I,see some jus load at 2.200 all the way to 2.260, how important is oal in an ar ? How do you guys determine what oal to load to ?

Depends on bullet, however bullets with cannelure I just seat to mid cannelure and end it. With trimmed brass at 1.750 I wind up around 2.220 COAL.

The max length without a cannelure with depend on the bullet, but the magazine is the limiting factor with 2.260 or so for a max COAL.

Probably the biggest issue with OAL for AR's is being able to fit rounds in magazines.   I can reliably push 2.250" to 2.260."

As other have said, if I'm loading bullets with a cannelure, I'll load to where that is aligned with the neck of the case.  If for nothing else seating any farther could really drop the amount of the bullet actually engaged by the neck.

OAL is determined by a few simple criteria.

Fit the mag.

Fit the chamber.

At least one (1) bullet diameter seated into he case for adequate neck tension.

Seat to cannelure if desired.

Seat for reliable function and accuracy.

That's it,  seat em so they fit-feed-fire in your rifle.  

Note:  Pressure will be increased the longer the OAL and decreased the shorter the OAL.

Not completely on topic, but not entirely irrelevant either if loading near max.

I see this quite often and have never understood it.

For sure pressure goes up if the bullet is into the rifling.

Otherwise, the longer the cartridge overall, the less bullet is in the case, so case capacity is larger which should produce less pressure.

What don't I understand?

Looking forward to learning something.

I would also like to see the answer to this. I load to 2.330" OAL for magazine loaded 77SMK/68Hornady/69SMK with the front of the magazine cut out. The bullet tips just miss touching the front of the rifle magazine well (and are flush with the front of the mag).
With a larger case volume at the start of burn, pressures spike much slower than a short OAL (for me, anyway).
Again, I am looking to learn also.

The amount of case capacity taken up by the bullet has little to no affect on Max pressure in a bottle necked rifle round as peak (max) pressure is not achieved until the bullet has exited the case.  What does affect pressure is how far the bullet travels before it enters the rifling.

This is from John Barness of Handloader Magazine.

Reducing OAL decreases peak pressure, for two reasons. The longer "jump" of the bullet to the rifling results in a lower peak pressure, since the bullet engraves more easily the faster it's going when it hits the rifling.

Also involved is the "progressive" burning of almost all modern rifle powders. This means the pressure increases relatively slowly from the time of ignition. Thus peak pressure occurs when the bullet beyond the barrel throat, with very slow-burning powders as much as 3-4 inches.

How are you measuring your Pressures?

Unfortunately, I can't anymore. Previously, I did at work when I was at the Hercules, Inc plant  where I worked on mostly caseless ammo on Gov't contract work for Frankfort Arsenal and then Picatinny Arsenal. Most of the routine pressure work was just peak pressure using the then industry standard copper crusher method (CUP). For the full detail pressure traces, a piezoelectric transducer method was used that was made by a company named "Kistler". This gave the entire pressure history versus bullet travel to the muzzle. For shots under 20mm, action time from hammer fall to bullet exit was usually 2.5 milliseconds (0.0025 sec).
This was also the plant that developed the Reloder (NOTE: THERE IS NO "A" IN RELODER) line of propellants.
Hercules Inc was previously "Hercules Powder Co" and is now "Alliant".
Edit: transposed letters for "CUP" (copper units pressure).

Where's popnfresh's pressure/jump thread again?

Pfft don't bother some people wont learn and cannot understand how a 30.06 can use more powder than a .308win with the same bullet but run the same pressure. The answer is case volume, usable case volume changes with seating depth.


Op, I seat my 45gr bullets to 2.170" I seat my 90gr bullets to 2.500". Choose your rough seating depth before working up a load, after your safe workup, a small adjustment either way wont make much difference.

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Pressure tested data from the University of Mich.

Note the shorter the OAL the less the pressure.



From an older load manual.

Note the shorter the OAL the less the pressure.



reason: Max pressure is not achieved until the bullet has exited the case, so volume occupied by the bullet has little to no affect on pressure.