Charge Adjustments Relative to Seating Depth

[9mmepiphany]

I've seen load suggestions of "XX grains of XX" seated to X.XXX - X.XXX and wondered if there is a common formula for reducing the powder charge as you reduce the seating depth.

I've been, by a local reloader that when he reduces the case diameter (increasing neck tension) of his 9x19mm loads (from .380 to .378) he drops the powder load by .1 grains per 1000th inch tightened and works his load back up from there while monitoring pressure signs.

I started with a 9x19mm reload at 1.150" and reduced the OAL, by .005", down to 1.130" and didn't see much change is velocity or pressure signs. What I did see is that my velocities between shots was more consistent as the OAL got shorter. I settled on loading to 1.140" and had some feeding issues, so thinking about going a bit shorter

I was running a pretty fast powder, 4.5gr WST, under a medium weight bullet 124gr Xtreme plated RN...making just over 1050fps out of the S&W M&P

Just wondering what others' experience has been

 

[Robert101]

I don't have an empirical formula for bullet setback. I do pay attention to COAL and try to stay close to the suggested data. In moderate handgun pressure cartridges like 38, 45 Automatic I usually don't pay much attention to shorter OAL. On magnum loads and 10MM I do pay special attention. Keep in mind that bullet setback does not create a linear increase in pressure - It is more of an exponential increase as your bullet is setback further and further in the case. As stated in many publications just work up a load to max. One last thought, regarding rifle cartridges - I mostly load close to max length.

 

[BigBore45]

there is no formula as there is different effects with different powders. its best to stay with the listed C.O.A.L. if you must go shorter start at factory coal or the max length you can go with the min charge and work up so watch for pressure signs. note when you compress powder it will change everything so do not seat that far.

 

[tightgroup tiger]

There is no formula. I calculate how much air space is in the loaded case at the longer OAL and try to maintain that air space by reducing the powder charge when I go to a shorter OAL.
That air space is critical in a 9mm, it acts as a shock absorber for the fast burning powders.

 

[LiveLife]

Hate to throw another variable in your load development but here it is.

When I was developing my match loads, many match shooters claimed jacketed bullets were always more accurate than plated bullets. Well, my own range tests verified this but I never really figured out why.

My current thoughts are:

- Plated bullets with softer lead bullet core may "squish" when taper crimped and reduce neck tension.

- Due to neck tension issues, if your rounds experience bullet setback when the bullet nose bumps the ramp, your "chambered OAL/COL" will be shorter than "working OAL/COL". If you experience different amount of bullet setback, you will end up with different chambered OAL/COL that will translate to varying chamber pressure build/muzzle velocities/larger SD numbers and less accuracy.

- So I would check the rounds before and after feeding/chambering from the magazine to see if you can detect bullet setback. Depending on the bullet nose profile/ogive, I find that different OAL/COL will aggrevate bullet setback (shorter OAL/COL).

- I think this is what many match shooters found with JHP bullets and switched from FMJ bullets as JHP bullets with longer bullet base with jacketed base may provide more consistent chamber pressure build and maintain better necktension.

As you may know, I have been a supporter of Berry's hollow base RN bullets for longer bullet base that may expand better to seal with the barrel but currently testing Rocky Mountain Reloading's 9mm 115/124 gr RN with "harder lead core" bullets (11-12 BHN) that seem to do better at maintaining neck tension and show no bullet setback so your chambered OAL/COL will be the same as the working OAL/COL you started out with. (So far, testing with 230 gr RN and 180 gr RNFP have gone very well and showed no bullet setback even after multiple chamberings) - http://www.thehighroad.org/showthread.php?p=9639622#post9639622


This is what's on RMR's website - http://www.shop.rmrbullets.com/9mm-...5FDCE0BB1AF3C6027F19BFF638B473.m1plqscsfapp01

Introducing our line of plated bullets! They have a harder lead core (11-12 BHN) than any plated bullet company that we know of. The standard plating on them is as thick or thicker than the "heavy plated" bullets from other companies. It is still a plated bullet so try to keep it within 1500 fps

 

[9mmepiphany]

- Plated bullets with softer lead bullet core may "squish" when taper crimped and reduce neck tension.

- Due to neck tension issues, if your rounds experience bullet setback when the bullet nose bumps the ramp, your "chambered OAL/COL" will be shorter than "working OAL/COL".

That is part of the issue I'm having.

I'm looking at reducing the neck diameter from .380" to .378" for a tighter grip on the bullet

I'd consider changing bullets, but it was pretty hard to pass up $40/500

 

[JRH6856]

That is part of the issue I'm having.

