How quickly does heavy bolt lift manifest itself?

Varget is a good powder. My Hornady shows it as one of the select powders for the smaller 243 bullets.

There should be good accuracy in a couple of nodes below max loads.

A 243 is a bit of a barrel eater so the lower you can run velocity the longer your barrel will last.

The 60 gr may want to be seated someplace different than the 75. Close or touch lands or backed off.
 
I've fired 7.62 NATO proof loads in rifles that produce ~67,500 CUP (~82,000 psi) peak pressures. Folks who've seen the fired primed cases often say they look much like their own fired cases. Or a bit warm but still safe.

Bolts opened manually with normal force.
 
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jmr40 said:
If your load manual says a max load will be 3000 fps with 45 gr of powder then the 3000 fps number is what you pay attention to. With individual rifles 45 gr of powder will match the books and give you 3000 fps.
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I disagree!!!.

The powder and primer lots are different as well as the barrel length and interior diameters.
 
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I think HiBC is dead on with both his post . Best to see the whole painting and not take one brush stroke as the be all end all of what’s going on with the load .

If benchmark is there accuracy load with that bullet . I’d test the H4895 next , light bullets and slow powders tend to be harder for me to tune . I really think the faster burning H4895 and the lighter bullet is going to shoot well .
 
jmr40 said:
A chronograph is only $100 and situations like this is why they are worth the money. By the time you start getting sticky bolt lift you are WAY over max pressure.

If your load manual says a max load will be 3000 fps with 45 gr of powder then the 3000 fps number is what you pay attention to. With individual rifles 45 gr of powder will match the books and give you 3000 fps.

But with other rifles you may reach 3000 fps at only 43 gr of powder and 45 gr may give you 3100-3200 fps and be a dangerous overload. In that rifle 43 gr is a max load.

In yet another rifle 45 gr may only give you 2900 fps. In that case it would be safe to increase powder above book max until you reach 3000 fps. But I strongly advise against doing so. If that ammo found its way into another rifle it could be dangerous.

I use a chronograph when developing loads and stop adding powder when velocity starts getting close to what the load manuals say should be the velocity I get with a max load. Or when I reach max powder charge. Whichever comes 1st.
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That's really not right. It probably won't cause actual damage in most instances (won't go over proof level), but it isn't a way to control peak pressure except in one specific set of circumstances in which:

1. Your barrel is equal to or longer than the test barrel.
2. Your charge weight is equal to or higher than the published load for the velocity.

If you achieve the published velocity in the published test barrel length with LESS powder than the published charge for that velocity, then your peak pressure is higher than the published load's peak pressure was.

The above is not obvious, but here is the cause: When two bullets reach the same muzzle energy in the same barrel length, then the average pressure they experienced in the barrel starting from the chamber and including all the changing pressure levels averaged out over the bullet's trip down the tube and until it clears the muzzle. The peak pressure, which is the one we worry about for safety, is only a portion of that average, as is the muzzle pressure, and these don't change in proportion to the average pressure as you alter the powder charge. A given average pressure can be achieved by:

1.) A combination of a high peak and a low muzzle pressure, or,
2.) A combination of a low peak and a high muzzle pressure.

Low and high are relative in those statements, and in this case relative to the peak and muzzle pressures the load developer saw.

The first one happens when you get to a given databook velocity using a faster (higher burn rate) lot of powder, thus finding you need a lower charge to reach that velocity than the book listed.

The second one happens when you get to a given databook velocity using a slower (lower burn rate) lot of powder, thus finding you need a greater charge to reach that velocity than the book author did.

The above is true because, with low muzzle pressure, more of the bullet's acceleration has to be garnered from the peak pressure and less comes from later pressure levels in the barrel, meaning the peak has to be higher to get the bullet to the same velocity. A lower powder charge produces less gas and therefore lower muzzle pressure when expansion completes, so that's how you know its peak had to be higher to reach the same velocity. Vice versa applies as well.

What changes the relative burn rate can be differences in components, differences in your chamber dimensions, and, as I mentioned, differences in your powder lot's burn rate. Whatever the cause, the principle of peak to muzzle pressure ratios applies and you need to be warry of a velocity that is achieved with less powder in a same-length barrel or if you need the same amount of powder to reach the claimed velocity, but your barrel is shorter than the test barrel was. Either situation means your peak pressure is higher than the occurred in the load test.


Robinny,

An old rule of thumb has been that if you get a beginning hint of sticky bolt lift or sticky case extraction as part of a load work-up, you should back the charge down 5%. The sticky extraction sign applies to all types of firearms. That number should give you a sense of what those symptoms indicate and how far above the happy pressure range you are getting.

As to how fast the sticking event develops, it is generally in about half a millisecond from the time the powder burn gets seriously under way. ;)
 
Are you saying that a barrel that is looser will not get a bullet moving faster at lower pressures?


I can think of friction difference between a hammer forged and a button rifled barrel (cut rifle as well but those are much rarer)

If so, substantially different?

