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(Poll) Reloading precision ammo on a Dillon

Most effective acurizing modification?


  • Total voters
    51

Jackomason

Poop-smith aka "Turd Herder"
Full Member
Minuteman
Dec 26, 2013
1,594
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Westcliffe Colorado
My wife just got me a new Dillon 550c as a gift. Defiantly no input from me hahaha.

I plan to make a video series on my journey with this press exploring some of the different methods people have been using to get single stage accuracy out of their progressive presses.

So out of curiosity, those of you who have been down this road before... what have you found to give the greatest improvement in accuracy (at the bench and on paper) over the stock press. If you could attempt to give it a % value based on increased accuracy or decreased group size. What would it be?

I plan on testing as many methods and modifications as I can and ranking them based on my results but I'd like to see what the opinion of the hide was before I started.
 
i do my sizing and expanding on a dillion 750 but most of the time i still load on a single stage and hand seat primers....hone the shell plate so its flat and resize on a separate tool head
 
I don't recommend trying to load precision on a progressive, the biggest issue is powder measuring. I use my 650 for 9mm, 45ACP, 300 Blk and 223, I can make 2 MOA ammo for my 223 but that's the best I can do YMMV. Even if you can rig up some chutes and ladders for an auto trickler the time suck kinda defeats the purpose of a progressive IMHO.
 
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I don't recommend trying to load precision on a progressive, the biggest issue is powder measuring. I use my 650 for 9mm, 45ACP, 300 Blk and 223, I can make 2 MOA ammo for my 223 but that's the best I can do YMMV. Even if you can rig up some chutes and ladders for an auto trickler the time suck kinda defeats the purpose of a progressive IMHO.
There are a lot of high level shooters "trying" to load on a progressive. It can be done and with some great accuracy. The fact that you are combining so many steps is the real time saver especially when you start separating out steps like decaping, sizing and expanding. Waiting on a scale is what it is. Changing dies and touching brass 2x for every procedure is unnecessary.
 
I size on my single stage and prime with a bench primer everything else in on a 550. I expand, charge with a v3 and a 419 funnel, and seat with a micrometer seater from Whidden. I’m also using the floating tool head from Whidden. Got some bins from inline and a turbo bearing on it to smooth out the shell plate.
 
I size on my single stage and prime with a bench primer everything else in on a 550. I expand, charge with a v3 and a 419 funnel, and seat with a micrometer seater from Whidden. I’m also using the floating tool head from Whidden. Got some bins from inline and a turbo bearing on it to smooth out the shell plate.
Have you had issues priming on the press? It seems like a lot of people prime off the press but I'd like to give it a go.
 
I cannot say what one will gain the most improvement but I think they all lead to better ammo. I personally started my precision reloading with the Armonov toolheads and lock rings so cannot give a before and after. I will say that honing the shell plates made operation a lot smoother and also produced less wobble in the plate.
I can very consistently produce .5 moa ammo on my 550 so don’t let anyone say it’s not possible.
 
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I have a 550B. I am new to PRS but have been reloading rifle (vast majority AR) and pistol for 27yrs.

Some sample accuracy (and I am by no means a great shooter, reading a lot here and working on technique):
0.7moa in a "beater" 223 ARP AR (all parts as cheep as I could source except barrel and trigger). This was a 69gr nosler CC load developed for the barrel ($49 primary arms black friday special) the ARP barrel replaced. Yet to dial it in for the ARP. I am generally a "poor" I've come to learn heheh.

0.25moa 6.8spc shot out of a savage axis I rebarrelled with an ARP barrel (limited run). Posted a pic in one of the savage beat down threads.

0.3moa 6.5cm in my new impact/krg bravo build. 140bthp hornady, 2000mr (before I sourced some 6.5cm appropriate powder, starline brass, cci450s). I threw the powder individually with a rcbs chargemaster lite but everything else was on the 550B. Will be restarting workup with StaBall and 144 bergers in fireformed brass.
 
Have you had issues priming on the press? It seems like a lot of people prime off the press but I'd like to give it a go.
Honestly I haven’t tried in the press priming. I had just bought the rcbs primer so I use it just to justify the purchase.
 
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You don't need to make any changes to load extremely accurate ammo on a dillon. Just pick a powder with the machine's limitations in mind if you want to drop power.
 
You don't need to make any changes to load extremely accurate ammo on a dillon. Just pick a powder with the machine's limitations in mind if you want to drop power.
I've been loading on a Rock chucker and dropping on a CM lite. I've been able to get very impressive groups and I'd like to replicate that load on the dillon. I'll try with everything stock and do a side by side.
 
