Please educate me about OAL

[SandSpider]

Ok, I think I understand two aspects of overall cartridge length.

First, with a semi automatic, the finished round must fit in the magazine and feed reliably.

Second, shorter OAL (all other things being equal) means the bullet is seated deeper, hence less case volume for a given amount of powder, hence more pressure.

But if I'm loading for a revolver, why would going for an OAL other than SAAMI maximum spec make sense?

More to the point, I'm loading .45acp for a S&W 625. I'm trying to find the most accurate load. So I build a round that is 1.275" OAL, load it from minimum load to maximum load for a given powder and find one charge that works best. Would it then make sense to start experimenting with different OALs to further fine tune the load? Seems to me that all that would do is change pressure, which I have already covered by trying different amounts of powder.

Am I missing something here? Why do reloading books publish OALs that are all over the place?


Thanks for any advice.

 

[Bugkiller99]

OAL is specific THAT bullet in THAT weight in THAT profile. So if you are not using the specific bullet, the OAL listed does not apply. One example would be a cast 200 gr LSWC. Using a Lyman 452460 mold, your OAL is 1.161. If you use Lyman 452630 mold 1.235. Different profile bullet. Different charges for same powder.

 

[OKFC05]

But if I'm loading for a revolver, why would going for an OAL other than SAAMI maximum spec make sense?

First rule on loading revolver cartridges is that if the bullet has a cannelure, that's where the crimp goes. So a different bullet with a different groove is crimped in a different place and your data from another bullet does not apply, as Bugkiller said. Do you see why there are so many OAL with different bullets?

If you are loading a rimless semi auto caliber for use in a revolver, you have more choices, but also more potential problems. Without a cannelure to help hold the bullet, you need enough bullet inside the case to hold it while firing. Also, a lot depends on what powder you are using; slow powders need more volume for the larger charges.

Since I load .45 acp with Titegroup , I load short and verify power factor with a chronograph. When shooting USPSA competition, I have to make power factor and playing with slower speeds to get a bit more accuracy might just get me disqualified. I've never found justification for my purposes to have separate .45 or .40 loads for semis and revolvers.

If you're just wanting to play with the loads and don't have to make any particular power factor, then the only concerns are getting too slow and sticking a bullet or getting too hot and damaging the gun.

 

[S&WIowegan]

Good points from bugkiller(where was he when I needed him?) Also, OAL is a critical factor in whether the round will feed from magazine to barrel chamber. Go ahead and play with OAL but always verify feeding.

Revolver OAL is often governed by the location of the crimp groove. The groove secures the bullet from jumping forward while you shoot another round. Crimp groove also restrains the bullet and helps achieve efficient powder burn.

You are thinking too much at this point. Just follow standard instructions in a loading manual of your choice, make some ammo and shoot. If it's too hot, too wimpy or something else you feel could be better, make a change in small increments.

Got a chrono?

 

[BLUEDOT37]

Ok, I think I understand two aspects of overall cartridge length.

First, with a semi automatic, the finished round must fit in the magazine and feed reliably.

Second, shorter OAL (all other things being equal) means the bullet is seated deeper, hence less case volume for a given amount of powder, hence more pressure.

.

I would make your second reason number three & submit that reason number two should be for chambering (in a semi-auto). If the COL" exceeds what your gun can accommodate the nose of bullet will be touching (jammed into) the rifling forcing (especially if it has a short leade) the rim too far rearward & not be headspacing on the case's mouth. This is why we say to basically ignore the listed COL" & seat the bullet so it passes the "plunk test" in your pistol's chamber.

I generally seat mine as long as I can, & still pass the plunk test, while not going over the SAAMI max. COL" for that cartridge.

As for the 45ACP in your 625, having a max. COL" won't make a noticable difference in accuracy, like it might in a rifle, because of the long throats.

.

 

[rwsmith]

Difference between the two.....

Modern cartridges and most semi auto cartridges were made with smokeless powder in mind. The volume is sized to deliver the proper performance and the bullet must be seated to the depth required for that and not more because of over pressure considerations. That goes for 9mm, .40 cal or any other modern semi cartridge. By modern I mean cartridges that were introduced AFTER smokeless powder took over in the early 1900s.

Many older cartridges that were originally designed for black powder, needed all the volume in a .38, .45 Colt or whatever case to get decent velocity. When they switched to smokeless powder, it both did a better job and used less powder. Therefore the volume in most revolver type cartridges is more than is needed. Consequently there is more available 'play' in the overall length of those cartridges. You are free to seat the bullet to the ogive or far enough out until it hits your forcing cone. Set them shallow or set them deep, whatever works in your gun is good. Most people just define a medium depth in bullets without cannelures that either work best or look 'right'.

