Plain base gas checks, who here uses?

[Soundguy]

I've been using regular gas checks since I started casting / using gas check shank bullets. Never messed with plain base checks..but decided what the heck and ordered a small pack of a bunch of different sizes to play around with. Might be interesting to speed up some cast loads that I only have pb bullets for. Will have to do some load research and see what might be my first victim.

[hc18flyer]

I have used them in .45 Colt and .45-70 for some 'warmer' loads, and not have to get a gc mold. I usually end up getting the gc mold. I had trouble keeping some on, so I put a tiny dab of gel superglue on the check before sizing. I know it is extra work, but I only needed a few. My 2 cents, hc18flyer

[Soundguy]

I can't wait to try them.

[gloob]

I've got a couple pistol calibers I would like to try them in. I plan to make my own check maker, but maybe I could save a lot of time if I tried some, first! OP, did you find a variety pack for sale?

I'm not worried about the check falling off, because my problem guns are in straight wall pistol calibers. I was hoping if my bullets don't need sizing, I could just slip them on before seating the bullet. That doesn't work with beefy gas checks, because it kills the neck tension. Has anyone tried this with plain base checks?

[Soundguy]

I did not find a variety pack but the place I bought from sold packs as small as 100 or 250 or 500 Etc but when you're buying them in packs of $100 you're only paying $4 so I just bought a bunch of packs of 100 to try out a bunch of different calibers. I don't think your plan of not sizing them will work because these checks according to what I've read are actually punched oversized so that they will slip over the base of a bullet so you you may not find that that works for you but who knows maybe they're thin enough that it will perhaps you could glue them on with a drop of super glue and then seat them and they might work because once the cartridges been fired it's going to be pushed from the rear anyway if you try that let us know how it works.

[Seeker]

I use them for .45 colt and 45-70. I size, then tumble lube with 60/40, install the check by pushing through the Lee sizer base first and tumble lube one more time. They work great and I have never had one come off.

[Soundguy]

Nice!

[Krh1326]

I no longer shoot any cast boolits, with out checks. Now, being retired, I have the time to fiddle around, and do what I want.
I will not say that pb checks have improved my accuracy, as I am still a terrible shot, lmao…. But I will say that my groups have tightened up, and that’s a bonus.
I have also noticed that pretty much whatever bhn my lead is at, or what kind of charge I’m running, I have zero leading in 9mm, .38, .357m , .40 sw, .44m and .45 acp.

I would say my realized returns, are consistency and cleanup.

[gloob]

When I first started reloading, I was more into calculating in cost, time, and effort per cartridge. And I shot a much higher volume per outing. Didn't matter if it left fouling. I'd just scrub the bore out with copper/bronze wool and maybe even using a cordless drill. And for pistol, long range accuracy didn't matter much, either. Also didn't matter if the bullets were ugly or if all the lube ended up on the exposed part of the bullet, ready to pick up dirt or lint, because I was just going to shoot it soon enough.

I don't shoot like that anymore, pulling the happy switch until my nerves start to tweak. And I can't afford to spend that much time picking up brass and replacing worn out semiauto rifle barrels. I can make more ammo now than I can shoot, and if I'm going to store it away I want it to be as close to perfect as possible!

I like the combo of gas checks and hard tumble lube that goes in the groove and stays put.

[missionary5155]

No loose condition ! Have proven molds that can now get cast softer yet maintain the fps,,, Bigger exit holes.

[Larry Gibson]

I make my own 45 cal PB GCs. I've used them on several different 45 ACP, 45 Colt and 45-70 cast bullets. Sizing, particularly to "crimp' them into place, becomes critical as to the method and amount of sizing done in one step. The thickness of the GC along with hardness of the bullet are also critical factors.

[gloob]

I take it the thinner the better, for a PB check? Do you use multiple sizing dies on any of your PB checks?

Sage's says their PB checks are 8-12 thousandths thick lithograph plate. I was hoping my 9-10 thous aluminum flashing will work for PB checks on my 40/10mm bullets. Mostly because I have enough of this stuff to make 25k 223 checks, and I don't think I'm going to use that many. :)

I've found $20.00 of parts that will make a 40 cal gas check maker pretty easy to build. But right now I'm still slogging through it with what I have on hand, hoping to avoid that. $20.00 will buy a box of fancy cat food that'll make my cat way happier than anything a bullet can do for me.

[Larry Gibson]

The thickest I've found to work well on softer BHN bullets (in the 8 - 12 BHN range) is .006 made from the Coors lite "bottle" cans. I found on harder cast 45 ACP bullets (commercial hard cast with a BHN of 15 - 16) it is best to initially run them through a .454 sizer then the .452 sizer. Also, with as cast larger than .453 it is best to step size the GCs on. With softer 45-70 bullets cast of binary 20-1 or 16-1 alloys I presize the bullets at .4615 or .459 and seat the GC on in the same sizer in a second operation.