I need to look at my data and see what different there was between a 270 Finnbear barrel and a Shilen barrel firing the same ammo (length difference of a couple of inches)
 
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Back when moly-coated bullets first became a craze, everyone noticed the lower friction caused about -20 to -50 fps loss in velocity with their favorite loads, and that bumping powder charge up half a grain in the 30 cal match rifles was commonly needed to get the velocity back again. It's because the powder needs confinement to build pressure against to advance its burning rate, and the effort to start the bullet moving and get it into the lands provides some of the resistance that pressure builds against (the chamber size and bullet mass inertia providing the rest). If the bullet goes down the tube too easily, expansion behind it happens at lower pressure and earlier in the powder pressure curve. Then the powder doesn't quite burn fast enough to make gas fast enough to keep up with that rate of volume growth. As a result, the average pressure is lower so the average bullet kinetic energy is lower, and velocity will drop as the square root of the drop in kinetic energy. You can achieve a similar pressure curve effect by reducing bullet weight without changing the charge. It still shoots, but the pressures and the resulting bullet kinetic energy are lower.

A favorite quotation of mine:

"First contemplation of the problems of Interior Ballistics gives one the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity."

Homer Powley, Introduction to Quasi-empirical Equations for Interior Ballistics​
 
Ok, phew.

The hypothesis is that a Hammer forged barrel has more friction as there is more surface in contact with the bullet.

So, a button rifled barrel would have less (rougher but less contact) and variations depending on how much lapping was done of course (I had an XC barrel that clearly was rougher than the Shilen barrels I use for the rest ). XC smoothing out over a lot of shooting.

So if you started with a Button Rifled barrel and load then the Hammer forged should have a higher pressure?

Somewhere in there length plays a part in velocity as well (or so I think regardless of the initial pressure peak which should take place early in the barrel ?)

I think I am hurting my bran now.
 
I read the OP’s comments of how quickly does sticky bolt progress as asking how quickly does sticky ball go from slightly sticky to kaboom . It’s always been my understanding once you start getting sticky bolts you’re on your way to Kaboom So never accept sticky bolts as a place to indicate elevated pressures but you could keep going . Short answer sticky bolts bad haha
 
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There's really no way to answer this because "Sticky" bolt lift is going to be different in every different gun and ammo component combination.

You simply cannot say "it happens at X.x level" because it does not. Likewise, you can't say it is ok at this level and gets sticky at .3gr more, or anything like that, UNLESS you are referring only to one specific rifle and load combination.

Change even just one factor and the point where bolt lift gets sticky can change. And, that's assuming you and I both agree on what is, and isn't "sticky".

It’s always been my understanding once you start getting sticky bolts you’re on your way to Kaboom
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Yes, but only in the same sense that when you get on the freeway in LA, you're on your way to Seattle. yes, you're on that road, but you have to go a long way on that road to get there, and most folks will not go all the way, and never plan to.
 
Metal god said:
I read the OP’s comments of how quickly does sticky bolt rogress as asking how quickly does sticky ball go from slightly sticky to kaboom . It’s always been my understanding once you start getting sticky bolts you’re on your way to Kaboom So never except sticky bolts as a place to indicate elevated pressures but you could keep going . Short answer sticky bolts bad haha
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While I can see how you could read my post that way, my real concern was going past a slightly sticky bolt without realizing it. Since I've never loaded any rounds to near or beyond max, I don't really know what a "sticky" bolt feels like and I am worried about going past a risky charge weight because I didn't feel the resistance in the bolt.
 
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Yes, but only in the same sense that when you get on the freeway in LA, you're on your way to Seattle. yes, you're on that road, but you have to go a long way on that road to get there, and most folks will not go all the way, and never plan to.
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Haha well sure I guess . Keeping with that same thought . My point was once you have sticky bolt lift you are out of CA and likely well into Oregon at that point . The OP has clarified he's always stayed in CA and is afraid if he blinks he'll miss Oregon and be in Seattle before he knows it . BAM !! how's that for an analogy ?? haha

I'd say you are not likely going to miss sticky bolt and go straight to Kaboom unless you are going up in very large charge increments for the cartridge . I like 1% increments , example if the likely charge weight will be in the 30gr area then test in .3gr increments , 40 grain area .4gr increments 50gr in .5gr increments . Another way is 223 in .25 to .3gr increments , 308 in .4gr , 30-06 in .5gr etc etc

When there are several grains between min/max I like to start low but only load a couple in the first charge increments . I do this so I am starting at min charge to be safe but I also know it very unlikely those low charges are where I will end up as my best load . So as the charges progress I start loading more rounds per increment .

Looks something like this
hX3EoL.jpg
 
I shoot a pressure ladder. I shoot 1 round at each charge weight at separate bullseyes. I do this to see a sweet spot where multiple charge weights shoot to a similar poi. I separate charges into 1% of max increments.

I find there is a pretty fat range of similar poi’s around max or just under. Then as I go over max, I get into flat primers, primer flow, high velocity and heavy bolt lift.

You do need to size cases to fit into your action with small clearance to see proper expansion and spring back.

I find checking mulitiple check items keeps me from missing over max and dialing back to a sweet spot.
 
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