I bought a couple of the Armanov toolheads with their floating rings and like them a lot. More consistent resizing from what little I've used them so far.
 
I have loaded all my precision ammo on a Dillon 550 for years, very happy with the results. I would personally look at the process in terms of dimensional results rather than trying to test accuracy - since accuracy is much harder to quantify and affected by many external factors (including the shooter).

Brass Prep - just measure whether it comes out with consistent shoulder bump and minimal or no runout. I find that using a FL die followed by a mandrel does a stellar job at keeping runout low regardless of whether floating toolhead (o-rings on a 550) or locked toolhead (1050). Shoulder bump stays consistent through a combo of annealing and using good lube like alcohol/lanolin.

Case loading - you can measure primer seating depth consistency, bullet seating depth consistency, and final runout of loaded round (obviously also affected by brass prep). Powder measured off-press and added with a funnel. I get good consistency on all fronts here as well.
 
I like my 550 for 223/308 but won’t use it for my bolt gun loads. The powder measure system is not consistent, at least mine wasn’t. I sold the powder system to a coworker and replaced with with a lee auto drum. Much more accurate but still not trusting it with bolt gun ammo.
 
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I’ve loaded match ammo straight off a Dillon 750 using the Dillon powder throw and prime….ammo shot great I think I won a match and did well in a few others the problem is inconsistent power throws caused a 40fps+ ES.

I stopped using the powder throw and went to a Dillon powder through die and a 419 funnel…this worked a bit better but then I found the Dillon was not seating primers deep enough to seat the anvil.

I tried hand seating then loading on the 750 next thing I found was that even when running slow that when the case with powder in it came around and stopped in the next station it kind of snaps to a stop and every now and then it would cause a few kernels to fly out…some times none other times up to 4-5 at a time.

I know there is a couple of fixes for this I just have not gotten around to it.

I will say the Dillon makes short work of decapping, sizing and expanding which are a few of the things I don’t like doing…come to think of it I don’t like reloading at all but I like the down range results.

9mm 124g JHP 5.4g CFE pistol

9mm 147g JHP 3.4g N320 super soft shooting and stupid accurate

I’ve loaded at least 12,000 rounds of 9mm and 500-600 BRA and have had maybe 50-100 side ways primes in the 9mm and any other problems I have had were either self induced or not keeping up the maintenance…my 750 runs like a champ when clean and lubed shit starts going south when it starts getting dirty or dry.
 
The Dillon 550C absolutely will load precision rounds. I load everything on it, 223, 6BRA, 6.5 CM and 300 PRC. Brass prep is done on a Forster; on the 550 - expanding, priming, powder pour, seating and measuring every round as it falls of the press. Seated rounds consistently +- .001 - .002. I use all the extras plus AutoTrickler.

My only gripe is I just can’t get primers to seat below flush.
(Googling Dillon 550C primer seating actually brought me to this thread.)
 
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The Dillon 550C absolutely will load precision rounds. I load everything on it, 223, 6BRA, 6.5 CM and 300 PRC. Brass prep is done on a Forster; on the 550 - expanding, priming, powder pour, seating and measuring every round as it falls of the press. Seated rounds consistently +- .001 - .002. I use all the extras plus AutoTrickler.

My only gripe is I just can’t get primers to seat below flush.
(Googling Dillon 550C primer seating actually brought me to this thread.)



View attachment 7732200
I've heard that there was some sort of modification you can do you get them to seat better. I'll do some digging too. I went the 2x tool head rout, one for case prep (decap, size and mandrel) and the next is a loading tool head with the decapping in #1 again just to clear the flash holes.
 
My only gripe is I just can’t get primers to seat below flush.

There's some really good info in the attached article by Scott Harris (an accomplished F-Class shooter) about getting the Dillon priming system to work well for precision rounds. See pages 3-6 for details with photos.

My 550 seats primers about 0.004 below flush.
 

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There's some really good info in the attached article by Scott Harris (an accomplished F-Class shooter) about getting the Dillon priming system to work well for precision rounds. See pages 3-6 for details with photos.

My 550 seats primers about 0.004 below flush.

Thanks, I’ve read that article before and it is helpful. I’ve already shaved abou 4-5 thousands off the primer cup already and it doesn’t seem to help. I’m leery of going any further. How much have you shaved?
 
