Velocity and OAL

Paleoman

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Hi,

Will increasing the OAL produce lower velocities?

I tested some Pecision Bullets 125gr 9mm RN coated bullets. I'm using CCI primers, and CFE Pistol powder. The Hodgdon site indicated that for LCN 125gr, I should start with 4.4 and max of 5.0. They had a OAL of 1.125". They said velocity should be 1041 for for start and 1156 for max.

Previously, I had done Berry's plated 115 gr RN, and was using 1.13-1.134" OAL, which gauge and feed fine in my two 9mms. So, when I made the 125gr, I set up for a similar COL, and was seeing 1.132-1.136".

I did sample rounds and chrono'ed sets of 10 at the loads I made up (4.2, 4.4, 4.6, 4.8). I'm seeing that, at 4.8gr, my velocity is 1040 fps on the 4" Walther PPQ, with a SD 6.97 and spread of 24.55. All the lower loads were with higher SD (20-30) and spread (66-85).

I didn't get as good of accuracy with the shots as expected (although my contacts were bothering me today, so I was having a hard time getting a clear front sight in an indoor range).

My 115gr Berrys give 1139 fps at the chosen load.

So, I'm trying to understand why I'm getting lower velocity and to decide on load. I could do 5.0 and possibly 5.1 and/or 5.2, to see if I get an improvement in accuracy on the target.

Thoughts? Suggestions?
 
The data in reloading manuals usually includes a very specific bullet. If you are using a similar bullet (not the exact one) you may have to tweak the OAL, and the powder charge. Not all 125gr RN bullets are the same shape, and even if seated to the same OAL may leave different case volume, and that will equal a different pressure and velocity.

If you are worried about going over the max charge, try seating them a little deeper, for a shorter OAL, and work up again from the starting load.
 
Sounds like a smaller OAL will increase pressure and hence velocity. So, the questions are...

Should I decrease the OAL (to 1.125") and start over with load, or increase the load to get velocities that are more within the desired range?

If I shorten the OAL as mentioned, is there a possibility of cycling problems with my Walther PPQ 4" or Sig P938 ~3" barrel?

BTW the Precision Bullets 125gr RN is much "fatter" of a cone, than the 115gr Berry's plated bullets, which are pretty pointy. When I first tried seating, with the seating die set for Berry's, I ended up with COL 1.10" on the Precision Bullets.
 
I would go to 1.10" , load some dummy rounds and see if they cycle by hand. Then load a ladder starting at min recommend charge.
 
You can get pretty close if you take a known load with a specific bullet by measuring said bullet's length. You can calculate how far the base of the bullet is seated into the case. Measure the new bullet's length and then calculate the seating depth to match the known bullet previously measured. Assuming bullet bases are similar, you'll be pretty close as far as case volumes are concerned.
I often see the same bullet seated to different COLs in loading data simply based on the powder used. Go figure...
 
Can pressure increase as you seat the bullet longer and get closer to the lands?
 
I would recommend a set of overall case length gauges if you do not have a set. I must have missed the type of powder you're using, so I cannot make a specific recommendation. I used to do 124gr LRN and Copper plated 115gr (IIRC - rainer brand) with 5.2 grains of unique and never had any issues. The max fps of that round is right around 1100fps. Be careful on seating depth, it can increase pressure and additionally separate military and commercial brass, the military brass is thicker and therefore there is less volume in the case, so pressure is increased. I used to decrease the charge by 10% for military brass.

OK, reread and see it's CFE powder. I have no experience with that brand.
 
the difference in velocity could also be due to your gun being a 4" barrel vs the test gun in the book maybe having a longer barrel

Sent from my SM-G930V using Tapatalk
 
The only way you're going to duplicate the velocity from a data source is to exactly match their every last variable, which is virtually impossible.

You're not even using the same bullet, let alone the same barrel, chamber, case brand, #of-times-fired for the case, powder lot, primer lot, velocity measuring equipment, temperature, barometric pressure, ad infinitum.

Also, they're not telling you what you're supposed to get. They're telling you what they got. There's a slight but very important difference.

Don't use their velocity as a goal - use it as a sanity check. If you're in the ballpark, you're OK.
 
The velocity that I'm getting for each load is below the starting velocity from the Hodgdon data for my powder (granted with the differences noted by EddieCoyle), except for my 4.8gr (highest load). That and the accuracy I was seeing was worse than with the 10 Berrys rounds from what I use currently that I checked as a baseline. So I'm wondering if I should increase the load or shorten the OAL and retry with starting load?

Since the 1.13x" OAL cycles fine in my guns, would I encounter any cycling issues, if the OAL is shorter? What checks should I do to verify? Load up a mag of dummies and try cycling them?
 
The velocity that I'm getting for each load is below the starting velocity from the Hodgdon data for my powder (granted with the differences noted by EddieCoyle), except for my 4.8gr (highest load). That and the accuracy I was seeing was worse than with the 10 Berrys rounds from what I use currently that I checked as a baseline. So I'm wondering if I should increase the load or shorten the OAL and retry with starting load?

Since the 1.13x" OAL cycles fine in my guns, would I encounter any cycling issues, if the OAL is shorter? What checks should I do to verify? Load up a mag of dummies and try cycling them?

Yes. Load up about 25 dummy rounds. At least three of the same depth. Vary the seating depth on each group and hand cycle each group to verify issues. Write OAL round length on casing of each dummy. Also you can do a chamber casting to see exactly what the dimensions are for your particular weapon if you really want to be anal. Good luck!
 
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