How exact do you have to be

[ar10]

I'm starting my next batch of loads and got pretty confused by the type and weight of the bullets available. The most important question is there a big problem with seating a bullet that is shorter than the recommended C.O.L.
For example I couldn't find any load data for the .308 Winchester service rifle for a 165gr SST in my Hornady 7th Ed reference. It only shows 155gr and 168gr. In each case the COL is 2.80.
I did find some 165gr Hornady SST's in the standard (whatever that means), Winchester with a 2.750 COL.
I pressed one of them into a gage cartridge and came up with 2.7490 after crimping.
I have been shooting NIB Rem 150g FMJ's since I bought the AR10 with a COL of 2.7880. and the first batch of reloads were 168gr SST Hornady and I had no problems.

How critical is the COL. and isn't there a relationship between the proper headspace and the overall length ?? Now I'm really confused.

 

[trickyasafox]

the profile of bullets- especially rifle bullets does not have a direct relationship with the amount of bullet that is in the case. I load as long as I can get reliable function- that for me, has produced the most accurate loads.
10 thousandths won't be harmful for your health, and I doubt you'd notice a grouping difference unless your a serious BR shooter at most distances people shoot at.

 

[SSN Vet]

I believe you will find two OAL specs.

The one typically given on a cartridge schematic is a max. OAL to ensure proper feeding through your rifles magazine and action.

The OAL listed in the load tables is a min. OAL, which is intended to make sure you have an adequate volume within the case. Observing the min for a given bullet weight will ensure you do not inadvertantly load a compressed charge.

If your not pushing the max. load published, you likely have more margin to play with and are not going to have a problem setting the bullet deeper. I've run into the situation where I needed to seat the bullet deeper than the min. OAL listed for that bullet and powder combo. in order to get the cannelure properly allined for a good crimp. I was no where near the max. load so I didn't worry about it.

Modern Reloading II lists 2.810 as the max. OAL for .308 Win and depending on the powder selected, lists min. OALs for 165 gr. jacketed bullets from 2.530 to 2.795.

So what powder are you using?

as far as how close is close enough.....I think you'll find few manufacturing processes that hold +/- .001. Getting into tenthousandths of an inch is very high end machine shop work.

 

[USSR]

I'm starting my next batch of loads and got pretty confused by the type and weight of the bullets available. The most important question is there a big problem with seating a bullet that is shorter than the recommended C.O.L.
For example I couldn't find any load data for the .308 Winchester service rifle for a 165gr SST in my Hornady 7th Ed reference. It only shows 155gr and 168gr. In each case the COL is 2.80.
I did find some 165gr Hornady SST's in the standard (whatever that means), Winchester with a 2.750 COL.
I pressed one of them into a gage cartridge and came up with 2.7490 after crimping.
I have been shooting NIB Rem 150g FMJ's since I bought the AR10 with a COL of 2.7880. and the first batch of reloads were 168gr SST Hornady and I had no problems.

How critical is the COL. and isn't there a relationship between the proper headspace and the overall length ?? Now I'm really confused.

ar10,

There are 2 possible constraints on OAL: magazine and throat. Finding the longest OAL in regards to your magazine is easy; if your loaded cartridge is too long, keep seating your bullet deeper until it fits. Finding the longest OAL in relation to your throat is a little more complicated, but there are tools that measure this, and you can even do it crudely without tools (do a search on "bullet ogive"). Actually, there is a 3rd constraint; don't seat your bullet out so far that you have less than 1 caliber still in the case neck. The OAL listed in the reloading manuals is simply the OAL that they used. I can see no reason to load to a shorter OAL than listed in a manual. You can use 168gr load data with a 165gr bullet. There is no relationship between headspace and OAL; they are separate and distinct measurements.

Don

 

[mtgale00]

A couple of often overlooked factors are your chamber and bullet ogive. Simply considering COL & OAL with the assumption that your chamber was cut to spec is problematic. See if can track down someone with a set of go/no go gauges in .308. They are pricey but a good set can be found at MidwayUSA. Also consider that different bullets have unique ogives and may contact the lands of the barrel sooner or later than other bullets.

If you have a decent vernier caliper, try this out. Using an unprimed piece of brass that has been neck sized, hand seat a bullet in it just past the tail. Now gently chamber and remove the "round" and measure the OAL and see if it falls within spec. The theory being as you feed the round in and bullet contacts the lands, the bolt will move the brass up the bullet and give you an idea of what your chamber depth is. It sounds crude but it is a good way to gauge a starting point for determining the the proper OAL for your rifle.

 

[ar10]

Thanks for the responses. I have made some progress Instead of being totally confused it's only "muddy" now. Learning all the ins/outs of reloading makes you think about everything. I figure by the time I reach 100 I'll have a good understanding of reloading.
I do like the idea of chambering an unprimed bullet to check the actual length, the rifle is a semi-auto so I can break it down to to put the bullet in.
Powder is Winchester 748 and I'm going to follow the 168gr reccomendation starting at 39.5 gr and work my way up.
The thing I'm sure of yet is whether or not I can use a bullet w/o the cannelure. And I couldn't find the go-nogo for the rifle yet. Armalite will not make any reccomendations stating reloading will void the warranty. I really don't care.

One of the things I found is the rifling is 1:11.25 for the 20" barrel. i know it's important when reloading but there's nothing listed in any of the data I found.
Thanks again.