Powder charge vs OAL

[Red Ryder]

So what influences accuracy more, powder charge or OAL? Will bumping the charge up by 0.1 or 0.2 (to increase FPS) or adjusting the OAL affect accuracy the most? I have found titegroup to be inaccurate at a power factor of 128 to 132 in my XDM 9 with 124 gr MG CMJs OAL of 1.150. When I increase the charge to get a PF of 135, the load was more accurate. If I want to make my load more accurate, where do I start?

[Skydiver]

As I understand things, the OAL affects two things: how quickly the bullet engages the rifling in the barrel, and how much pressure is built up in the casing that ultimately affects the velocity. The powder charge affects pressure and velocity more directly. If a bullet is going too slow, the spin imparted by the rifling doesn't provide enough of a stabilizing effect. If a bullet is going too fast through a barrel, not enough spin is imparted on the bullet before it exits the barrel. Sometimes it maybe going so fast that jackets/plating is torn off the bullet. Obviously, optimizing the velocity to the twist rate of the barrel will give you the most stable flying bullet which will then be more precise.

[Red Ryder]

As I understand things, the OAL affects two things: how quickly the bullet engages the rifling in the barrel, and how much pressure is built up in the casing that ultimately affects the velocity. The powder charge affects pressure and velocity more directly. If a bullet is going too slow, the spin imparted by the rifling doesn't provide enough of a stabilizing effect. If a bullet is going too fast through a barrel, not enough spin is imparted on the bullet before it exits the barrel. Sometimes it maybe going so fast that jackets/plating is torn off the bullet. Obviously, optimizing the velocity to the twist rate of the barrel will give you the most stable flying bullet which will then be more precise.

So eliminating variables such as ballistic co-efficient, bullet weight, bullet shape, case volume, etc by using the same bullet make and weight, same barrel, same brass maker, same powder etc should make the equasion pretty simple? Changing velocity makes the greatest impact when determining accuracy? (Making the assumption that OAL variation by +/- 0.005 affect velocity minimally, from my humbled experience with Titegroup, N320 and IMR SR7625.) You make it all sound so easy!

[Hi-Power Jack]

So what influences accuracy more, powder charge or OAL?

Red, my BHP is more accurate with a shorter OAL than

will feed consistently, using MG 147 gr & WW231.

So, I had to increase the OAL to get the consistency and lost

a little accuracy.

Seems to me, that both might be important in some guns???

Jack

[Dr.Woo]

This should be interesting. I will watch this thread and perhaps learn something. I have mostly figured out an OAL that worked for a given bullet (read profile or shape) and then tested different powder charges to see what seemed most accurate.

[NA_Wreckdiver]

This subject has often caused me to wonder.

Saami specs say 1.169 OAL for 9MM.

Yet most people (including manuals) use/specify less usually anywhere from 1.09 to 1.12

Now understandably, powder charges vary as wildly... shorter, less powder.

Looking at 2 pistols: Ruger P85 & Tanfolio Witness Match...

both chambers appear (as best as I can measure) to be around 1.18 before a 115g Rainier touches the rifling.

Loading with this bullet to 1.165" the cartridges will drop right out of the chamber. (even if pushed in hard to be sure)

Some examples:

Lyman 49th: Hornady XTP 115gr COL: 1.090" w/ 231 from 3.5g to 4.9g pressure: 20.7K to 32.1K Vel(f/s): 959 to 1253

(doesn't even list a 115g FMJ... seems odd)

Hodgdon: Speer GDHP 115gr COL 1.125" w/ 231 from 4.7g to 5.1g pressure: 25.3K to 28.1K Vel(f/s): 1075 to 1167

Speer 11: Speer 115gr (HP or FMJ) COL: not specified** w/ 231 from 5.2g to 5.7 No pressure given Vel(f/s): 1125 to 1191

**COL from Speer 11 in intro to 9mm has warnings about setting deeper, says Saami spec 1.169", but then says best function for

100g is 1.080" & 125gr is 1.100" (of course this manual is old, and most consider some loads to be pretty hot)

I realize the bullets are not EXACTLY the same, but they aren't as different as the COL.

Why so much variation from Saami spec? Wouldn't it be like with rifles, closer to the lands, is usually better for accuracy?

I have not noticed (maybe there is) that much variation in other calibers for the same type bullet.

[Cheesewhiz]

Length specs in reloading manuals are typically minimums. You should not load the max powder load shown at below that minimum length and think before you try to extrapolate a less than max load to shorter than the listed length.

The SAMMI spec for OAL on a 9mm is in fact 1.169" but many bullets because of their shapes will come in contact with the rifling of the barrel at less than that length. It is a cooking dinner science and not chemistry one so much.

HP bullets tend to need to be loaded at a short length due to the bullet shape and avoiding contact with the rifling when chambered, this also makes the case (powder) volume less. Many guys load even FMJ RN short to create more pressure with a lighter powder load and in some mid to slower powders this may clean the burn. I find true accuracy is achieved at the long as you can go length but this causes some issues with minor loads being clean or consistent.

..but I will tend to go for the accuracy side of the equation and really sometimes manipulated lengths can cause their own inconsistencies.

Edited April 3, 2012 by Cheesewhiz

[sroe3]

Deleted...I didn't read from the start of the thread.

Edited April 3, 2012 by sroe3

[Sarge]

So what influences accuracy more, powder charge or OAL?

I would have to say OAL.

My M&P was most accurate with 1.14-1.15. Those loads sucked in my Glock 34. In that gun 1.13 was the magic number.

[littletoe]

I kmow that in my limited elite witness that a longer load is way more accurate than shorter length....it does great from 1.160 up to1.170.....i like to make the loads as longas the gun will allow

[Youngeyes]

Two issues in the past have had the greatest effect on accuracy. The first was the crimp(I know, that wasn't a choice), and the velocity. When I "wimped" on a load the accuracy suffered. My only issues with OAL have been on feeding problems. Lower velocities caused keyholing and increased group size. My answer to the question( well finally )would be powder charge has the most effect.

[Red Ryder]

Two issues in the past have had the greatest effect on accuracy. The first was the crimp(I know, that wasn't a choice), and the velocity. When I "wimped" on a load the accuracy suffered. My only issues with OAL have been on feeding problems. Lower velocities caused keyholing and increased group size. My answer to the question( well finally )would be powder charge has the most effect.

Thank you for responding. I believe that powder charge has the greatest affect on accuracy so long as crimp is minimal. My Titegroup loads suck at 130 PF but grouping was much improved with 140 PF. I no longer choose to use TiteMess anymore! N320 and is just so nice.