RCBS Matchmaster bullet seater issue

JEBruns

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I've had this die for a year or so. Use it on my Dillon 550, which is setup strictly for 6.5CM. It works well for months, but very recently I've noticed more and more of my reloads don't seat all the way in my Hornady case cage (I check every reload). To the point were some won't chamber in my Tikka T3X Tact A1.

I narrowed it down to the RCBS MM die. So I messed with that a bit. Raised it in the press so the bushing was just touching the plate. Lowered it so that the die body was hard against the plate. And tried it in between. Same results. Not every case gets flared at the bottom, but more and more of them do. Tried different brass (Hornady and Aquila), tried brand new Hornady brass, same-same.

Normal brass routine is anneal, lube, size/deprime, check/adjust case length, tumble with pins, dry, hand prime. And they pass the case gauge before going into the 550.

Really has me baffled. I haven't changed the sizing die nor adjusted it. I have a call into RCBS. Been waiting a few hours for their "die tech" to call me back, but figured I'd post about here also. I really like the die. So nice to be able to drop the bullet into the window and be able to quickly and accurately adjust the COL for different loads. I do have a couple of other 6.5CM seating dies (Hornady and Lee), so I guess I'll try one of those if I don't hear back from RCBS soon.
 
When was the last time you checked and trimmed the brass?

Mark up the bullet and brass, then push into the case gauge. Look for where the marking got rubbed off, that should give you a clue as to where to start looking.

If a freshly sized piece of brass pass the gauge and chamber test, then next thing is bullet.
 
When was the last time you checked and trimmed the brass?
As I said above, those are part of my brass prep. Every time.
Mark up the bullet and brass, then push into the case gauge. Look for where the marking got rubbed off, that should give you a clue as to where to start looking.
They are flared a bit at the bottom.
If a freshly sized piece of brass pass the gauge and chamber test, then next thing is bullet.
Been using the same bullets, Hornady ELD-M's, 120 and 130 grain.

I've taken the reloads that didn't chamber back apart. The case hangs in the gauge, 1/4" or so above the rim.
 
So a freshly sized case passes case gauge, then after seating a bullet the case hangs in gauge 1/4" past the rim?
 
1/4 inch out of the case gage is huge!

Check your cases that don't fit in the gauge for signs of shoulder buckling. You may be annealing too much and the brass have become too soft, which could lead to shoulder bucking when seating a bullet.
 
1/4 inch out of the case gage is huge!

Check your cases that don't fit in the gauge for signs of shoulder buckling. You may be annealing too much and the brass have become too soft, which could lead to shoulder bucking when seating a bullet.
But brand new, never been fired Hornady brass does the same thing. It's not always 1/4". That's probably the high end. But they all fall all the way into the gauge before bullet seating.

Still waiting on a callback from RCBS. Been 6 hours. A bit disappointing.
 
But brand new, never been fired Hornady brass does the same thing. It's not always 1/4". That's probably the high end. But they all fall all the way into the gauge before bullet seating.

Still waiting on a callback from RCBS. Been 6 hours. A bit disappointing.
Try the magic marker tick to see where the brass is rubbing in the case gauge.

I'm not familiar with the rcbs match seater, but if it is like the redding one, there is a section that is spring loaded that reacts against the case body. I would recommend disassembling it to check for broken spring or some kind of obstruction that is preventing the body section from sliding properly.
 
I will try the magic marker thing.

The RCBS die does not have any springs, but I have had it completely apart for inspection. I sure didn't find any problems with it.

Still no call from RCBS. :mad:
 
^^^^ Are you crimping at the same time.

If so your collapsing the brass during the process. Back of the body of the die so your not crimping/pinching the brass&bullet forcing the body down.
 
No, the RCBS MM die does not crimp. I am giving it a very light crimp in the next station, with the Lee Factory Crimp die. But that is not what is causing the issue.
 
My match master die set came with a neck sizing only bushing die and the window seating die. Is that the senerio here or is this a full length bushing die?
 
Insanely compressed powder charge blowing the case out?

Can only think of 3 things. Die is screwed in too far causing it to buckle case, brass is so extremely soft that merely seating a bullet crumples it or an extreme compressed charge. With a charge that compressed you would get severe ring dents on the bullet.

I'm guessing die is screwed in too far.
 
Insanely compressed powder charge blowing the case out?