I don't think I had to shave any off my primer cup, it was already dialed in when I started out.

How hard are you pressing forward when you seat the primer? I push forward with a fair bit of force.
 
How much time is spent getting a good adjustment on the primer stem on your Dillon? Keeping them clean and adjusted is essential, plus a good consistent stroke on seating.
 
I never adjust anything on mine, I wouldn't exactly call it clean though I do wipe the decapping puke from off the lower portion of the press periodically. I do have a consistent priming stroke - push forward all the way, hard. Probably 30-40lbs of forward force on the handle. My press is rock-solid mounted on a strong mount on super sturdy bench, roller handle about chest high. I give it a good straight arm full body lean into the press to seat the primer.
 
I never adjust anything on mine, I wouldn't exactly call it clean though I do wipe the decapping puke from off the lower portion of the press periodically. I do have a consistent priming stroke - push forward all the way, hard. Probably 30-40lbs of forward force on the handle. My press is rock-solid mounted on a strong mount on super sturdy bench, roller handle about chest high. I give it a good straight arm full body lean into the press to seat the primer.
I thought mine was good to go until I took it all apart and cleaned and readjusted everything. Lots of powder residue built up in places I didn't know existed.
 
I bought a secondhand RL550b in the early 1990's, when I was starting out with 3-gun Bullseye, loading 45ACP pretty exclusively. It served my needs admirably, simply using it as it was designed to be used in progressive mode.

In the later 90's, I began shooting 308, 30-06, and 223, never gave it much thought, and did fine. Over time, many (MANY) tricks, tools, and techniques came and went from my loading bench, each contributing their benefits (and hassles), and guiding me to a current method.

That method uses the press progressively, but in two stages. It divides into the before charging/after charging portions of the process. Charging employs the RCBS Chargemaster Lite, and it is a crucial part of my process. Several of the poll options were tried, but my conclusion was that the RL550b press worked well, best for me, exactly as designed.

Could I get better ammunition from a single stage? Probably. But I found that all those sleights of hand and equipment manipulation simply added more time and effort to the process, and while improvements were obvious, they did not justify the overhead. At 75, adding time to the process is counterproductive for me; and my accuracy needs are not the same "accuracy uppermost, whatever the cost or means" that one finds in the several ELR or BR disciplines.

At one time, my press was being used by an entire shooting team as a team press. I cautioned my teammates that if they had to put a lot of force into the process, something was going wrong; to stop, re-examine their process, correct the issue, and proceed onward without they extra force. They still managed to break the priming system, twice, anyway...

Greg
 
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I never adjust anything on mine, I wouldn't exactly call it clean though I do wipe the decapping puke from off the lower portion of the press periodically. I do have a consistent priming stroke - push forward all the way, hard. Probably 30-40lbs of forward force on the handle. My press is rock-solid mounted on a strong mount on super sturdy bench, roller handle about chest high. I give it a good straight arm full body lean into the press to seat the primer.

This.
I grab the back of the press frame with my left hand and push forward with my right; never had trouble seating primers deep enough that way.

OP - if you're applying enough force but still having trouble getting primers seated, you might need to clean the primer pockets. I don't normally do that for anything loaded on a Dillon, but multiple firings in a rifle case can leave enough residue to make primers sit high (or just require more force to seat them correctly).

Although my first guess is that you're probably just not pushing hard enough to seat the primers.
 
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If you're using a stick powder, just get the powder funnel and use an acceptable off-press measuring method. (Auto-trickler is cool, but just having a good tuned balance is fine).

If you're throwing a ball powder, just go for it.

I size and prime on 1, inside neck mandrel on 2, funnel on 3, seater on 4.

One of these days I'm going to figure out that I should just run a caliber that likes a ball powder, but I've been using lots of h1000 and retumbo in the 243ai and 25-06.
I've had very good luck with a Redding benchrest powder thrower and 6.5 sta-ball in the 6.5 cm. Haven't needed to do enough volume to justify switching the Dillon over to try it yet.


I should add, my 550 was a 450. I'm the 3rd owner I know of, and have done full tear-down and cleaning/lubing every few years. It's well broke in, and just keeps going.
I do think the 550 does have an advantage, in the lack of auto-rotating the shell plate. You can move it nice and easy by hand and ensure you're not spilling any powder.
 
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Agreed, I really prefer the 550 for precision rifle stuff. The 650 is fine for volume loading, IF you have the right combo of powder and bullet so that nothing spills or falls off the case mouth, but it's definitely less versatile than the little 550.