Any material [aluminum, brass, copper] over a .010 thickness is very difficult to cut in 45 cal tool. It is even a bit difficult to cut the discs when making 35 GCs with aluminum flashing of .014. For the 45 and 35 GCs my are Pat Marlins. I have not problems cutting them of .014 or .015 brass or aluminum in my other GC makers using an arbor press.

[gloob]

Interesting, thanks! Too bad I don't consume anything in an aluminum bottle, and I have no interest in paying money to drink Coors Lite!

In 40 cal specifically, I've found some people using regular soda can, and some using the lithograph plate checks up to at least 8 thous, just with a normal sizing die. I hope that an extra thousandth and a half of thickness won't make too big a difference. My bullets are probably 12 BHN at most, maybe less. The majority of my lead supply lately is from airgun pellets.

Yeah, I noticed that some of the gas check dies demonstrated on Youtube aren't adjusted (adjustable?) to the peak of the ram, and there's a lot of force/jerkiness involved, even for 30 cal checks. I wonder if this is part of the issue for your 45 die.

My only checks so far are the teeny 223, so that's only a 316ish disc; should be almost 60% more force for a 40 check at near 500 thous. But I adjust my die to the peak leverage of the press. It's pretty smooth and easy even on the 13 thous aluminum. I don't know where my 40 die will end up being bodged into the press, if I ever complete it, but I'm aiming for peak leverage.

The strip of flashing ends up actually touching the O frame of my press at the end of the follow through. Then I drop it down a bit to see and position the next punch and just hold the strip there while I work the lever. I suppose this is why some of the commercial makers have the super long punch positioned way lower. I think they're maybe doing it wrong, because it's super easy the way mine is setup.

[Larry Gibson]

My dies are adjusted to the peak leverage point on the press. Still a lot more difficult than using my 8mm and 30 dies and I'm sure a lot more difficult than cutting a 22 cal disc.

Strips cut from soda can are used by many, but I've not found them to be that effective unless doubled or tripled up. Then I had the problem of the outer ones coming off before even loading. Also, on regular GC bullet shanks any GC less than .010 or .012 don't crimp on tight enough and stick in the H&I sizing die. Of course, that's different with PB GCs.

Picture of you setup?

[gloob]

When you double up on soda can, that's for GC shank bullets, right? I think one soda check works for a PB bullet?

Thanks, again. Here are some pics of my homebrew 223 die. The button is reversible. I have one side for 13 thous, and one for 9 thous. See how short the punch is? And I still only screw the die in 4 turns.
https://i.imgur.com/mZW6guk.jpg

As you can see I have to drop the ram a bit extra to see and position the strip. I could drop my die down a lot deeper so as not to have to move the ram as much. But then the leverage drops a lot. Now, I'm no weakling. So it's not a matter of strength. When the leverage drops, the ram/lever jumps into the follow through when the disc cuts, and it's not smooth. And my bench rattles and stuff fall off during the course of making lots of checks. And the sudden jerk adds up after doing a bunch, not feeling very nice to my nerves and joints.

https://i.imgur.com/HRQVOXU.jpg


Same ram position as above, approximating my POV when using it. I drop the ram to where I can just clearly see and move the strip.

https://i.imgur.com/IABwDNm.jpg


So it punches the disc out at this position, just a fraction of an inch shy of TDC and maximum leverage.

https://i.imgur.com/3Y5PbBT.jpg


This is TDC of my press, with the strip hitting the top of the press frame on the follow through to form the cup and advance it through the hollow punch. I lucked out, I didn't make the bottom part longer than this.
https://i.imgur.com/5GMncNq.jpg


Now, I didn't give any of this more than a nickel's worth of thought while making it. I wasn't sure it would even work. But after using it a bit, this is how I adjusted it. Peak leverage makes a lot of difference when making a lifetime's worth of checks over a week of playing with your new die. It's a marathon, not a sprint! :)

[Larry Gibson]

"When you double up on soda can, that's for GC shank bullets, right? I think one soda check works for a PB bullet?"

Yes, to both questions there. Soda cans run .003 - .004 and even doubled and tripled up the didn't stay on the GC bullet shanks w/o gluing which I found to be a pain. I've found sometimes even a single .010 thick GC won't stay on most shanks. However. .012 -.015 thick ones do. One soda can thick check will stay on PB bullets though. They cut easy enough but I've found the .006 thick onse seem to be a bit more accurate. On bullets of 40-1 up through 16-1 alloy they swage on quite easily. I occasionally have one of the Coors but mostly a couple friends drink one or two during BS sessions solving the world's problems down in the man cave. I get 80+ of the 45 PB GCs out of one can so it doesn't take many of the can "bottles". I'm sure there are other thicker can materials than soda cans out there. The .006 GCs crimp on and work very well in my suppressed M98 45 ACP cutting down the lead deposits on the suppressor baffles. I use them mostly on 20-1 alloy Lee 452-230-TCs.

