What are the effects of different OAL's?

[Oreo]

This is an academic question for me to understand things better...

If all else stays the same- powder charge, bullet, gun, etc. will a longer or shorter OAL have an effect on bullet speed?

So far, I understand that too long OAL results in feeding problems. Too short of an OAL can result in high pressure problems. So, given the same powder charge, will a shorter OAL result in higher velocities because of the higher peak pressure?

[AdamN]

Yes

[ISUSteve]

Not so much in pistols, but it can really effect accuracy in rifles.

[918v]

Not necessarily.

Think of powder as fuel. In most cases this fuel is never burned completely in the barrel. That is why you get muzzle blast and flash. In others, powder combusts completely with little bast and almost no flash.

If you seat a bullet deeper you increase pressure, but that increase in pressure will yield nothing if the powder is being burned at a 100% rate, like with Clays or Red Dot, or even Unique.

Seating a bullet deeper will increase velocities with powders that do not burn completely in the barrel, reason being that the higher pressure will combust the slower powder more efficiently.

Where bullet seating depth is really important is in changing barrel harmonics and accuracy. I can completely ruin many of my accuracy loads by seating the bullets deeper or shallower.

[Oreo]

So then, if I'm not at a maximum load & I'm getting muzzle flash, shortening the OAL might reduce the muzzle flash?

How much will the OAL affect the accuracy of a pistol? Is this something I should be experimenting with for my G23?

[918v]

Depending on how much pressure increases and on the burning rate of the powder, it is possible to reduce muzzle flash. How much is another story. How much are you willing to raise pressure? I don't know how efficiently WSF combusts in pistols. QuickLoad does not list that powder. It lists WAP and 231. WAP is 98% efficient at max pressures. I assume WSF is similar. That should make it a pretty low flash powder.

I'll give you an example with Power Pistol:

Per QL, PP is 85% efficient in pistols at max pressure. I was working up a target load using 6 grains under a 115gr. FMJ at 1.150", a moderate pressure load. The report and recoil were moderate as well. Reducing the OAL to 1.135" increased the recoil and the report increased in pitch. I'm assuming the velocity increased as well as the pressure.

In another experiment, seating a 147gr XTP .010" deeper increased group size from .5" at 15 yards to 1". Seating that bullet .010" shallower increased this group to .75" at the same distance.

[Oreo]

I'm not having a muzzle flash problem with WSF. Like I said, it was an academic question. However, it sounds like pistol accuracy can be pretty significantly affected. So I guess I'll have to do some more home work & perhaps play with OAL a bit.

[creophus]

Oreo,

When shooting pistol you have two things that dictate your OAL. Magazine size and feeding.

If you get a load that will feed reliably, I recommend leaving the OAL alone.

Unless you're at an expert level of shooting, you may not notice a difference in accuracy.

Shortening the OAL on a MAX charge could cause a KB. If you do want to play with OAL (especially on that MAX charge) start from the bottom and work your way up again. Do this evrerytime you change OAL.

Safety first, everything else come second.

[918v]

When working-up a load, I have found that the accuracy node occurrs at several different charge weights, like 3.7 grains and again at 4.3 grains for example. I like milder loads, so I usually pick the 3.7 grain weight and then play with bullet seating depth. If the 4.3 grain node is not max, then I play with seating depth there as well.

Certain calibers are more sensitive than others. 9mm is pretty sensitive. 45 ACP is not. I haven't worked with the 40 enough to label it.

[fredj338]

Even w/ really fast powders like Clays, it's still burning as the bullet exits a 4" bbl. Pushing the bullet deeper will raise pressure & vel. If you have a chrono, you can check for yourself by using the same powder charge & checking vel. after seating the bullet say 0.01" deeper. I think it's one of the biggest reasons yo usee so many KB stories about the 40s&w in a Glock.

[thorn]

I seat my 9mm's using the advice Creophus wrote above. The load data i had showed anything from 1.090 for a 124gr FMJ, all the way to a measured 1.165 for WWB factory ammo.

I cross-referenced a few bullets and powders, and finally decided (leap of faith + research + online advice) that I'd get as close as possible to 1.145 and if it fed perfectly, call it done. I'm not seating BELOW any published COL, so I've decided that's safe... and my variations for now are only on the powder variable.

I may screw around with the COL at some point once I'm more experienced, but for now i'm going to leave it alone. My targets indicate it's working pretty well. :)

thorn

[creophus]

My targets indicate it's working pretty well. :)

thorn Show us some pics!!

[918v]

Even w/ really fast powders like Clays, it's still burning as the bullet exits a 4" bbl. Pushing the bullet deeper will raise pressure & vel. If you have a chrono, you can check for yourself by using the same powder charge & checking vel. after seating the bullet say 0.01" deeper. I think it's one of the biggest reasons yo usee so many KB stories about the 40s&w in a Glock.

That depends on caliber and pressure. QL shows Clays to burn 100% in 4" barrels in most applications. Of course, seating a bullet deeper will raise pressures, but it will not increase velocity with Clays when you are already at max.