nominal but fat chamber reloading

lonerockut

Private
Minuteman
Apr 4, 2023
3
1
Utah
I've reloaded for hunting for decades but to me 300 yards was a long shot. I measured out on family land 100, 200, 300, 400, 500 meters and sat up milk jugs at those ranges. Me and a couple of friends thought about getting into silhouette shooting. It became clear that 200 meters off hand was my limit back then. I had to take a sit to hit the milk jugs at 300 m.

I've decided to get into longer range shooting again. I sold my 700 in 6.5 swede so I'm looking to use my Win M70 308 while I build a 7PRC. I have equipment for 308 instead of full length resizing I set up my dies and was working to just bump my fireformed brass back .002. But, my problem is my brass body was squeezed down so much by my dies that my shoulder datum was growing as I worked the die down to my desired position. I was back to full shell holder contact with cam over to get my resized datum back to the zero datum measured by my gages used on the fired brass. I am just using the stoney point/Hornady comparator with my Mitutoyo Calipers (i'm a machinist by trade).

I've ordered the lyman shell holder set with the + and minus holders. I am considering going to a Neck die or purchasing a bump die to leave the body less worked while I practice and improve my technique. I am building a heavier barrel rifle in the 7 prc as money allows so I don't want to re-chamber the 308 right now. So I've got a chamber that is wide but not long on headspace. For hunting perfectly adequate, but what would you guys and gals suggest for brass prep for longer range accuracy. In factory ammo this rifle has not been super accurate until I hit 175 or 178 grain bullets. Reloading has been with full length resizing, pocket uniforming, trim to equal lengths, head stamps matched, Ohaus 10-10 scale,and thats about it. I use the mag and that means Jump on seating on this rifle. I'm willing to single load and seat into the lands for longer range practice. I have the equipment to anneal and neckturn from converting brass for obsolete cartridges in the past. I am capable of reading mics and calipers etc. I do not have a concentricity gage but I have dial test indicatores and v blocks and a small granite surface plate as pieces of my personal equipment, which is at home since right now I work for a ISO 9001 company and not in a job shop.

So what would you more experienced long range shooters theorize with this chamber to squeeze the most accuracy out of it. I'll be practicing again. Since I need a bench or some other support beyond 400. I'm a mediocre shot and experienced reloader only for hunting and practice just re-starting into longer ranges. I've set on 178 eld-x for the bullet, my present loads use IMR 4895 and CCI 200 primers. I'm willing to work with other powders, although as a hunter I haven't really had temperature problems in my 300 and under shooting, after I get my brass technique sorted out.
 
If I understand your description correctly the brass is doing what it does when you full length resize. Have you taken measurements on the brass cases after firing and after resizing? (Other than the shoulder datum location) How much is the resizing die reducing the diameter on the case body slightly below the shoulder? How about the diameter of the case body slightly above the extraction groove?

You could also take a look at the SAAMI drawing for the cartridge to see how large the chamber could be and the specs for a loaded cartridge case.
 
If I understand your description correctly the brass is doing what it does when you full length resize. Have you taken measurements on the brass cases after firing and after resizing? (Other than the shoulder datum location) How much is the resizing die reducing the diameter on the case body slightly below the shoulder? How about the diameter of the case body slightly above the extraction groove?

You could also take a look at the SAAMI drawing for the cartridge to see how large the chamber could be and the specs for a loaded cartridge case.
Fair enough, I've taken some measurements but I will take more this weekend. The brass is at home and I'll be out of town until this weekend. It seemed to be just fine above the web. Most of the expansion was up front. I'll get average numbers when I get home and post them then. If I do have quite a bit of radial growth on the forward body like it seems to be, would I be wrong with just neck sizing after 1st and second firings, work up my load on third firing and just let the brass go when it got to tight to chamber while neck sizing after that?
 
I have no idea what your actual problem is.
Yeah I don't explain well. I'm trying to build better loads for longer ranges to practice with in a older hunting rifle while I build a dedicated rifle for longer ranges. I've loaded just for normal range hunting for years but have only experimented with long range once years ago. I'm trying to learn how to make this ammo more consistent with the old rifle for practice while building the dedicated rifle as money allows. Initial work with this rifle suggests that the chamber allows the forward body of the brass the expand so much radially up front that my dies move it quite a bit when resizing. I'm trying to decide what to do to make more consistent loads for this rifle as is, with what appears to be a fat chamber but not to long of a chamber short of setting the barrel back and re chambering. Im asking here since long range and reloading for long range will be in you guys wheelhouse. Just spit balling for possible fixes you guys might know of or see for this problem. I'm starting with Shell holders, if that doesn't work I'm thinking neck sizing only, one step at a time. If this chamber is as believed what would you guys do next?
 
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Ok so I re-read it.
I gather you think the body diameter is growing more than it should because you were actually pushing the shoulder forward. Well this will happen when you don't have the die set up correctly.

If the die is only sizing the body and not touching the shoulder it will actually move ahead. If you need to cam the press to push the shoulder that is fine and usually the most consistent way. You can try the graduated shell holders to get the feel you want.

I think everything is fine and you need to set the die properly
 
Fair enough, I've taken some measurements but I will take more this weekend. The brass is at home and I'll be out of town until this weekend. It seemed to be just fine above the web. Most of the expansion was up front. I'll get average numbers when I get home and post them then. If I do have quite a bit of radial growth on the forward body like it seems to be, would I be wrong with just neck sizing after 1st and second firings, work up my load on third firing and just let the brass go when it got to tight to chamber while neck sizing after that?
Some guys do what you are thinking. These days the general belief is to full size the brass each time. However, after you take some more measurements, ( fired case and resized case), and compare the numbers to the SAAMI specs, we'll have a better idea on how to proceed.

Here's a link to the SAAMI specs. Scroll down to Z299.4 and open it up. These are the centerfire rifle drawings

 
I'm thinking of trying neck sizing only after the first and second firings, and then working up my load on the third firing. Would that be a good approach? And if so, how many firings do you think I can get out of a piece of brass before it becomes too tight to chamber?
 
Sounds like you are overthinking it. FL size the shoulder back 1.5-2 thousands every time. I chamfer each time as well. Put in powder, seat bullet, shoot.
 
For fat chamber, Redding body die to bump back shoulder .001" or .002", neck bushing die, to set neck tension ...then every 3rd firing use Redding body die to bump sholder back .002" again...and trim case overall length, deburr, champher.
If sizing body is difficult use the white Lee Resizing Lube.
No need to anneal or do any other case prep....especially for 500 yds and closer...and these can be loaded on a Dillon progressive with a case activated Hornady drum powder measure....and hit clay birds at 600 yds with ease, with most any bullet 125 gr TNT and heavier...even use primed LC brass and Win 748 for this plinking endevor, along with the cheap 125 TNT bullets...
Pictured is a box of 1000 primed LC brass already fired through various 308s. It shot .3" and .4" 5 shot groups back to back in AR 10 18" proof with W748 and 130 gr Speer Varmint bullets.

But sometimes I neck turn and shoulder bump with a ground carbide tool in the lathe for specific cases like this 6.8X51 hybrid case necked up to 308, this procedure, along with a mandrel gets rid of donuts in the neck.
I just got done doing this... for two specific 308s with 8 and 9 twist barrels, for mostly 200 to 230 gr bullets, not needed for your average 308. These are for high pressure loads with minimum chanbers, made with the same reamer on my lathe.
 

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