I'm looking at reducing the neck diameter from .380" to .378" for a tighter grip on the bullet

I'd consider changing bullets, but it was pretty hard to pass up $40/500

The thing is, brass will rebound slightly after the crimp is applied, as will a copper jacket and to a degree, hard lead. Soft lead will not, even when plated. So no matter how much you reduce the neck diameter when crimping, the rebound will mean less neck tension with soft lead bullets.

 

[9mmepiphany]

I didn't know that, thank you for the explaination

 

[1SOW]

I load 9mm.
Load Data does not give a "suggested OAL". Load data gives the OAL the test was performed at and shows the pressures generated in their bbl fixture. Different data sources may give different OAL results. Look for those first.

Most 124 gr JHPs/FPs (for instance) won't load at 1.150" in a short chambered pistol like CZ/XD. The maximum the chamber will accept may be 1.10" or even shorter. The Berry's 124 PHP can only be about 1.065"

My chrono experience shows .005" shorter will up the speed a little--maybe 1-2 PF with a powder in the area of n320/sr7625 burn rates. If you start at the low end of the data and work up, no biggy for shortening .01".

With well-behaved powders like mentioned above, and shortening oal more than that, you can lower the starting load by using OAL/starting load proportions compared to NEW OAL.
1.150/4.2 = 1.110/?? (as an example)
Solve and you get 4.05grs So 4.0grs would be a reasonably safe NEW starting load. Make sure that first shot hits paper and the slide cycles. This method has proved conservative for me.

With a powder like Titegroup, I would err on the side of caution. The short load range and spikey nature of this fast powder is not user friendly for big changes.

JMO, and what has worked successfully for me.

re taper crimp: neck sizing retains the bullet. I close any belling used to .376+ to .378+, long to short cases. With the Berry's .356 bullets, I may add another .001" to those numbers even using the 124 HBRN-TP. Seating bullets "deeper" will retain the bullets MORE/Longer before they release. Pressures will be higher than a longer oal to get the the same speeds for both.
I don't use lead.

 

[9mmepiphany]

Thank you...that makes sense and gives me a starting point.

When I referred to suggested OAL. I was referring to posters suggestions as opposed to published data...as there just isn't a lot for using WST for loading 9mm

 

[tightgroup tiger]

http://stevespages.com/355p_4_124.html

That's all I found and there's no mention of OAL.

 

[rsrocket1]

There is not a "rule of thumb" formula for pressure and velocity as you change seating depth. That's because while velocity increases fairly linearly with seating depth, pressure climbs up exponentially. Coincidentally, I posted a graph a few days ago I made with excel when I ran a number of load calculations through Quickload showing the relationship between seating depth and muzzle velocity and peak pressure. I'll post it again here for you. This is just an estimate (although Quickload seems to perform very good estimations).

Neck tension affects peak pressure a little bit, but once the bullet starts moving and the brass starts expanding from the gases, neck tension doesn't play a big part in holding the bullet back anymore.

Setback will affect peak pressure a lot if it starts getting into the 10's of mils so you don't want that to happen.

Be sure you cannot push the bullet into the case. I can't get my bullets any deeper even by pushing the bullet upside down against a table.

Don't chamber and rechamber a round in your gun. That may happen with defensive loads, but you should rotate your rounds and shoot them and check OAL occasionally.

 

[Walkalong]

I've been, by a local reloader that when he reduces the case diameter (increasing neck tension) of his 9x19mm loads (from .380 to .378) he drops the powder load by .1 grains per 1000th inch tightened and works his load back up from there while monitoring pressure signs.

I can almost guarantee that if you add .001 "crimp", and you drop the powder charge .1 with a fast to medium powder, you will lose velocity. Neck tension is controlled by the sizer, the expander, and how much spring the brass has, which, as explained, is more than lead. Over crimping can actually ruin neck tension.

More pressure can help the burn and tighten up the ES & SD, sometimes. Neck tension will help the burn. We want good neck tension with 9MM, but not any "crimp". We just adjust the "crimper" to remove the bell or a hair more.

Changing the OAL .005? Stick with the powder charge you have. Changing it .020? Time to start think about dropping the charge .001.

Running a 125 at 1050ish is not on the ragged edge, unless you are using a fast powder. WST is fairly fast, so you do want to be careful about any drastic change in OAL. But .005, nah.