Can only think of 3 things. Die is screwed in too far causing it to buckle case, brass is so extremely soft that merely seating a bullet crumples it or an extreme compressed charge. With a charge that compressed you would get severe ring dents on the bullet.

I'm guessing die is screwed in too far.
I think the op would be posting about rings on his bullet from the seating stem if the charge was that compressed. Might just have that perfect bullet fit who knows.
 
My match master die set came with a neck sizing only bushing die and the window seating die. Is that the senerio here or is this a full length bushing die?
The MM die comes in several varieties. I bought just the one with just the seating die. I already had 2 sizing dies, RCBS and Lee full length. Been using the Lee, going to swap out to the RCBS one to see if makes any difference.
 
Insanely compressed powder charge blowing the case out?
No, cases are not full, let alone overfull. Powder comes up to about the beginning of the shoulder. Although that is a change I made recently, trying some H4350. I'd been using Varget and IMR 4350. I'll switch back to see if that makes any difference.
Can only think of 3 things. Die is screwed in too far causing it to buckle case, brass is so extremely soft that merely seating a bullet crumples it or an extreme compressed charge. With a charge that compressed you would get severe ring dents on the bullet.

I'm guessing die is screwed in too far.
As I said, I tried the die in 3 very different positions. Didn't make any difference.
 
The MM die comes in several varieties. I bought just the one with just the seating die. I already had 2 sizing dies, RCBS and Lee full length. Been using the Lee, going to swap out to the RCBS one to see if makes any difference.
Yeah I saw that when I bought mine and for some reason the two die set was cheaper than the seating die alone.... now a proud owner of a die ill never use...
 
I'd just make some dummy rounds and check/inspect them each step. It could be anything, maybe you have something stuck in the case gauge. The marker trick works really well, you just paint up the case with the marker, give it a minute to dry, drop it in the gauge or chamber, and I just rotate it back and forth like 1/32" just enough to score the case wherever it is rubbing, and it comes out with a clear mark. If your brass is old, it could be springing back after sizing and not sizing correctly. See if the sized brass will pass the gauge.
 
I'd just make some dummy rounds and check/inspect them each step. It could be anything, maybe you have something stuck in the case gauge. The marker trick works really well, you just paint up the case with the marker, give it a minute to dry, drop it in the gauge or chamber, and I just rotate it back and forth like 1/32" just enough to score the case wherever it is rubbing, and it comes out with a clear mark. If your brass is old, it could be springing back after sizing and not sizing correctly. See if the sized brass will pass the gauge.
I checked the cases just before feeding them into the 550. Then I check them after each step (3 separate steps - powder, seating, crimp). It is for sure the MM seating die that is causing the issue.

Many of the rounds pass the case cage, but too many do not. I've cleaned the case gauge too. It is not a case gauge issue.

I did do the mark up a case thing. The interference/expansion is at the bottom of the case, near the rim.

I tried different powder and different sizing die. Didn't fix the problem.
 
Is this a new lot of bullets? If so some measuring may be needed. I've run into some over the years that varied as much as 0.001" from min to max OD. This is enough on a tight chamber to cause problems.

Have you taken the die apart and cleaned it. May be something stuck to the internals.
 
I checked the cases just before feeding them into the 550. Then I check them after each step (3 separate steps - powder, seating, crimp). It is for sure the MM seating die that is causing the issue.

Many of the rounds pass the case cage, but too many do not. I've cleaned the case gauge too. It is not a case gauge issue.

I did do the mark up a case thing. The interference/expansion is at the bottom of the case, near the rim.

I tried different powder and different sizing die. Didn't fix the problem.
That is a sign of overpressure, and is called clickers in a bolt gun. One can try and find a small base die and address the issue, use a push through sizer, or a roll sizer. You may try and have a custom die made, but I would be using a micrometer and looking for exactly how close to the case head it goes out of Sammi spec.
Re-read the post and it passes until seating..... disregard
 
If the base is rubbing after seating operation, the only thing that I can think of that may cause that is really bad concentricity.

I highly doubt the seater die is causing the base to bulge.
 
If the base is rubbing after seating operation, the only thing that I can think of that may cause that is really bad concentricity.
The RCBS MM seating die pretty much eliminates that possibility. You drop the bullet in the window and it aligns it.
I highly doubt the seater die is causing the base to bulge.
I don't blame you for doubting it. But that is the reality of the situation.
 
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