Speaking of a cartridge that just likes ball powder - the Grendel family in either heavy bullet 6mm or mid-weight 6.5mm flavor just loves Lever, enough so that I don't use anything else for the 6mm version any more. I haven't set up my 550 for that cartridge yet, but if I do it'll be a no-brainer to just see if the Dillon measure will throw consistently enough (and it should).
 
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Start here:
Tool Heads and Free Float Lock Rings will go a long way.

And this for the 419 funnel kit for throwing charges off-press and dumping in case on-press

F Class John has some great videos on these two parts. I believe him and Erik Cortina are doing their loading on the 750XL with Mark 7 auto drives. I've recently made the jump to 750 and weening myself off the Co-Ax... it's a process. I'll be doing powder off-press on the Auto Trickler and dumping into case on press, but all other steps on the 750. Big precision loading project coming up so I'll finalize my process during that time.

Also there is a seller on eBay that makes some upgraded parts to smooth out the action on the shell plate for the auto progressives.
snowshooze
 
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Start here:
Tool Heads and Free Float Lock Rings will go a long way.

And this for the 419 funnel kit for throwing charges off-press and dumping in case on-press

F Class John has some great videos on these two parts. I believe him and Erik Cortina are doing their loading on the 750XL with Mark 7 auto drives. I've recently made the jump to 750 and weening myself off the Co-Ax... it's a process. I'll be doing powder off-press on the Auto Trickler and dumping into case on press, but all other steps on the 750. Big precision loading project coming up so I'll finalize my process during that time.

Also there is a seller on eBay that makes some upgraded parts to smooth out the action on the shell plate for the auto progressives.
snowshooze
The armanov stuff is sweet. One side note, the inline fabrication press light doesn't agree with the armanov lock rings. Grabbed the armanove stuff and the A419 funnel right away though, Little underwhelmed by the funnel but it works.

I probably would choose the 750 if I were loading one caliber a lot, but there are a hand full of calibers I shoot often. Caliber conversions have been manageable on the 550c.
 
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I was able to still utilize the inline light I just taped it up a bit and it sits a little higher in the hole, resting on lock rings.

Also agree the Armonov head and lock ring setup is pretty nice. I have no problems using the factory $7 Dillon powder funnel, but I’m one of the poors. 😂

I also highly recommend polishing the bottom of your shell plates that smoothed and tightened my shell plates up considerably.
 
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The armanov stuff is sweet. One side note, the inline fabrication press light doesn't agree with the armanov lock rings. Grabbed the armanove stuff and the A419 funnel right away though, Little underwhelmed by the funnel but it works.

I probably would choose the 750 if I were loading one caliber a lot, but there are a hand full of calibers I shoot often. Caliber conversions have been manageable on the 550c.
Fair enough. I sold off a bunch of gear that I wasn't using often to fund the Dillion and extra change kits etc, one of the items being a Hornady LnL progressive. I've always wanted a Dillion but never had the extra cash.

I usually prep brass in large batches (500+) and load in 100-200 round lots, so the goal was to gain any advantage I can with speed and not sacrifice precision. I'm still new to the 750XL but based on the steps I've completed so far with brass prep, I'm very impressed. Processing and priming 308WIN has been a breeze. The press runs like a champ.

With respect to powder, I still haven't done the off-press drop --> on-press dump but I see what you're saying about the 419 setup. I used some plumbers tape to tighten up the system. Also, StaBall seems to be a viable powder for PRS shooting and I might start heading in that direction after my H4350 is gone. This could potentially lead to all steps being performed in-line, at one time, on the press... THAT would be a hell of a deal.

I also highly recommend polishing the bottom of your shell plates that smoothed and tightened my shell plates up considerably.

Can someone give me some pointers on honing the bottom of the shell plates? I bought some polishing paper (cant remember the grit, its whatever FC John recommends) for this, but I'm scared to do it. I cant find anyone giving an explanation on what to look for, how to know when to stop.
 
Fair enough. I sold off a bunch of gear that I wasn't using often to fund the Dillion and extra change kits etc, one of the items being a Hornady LnL progressive. I've always wanted a Dillion but never had the extra cash.

I usually prep brass in large batches (500+) and load in 100-200 round lots, so the goal was to gain any advantage I can with speed and not sacrifice precision. I'm still new to the 750XL but based on the steps I've completed so far with brass prep, I'm very impressed. Processing and priming 308WIN has been a breeze. The press runs like a champ.

