OAL and accuracy... In pistols?

[Trey Veston]

I've only been reloading for a few years and did a lot of reloading of pistol ammo for matches and woods loads. I figured out that I could get more accurate loads by figuring out what powder and what bullet a pistol liked.

I was taught to load to the recommended OAL in the book, and then verify all was good by doing a plunk test. No mention of adjusting the OAL other than making sure it will chamber.

But, seems to me that I could squeeze out a bit more accuracy by paying more attention to the OAL.

So, where do I want my OAL to be to maximize accuracy?

 

[243winxb]

For 45 acp lswc the oal should place the bullet into the rifling. Best for 50 yard slow fire, not timed & rapid. The barrel leade has to be on the short side.

I learned it from an old NRA reprint on the 45 acp.
https://www.thehighroad.org/index.php?media/45acp.900/



This requires a very accurate target gun to tell the difference.

 

[mdi]

Any change can affect accuracy. Changing bullet seating depth can change pressure which is akin to changing the powder charge. In my limited experience in hand guns the changes in accuracy from changing bullet seating are so small they are difficult to determine. So, I have always plunk tested for my semi-autos and seated to cannelure/crimp groove for my revolver handloads. I have stumbled on some very accurate handloads and OAL was the last change/consideration.

 

[Blue68f100]

What I did was to start changing the OAL 0.005" in and out to see if it makes any difference. On one of my 9mm load I found that shortening the OAL made the group size shrink. The other one did not make a difference.

The only way to know is test. Know where you will be into the lands and start working back. If your at max load go slowly looking for pressure signs. Most BE loads are reduced so it's not a problem.

 

[AJC1]

Pistol bullets are shaped in a way that they are very jump tolerant and tuning is possible but huge changes in accuracy have not been observed in my testing. I focus on bullet canalure or plunk test for pistol. If your shooting a 5.7 or 22tcm maybe then.

 

[FROGO207]

I take pistol ammo OAL as a do not go shorter when using this shown data as that what worked for us. I generally will load a bullet to feed in the MAG. Then I plunk test until it rotates and falls out freely. Then I do a ladder test and might move the OAL in to try and improve on things. Or try other combos and see. For revolver ammo I use the cannalure as a length guide and roll crimp to the center of it, then work up loads. Bullet size in the chamber and cylinder to barrel fit can make a difference as well. More so with lead bullets. I have seen some accuracy improvments over factory but not night and day like in a rifle might be.

 

[kidneyboy]

If you are just short enough to pass the plunk test the only way to go is shorter. All bullets/barrels will react different to shorter OAL's. My G34 w/match barrel liked a slightly shorter OAL.

 

[Charlie98]

I have sort of a different spin...

I was working with W244 in some test .45ACP loads. I normally load to max OAL, check to make sure it plunks, then evaluate cycling reliability... adjusting as necessary. For some reason, W244... which is touted as one of the New Breed of powders that burns 'clean' (my emphasis...) and I was quite disappointed with my initial results. I decided to shorten them up a tad... and it was like an entirely different load... velocity picked up, which I expected, but not only did it actually burn pretty clean... vs my previous results... but the accuracy picked up as well. Win win.

There are so many different factors in handgun loads... and particularly revolvers where cylinder and forcing cone tolerances come into play... any change in anything can produce a different outcome... including OAL.

 

[SingleActionAndrew]

OAL is important. It's effectively a case pressure multiplier, on top of whatever other considerations like fitting a magazine or engaging rifling.

You really need to share the cartridge and platform. What's appropriate depends on the conditions.

Within the range of a safe OAL, the importance of a precisely consistent OAL is highly debated. I personally shoot for +/-0.002 on 45acp but I am passionate about being sure the performance when shooting is my own.

