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Discussion Starter · #1 ·
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?
 

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Hi Casebro,

The rules all have truth in them, but ever barrel and chamber is kind of it's own beast in a way, also. I hate to answer a question with "yes and no" but I feel like something is just not jiving here.

What kind of brass are you using, and do you know where your rifling is in terms of your seating depth? Or the headspace of the rifle? Or how much you are resizing the brass in relation to that headspace?

If it's an M14/M1A and the rifle is headspaced on the sloppier side of military "go", we might see the early case fatigue no matter what. It shouldn't be happening though, if you are seating your 168 SMK's to the conventional 2.800" most shooters go with.

If someone is loading say, a bolt gun, and touching the rifling with their projectile, there is a really good chance that they reach a max load before they ordinarily would have, but the real reason this is usually a gain in the accuracy department is because of a loss of concentricity between the chamber and the bore. Or between the bolt and chamber and bore. When the bullet makes the jump into the leade and contacts rifling, if the chamber is not cut in good squareness with the bore then one side of the bullet will be engaging more than the other, and it will tend to start to "porpoise" as it flies and open up group size. Seating the bullet further out does minimize this somewhat, as it can be allowed to "center" itself better before engaging the rifling.

Likewise with neck size reloading. It's more accurate because the shooter is circumventing some machining in his rifle that is less than true ;)

I've never had an accuracy need to seat right up against the rifling. In a precision bolt gun load, 10 thou off was fine by me, and I work up from a low starting load...as I was saying, sometimes you do reach max faster than what the manual says, but it depends on a lot of factors.

Sometimes it just happens...like the Swiss K-31 rifles. The seating depths listed in American manuals are downright out of whack for the throats on those rifles!!
 

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Discussion Starter · #3 ·
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'....
 

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Thats really weird, Casebro.

If there's one more test we might do, the only one I can think of would be to seat that bullet long, in an unprimed case, and use your bolt to finish seating it. What I mean is, forcing the bolt closed will seat the bullet deeper and give you a decent read on where your rifling contacts the round. Unless you know already through the ink or candle soot about where that is.

I would really like to know for sure how far off the lands you are...I really can't see a tight chamber and normal leade giving you stretched out brass and flat primers, and the load you are using developing only 2400 fps...think this one has me stumped.
 

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Discussion Starter · #5 ·
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.
 

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Flattened primers and 2,400 fps with a 168 SMK doesn't compute for me either.

From post #3 it sounds like you may not be pushing the shoulder back enough. "Just snug, no slop" is exactly what I'd be looking for in a bolt action, but you want the case headspace .003 to .005" shorter than the chamber.

"Lots of stretching" is a function of this rifle AFAICT. What sizing die are you using? I really like Hornady dies in general, but switching to an RCBS X-Die for sizing made a huge difference in how much the cases stretch. I literally didn't have to trim at all after using the X-Die for the 2nd time on a given group of cases. First time that ever happened for me.
 

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Do you clean the lubricant off of your cartridges after you finish building them?
 

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Read this, it might help.

It is possible that your dwell time is short, if it is the extraction happens while the case pressure is high.
This link explains it.
http://m14forum.com/m14/103625-dwell-time-pertains-m14-how-adjust.html

Another possible solution/problem, is your chamber clean and smooth, brass can stick in the chamber, if it does it takes more force to extract.

Jim
 

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Discussion Starter · #9 ·
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?
 

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It certainly could. I am not sure of the exact pressure ranges, but a bullet seated too far forward or too far back can both raise pressure significantly.

Sometimes when you seat one too far back, gas flowing past the projectile can mitigate that, but not always.

I'd be real curious to seat a bullet real long in a case thats been very well bevelled inside the mouth and let the closing of the bolt act as your seating die, and measure the OAL. That usually gives a read of a little longer than where your rifling touches ogive.

Jake, in regards to chamber, I was taught the opposite...clean and smooth provides the best extraction whereas grime, tooling marks and especially pits cause sticky extraction. It's been the case for me a few times where a semi auto rifle that was showing poor extraction and roughing up cases has been sorted out by using a bore brush wrapped with Scotchbrite pad :)
 

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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?
With that load bullet jump is not the issue. Over sizing the case for the chamber is, along with using regular dies.

Suggest you get the regualr (SB die is not needed) RCBS X-Die to FL size your cases. I get 20+ firing per case with LC brass and stretching is contained so I do not trim at all.

With either the X-Die or the FL die you are using back the die out one full turn. Size a fired case and attempt to chmaber it not letting the bolt slam shut but just snaping over the rim. It should not chamber as the case headspace dimension should be too long. Turn the die in 1/8th turn and size/chamber again. Repeat until the case with just chamber. The cases then are being sized so their headspace "fits" the chmaber headspace on your rifle. Lock the die in that position.

The X-Die is the real and easiest solution.

Larry Gibson
 

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Discussion Starter · #12 ·
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...
 

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Discussion Starter · #13 ·
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?
 

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Discussion Starter · #15 ·
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.
 

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I don't know that your results are right--I think you're setting the shoulder back by pounding the case into the chamber.


To find the length to the lands, take a properly sized and loaded case and stuff it into the chamber with your thumb. If it drops out just by tipping the muzzle up, then the bullet is not in contact with the lands. So what you do is seat a bullet long, then check it; keep seating deeper until the case drops out on its own. This is a lot easier and more repeatable than say the RCBS precision case mic. It also makes it easy to set the jump since the seating die is now set to jump=0.
 

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Discussion Starter · #17 ·
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...
 

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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...
I wasn't saying you'd want 0 jump. You can measure the ctg OAL at that point and then dial the seating die down to get the exact jump you want. The standard match bullets work fine with 0.020" jump.

I get flattened primers (WLR and Rem) at nominal velocities with 0.020" jump.
 

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The RCBS "X-Die" for re-sizing comes in both normal size and "small base" size:
https://shop.rcbs.com/WebConnect/Ma...yDisplay&categoryId=C09J049N022&route=C09J049

If you're going to buy a new sizing die, why not get a better seating die while you're at it? Forster's Bench Rest Seater simply is a better mousetrap in terms of ensuring that the bullet is seated as dead-center as possible in the case:
http://www.midwayusa.com/viewProduct/default.aspx?productNumber=202919

Meanwhile, I'd really like to know the answers to these questions:
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've got an M25 that is generating unexpected chamber pressure according to a friend's calculations in QuickLoad. The jump to the lands appears to be about 0.040" in this rifle with a 168gr SMK seated to 2.82" COAL. Is that too much jump? (measurements done using Hornady OAL gauge)
 
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