OCW/COAL question

[tostado22]

Ok first I want to apologize if this seems like I'm rambling on. Ive been doing just that and my wife is tired of it lol.

Long story short, I developed a load with my Rem 700 before I got it set in a Manners stock w/ a Badger M5 DBM. Now that the rifle is back I realized my previous load will not fit the magazine. I took my pilot dummy cartridge and seated it further so it would fit. Then I found out that even though it fit the magazine, it still would not feed due to the bullet hitting the bottom of the feed ramp as it came up from the magazine. So just to get an idea of where I needed to be for OAL I seated the bullet to match FGMM. Now it feeds just fine.

The difference from my previous load to the OAL of FGMM is significant (around .095", also the throat on this gun is waaay out there) at least I feel like that is a huge amount. I'm still new to reloading for precision.

So my question is, will that difference in seating depth and jump to the lands have an effect on my OCW? I'm looking for the way forward in load development. Do I keep my previous charge weight and play with the seating depth within the new window (limited by mag length) or do I start from scratch? Also if I start from scratch, where should I set my COAL while I find my charge weight?

I know that was more than one question but my wife is tired of hearing me go on about it. Also you guys are probably going to be of more help haha. I appreciate any help, thanks!

 

[briang7511]

Have you tried shooting a group yet? Report back when you do.

 

[tostado22]

Not yet. Just going to see if there was anything that I'm missing before I load the rounds tonight. I'm going to load some similar to the previous recipe for sighters and to just see how it works.

 

[CharlieNC]

A definite maybe.

 

[Twoboxer]

I understand why you asked the question, but our guesses really don't matter.

Could be the barrel harmonics have changed if the barrel wasn't free-floating before and it is now . . . or vice-versa. Maybe the new stock changed something, maybe it didn't. Could be better, could be worse, could be same.

If the barrel harmonics have not changed, it could be that your OCW isn't changed but the groups aren't as tight as they were due to the OAL change. Or they are tighter due to the same change

if you are going to shoot from the magazine, you are restricted to that length. But you can always single feed.

So, as said above, shoot a few at mag length, and maybe single feed a few at the old COL to compare. Then report back - would love to hear what happened

 

[tostado22]

Ok thanks for the replies! I couldn't think of any reason it would work out one way or the other. Just checking my work haha. I'll do a set of the old recipe, at magazine length and the old OAL, and report back this weekend.

Charlie, that's the best answer I could come up with by myself.

 

[bax]

The book COL for 308 is 2.800. If "fits into the magazine" is critical then use 2.800 and stop worrying about seating depth. You will probably find that you need to play around with the charge a little. With more jump you may be able to use a higher velocity node without excessive pressure. That is your call.

For me, "fits the magazine" is critical. I use LC LR brass with a COL of 2.800 minus 0.006. IMR 4064 at about 41.0 grains. Sierra 175 HPBT Match. FED 201M. Brass is fully prepped except I do not turn necks - not worth it for this weapon and application. I seat bullets with a Wilson hand seater. I adjust the charge depending on the case weight. All my 308 ammo shoots to the same point of impact at 600 yards -- about 2,605 fps 15 feet from the muzzle.

When I load Lapua brass, the charge weight is 42.2, everything else is the same.

Full preo means: shoot or fireform, tumble, full length size to chamber to -.001 or -.002, tumble, clean primer pocket, debur flash hole (one time only), trim to 2.005. I full length size on an A2 press using a Dillon carbide die. I seat primers using a Sinclair tool.

If your rounds fit the magazine and you have a long throat, you may give up some accuracy. With the loads mentioned, my rifle shoots between .4 and .6 MOA at 100 yards. I normally shoot this rifle at 500 to 800 yards. If I do my part I can put 10 consecutive rounds on an 8-inch plate at 600 yards in real-world conditions. If I miss the plate, it was close enough to do the job.

 

[Pinecone]

I would test to see if there is a length between FGMM length, and barely fits in the mag that will feed.

Also, test the various seating depths from FGMM length (or even 10 thou shorter) to the max length that will feed. You might find another sweet spot.

 

[dauntedfuture]

drop change 1g, go shoot and see what happens. Remember that this is a factory barrel and not a Krieger etc. and as such as limitations.

 

[tostado22]

Pinecone, that was my plan once I find a charge.

Dauntedfuture, why drop the charge 1gr? Just curious.

 

[Wannashootit]

Same issue with both my son's new rifles- one a .260 in an AICS, and the other an AR-10- both used for long-range.
I'm getting new mags for the AICS that will allow for more seating length, if your bottom metal is compatible with AICS than you might consider that option.
Thing is, you don't know if you need it yet- shoot it, and find out if the jump adversely affects accuracy.

It's not a big deal, either, to single-load if needed esp. if it's a target rifle.

In the case of the .260 with 140 Amax's, the much longer jump (I forget the exact measurement- but seating them to 3.89 mag length really shortened them) didn't seem to affect performance.
More testing needed, but I was surprised especially considering that his chamber is throated .260 Match (.04 more freebore) so it has a LOT of jump...
He still was hitting a 4 inch plate at 565 yards.

 

[CharlieNC]

From memory, looking at this using Quick Load a while back showed a change of .010" seating depth gives about the same pressure and velocity deviation as 0.1gr powder for average 308 loads. Since you are loading shorter, the pressure increase associated with seating into the lands would not factor into this case. Outside of adjusting for the decreased case capacity, I don't think it would affect your ocw node significantly. But back off on powder and work back up safely.

 

[tostado22]

Just got back from the range. Got some good data to go off of. I started at my min charge and worked up in .4gr increments to max. No signs of over-pressure.

I seated all bullets to match 175gr FGMM. After I explore this node a little further I will start playing with seating depth.

My next question would be, for an OCW test do I take any notes of good groupings from the first powder charge test? Or am I simply looking at vertical dispersion to find a particular node?

 

[Wannashootit]

OCW Overview - Dan Newberry's OCW Load Development System