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Seating Depth problems w/550 b


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Just working the bugs out with my new 550. I have only about 300 rds. run sofar of assorted ammo. Yet to have everything all set to run off 4-5 hundred yet. Would like to get it all set so I can get into the grove and start knockin em out with some decent speed.

Today, setting up 9mm. Get it all set to run so I start knockin out a few and check them, all is well. started up again and I had about 15 total done so wanted to check them, I ran them through the mic. and the OAL has changed. My target length was 1.160 and ended up with several at 1.166.

I reset everything and double checked then I Loaded about 40 rds with only 9 that were spot-on, and again the rest were 1.166 or very close to that. I let them all fall into the box so can't say if the good ones were all run together or if they were mixed in with the long ones.

My thinking is that it has something to do with the uneven pressure when I have a more difficult case in the decapping & resizing die. Have some slack in the die plate is all I can think of.

I am running all the same stamps (Win) and they are mostly once fired, clean with slight One Shot added.

It has to be something simple so thought I would ask the experts in the forum.....What da ya think is goin on here?

Seems like I spend more time tinkerin than I should be with this thing. Maybe I am asking too much of it?

Thanks for any suggestions you can offer.

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First call Dillon, they have run across every problem under the sun. Check your die and make sure it is not loose, which I am sure you did. If loading lead, look at the inside of the dies and see if there is any junk gathering. Make sure your shell plate is snug and not moving. More than likely It could be that the contour of your bullets are not uniform and are hitting the seat-er differently.

Good Luck, Buddy

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Buddy, I think I have done everything on your list.

My shell plate is an area I will double check.

I have had the gunk build up before (many years ago) when loading heavy coated bullets. This problem acts much like the gunk problem except that my OAL seems to be either one length or the other with not much inbetween.

This makes me think it's a problem with loose parts possibly. I am using Rainier plated bullets, and that's all I have ever used. The dies are new, maybe 500 total rds. all Rainier of .40 & 9mm cal. These last few (50 or so) rds. are giving me the problems. Prior rds. have little problems I had worked out.

yoshidaex, Your idea, this is a new one to me. I don't recall reading that in the manual from Dillon (I could have missed it) but after thinking about it, I would like to give that a try. Thanks for the tip!

Calling Dillon would probably be the best way to go, however my reloading time is most always when the kind folks at Dillon are in bed, sleeping. But I can work out a time to call if I can't get it going.

thanks for all the suggestions. :cheers:

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The difference is in the ogive of the bullet. Check the OAL with a comparator, they will be within a thousandth or two tops. The press is a lot more consistent than the bullets without any of the toolhead clamps or any other 'fixes' applied.

Sort the ammo by length, and shoot some groups from a bench. You won't be able to tell the difference, not even with a gun that will shoot an inch at 50 yards. Load them up and keep going.

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Heres a better explanation courtesy of Frank aka Franksremote.

I took it out just a while ago and the flat side gives a much better fit. Can you give me a good explaination as to why it matters with a full station?

The natural play (lopsided dip) in the shellplate is balanced when there are shells in each station. When setting seating depth with just a shell in that station, you are not compensating for the fact that there will be a shell in the decap station when you start reloading. Therefore, the depth you set without shells in all stations will end up to be shorter when you have the shellplate full because it will "tilt" further down than when there is balanced opposing force on the other side. It's doing / vs _ when full.

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I know this is probably the wrong answer, but I just accept that sort of difference with my 550b. Match bullets in rifle rounds are the only rounds I have ever seen that are very consistent in the 550b. I figure these are the most consistently made bullets on the market so +1 to whoever said OAL varies on the quality of the bullet and ogive


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I had a similar problem with my 550. What I found was that the shell plate was a bit loose. I removed the set screw in the ram, tightened down the shell plate until it wouldn't move then backed off the center bolt ever so slightly until it indexed rather tight. I reset the set screw in the ram, re-adjusted all the dies, set up for OAL with a full shell plate and was good to go. This was a result of calling Dillon customer service. My OAL has been running within .003 using mixed brass.

Another cause can be slightly too much belling of the case and when you get to the crimp station the crimp die nudges the bullet down a bit. Check a round after seating - then check size after crimping that should tell the tale there.

One last tihng to check before tearing into shell plate set up - check the internal part of the seating die to determine if you are seating with the RN insert or the SWC insert - that can make OAL differences too. On a dillion die there should be a hairpin clip that when removed will let the actual seating assembly drop out. One side is blunt one side is concave. I have the best luck with the blunt side loading RN, RNFP, &TC styles of bullets.

Hope this helps.

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