Concerned about short OAL in 9mm

[PodPeople]

I loaded up some Friendswood 115gr LRN bullets for my S&W Shield 9mm. I found that due to the shape of the bullets and the Shield's chamber size I had to seat them to 1.070 in order for them to properly chamber. I used 4.4 to 4.5 grs of W231. The Lee and Hogden manuals show a minimum OAL of 1.100 and loads of 4.3 to 4.8 grs. I shot a string of 11 of these bullets and measured the velocities. They ranged from 1039 to 1074 with an average of 1054. For this bullet/powder combination the Lee and Hogden manuals show a starting load velocity and a "never exceed" velocity of 1079 and 1135. Can I assume that the chamber pressures are not dangerously high and that these bullets are safe to shoot? Or could the short barrel length of the Shield result in acceptable bullet velocity even though the chamber pressure may be dangerously high? Is acceptable bullet velocity a sufficient indicator of safe chamber pressure regardless of barrel length?

[MtGun44]

Chrono some factory 115s and 124s and see how they compare to the book numbers.
Use this loss as a rough correction factor on your loads to compare to book numbers.
Of course, boolits usually run faster than bullets.

Bill

[fecmech]

Cartridge OAL's are bullet specific and are meaningless with other bullets. Many published oals are for basic RN bullets and don't translate to other designs well. Even with the truncated cone designs of the same weight the length of the nose makes a big difference. A prime example are the Lee TC and Lyman TC of the same weight. I don't have specifics in front of me but the Lee OAL is about .060" less(it is not as "pointy" as Lyman) than the Lyman but both have the same bearing surface and same amount of bullet in the case and will run similar pressures at two very different oal's.

Pressure is pressure, once you exceed the safe max you are in dangerous territory.

[fredj338]

You can NOT compare data in the manuals with a gun/platform that is not even close. So you have to extrapolate & read pressure signs. OAL is ALWAYS gun & bullet specific. So you can't just plug in bullet A & use the OAL & powder charge for bullet B in the book & get any meanigful correlation. If you stay under midrange, even larger OAL diff like 0.050" will not be over pressures. It does raise pressures, but you are well under max loads. When running the top end of the data, everything affects pressures; OAL, bullet mat'l, primers, case volume, everything.

[PodPeople]

Chrono some factory 115s and 124s and see how they compare to the book numbers.
Use this loss as a rough correction factor on your loads to compare to book numbers.
Of course, boolits usually run faster than bullets.

Bill
Winchester White Box 115 gr. FMJs run about 1025 in my Shield. So my rounds are running about 2.8% faster than the WWBs.

[runfiverun]

which is about right when comparing lead to copper.

[Huskerguy]

I had the same thing with some Berry's 124 grain HBTP bullets I was reloading for my CZ SP01 Phantom. I had tried 1.120 and they would chamber but were tight. I took my barrel off and started measuring with a fired case and bullet. I ended up with an OAL of 1.065. To compound my dilemma I use titegroup powder which has a small range from start to max. I have been using 4.0 grains for a 124 grain bullet with great results. Bottom line is I kept the 4.0 grains and loaded to 1.065 and checked each piece of brass and primers for pressure signs. Nothing. I am going with it even though it seems short, it works perfectly. I will run these through a chrono but I am not certain at this point it will tell me much except how fast.

[fecmech]

People get hung up on OAL's but what is really important(aside from actual bullet weight) is how much bullet is in the case and bearing surface of the bullet. If you have 2 bullets with the same weight and same amount of barrel contact( but different bullet lengths due to design) and the bullet base is the same depth in the cartridge your pressures will be fairly equal irregardless of the OAL.

[MtGun44]

+1 on Fecmech and R5R. LOA is set with your boolit shape and your throat and book numbers are irrelevant unless you are shooting the same exact boolit in the same
exact gun, and even then throats vary over production runs. Seating a LOT deeper
raises pressures and this is more important in tiny cases like 9mm. Sounds like
you are in good shape looking at your velocities.

Bill

[Shiloh]

What is the starting load?? Is it 4.3 gr.?? I'd have started a bit less than the start load and moved up from there.

SHiloh

[PodPeople]

The starting load was 4.3 gr. I made some of those up and shot them with no problem. Then I bought a chronograph and made up some more with 4.4 and 4.5 grains to test for velocity.