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I would mildly disagree with your thoughts on pressure in front of the bullet. I understand what you suggest, but
1 - the muzzle is open. Without confinement, significant pressure is hard to build.
2 - the pressure behind the bullet is so much higher than whatever pressure might exist in front of it, it may be irrelevant for practical purposes.
You're probably right about pressure in the barrel in the scenario described, it's all I could think of. Interior ballistics events take place so fast, it can get complicated. I don't have any particular worries; it's practically never that I load in max. territory.

Regarding #3, when it comes to most longer match bullets they have a bearing surface thats longer than .250" so it should bridge the gap from the case mouth to the lands thus sealing it by in large.
In sure there's a bit of gas blow by on all bullets regardless. Like the corners of the lands that's why there's gas checks right? Correct me if I'm wrong..
Yes, I'm sure you're right about this. I was considering bullet design being a component of just how much freebore might exist to permit blow-by. Once again, I say, it happens very fast.

Back to the OP's original question for a minute. I was reading, I think it was, in Nosler's manual. In it they discuss the Cartridge Base to Ogive (CBTO) length. Once the issue of magazine fit is addressed, CBTO is more important than COAL. Because that place on the bullet where the ogive begins is where engagement with the rifling will occur. Not the tip of the bullet, which is what COAL is measuring.
 
Because that place on the bullet where the ogive begins is where engagement with the rifling will occur. Not the tip of the bullet, which is what COAL is measuring.
Uh well, you're not wrong.. But CBTO is way more consistent. Most all bullet meplats ("just the tip" ayo! ;)) is very inconsistent. They very wildly in the same lot. This is the main reason why CBTO is a higher tier of critical importance.
This is also why I mentioned a decent pair of calipers and also the comparitor inserts are necessary.

Which also leads into another factor worth mentioning. Those camparitor inserts aren't really interchangeable. Meaning from the same size dia. They all have some degree of chamfer on the mouth and depending on the depth of that chamfer it will vary from insert to insert of the same dia. of the same maker. I like the Sinclair inserts because they are stainless and have a very small chamfer. I also have the hornady ones and the Brownells hex nuts that combine six different popular diameters into one. These ones are entirely cut with a taper unlike the others and the bullet can go quite a ways into the hole before "engaging" so maybe a better way of saying that is the measure the ogive further out than the actual ogive??
They all work. But some better than others.

The main thing to keep in mind is this doesn't need to be exact. Its a relative measurement. It will give you a solid baseline at "x" point in space and you can adjust your bullet to "y" point which you know or suspect will be better.

Thats all an long winded way if saying don't intermix your comparitor inserts if you have several like me. Pick one maybe even make note of it in your recipe and use that one from then on.

I'd start with the hornady set which is cheap and get the Sinclair's if you need one down the road not included in the set. Check the hornady ones for big dings in the opening before using, you can file these out and removing material won't really affect anything and long as your only hitting a small portion of the circumference (the bearing surface)

Oh and keep in mind you can book mark this thread for reviewing later.
 
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Uh well, you're not wrong.. But CBTO is way more consistent. Most all bullet meplats ("just the tip" ayo! ;)) is very inconsistent. They very wildly in the same lot. This is the main reason why CBTO is a higher tier of critical importance.
This is also why I mentioned a decent pair of calipers and also the comparitor inserts are necessary.

Which also leads into another factor worth mentioning. Those camparitor inserts aren't really interchangeable. Meaning from the same size dia. They all have some degree of chamfer on the mouth and depending on the depth of that chamfer it will vary from insert to insert of the same dia. of the same maker. I like the Sinclair inserts because they are stainless and have a very small chamfer. I also have the hornady ones and the Brownells hex nuts that combine six different popular diameters into one. These ones are entirely cut with a taper unlike the others and the bullet can go quite a ways into the hole before "engaging" so maybe a better way of saying that is the measure the ogive further out than the actual ogive??
They all work. But some better than others.

The main thing to keep in mind is this doesn't need to be exact. Its a relative measurement. It will give you a solid baseline at "x" point in space and you can adjust your bullet to "y" point which you know or suspect will be better.

Thats all an long winded way if saying don't intermix your comparitor inserts if you have several like me. Pick one maybe even make note of it in your recipe and use that one from then on.

