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M1A and Odd Headspace Question

5K views 34 replies 15 participants last post by  canmancan 
I have the similar problem. My rifle has always suffered frim short case life- 2-3 firings. My brass stretches about .020" each time, necessitating trimming every time. I fire-formed new Winnie brass with a light load and bullet, then sized to the max that the head space can handle- stripped bolt closes by finger, but has no slop. (interesting, to make the brass .005 longer than just full sizing, I needed to set the die .020 from the holder.) Anyway, brass fits headspace, loads of 43.5 IMR 4895, 168gr HPBT, Win LR or Fed 210 primers. Primers are flat, brass grows .020.

Sak hmmm 67 barrel, headspace, lands, etc matches my Win spare.

I use the Win spare as a case length gauge, along with a depth micrometer. I have compared the two chambers last time the SAK was loose, various cartridges measure the same in both barrels. And sizing .005 loner than the RCBS dies full length to, and being just snug in the rifle, would mean my chamber is about right. Full length sized brass is a good match to several brand new factory loads- M80 ball, Musgrove, and FGMM. No function probs with the longer brass.

I had allowed my length to creep up to 2.835- still fit in the mag. But reading up on 'bullet jump', it seems seating to where the bullet touches the lands = an extra 7,000 psi. I seated a bullet long, inked the bullet, dropped it into the chamber, rotated to mark the lands, mic'ed the head depth, to establish land depth. Adjust COAL to suit the particular bullet ogive. 2.830 would be just touching. Last set of loads, I made the coal fersure 2.790, so a bullet jump of .040? No help, still flattening the primers, still stretching to 2.020.

Whaddya think, try a longer bullet jump? Shorten coal to 2.760? Any other reason for high pressure signs?

Next item would be chamber diameter. Both barrels, brass rattles around radially- like .010 ? Is a "Large Base" die available? I know shot shells have a 'small base' die.

Hey Art L., could shell diameter be the prob re: one of your questions about re-forming 30-05 brass to 308? How it is accurate first firing, but second + loadings are sub-accurate?
 
Some food for thought:

Here is a link to chamber and cartridge designs: http://m14forum.com/ammunition/84411-chamber-drawings.html

The smallest chamber, and largest diameter cartridge would be .001 different.

The largest chamber diameter and smallest (most squished by resizing) cartridge difference is .011.

IIRC, my cartridge/chamber clearance is about .010.

So, our problems with case strength length wise, is really case stretch radially. (I measure my stretch after re-sizing, where it counts).

See, when fired the case gets bigger in diameter, when resized, the excess diameter is squashed into excess length, NOT merely compress back in to a thicker wall.

Adjusting final length is easy, as I've done by adjusting die 'depth'. But the extra width turns into extra length when squashed back to the original diameter.

So, I think me and Welding Rod need "wider base dies".

I wonder if I can cut down to some other dies? To get a wider base and still the correct head space?
 
I've been through the squareness question. It's a Fed Ord receiver, the barrel had been lock tited in, seemingly crooked. R&R, cleaning out the lock tite, now seems OK. Cases used to be crooked, and rip at the bottom after one or two firings. Now I'm getting 2-3 and case bottom are symmetrical to the sides. And head space is tight, with my "partial length resizing".

Let me conceptualize a bit about sizing the brass:

Lets think of a cartridge slit and opened up, into a rectangular shape sheet of brass. Before sizing, it may have grown .010 in length. But, due to a .010 looseness in the chamber, it has grown .031 in width. (Pi x diameter = circumference, or width). So, before sizing, the brass is .010 x .031 greater in area. So we resize, and the area stays the same, but circumference is squashed back to size, meaning the length grows by enough to off set the same area, length grows by ummm an extra .030? Minus some, a bit of the brass is made thicker when worked, so extra .010? So stretch is not due to head space, stretch is due to "diameter space" ?

So, less diameter sizing while still re-sizing length to head space specs?
Maybe size the body in a 30-06 die, to attain max diameter, then cut off a 308 die to use only for neck and shoulder, and head space length?
 
casebro,

That's a pretty stiff load of IMR 4895, especially in a service rifle.

"Anyway, brass fits headspace, loads of 43.5 IMR 4895, 168gr HPBT, Win LR or Fed 210 primers. Primers are flat, brass grows .020."

The Sierra manual lists 41.3 as a max load giving 2600 fps and the Hornady manual lists a "Service Rifle" max load is listed as 41.4 giving 2500 fps.
Speer says 47, Lyman says 42.5 makes only 47K, and the chronny seems to agree. Plus a ton of on line references, right on this site.

I use 41.5 in GI/match brass, 43.5 in Civvie.
 
casebro,

That's a pretty stiff load of IMR 4895, especially in a service rifle.

