9mm: Worth Messing With Seating Depth For Accuracy?

[Walkalong]

Something is wrong with that.

Anyway, unless you are going to do that over and over and over, 005 to .008 isn't something to worry about.

Neck tension is what holds bullets in 9MM, not the taper "crimp" that should only remove the bell or a hair more, maybe .001) The reason is that the 9MM headspaces on the case mouth, as well as too much crimp can actually hurt neck tension, even if the over crimp pushes the case into the bullet, stopping it from moving back. That's hurts the consistency of the burn. It is important to have the 9MM sizer all the way down since the case is tapered, and for the expander not to be too big.

 

[murf]

yes, but you won't see the difference @ 7 yards. you can see it @ 25 yards.

murf

 

[Walkalong]

Yep, sometimes things that look good at 7 yards don't look good at 25 yards and out. No doubt.

 

[murf]

Yep, sometimes things that look good at 7 yards don't look good at 25 yards and out. No doubt.

actually, with my bad eyesight, things look great at 25 yards until i get closer to the target.

murf

 

[Dudedog]

actually, with my bad eyesight, things look great at 25 yards until i get closer to the target.

Some people can see the bullet holes that far away, I'm happy I can still see the target, bullet holes at that distance are out of the question.

Oh to be young again.
(of course I might not survive being young a second time around)

With 9mm it doesn't make much difference considering there are no match grade bullets around.

Some 9mm bullets are much better than others.
There are 9mm bullets I consider "match grade" which is really nothing but a label.

 

[LiveLife]

Some people can see the bullet holes that far away, I'm happy I can still see the target, bullet holes at that distance are out of the question.

For us visually impaired, there are many good scope options.

 

[Dudedog]

I got a good laugh at my last match.
I dumped a 3rd round into a target at the back of the bay say maybe 20 yrds.
When I finished the RO said nice make up on that C hit.
I can't see them that far away, just shot another round at it in case.
He could see them and thought I could to.

 

[LiveLife]

With 9mm it doesn't make much difference considering there are no match grade bullets around.

Some 9mm bullets are much better than others.

There are 9mm bullets I consider "match grade" which is really nothing but a label.

When I shot USPSA matches, compared to bulk commercial jacketed bullets, Montana Gold FMJ/JHP bullets were popular with match shooters and more consistent in bullet weight variance of under 1 grain with pretty good ogive variance for more consistent OAL/COL variance.

With Rocky Mountain Reloading 115/124 gr FMJ/FN/JHP bullets manufactured on brand new machines and dies, I find bullet ogive to be very consistent and Jake is particular about using proper lead alloy mix to produce more consistent weight variance of less than 0.5 grain and OAL variance of less than .005" (mostly around .002") on Pro 1000 and less than .003" (mostly spot on) on C-H 205 single stage.

I have reloaded Hornady 115/124 gr HAP, Remington 124 gr FMJ, Winchester 115 gr FMJ and Zero 115 gr FMJ (Which I believe is one of several bullets Atlanta Arms uses to produce their match grade Elite AMU ammo that is certified to produce under 1.5" at 50 yards using barrel fixture). RMR bullet variance is comparable if not better than Hornady/Montana Gold/Zero variance and as close to "match grade" as you will find and produces sub 3/4" 10 shot groups with accurate powder loads and even 1.0" 10 shot groups at 25 yards using Promo plinking load with my JR carbine - https://www.thehighroad.org/index.p...-what-am-i-in-for.824002/page-3#post-10606695

 

[Walkalong]

I'm going to quit griping about my poor (compared to my youth) eyesight, I can still see 9MM holes in white paper at 75 yards. Fuzzy these days though.

I always test at 7 yards shooting through the chrono at 5 yards (Did one load (.38 Spl Load # 114) in three revolvers today, 18 rounds each, PB, PF, & PL in each. It is almost the same as Load #82, but used a different primer (S&B), and the new design Berrys 148 gr HBWC. I don't know when they changed it.

If they look good there, I shoot them at longer distances to check them. Sometimes they can't cut it.

I load 9MM to function, and since I have been able to find very accurate loads at those OAL's, I don't worry about adjusting OAL to see if it will shoot better.

 

[Axis II]

Last night it took 124gr RMR 9mm FMJ and my good load of HP-38 I use for plated and did 10rds at 1.135 and 10rds at 1.145 and the 1.135 put 10 in a baseball group at 10yards and the 1.145 opened up a lot. Sometimes it is worth it.

 

[rfwobbly]

On the CZ Forum we have collectively done quite a bit of testing with seating depth. The results are that the 9x19 Luger does enjoy some increase in accuracy when seated into the case deeper than 0.200", with the optimal being close to 0.250". Of course we can't decide why this is happening. Some members feel it allows the chamber pressure to build longer before the bullet is released. Others feel that there is greater physical rigidity to the cartridge, and thereby less opportunity for the bullet to be knocked off-axis when its slammed into the feed ramp. Whatever the reason, the results are real.

Of course there is a caveat. You need to be very careful with some brands of brass, especially those with "stepped" interiors. Deep seating, especially with bullets heavier than 124gr, can bulge the cartridge at mid-case. Because of the 9mm's tapered chamber, without thorough evaluation this can show up as a cartridge jammed half-way into the chamber.