Overall Length Implications

[klewan]

Alright I am buying a dial caliper as soon as I can get to the store. Thanks guys.

I was originally posting because I was curious more about how precise within the SAAMI range I should try to be and why it would be important to be so precise.

It's the pistol ammo; have the bullet .05" deeper into the brass and the pressure doubles. It's only when you have some experience with reloading, and you understand what's happening, do you sort of understand.

[Whiterabbit]

Alright I am buying a dial caliper as soon as I can get to the store. Thanks guys.

I was originally posting because I was curious more about how precise within the SAAMI range I should try to be and why it would be important to be so precise.

Vernier all the way cause I pretend to be a snob . But I use the dial for everything here.

Anyways, the impact of OAL is nil on safety, unless you are arbitrarily seating deeper and deeper without considering the powder charge, backing off if needed, making large jumps without checking for pressure signs, etc....

In short, it's like you asked if you can use more and more powder in the same case. Same answer. Of course you can, assuming you aren't being arbitrary, you are working up, you have your head screwed on tight with your common sense cap on, etc etc etc....

Is it important to be in the SAAMI range? well, not really, but I will say that there is a reason they give you a range, and safety only has partly to do with it. Everyone likes to think their gun is special, but chances are your accuracy node is within the range they gave you. Afterall, they are the experts, and their goals and reasoning are not narrowly targeted like you will be for load development.

[thenodnarb]

How important have you found overall length to play in regards to reliability and accuracy (not to mention safety issues from too high of pressure)?
What are the implications specific for pistol?
What are the implications specific for rifle?

I have read that reliability and accuracy can be inversely proportional for longer vs shorter OAL.

Shorter OAL with the same bullet means the bullet is seated deeper in the case. This makes less case volume, and with the same charge, will increase pressure.

Feeding reliability isn't inversely related to accuracy. It has more to do with bullet shape in most guns.
In general, loading the bullet so that it doesn't have much of a jump to the lands leads to better accuracy. Depending on bullet, gun, powder etc, it may like a little more or a little less lead(that is, distance before it engages the rifling)With a rifle like the ar-15, you can load as long as the magazine will allow, and still not have the bullet engage the rifling when chambered. In guns like a remington 700, there is plenty of magazine length to allow you to seat out longer.

Remember that OAL is relative depending on bullet shape. a round nose 180 grain .308 projectile will be much shorter than a VLD(very low drag) bullet of the same weight that is long an pointy. OAL means nothing compared to each other in this situation. One might feed fine, and one might not feed at all. Depends on the gun.

With semi-auto pistols, feeding may very well be an important issue. But if you choose a bullet that doesn't feed well in your gun, its better to just switch bullets rather than play with seating depth to make it run. I did this with .45 ACP. I had some semi-wadcutters that I got a really good deal on. They wouldn't run in my springfield XD at ALL. It was a jam-o-matic with those bullets no matter what seating depth I tried. However, my 1911 shoots them just fine, regardless of seating depth.

Bottom line, don't experiment too much with seating depth. Well you can experiment, but were talking a max of like .020, and usually you err towards longer than what the book says. Remember that seating too long in a rifle can also bump the pressure up. If the bullet has no jump to the rifling, it has no inertia when engaging the rifling and pressure can build too fast. Its not always a problem if you have a safety margin, but at max load it can be a problem.

Hope that helps. BTW read the hornady reloading manual chapter on accuracy. It will get you 95% of the way there in understanding all this stuff, and the diagrams are really helpful when you are first learning about headspace, pressure etc.

[1979Standard]

Great reply Nodnarb. Thank you very much for taking the time to spell all of that out for me.

[1979Standard]

9mm Luger can be loaded with a wide range of ammo weights, from under ~65gr to ~147gr. This is why the OAL can vary by over 1/8". The lighter bullets need to sit far enough in the case to still get a grip on it, and the heavier ones need some room out front.

Ok, got the calipers and measured some factory 115gn cartridges that read 1.156 and I previously had setup my bullet seating die to match that height prior to having the calipers. Hodgdon recommends C.O.L. Of 1.150 for the 124gn bullets that I am loading however. I now am understanding why they need to be shorter, because of what twotacocombo said above with "needing more room up front" which I am assuming allows more momentum before engaging the rifling and will therefore not build as much pressure than that of a longer cartridge that is pushing the same weight bullet. I also understand that 9mm pressures build faster than other caliber cartridges and the thousandths of an inch in length as well as tenths of a grain of powder really can have a compounding effect on the pressure. So I suppose I should get my seating die a little bit lower and make sure all my cartridges are exactly 1.150" when loading the 124gn RN bullets with the 5-5.5gn CFE Pistol powder? Thanks everyone.

[jtake]

To add what has been said before, bullets in the lands, or jammed, will have greater pressure. So if you develop (note the last word) a load at max pressure and with jump, if you reseat the bullet so that it is in the lands, you may now have a dangerous load for your rifle.

The key is to develop a load. Don't start off with the max or someone's recommended load, as that load was for their gun and yours may be different. Start a little lower and build up. Load 3 rounds for each of the different charge weights and examine cases for pressure signs as you fire them, stopping when you see signs. Use multiple reputable sources (powder manufactures and bullet manufactures all usually provide load data and check) for load data and start on the low side.

In this way, you can understand what are safe loads for your gun and you just don't jump into to a load that might be unsafe for your gun.