"Anyway, brass fits headspace, loads of 43.5 IMR 4895, 168gr HPBT, Win LR or Fed 210 primers. Primers are flat, brass grows .020."

The Sierra manual lists 41.3 as a max load giving 2600 fps and the Hornady manual lists a "Service Rifle" max load is listed as 41.4 giving 2500 fps.
Speer says 47, Lyman says 42.5 makes only 47K, and the chronny seems to agree. Plus a ton of on line references, right on this site.

I use 41.5 in GI/heavy match brass, LCM or FGMM. Perhaps my 43.5 was a misprint? a load of 41.5 in civvie brass gave 2405 on the chronny.
 
The cartridge tears about 1/2-3/4" from the bolt, leaving the front part in the chamber. Best tool to remove the remnant is the chamber cleaning brush. on a section of cleaning rod. Just jam it in and pull it straight back. The wires will act like barbs and grab it good.

I wish I didn't know this. But there is a reason I've been posting to this thread.

Other idea, from working on a M94 Win 30-30. The make a 307, basically a 308 with an added rim. Shells are heavy walled, heavier even than LCM. Making them into custom 308 wouldn't be too difficult. Chuck in a lathe, turn off the rim, deepen the groove, touch it with a file to round off the 'rim' of the rimless case. More brass = longer case life?
 
I emailed RCBS. They got right back to me.

RCBS X mandrel won't retrofit into the usual die, I asked them. Of which I already have two sets. So I may turn out my own mandrel that will retrofit, just for the sake of a test drive. I'll simplify it, probably need one pass to do the X die thing, then a trip through the usual die de- and re- cap plus expand the neck. But it takes 3 operations to trim: trim, chamfer ID, chamfer OD, so I would be two steps ahead, and get much longer case life.

They do sell the X sizing die separately. but it cost only about $2 less the the set. Plus the mandrel is a much heavier de-capping pin shaft, better for use in crimped primer cases. Too bad it wasn't an option 25 years ago when I bought the gun and dies.
 
I don't know the limit, but you can burn a ring into your chamber. Not beneficial.

Usually, a case it good for umm 2-3 trimmings, then discard next time it grows to max, listed in every reloading manual.

I did make up my own mandrel to retrofit my old sizing die. Sure does work to shorten cases. I could feel somehtin happen in the last bit of stroke, must be the excess 020. getting pushed back to where it started. A quick trip to the range, with the twice-trimmed, once X'd, cases did give me a separation. So maybe two trimmings, plus fire one more time, is the limit?
 
Success! Longer bullet jump = lower pressure.

I do believe I've got my problem solved.

I loaded 43.5 gr IMR 4895 in Civvie Win brass, Nosler 168. To two different seating depths. Ten each. COAL of 2.760 and 2.740. Brass was fired two or three times previous to resizing with my home made X-die.

Had three case separations in the long ones, and stretching to 2.015 - 2.020 in those that didn't break. Flattened primers too.

Shorter loads, No separations, stretched to only 2.008-2.010 in the shorter loads. Primers still slightly rounded. I'm thinking that gives me a bullet jump of about .040".

I guess now I need to work up the load for accuracy again.
 
I've always liked the Lyman book. It gives an asterisked load, which is the load that gave the most constant internal ballistics. Accuracy starts in the chamber, if you are not consistent internally, you can't be consistent down range.

In the case of 168gr HPBT, 13 powders, two show the asterisk. IMR 4064 and 4895.

But OOOPs, the max. * they show for 4895 is 42.5. Maybe I ought to keep my glasses closer to my library. Still, other manuals say up to 47. So I guess my 43.5 load may have gone too hot for accuracy?

Now, back to my regularly scheduled bedding experiment.
 
Another trip to the range today.

Setting the bullets in deeper seemed to lower the pressure. .060 shorter COAL. In civvie Win and GI WCC '67 brass. 41-42.5 grains Looks like my gun ought to like about 40gr of H4895 in either civvie or commercial brass. 41 was tighter than 42 in either case today.So something is making sense, finally...

30 rounds, slight rounded edge on all primers still, no case seps. Though flattest was GI with my high load of H-4895.

I haven't sized them yet, but some of the GI cases are actually mic shorter than before firing. I guess they must have stretched in the diameter, pulling the length back? The civvie Win stuff mostly stayed at 2.000, with a couple stretching to 2.010.

24 years with this gun, looks like my problem is solved. Hallelujah !

eta: Makes me wonder of the lore about how "GI guns CAN'T have long case life" is malarky. Many may have short bullet jump, where the bolt guns in the civvie world all have long jump to preclude high pressures?
 
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