains? What is the correct way to move forward. If i'm way over complicating this I blame it on my machining background haha.

 

[straightshooter1]

Where I am at now is I fired 20rds of off the shelf Winchester Super X 150g through it to get my starting brass now I'm at step 1 determining headspace. I'm using an RCBS precision micrometer and getting right at 0 for every case. If I understand correctly the micrometer is set to zero at SAAMI minimum which for .308 is 1.6300/1.6400 so that means i'm already at 1.6300 minimum length before sizing. So when sized it will be at 1.6270/1.6280 I have read some information that says SAAMI is a recommendation and the measurement can be LONGER limited by the ability to feed the round but nothing that has said you can go SHORTER. My concern is if I push the headspace smaller I will actually increase the pressure in the case even at the recommended minimum starting loads. One idea I had was to try reinstalling the barrel with a lighter feel on the headspace gauge to try and get a few extra thousandths headspace? Would I be safe to just decrease the minimum charge by a few grains? What is the correct way to move forward. If i'm way over complicating this I blame it on my machining background haha.

I regularly use the same micrometer and I've measure factory cartridges before firing them and it wasn't unusual for them to measure less than -0- . . . as much as .004 below and there were no problems when firing them. So, when you're sizing the cases and getting them .002 - .003 under that zero, you will be fine. (note: keep in mind that Winchester brass has more case capacity than most other brands of brass). No, I wouldn't reduce the "minimum starting loads" as you've got lots of room between minimum and maximum to work with safely.

If it were me, I'd probably try and reset the barrel for a little more headspace, IF . . . my go no-go gauges allow.

 

[MotoFlier]

Go no go give me .004 so I should be able to tweak a thou or two but probably gonna be alot of back and forth to hit the exact sweet spot. If guys are running slightly under without issue than I feel comfortable. I don't plan on shooting this ammo in any other rifle so it should never overwork the brass stretching it in another chamber.

 

[Longrange403]

I regularly use the same micrometer and I've measure factory cartridges before firing them and it wasn't unusual for them to measure less than -0- . . . as much as .004 below and there were no problems when firing them. So, when you're sizing the cases and getting them .002 - .003 under that zero, you will be fine. (note: keep in mind that Winchester brass has more case capacity than most other brands of brass). No, I wouldn't reduce the "minimum starting loads" as you've got lots of room between minimum and maximum to work with safely.

If it were me, I'd probably try and reset the barrel for a little more headspace, IF . . . my go no-go gauges allow.

I agree with sraightshooter, I would try and get a little more headspace if possible. If you cant get more headspace however i wouldn't worry about the minimum Charge weight, the numbers imo are published a bit low to save the companies ass in the case of a catastrophic failure. Despite the fact we load are own and know the risks there’s always that guy who will try and sue even if its his 100% fault

 

[BrienM]

Great looking rig Moto! Welcome to reloading. I have a bump gauge by forster I use to measure how much bump I get. One thing many go by is how tight the die has to hit the shell holder. If when it cams over and makes everything on your reloading bench jump, it needs more headspace. If not, it is probably not too tight.

 

[ShtrRdy]

If you look at the SAAMI cartridge drawing the spec for headspace dimension is 1.634 -0.007. So this means your minimum dimension on the case is 1.627"

 

[DownhillFromHere]

You're overthinking it, quite a bit. Not necessarily a bad thing - better than not thinking enough - but not necessary. I've read your post a couple of times trying to see if I've missed something... I don't think so.

Bottom line: You have fired cases from YOUR rifle. Bump the shoulders back 0.002" as you've noted and load 'em, checking after each firing to insure correct total length.

Be aware that total case length is NOT necessarily a direct correlation to headspace. The case neck is going to lengthen with each firing, necessitating trimming. In other words, headspace (base to shoulder measurement) can be perfect and the case is still too long. So, you want to measure total case length AFTER resizing.

Do not worry about increasing pressure by reducing headspace. Just don't. If you can chamber factory ammo - which in my experience is usually slightly below SAAMI spec - you're good. If you can't chamber factory ammo, there is a problem way beyond a couple thousandths headspeace difference. If you've read the stickies and so on, you're aware that different brands of brass and different lots within a brand are going to have different internal volumes. Those internal volumes matter if you try to jack your loads to the ragged edge of safety - but shortening the headspace too much would result in the discharge simply expanding the case to available chamber volume. Would there be a pressure/velocity difference? Yeah, a little, probably. But inconsequential.

As far as trim length is concerned, I'd say consistency is the goal. When I started loading 6.5CM, I targeted 1.910" - in the center of the 1.900-1.920" SAAMI spec. Now I look for 1.915 due to a weird compulsion to have as much neck surface holding the bullet as possible. Ya gotta be a little weird (spelled a-n-a-l) to do this precision rifle mess. I may well go back to 1.910" next time I have a pile of cases to trim.

 

[pmclaine]

Ive measured a bunch of FGMM with the Prec Mic and they generally fall -.003.

Ideally you measure a fired case than set shoulder back .001-.002 to make best fit for your rifle.

Should save your brass life and create best accuracy.

I own more than one .308.

I try to size to 0 on the Prec Mic.

 

[MotoFlier]

Thank you for the information guys certainly makes me feel like I'm on the right track.
@ShtrRdy I haven't seen that spec I was using what was referenced on the chart that came with the precision mic.

 

[pmclaine]

I like the RCBS precision mics.

I like the Hornady headspace gauge tool.

My only issue is that they are all "relative" and I dont k now what they are relative to.

How sure can we be the RCBS is accurate or what does "0" mean. If you use it to measure a fired case it accurately shows you what action the sizing die performed after sizing by remeasuring that case so it shows you a change "relative" to your beginning.

Ditto the Hornady pretty much.

They work. I just think about shit more than I should.

I want an actual headspace tool like is used to cut a chamber that I can use as my standard reference. It would be cut to represent the median SAAMI shoulder. Id use that to determine how accurate the RCBS is or Id use it to set "0" on the hornady than measure the + or - result of my sized cases from SAAMI.

Im more interested in making .308 for a few guns than just one gun.

 

[ShtrRdy]

If you're interested ...

Cartridge & Chamber Drawings - SAAMI

Cartridge and Chamber Designs Standardized by SAAMI Current Cartridge & Chamber Drawing documents are contained within the SAAMI Standards – American National Standards Published by SAAMI Newly Accepted Cartridge and Chamber Designs Links to technical data and drawings for the newly SAAMI...

saami.org