[casebro]

I seem to find conflicting opinions re bullet jump and pressure. Some say touching the lands can cause 80,000 psi, some say too much jump will raise pressure 7,000. Other say different bullets need different jumps. Or seating a bullet an extra .030 into the case causes pressure to rise.

41.5 gr IMR 4895 168s is giving me flat primers and short case life, lots of stretching. Jump is about my last variable.

Whaddya think?

 

[casebro]

I've worked it up, I've worked it down, used every brass I could get my hands on.GI wcc, LCM, Win commercial, FGMM, Fed nickle plate...

I size them .005 long, compared to M80 or other brand new shells. Bolt closes just snug on them, no slop. So, head space is good, plus the 'long' sizing removes that from the equation. 41.5gr in the commercial brass gives 2400 fps.

Far as i can tell, jump is my last variable. Looks like this barrel is shorter jump than my spare. I loaded one long, inked it, slid it into the spare, gave it a twist. Nice clean line, Same shell, in my asembled gun, a new line, closer to tip... I thought that was longer...hmm, that is not longer, it is smaller, would need shorter loading.... I may repeat that...

Ive tried 2.800, 2.830, 2.790. Next batch will be 2.760. or 2.750 ?

I go search now for 'short lead'....

 

[casebro]

I found this thread by Art Luppino http://m14forum.com/m14/58604-changing-head-space-chrome-chamber.html

with this; "If you have to ream, make CERTAIN the reamer has cutting potential only through the shoulder, and it does not have the normal cutting qualities that ream into bore... This is called a NO LEAD reamer, the Military pull through head space reaming tool does not cut the rifling. "

So, if the GI contractors reamed the rifling separately, perhaps mine was made with short lead? GI SAK '67, has been a tack driver in the past. Years, but not many rounds ago.

 

[casebro]

Dwell is good, set by trimming gas plug per directions here. No help.

Yes, lube wiped off.

Snug sizing of cartridge = minimal room to grow. No feeding probs. RCBS dies. But even M80 ball and factory FGMM ammo does it.

So, I'm left with "what could be different about THIS rifle?", and lead is the only variable left. I'll try the inky long seated bullet again, see if I misinterpreted it last time. That is assuming that short lead = high pressure, some say extra 7,000 psi, others up to 80,000 peak. Could explain things?

 

[casebro]

Okay, I re-did the inky-long-seat trial. My spare barrel, a Win '62, twisting the cartridge, makes one fine line at 2.225. Tapping the cartridge in til shoulder hits yeilds a blurry mark, 2.225-2.275. The mounted SAK, slamming the bolt, shows four wide blurry marks at 2.200- 2.255. So the SAK IS 030 shorter int he lead department?

So the SAK might need bullets seated .030 deeper, to get the same jump?

Link to chamber and cartridge drawings: http://m14forum.com/ammunition/84411-chamber-drawings.html

Specs say the OE taper starts at 2.139, ends at bore dia at 2.303. Looks like I'm in the middle, at 2.200 ? OKay for throat erosion?


I can't see my out of spec-ness being wear? More likely a funky reamer/ experiment?

Anybody know the specs of a T.E. gauge taper?

Sometimes I think the sum of the total of my knowledge is less than the total of it's components. If only I could remember how to run a double entry accounting page to check my sum...

 

[casebro]

Re: X die:

Is it a "large base die"? See my post, #12 here http://m14forum.com/m14/103917-m1a-odd-headspace-question.html

In that post I did conceptualize about how a large diameter chamber could cause longer stretching than longer head space.

And yes, I do custom set my dies to maximum dimension, so long as the bolt closes.

So, RCBS 15501X would be the catalog number?

Midway has them
http://www.midwayusa.com/viewproduct/?productnumber=287168

Looks to me that it doesn't allow the case to grow in length when re-sized, forcing the stretched brass back to where it belongs. Ought to solve case life probs. Well worth the cost in brass savings.

Larry, any difference in lubing? Make real sure to get some inside the neck?

 

[casebro]

Is the barrel test (or headspace test) actually valid without a bolt chambering and closing the cartridge or case, though?

In the assembled rifle, checking for lead depth, I did slam the whole goddammit shut. In the loose barrel, I tapped the case home with mallet, until it stopped at the shoulder. I verified this with before and after measurements with a depth mic. And last time I had both barrels loose, I compared the same cartridge in both chambers, got the same depth mic reading. I did it with several cartridge brands, both barrels were the same with each cartridge. New cartridges, factory loaded, read .045" below the edge of the barrel. My 'long sized' cases read .040", so are a maximum of .005 longer headspace than the absolute minum. Well within tolerance.

I do use a stripped bolt to set die length for re-loading.

 

[casebro]

Yeah but jump = 0 = higher pressure, from what I've read. I just read the Speer manual, says .060.

But if we go back to my OP, has anybody else had high pressure signs from short jumps? Signs that went away with deeper seating? What is the optimum jump in an M14? How much is too much, before pressure rise due to lower case volume, like raising the compression ratio in an engine? I know 'pinging' is bad...