 

[Blue68f100]

There is no rule/formula that you can use. But in general if your at max, drop your load and work back up. If your mid range you probably will not have any problem with a small change, <0.030". There was a article on TG and 40 cal several years ago. Where a small reduction (0.050") doubled the pressure. aka KBOOM. So powder does play a big part in it. A slower burn powder does not respond this quickly. Thermal change does play a part. Loads developed for the cold may be over pressure in the hot summer. Then there are a few powders that are reverse sensitive. Meaning pressure goes up as the temp goes down. WST is one of these. So you gain velocity as it gets colder, loose it as them goes up.

This is why it's always best to workup your load with any change.

 

[Walkalong]

I load almost all RN 9MM bullets at 1.030 to 1.035 OAL. The exception is the Berrys 124 Gr HBRN-TP @ 1.040 to 1.045 OAL. I am now saving those for .38 Super though.

A swing of .005 is fairly normal, although the less flex in the press and the better the seater stem fits the bullet the better the spread will be. Over a .005 spread isn't unusual with some applications, although we should be able to cut that down.

 

[LiveLife]

I started with a 9x19mm reload at 1.150" and reduced the OAL, by .005", down to 1.130" and didn't see much change is velocity or pressure signs. What I did see is that my velocities between shots was more consistent as the OAL got shorter. I settled on loading to 1.140" and had some feeding issues, so thinking about going a bit shorter

I was running a pretty fast powder, 4.5gr WST, under a medium weight bullet 124gr Xtreme plated RN...making just over 1050fps out of the S&W M&P

I take it that you are trying to make 125+ PF for your match load while pursuing accuracy. 1050 fps with 124 gr bullet will give you 130 PF which is where you want to be.

When I started USPSA match shooting with 9mm/45ACP, I tested various powders (Bullseye/Clays/Titegroup/WST/W231/Universal/HS-6/WSF) that other match shooters were using and was told WST burns spikey near the top and WSF would be a better choice for higher velocity loads.

My experience with 9mm and OAL/COL has been similar to yours. With mid-to-high range load data and some powders, accuracy increased as I decreased the OAL from 1.160 down to 1.135" probably due to increase in neck tension from deeper seated bullet base for more consistent chamber pressure build that results in more efficient powder burn. But since 9mm is a tapered case with wider base, using shorter OAL with some plated bullets decreased the neck tension to the point where I could push the bullet in deeper with my thumb pressure. With plated bullets (especially those with softer lead core), I try to use the least amount of taper crimp so not to squish the bullet which will reduce neck tension so pull the loaded round and if you see a deep indentation in the plating, decrease your taper crimp until you barely see any mark (for .355" diameter plated bullets, I use around .377"-.378" taper crimp).

But if you are getting bullet setback that will vary the "chambered OAL/COL", you are going to negate the benefit from shorter OAL/COL. With high-to-near max load data, I could use longer 1.150"-1.160" OAL/COL to produce greater accuracy from the benefit of less high pressure gas leakage around the bullet but it's often a struggle to determine where this powder charge threashold is. I am currently testing RMR's new thick plated 9mm RN bullets in 115/124 gr with W231/HP-38, Titegroup and AutoComp at 1.135", 1.150" and 1.160".

I can add WST to my load development and range test them this coming weekend. You can follow my powder work up and range tests while I pursue the most accurate loads with W231/HP-38/Titegroup/WST/AutoComp on this thread (I may test other powders as they are requested) - http://www.thehighroad.org/showthread.php?p=9639629#post9639629

 

[Potatohead]

I plan on eventually testing with a chrony, and maybe someone around here could get to it before me (Ahem, BDS!), the velocity increase in 9mm at each shorter seating. Like what is the velocity seated at 1.15, then 1.14, 1.13, and on down. To see how much it changes things.

I've heard Gamestalker reference something similar from the Speer manual but it was more of just a warning IIRC.

Sorry if Im off base here or this has already been touched on, I must confess to only reading 9mmEpiph's title before posting.

 

[LiveLife]

I wish I could chrono the test loads while I conduct my powder work up but I mostly shoot at an indoor range close by and can't set up a chrono.

I have an outdoor range that is a drive away but it's still hovering around 100F and don't want to do range test in scorching heat/sun.

Thankfully by next month, I am taking a job transfer closer to my retirement house that is cooler in climate with an available outdoor range that is close by so I will be able to post chrono data along with my future range tests.

 

[Rule3]

Has anyone mentioned the actual bullet?

