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Brian Enos's Forums... Maku mozo!

Bullet size and velocity


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After a search I wasn't able to find a direct answer to my question.

I am in the process of developing a load for my new open gun in 9x19 and I am working on a load suggested by the Dan Bedell who built my gun. When I chronoed this load (working up of course) my velocities were somewhat erratic and my SD's were big double digits 20-25. Dan had suggested I use a bullet with a .355 diameter. So I ordered 125 gr jhp 9mm form zero that are listed on zeroes site at .355. I just got done measuring 50 samples from 3 different boxes and I have to hand it to zero for making a very consistent bullet, they didn't vary a bit but all were .356.

So my question is if my barrel (scheuman ultimatch 9x19 AET) needs .355 bullets would the oversize bullets be causing my velocity problems?

thanx in advance, Craig :D

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Probably not. Undersized bullets show velocity variances, as they are likely to have greatly different bore friction values. An oversized bullet tends to higher pressure and more leading/jacket fouling.

An SD of 20-25 is not unusual, even if it isn't desireable. What matters more, is what was the pattern leading up to your final load? Did the SD increase as you went up, or did it stay steady until some lesser load, then suddenly increase?

You may simply have to go to another powder and start over, or if the load makes Major and is sufficiently accurate, just accept a higher SD.

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Guest Larry Cazes

How consistent is the OAL of your finished rounds? Have you checked to be sure that the bullets are not setting back considerably as they load into the chamber? Variability in either of these will cause variation in pressure and resulting velocity. 9mm cases have a relatively small volume and small changes in OAL will be significant.

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Yes, his load suggestion was 125gr Zero (.355) 8.0gr of Power Pistol loaded to 1.17 with WSP primer.

Paul Whitacre is shooting this in his gun and is very happy with it. In shooting it for testing I like the way the gun behaves. I was just concerned about having a 100fps velocity spread in a ten round string. I have loaded a lot of .40 and my load only varies 10-15fps with standard deviations in the low single digits. I just want to be careful as I go up this Open gun learning curve. It seems there are quite a few more variables to keep track of.

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