Help fine tuning 9mm 4756

[JBrady555]

Hey fellas I finally got a decent load together in 9mm with 4756. It's actually a tenth above imr's max recommendation but their data has always seemed on the weak side and I found numerous sources on the web of people pushing as high as 6.3gr in a compressed load. My load is 5.5gr of 4756 under a precision delta 124gr hollow point loaded to 1.140. I tried the middle ground of imr's recommendation at 5.2 but it was too light and jammed in my glock 17, 5.5gr had a nice pep to it but the primers and brass showed no signs of over pressure.

Although accuracy seems to be at least as accurate as I am, I want to try to tweak it more but working with a already peppy load I don't want to create a dangerous situation. The 124gr PDHP looks like it needs to be seated deeper, a lot of bullet out of the brass. Do you think moving to 1.125 with 5.5gr 4756 would be to much of a leap? Is .015 shorter the equivalent of adding tenths of powder? How do you guys tweak loads working near max pressure? I heard 4756 in 9mm likes working near max to produce best accuracy. Thanks for any info.

 

[Peter M. Eick]

First off you know that 4756 is being discontinued this year so it will become harder to replace and eventually unavailable.

4756 is known for lot to lot minor variations. It is also position and temperature sensitive. For these reasons I just load over a chrono and work up to the book listed load velocity that has been barrel length adjusted. This has worked well for me but does not specifically tuned to your question.

I find that in the 38 Super it burns very cleanly at high pressures and tends to be quite consistent from round to round in a lot which is what I like.

 

[TfflHndn]

Nothing wrong with the bullet showing above the case, as long as it plunks and doesn't get hung up on the feed ramp. If you are going to shorten the OAL (i.e., because of jamming in your Glock) best to reduce the load and work back up with the shorter length Don't try to guess what effect the shorter length will have with the same max (or over-max) load.

 

[Blue68f100]

With the high pressure round like the 9mm, I would recommend dropping the charge 0.2 gr then creep the charge back up.

 

[LeftyTSGC]

As mentioned by others, you need to get a chronograph and reduce your load if you reduce your OAL. 9mm is sensitive

 

[JBrady555]

Yea I need a chrony