With respect to powder, I still haven't done the off-press drop --> on-press dump but I see what you're saying about the 419 setup. I used some plumbers tape to tighten up the system. Also, StaBall seems to be a viable powder for PRS shooting and I might start heading in that direction after my H4350 is gone. This could potentially lead to all steps being performed in-line, at one time, on the press... THAT would be a hell of a deal.



Can someone give me some pointers on honing the bottom of the shell plates? I bought some polishing paper (cant remember the grit, its whatever FC John recommends) for this, but I'm scared to do it. I cant find anyone giving an explanation on what to look for, how to know when to stop.

I haven't quite wrapped my head around honing, I get what to do but I'm not sure I see the value. I'd test it on a piece of glass (probably hone with that under the sand paper too) but just see if it rocks any direction. Wouldn't the head of the ram be the part you'd want flat? Maybe I'm missing something there.

I'm curious about loading my trainer ammo (224 valk) on this press. I don't plan to use multiple tool heads for this so cases will go in lubed and come out lubed. For the 5.56 I've used isopropyl and a towel to take off the extra but I'm not sure how this whole process will effect accuracy.
 
After deep diving into Erik's and John's videos recently, I'm not sure WHAT matters anymore.

FC John and rice in the flash hole


Erik shooting ammo in F Class Worlds with ammo that was visibly non-concentric.. I cant find the video but he talks about concentricity here


So what matters then? If all things are the same (brass, primer, powder, bullets), my educated (non-expert) opinion to make really great ammo is:
  1. consistent powder charges (throwing to the kernel is necessary, but we do it anyway)
  2. consistent neck tension
  3. seating depth testing
And maybe is only one or two of those.. One member on here has challenged anyone to throw out a reasonable powder charge and he'll make it shoot with seating depth testing, I believe it was @Dthomas3523 ... I don't recall the details but I think the discussion was centered around velocity flat spots being unreliable data points for load development. I've gone back in post history but I couldn't dig it up.

With new tools like the AMP press hitting the market, I'm excited to see what reloading will look like in the years to come. The SuperTrickler has a SuperFiller machine where you can line up a sled full of prepped brass and the machine will dump powder automatically. Mix the two machines and you can literally line up a room full of brass and go to bed, wake up, shoot a match. We're probably not far off.
 
Fair enough. I sold off a bunch of gear that I wasn't using often to fund the Dillion and extra change kits etc, one of the items being a Hornady LnL progressive. I've always wanted a Dillion but never had the extra cash.

I usually prep brass in large batches (500+) and load in 100-200 round lots, so the goal was to gain any advantage I can with speed and not sacrifice precision. I'm still new to the 750XL but based on the steps I've completed so far with brass prep, I'm very impressed. Processing and priming 308WIN has been a breeze. The press runs like a champ.

With respect to powder, I still haven't done the off-press drop --> on-press dump but I see what you're saying about the 419 setup. I used some plumbers tape to tighten up the system. Also, StaBall seems to be a viable powder for PRS shooting and I might start heading in that direction after my H4350 is gone. This could potentially lead to all steps being performed in-line, at one time, on the press... THAT would be a hell of a deal.



Can someone give me some pointers on honing the bottom of the shell plates? I bought some polishing paper (cant remember the grit, its whatever FC John recommends) for this, but I'm scared to do it. I cant find anyone giving an explanation on what to look for, how to know when to stop.
I wet sanded 1500,2000, than 2500 on a price of glass. I went until the whole thing was almost mirror finish. You will see the high spots as you go as they will loose the finish first.

Before I honed the shellplate I would find certain plates would bind while spinning therefore would have to back the screw off to the point where there was quite a bit of play in the shellplate. After honing I was able to tighten them down more to reduce that “wobble”.

Wether it does anything for precision 🤷🏿‍♂️, but it probably took all of five minutes per shellplate.
 
I have found powder charge consistency and neck consistency to be the biggest factors.

Before I used a mandrel I had sd's in the 30's, and before the fx7i scale I couldn't get it below 12. Both those things have brought me into the 5-10 range regularly.

I trim and chamfer brass when I absolutely have to. I don't weigh cases. I don't measure case volume. I don't do anything with primer pockets (Dillion swager for military brass). I don't measure case run-out/bullet run-out.

I'm realistic that if I can make $450 pre-fit barrels shoot .2-.4 with minimal prep and load time I'm happy. That's more time doing other things, not trying to be bench-rest perfect.
 