The COL is going to vary by what actual bullet was tested. Even if it is a similar weight and style there is variances in every one. I can use Speer or Hornady, Hodgdon data but I am not using their bullets, so it's all a little bit of guesstimate whenever you load.

 

[murf]

bullet setback should be checked first:

measure col of a round, load that round in the magazine, fully load the magazine (say a ten round mag cap), shoot eight rounds, eject the mag, measure col of the tenth round in the mag, insert mag, shoot ninth round, eject tenth round from chamber, measure col.

first measurement is control. second measurement will show amount of bullet jump from recoil. third measurement will show amount of setback from feeding.

murf

 

[9mmepiphany]

Neck tension is controlled by the sizer, the expander, and how much spring the brass has, which, as explained, is more than lead. Over crimping can actually ruin neck tension.

More new knowledge for me. Well, I was told not to over expand, but didn't understand why... thought the crimp would just straighten it out.

Time to get that Lyman "M" expander die

Over a .005 spread isn't unusual with some applications, although we should be able to cut that down.

My Hornady LNL has been pretty consistent. I was worrying about a spread of .001-.002, until I read that .005 wasn't uncommon in the other thread

 

[9mmepiphany]

I plan on eventually testing with a chrony, and maybe someone around here could get to it before me (Ahem, BDS!), the velocity increase in 9mm at each shorter seating. Like what is the velocity seated at 1.15, then 1.14, 1.13, and on down. To see how much it changes things.

...Sorry if Im off base here or this has already been touched on, I must confess to only reading 9mmEpiph's title before posting.

Should have read the OP too ...I did it in increments of .005" before I found out that that was an acceptable variance

That is how determined the 4.2grs and 4.4grs wasn't going to get me there

 

[9mmepiphany]

I guess a little more information might help.

I'm actually dealing with several issues at the same time...one of my failings is an inclination to multi-task; otherwise I get bored

As bds surmised, I'm trying to develop an 9mm load with the 124gr Xtreme plated RN and WST to get me to the power floor of 130 in my S&W M&P9 4.5" barrel.

My local loading mentor wants me to keep COAL to 1.150 and is already nervous at 4.0grs of WST because of the limited published loading data...that wouldn't even get me over 1000fps. 4.4grs barely touched 1050fps and 4.5grs would consistently get me there when loaded to 1.145"

I had feeding issues with rounds, R-P brass, not fully chambering...and then, of course, not extracting. My bad, didn't plunk all the rounds through my barrel. Turns out 50 out of 300 wouldn't fit all the way in...range pick-up Glock brass strikes again.

Several folks suggested the Lee Factory Crimp Die...got one on the way (it was only $16)

Had another failure to chamber. Another experienced reloader asked if I mic'd the case mouth after crimping. His thinking was that the bullet was being setback when entering the barrel and causing the case to budge.

Went home and mic'd all my loads...came out to .380" (same as in the Lyman manual). Easy enough to adjust it to crimp to .378"

Contacted a friend from Apex Tactical who also runs a M&P9 and the 124gr bullet. He said he found his most reliable feeding was loading to 1.125". He also added that he "crimps super deep too" ( it was via text message). A difference is that he is loading with WSF.

So the question that started this thread was based on my desire to take the 400 rounds I already have loaded and shorten them to 1.125" and tighten the amount of crimp by .002".

NO ONE have a heart attack...no rounds have been changed. I have only run up a dummy round, no primer or powder, to check adjustments.

Rather than go the combo route, I can also do an either/or instead

 

[rsrocket1]

You do need to plunk all those 400 rounds if you want reliable ammo. I do that with all my 9/40/45 ammo. It's not difficult to do with each round as you take it out of that red bin, plunk, then put it into the carrying box.

Take a round that will not plunk properly, color the whole thing with a magic marker and see where the ink rubs off. It may be the case mouth, it may be the bullet just above the case mouth or it may be down by the case base where your die did not resize the range pickup all the way through.

If that's the case, you can use a Lee push through sizer or what I do with bulged 40 cal cases is run it through a single stage press with a FCD and the stem from the lead bullet sizing kit. It pushes the case all the way through the sizing ring.

 

[moxie]

Haven't used a formula, other than trial and error.

Here's one load I've settled on:

MBC 124RNL
4.3 Bullseye
OAL 1.116"
OD case mouth ~.377" (mixed brass)
Chrono avg. 1121 fps (M&P 9c)

Reloads done using RCBS plain Jane 3-die taper crimp die set.

Seems pretty accurate. Similar feel and POI of HSTs and Gold Dots. No setback. Good load.