rhyrlik

If the machining marks run parallel with the bore line, then they will not influence leading. If your groove diameter is .357", then your bullet diameter needs to be at least .357" and possibly .358"+.

They get swaged down by something like .0002" which is insignificant in terms of bullet to bore fit and leading.

While your bullet diameter may be the right size for the bore, it is prolly too small for the throat. You have to use throat diameter as a guide, just as you do with revolvers. I use .359" bullets in my 9, with Bullseye and 231. I like Lasercast the best as they make the most consistent cast bullet, but I also use Missouri. My favorite is their Cowboy #2 TC on top of 3.2grs of Bullseye at 1.040" OAL using CCI or FC primers. No leading, even after hundreds of rounds. My chamber throat measures .359" but these are soft enough to obturate.

I have some 9mm WCC brass that weighs 61 grains. I also have some FC brass that weighs 51 grains. There is a huge difference between these in neck tension. The WCC brass needs a different load to gimmie the accuracy I want. I sort my brass.

How does the KKM barrel fit? There could be a headspace issue. For one, if the chamber is too long, the case is headspacing off the extractor hook. That is bad for ignition which would explain your huge ES.

What I ususlly do with FMJRN is start with a given powder charge at 1.170" OAL and reduce in .020" increments until I get the accuracy. You could try 1.170", 1.150" and 1.130" with 4grs of TG to start. Then, try 4.2, and 4.4grs. Sort your brass and try different primers. Bell the case mouth minimally and don't crimp. Just remove the bell. If you overcrimp plated bullets you ruin accuracy. I choose not to crimp at all, relying on case tension to hold the bullet. 9mm's seldom have setback issues.

I vote media clump. If you decrease case vlolume by a significant margin, you create a pressure spike which can blow the casehead. In all the KB aftermaths I ever saw, the primer looked normal.

OAL affects accuracy by changing the internal ballistic properties of your round. It affects peak pressure, how pressure builds, and the time the bullet spends in the barrel. In my Glock, 1.130" is more accurate with 147's than 1.110". Primers affect accuracy the same way. For example, in a certain load, FC-100 primers produce much larger groups than CCI-500 primers. This is all gun/load specific, though.

I loaded up some 9mm with a light load of Longshot and FC-200 primers from the old red box. I got primer leakage. Your erosion theory is plausible.

OAL affects point if impact more than accuracy. Work up a load, then fine tune it with changes to OAL.

That sux. Maybe cou could try a different powder/bullet/primer? I have worn out a bunch of different combinations in my pursuit of the ultimate 147gr load. They all have different properties including recoil.

Have you tried using a lighter recoil spring?

EGW's U die sizes the case completely. Standard dies do not. A new factory case ran through a U die will actually lengthen and this is good because factory 9mm brass is too short (.745" where the chamber is .762") A U die will lengthen the brass to .750"+.

Why not vary the OAL in addition to the powder charge. I have found OAL to affect accuracy just as much as powder charge weight. I have loads where a change of .015" in OAL will cut groups in half. I start long, then shorten the OAL in .010" increments until I like the accuracy.

If n320 is too fast, try N330.

WWB is loaded with a 115gr hollow based FMJ which is very long, hence the long OAL. Many115 FMJs on the market are very short and have a flat base, hence the shorter recommended OAL. If you want to duplicate the WWB OAL, get some 115gr HB FMJ.

Conversely, if the load is seriously over pressure limits, as nearly 9mm Major loads are, then the primer may be the straw that broke the camel's back. My research indicates that Power Pistol is the most forgiving powder in that respect. I am assuming by using the word "research" you are referring to documented load data coming from an instrumented test barrel, correct? Or are you just referring to uncontrolled chronograph and load data from your pistol? I'm talking about fully supported 9mm pistols surviving double charges of PP under 124gr and 147gr bullets. So the answer is.... NO, not research just anecdotal opinion. By your standard, none of the information posted on this site is of any value.

Conversely, if the load is seriously over pressure limits, as nearly 9mm Major loads are, then the primer may be the straw that broke the camel's back. My research indicates that Power Pistol is the most forgiving powder in that respect. I am assuming by using the word "research" you are referring to documented load data coming from an instrumented test barrel, correct? Or are you just referring to uncontrolled chronograph and load data from your pistol? I'm talking about fully supported 9mm pistols surviving double charges of PP under 124gr and 147gr bullets.

Using new brass, or brass that has been cleaned in stainless media to remove all residue from the innards, will result in a better case wall adherance to the bullet shank. This will make combustion more consistent.

Conversely, if the load is seriously over pressure limits, as nearly 9mm Major loads are, then the primer may be the straw that broke the camel's back. My research indicates that Power Pistol is the most forgiving powder in that respect.

Mee too. Bullseye is the best powder for the 45 ACP.

No. A brass case is not a balloon. It is like any other metal container. If you fill it too fast it will rupture. If you fill it slow, it will swell. Not all brass is the same. Some have internal defects that may not ever manifest themselves unless the cases are abused. 9mm brass is not designed for 50000PSI+, so when you run pressures up that high you should take care to gave the most gradual pressure curve possible. Primer type plays a very important role in the shape of the pressure curve. Use too strong of a primer with too fast of a powder in a small capacity case and problems will emerge. This isn't rocket science. Get Quick load and see for yourself.

Velocity and pressure do not have a linear relationship. Just because you saw a 20 FPS difference on your equipment does not mean squat. What blows cases is not pressure, but the shape of the pressure curve. You can blow a 9mm case with 35000 PSI just as easy as with 70000 PSI.

Maybe the primer is too hot and is causing the pressure to spike. Try a standard primer.

It could be your load sux. Try a different load, i.e. a 147 on top of 4grs of N340 which is universally super accurate.