 

[rwsmith]

Between my full size semi autos......

If you're just wanting to play with the loads and don't have to make any particular power factor, then the only concerns are getting too slow and sticking a bullet or getting too hot and damaging the gun.

When reloading for my full size 5943 I just loaded what I wanted to and they shot fine. When I added two compacts to my arsenal I was scrambling to make ammo that would operate in ANY gun. Bullet profiles and seating made a BI-I-I-IG difference in reliability. I don't want to make different batches tuned to certain guns... bummer.

 

[scooter123]

Something I didn't see mentioned is that if you change your overall length it's advisable to start over on the powder charge workup. Because changing the length will also cause a change in pressure. So your idea of fine tuning length AFTER you've found the most accurate powder charge amount could pose a potential for a load with too much pressure.

I'll also note that I don't bother with trying to fine tune for accuracy for with my handgun loads. Because unless I'm shooting from a rest with optics I am just not good enough to see any real changes in accuracy of my loads. It's been my experience that handguns are fundamentally accurate and seem to be less sensitive to changes in the bullet velocity than rifles, so it takes an exceptional shot to see any benefit in a velocity change of 50 or 75 fps or so. What I've found can have a noticeable difference in accuracy for handgun loads is the bullet used. So I spend most of my efforts at working up accurate handgun loads on trying out different bullets. I'll also note I've grown rather fond of the Hornady XTP lineup because they have proven to be very accurate bullets in my loads. Just something to think about.

 

[DWalt]

In regard to semiautos, so long as the finished round fits in the magazine and chambers completely, there's not much to worry about. For revolvers, the bullet cannot stick out the front of the cylinder. In most cases it should be crimped to prevent creeping out under recoil.

OAL is far more important in rifle loads, and often finding the correct OAL for a particular load and bullet (assuming it fits OK in the magazine) will make all the difference in the world as to how tight a group it will shoot. For rifle ammunition, aside from the uniformity of the bullet and powder charge, the two most important considerations in achieving precise grouping are uniformity of case length and finding the correct OAL for that specific bullet. Bench rest shooters spend a lot of time in determining the correct OAL for the best performance in a specific barrel.

 

[Towns]

Only that I would add (unless I missed someone else already stating it):

I have found shorter OAL to give me more consistent (lower Sd) loads, until you start compressing your powder. But, there are other factors that might trump this.

 

[gwpercle]

OAL's are a recomendation , a starting point. The OAL listed is what was used to work up the published data in the book.
It's not a magical , cut in stone dimension you have to hold to.
If loading near max charges and you need to seat bullet deeper, back off powder charge and work up. Seating out farther will not cause any pressure problems.
It's sometimes difficult to figure these nuances out, a lot of people have the mistaken notion that OAL dimension must be adhered to at any and all costs or your gun will explode....not quite right.
Gary

 

[lrrifleman]

This response is more applicable to rifles than handguns, but if you are looking at long range pistol precision for IHMSA type 200 meter matches, OAL considerations apply.

The bullet jump, or leade, is the distance from the bullet ogive to the rifling. The longer the leade, the looser the group shoots. In my target rifles, leades of greater than 0.010" can amount to a 1 MOA group at 1000 yards opening up to a 6 MOA group at a 1000 yards.

Remember that in revolvers, many cylinders do not have the same internal diameter at the face of the cylinder as the chambers. In many cylinders, there is a step that can help to head space the cartridge (or prevent a longer cartridge from being loaded in a shorter chambering), and that step can shave the bullet, effecting the symmetry of the bullet and impacting the flight characteristics and the resulting accuracy. Note the fouling that you encounter when you fire a Special in a Magnum chamber ... the fouling isn't always just powder!

 

[SandSpider]

I'd like to thank all of you for taking the time to reply. I learned something.

SandSpider

 

[noylj]

>I'm loading .45acp for a S&W 625. I'm trying to find the most accurate load. So I build a round that is 1.275" OAL

For normal handguns, COL is mainly down to "get the ogive as close to the lede as possible" and work up the load from there. I have never found a COL in my handguns that was both "most accurate" and didn't have the bullet as close as possible to the lede/rifling.
For a revolver, COL is only important in that the bullet can't extend beyond the cylinder and, if you need a roll crimp, the roll crimp needs to be either in a crimp groove/cannelure or over the bullet shoulder. If you don't need a roll crimp, than you need to be sure that there is enough bullet in the case that the taper crimp holds the bullet from creeping out of the case and binding up the cylinder.