 

[Shaggy357]

The first order of importance in handguns is safety. Be sure you are referencing known data. Crimp grooves and cannelures are on a bullet for a reason. Some reasons may be more specific than others. Most bullet manufacturers do their testing using the crimp grooves designed into their bullets. Some bullets may be more specifically designed for one cartridge vs another. 9mm, 38s, and 357s come to mind here. Cylinder length, magazine length, case length, and chamber throat all can play with OAL limits and resulting internal pressure. I can load some RN cast bullets for my Ruger that are too long for my Colt cylinder. Some people have to judiciously trim their 357 brass in order to crimp in the groove and keep their OAL standard. It takes practice, experimentation, and lots of studying to make changes to OAL. What may work in one gun may not work in another. A buddy and I shoot competition. Same load. Same brand gun. Consecutive serial numbers. I can shoot his reloads. He cannot shoot mine. Don’t fit in his gun.
Important thing is to think safety (gun function and internal pressure) first and foremost in your experimentation. Dummy rounds are ok. I have lots of them.

 

[nettlle]

Seat your bullets so they contact the lands. Then adjust your seating die to seat .015" shorter. On auto loaders this is a double edged sword. Feeding has to be taken into consideration. If it shoots well but doesn't feed................

 

[murf]

maximize accuracy?

after you get your plunk test oal settled, reduce in .005" increments, no more than .020" total reduction in oal (9mm, 45acp). if no accuracy improvement, go back to the original oal.

luck,

murf

p.s. monitor your case ejection distance and direction while reducing the oal. if the distance increases significantly, stop reducing oal and go back to the starting oal. the significant distance increase means an increase in chamber pressure which may be overpressure. if this happens, try a different powder.

 

[Trey Veston]

Crimp grooves and cannelures are on a bullet for a reason. Some reasons may be more specific than others. Most bullet manufacturers do their testing using the crimp grooves designed into their bullets.

None of the bullets I use for 9mm, .40 S&W, and 10mm have either crimp grooves or cannelures. Ones for my .45 Colt and .450 Bushmaster do, however.

 

[LiveLife]

9mm, .40 S&W, and 10mm ... OAL and accuracy... In pistols ... I was taught to load to the recommended OAL in the book, and then verify all was good by doing a plunk test. No mention of adjusting the OAL other than making sure it will chamber.

But, seems to me that I could squeeze out a bit more accuracy by paying more attention to the OAL.

So, where do I want my OAL to be to maximize accuracy?

The method I use is:

1. Determine the maximum OAL that will pass the barrel (Plunk test)
2. Then determine the maximum OAL that will reliably feed from the magazine (Working OAL)
3. Then conduct powder work up to identify the most accurate powder charge
4. If you are not at max charge, incrementally decrease the OAL by .005" to see if accuracy improves
5. If you are at max charge, incrementally decrease the OAL without going shorter than published (Focus is bullet seating depth)

With 9mm bullets, especially 115/124 gr FMJ/RN profile bullets with shorter bullet base length, I found loading them shorter down to 1.130"-1.135" produced smaller groups than loading them longer to 1.150"-1.155". With 115 gr FMJ/RN, I have gone down to 1.110" to squeeze a bit more accuracy. I attribute improvement from shorter OAL to greater neck tension. FP/FN/JHP profile bullets are less affected likely from longer bullet base producing greater neck tension -
https://www.thehighroad.org/index.php?threads/myth-busting-oal-col-long-vs-short.819257/

And if you are experiencing bullet setback issue, consider using thicker case wall brass to improve neck tension - https://www.thehighroad.org/index.p...neck-tension-and-bullet-setback.830072/page-4

With 40S&W bullets, especially 165/180 gr TCFP/JHP profile bullets with longer bullet base length (Think much more neck tension), I found loading them longer than SAAMI max of 1.135" to produce smaller groups. For my 40S&W Glocks/M&P, 1.149" OAL is max OAL but longer than 1.145" length binds in the magazine and I use 1.142" as max working OAL for typical TCFP profile bullets and 1.155" for RNFP (Many match shooters use 1.180"-1.200" depending on pistol/barrel/magazine) - https://www.thehighroad.org/index.p...-for-lead-plated-bullets.743416/#post-9363753