I wet sanded 1500,2000, than 2500 on a price of glass. I went until the whole thing was almost mirror finish. You will see the high spots as you go as they will loose the finish first.

Before I honed the shellplate I would find certain plates would bind while spinning therefore would have to back the screw off to the point where there was quite a bit of play in the shellplate. After honing I was able to tighten them down more to reduce that “wobble”.

Wether it does anything for precision 🤷🏿‍♂️, but it probably took all of five minutes per shellplate.
thanks for that explanation. I might get brave and give it a shot this weekend.
 
I wet sanded 1500,2000, than 2500 on a price of glass. I went until the whole thing was almost mirror finish. You will see the high spots as you go as they will loose the finish first.

That misses the point of honing the shell plate though. The intent is not just to polish it, as you did, but to actually remove material so that the cases in the shellplate are held tighter and don't wobble. Check out the article posted by Sheldon N earlier in the thread; it mentions removing .005-.015", which is a lot to remove by hand.

1500 grit doesn't do jack to remove any significant material by hand from a surface that large; you need to start with something much coarser. Finishing with fine grit like that is fine, although it doesn't have to be mirror polished to be smooth. You could even finish at 600 grit and it'll rotate smoothly with just a very thin film of lube (whether oil, grease, or dry). Personally I like dry teflon or moly spray.
 
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That misses the point of honing the shell plate though. The intent is not just to polish it, as you did, but to actually remove material so that the cases in the shellplate are held tighter and don't wobble. Check out the article posted by Sheldon N earlier in the thread; it mentions removing .005-.015", which is a lot to remove by hand.

1500 grit doesn't do jack to remove any significant material by hand from a surface that large; you need to start with something much coarser. Finishing with fine grit like that is fine, although it doesn't have to be mirror polished to be smooth. You could even finish at 600 grit and it'll rotate smoothly with just a very thin film of lube (whether oil, grease, or dry). Personally I like dry teflon or moly spray.
Your probably right but it definately smoothed out the surface I kept inspecting it and could see where certain parts would lose their finish before others which in my opinion would be the high points. I kept going until all finish was off and down to bare metal than polished.

Whatever I did was an improvement and I’m happy with it and I have no play in shellplate or brass so I’ll leave it at that.
 
Your probably right but it definately smoothed out the surface I kept inspecting it and could see where certain parts would lose their finish before others which in my opinion would be the high points. I kept going until all finish was off and down to bare metal than polished.

Whatever I did was an improvement and I’m happy with it and I have no play in shellplate or brass so I’ll leave it at that.
For anyone else doing this, it's important to realize that doing this by hand on a piece of glass will wear some areas faster than others, specifically the leading and trailing edges as you move front and back or side to side. Because of that it's important to keep rotating the part in you hand, and try to keep pressure in the center as much as possible rather than on the edges.
 
Listened to the 'Just Fn send it' podcast this week. EC was talking about reloading on his 750 and made a comment that he doesn't seat bullets on the 750 (this was before he got his auto drive so he may have changed that now) but his reason was that he would get 5 thou variance in seating depth. He ran a test where he put a dot on one station and kept track of seating depth based off their position on the shell plate.

Anyway I ran the same test on my 550c and found it was a non issue! There was no consistent variance. The ES was 2 thou and that could very well be the cheap hornady bullets. And that one that was off was on slot 1 where I zeroed my calipers.

20211205_144151.jpg
 
Listened to the 'Just Fn send it' podcast this week. EC was talking about reloading on his 750 and made a comment that he doesn't seat bullets on the 750 (this was before he got his auto drive so he may have changed that now) but his reason was that he would get 5 thou variance in seating depth. He ran a test where he put a dot on one station and kept track of seating depth based off their position on the shell plate.

Anyway I ran the same test on my 550c and found it was a non issue! There was no consistent variance. The ES was 2 thou and that could very well be the cheap hornady bullets. And that one that was off was on slot 1 where I zeroed my calipers.

View attachment 7754431

Your observation makes sense, because the shell plate should have zero impact on seating depth. During seating, the base of the cartridge is pressed against the head of the ram, and the shell plate does not have any influence on it axially. Since the head of the ram does not rotate, and neither does the seating die, every bullet seated is done so between the same points on the press.

Good example how some people will find a variance and then attribute the wrong cause to it without thinking it through far enough.

What can affect seating depth are things like other die stations being filled or not, or sizing effort differences from one case to the next. Those can cause the floating tool head to move around a little differently and affect seating depth.
 
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