I'd start with the hornady set which is cheap and get the Sinclair's if you need one down the road not included in the set. Check the hornady ones for big dings in the opening before using, you can file these out and removing material won't really affect anything and long as your only hitting a small portion of the circumference (the bearing surface)

Oh and keep in mind you can book mark this thread for reviewing later.
THANKS AGAIN!! COMPARATER JUST GOT DROPED OFF HORNADY
 
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Congratulations on loading your first ammo, and I applaud you for asking questions to help understand new and unfamiliar aspects better and learn, and most importantly, making sure you are being safe.

Reading through the thread, excellent advice from a number of folks here to help.

It takes me back to when I loaded my first rounds. I remember thinking, what if I did something wrong, even after reading, and studying, and double checking everything.

And then loading that first round I made into the gun, feeling nervous. And thinking, ok, what is going to happen when I pull the trigger?

I’ll tell you what. You do your homework, follow published loads, you check and double check everything, and you ask questions, and pay attention to details along the way, like it appears you have. Your gonna feel a lot better after you fire the first shot.
 
I started collecting equipment back in about 2010. And could have probably loaded rounds somewhere around 2012. But sadly never loaded any until probably 2019, because i never felt comfortable shooting without a chrony and just going by pressure signs. But hey it gave me plenty of time to study and research! Lol. And better safe than sorry! I hate hospitals! I mean nurses aren't bad. And children's hosp. nurses really aren't that bad, those cute nurses sure love their cute kids! but not as a patient... Oh I'm getting off track aren't I?!? *sorry.
 
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Uh well, you're not wrong.. But CBTO is way more consistent. Most all bullet meplats ("just the tip" ayo! ;)) is very inconsistent. They very wildly in the same lot. This is the main reason why CBTO is a higher tier of critical importance.
This is also why I mentioned a decent pair of calipers and also the comparitor inserts are necessary.
Agreed. But you're getting into the real nuts and bolts of this. What I was referring to was relative to the reloading book recommendations that provide COAL. Which are bound to be inexact in terms of position relative to the the leade of the rifling. For the reason that rifle chambers are crafted in different configurations. And a generality is the best the composers of the manuals can come up with. Likely many reloaders using these manuals look at the recommended COAL, and for them, that's the number, not giving much thought to engagement in the rifling. But that's good enough for probably 90+% of the people using the books.

I've been reloading for decades, never got into a comparator. When the need came up for measuring, I've put together dummy cartridges and used Prussian Blue on the bullet. On bolt rifles that I've used for accuracy, once I settle on a bullet and load, I stay with that. For self loaders, I don't fuss around with seating depth all that much. Function comes first for those, and honestly in my case, I don't do much match shooting with them. In fact, none for several years.

I've got a new-to-me Winchester Model 70 in 7x57, I'm just getting started with load development for that. Recently I drove miles out to the woods only to discover that my chrono was balky, didn't get a single reading. Suspected bad cord, which I've since repaired. Also discovered that my line of sight was quite low (rifle has fixed sights), so I had to buy a .25 front sight to replace the .31. Eventually, I may even get around to actual load development for accuracy.

I use a BB gun at home to test the chrono, it's cheaper than firing centerfire rounds. My Glock 19-like BB pistol will clock 365 fps with a fresh gas cartridge.
 
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Confused on the measurements. First is 0.005 then you give 1.85 and 1.90. 0.005” will not make a difference. 0.050” May start to make a difference.

Don’t confuse SAAMI OAL with cartridge OAL. SAAMI length is used for things such as fitting in the magazine. Cartridge OAL is typically limited to the lesser of SAAMI length or maximum length the cartridge can be before the bullet engages the lands. Most of the time SAAMI OAL governs. However, short lead chambers or bullets very wide out front can govern max length.

For rifles, the slender cartridge usually allows good reliability for semi-autos. Semi auto pistols can be very picky about cartridge OAL and bullet profile because of the short and fat cartridge and angle of feeding.
STRAIGHT-sided handgun cartridges of the RIMLESS format are actually spaced in the chamber by the neck of the cartridge case. Too short means that the firing pin/striker has to travel - even a small amount - to make impact with the primer, and the case MAY be subsequently stretched. Too long means that the primer effectively protrudes out of the chamber, and the closure of the breech-block might, with an inertia firing pin and weak spring, actually cause the cartridge to be set off before the cartridge is fully in the chamber.

This is not good.

Some blow-back action submachine guns, like the Patchett/Sterling are designed with deliberately short chambers, and fixed firing pins in a heavy breechblock, so that the forward-travelling breechblock picks up the cartridge, and rams it into the short chamber with the fixed firing pin setting it off at the instant of breech closure. This is NOT what you need in any non-Class 3 firearm.
 

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