[gloob]

Thanks. I bought the 9 thous material because that's what I measured for my 223 Hornady checks. They fit just right on my bullets. I'm just hoping to get a two-fer out of it, using it for PB checks, too.

For all I know the 13 thousandths checks would also fit just right on my 223 bullets, too. They stay on fine, but they're too tight to place on by hand. If I use the same size plug as for 9 thous, they start to tear. I'd have to open up the ID on my punch, and there would be no going back.

Seems like there are several thickness standards for gas checks and bullet shanks, depending on the caliber. 9 thous for 223. 17 thous for 30 cal, IIRC. There's a list posted on the forum somewhere. I was more curious about the PB checks.

I didn't see any other gas shank caliber that would use 9 mil material, not that it matters. I don't shoot any other rifle caliber enough to worry about using up 1000 factory checks. And the only pistol bullet I have fouling with is the 40/10mm.

[Larry Gibson]

Hope fully the the PB GCs will solve the problem. I had some coated bullets 452-230-TCs the coating would severely foul the barrel of my M98 45 ACP. First 3 shots out of the clean barrel would go into 2" at 50 yards then the other 5 in the mag would open the group to 4 -6". A second mag of 8 rounds and the group would be 12 - 16". With the .006 PB GC on them they didn't foul the bore and two mags would go into 3" +/-.

[n.h.schmidt]

Hi guys Have either of you guys considered making changes to the linkage of the press to ease the effort and reduce the jolt of punch through. I used to make plain base gas checks for sale.I did it on three presses and with help made about 250,000 plane base checks. I made changes to all three presses to make it easy. On my Lee Challenger press ,the ram had a extra hole drilled 1" above the bottom normal hole for the cross pin. When I moved the linkage to that higher position That allowed the ram to top out 1" lower . Made the punch through very easy. Gloob your lee press could easily have that extra hole drilled in the ram to give you much better leverage . My other presses were harder to mod.

[gloob]

Never would have thought of it. Thanks! I'll sock that away for a rainy day.

Today, the sun shines! I finished my check maker, and it came out good.

Checks push/snap on firm and level by hand with just a firm push. Then a run through the sizing die NOSE UP, like normal. And just look at the results. The check is flat and level on all of them. There's a bit of variation in height, on my homecast. But they had already been through my sizing die twice, so no resistance.

It might look like some of the checks are not symmetrical, that they're real thin on one edge. They're not. They're almost perfectly symmetrical. It's lube. The checks consistently pinch in a bit at the mouth, forming a tiny lube groove.

Seating and sizing is same as doing normal checks on bullets made for it. EZ peezy. Just had to stone the mouth of my sizing die a wee bit to smooth out the little sharp ledge.

https://i.imgur.com/UuZb4BW.jpg
https://i.imgur.com/yV0BgO2.jpg
https://i.imgur.com/v3IPH3o.jpg

And my press reaches TDC on this one, too. Utterly smooth. No jams.

[gloob]

Hmm. I'm starting to see some of the finicky nature of seating thick PB checks. Now I see why you might size in steps.

I made up a fresh batch of bullets, and the checks won't go on the unsized bullets, at all. To get them on straight, I have to size them, first. So I still have a huge variation in OAL after crimping them on, and it may be due to the lack of resistance.

The problem I have going base-first, the bottom of the check ends up convexed rather than flat, and it might just be esthetic, but I don't like it. My button is maybe 4-5 thous smaller than what they're using in the sticky, and that might be why I get the cupping, base-first. (So if you want to get flat checks when going nose-first, you might want to try a smaller button; it seems a common complaint that the checks end up concave, when sizing nose first, but not with mine).

I may just leave my check dimensions alone and buy a second sizing die. Size, add check, size smaller. For pistol bullets, I'm sure they'll work fine, even if this doesn't improve the consistency. But hopefully the OAL tightens up closer to what I get with my MBC bullets. The presized MBC's take the check perfectly, and the 18 BHN hardness gives a lot of resistance going nose up through my sizing die.

It looks quite challenging for a PB die/check seller to get a customer exactly what they want.

[Soundguy]

Your setup looks great. Thanks for posting. Loving the discussion and all the ideas and info being bounced around. Thanks

[gloob]

Thanks. I'm glad some of it is useful.

I found a potentially better and certainly cheaper way for me to pre-size just the base of my bullets. I found the opening of my Lee 9x18 Makarov expander die is right on 401. A bit of polishing of the mouth and fabricating a couple new parts, and she's right.

I made a .556" circle of 1/8" steel plate to slip into my ram for a "push thru stem" but with negative height. The nose of the bullet sits partway into the hole in the ram, this way. So I can get full leverage without having to set my sizing die way up into space. Then I set the die so I can go all the way to TDC, sizing the base of the bullet deep enough to clear the height of my checks, plus a smidge extra.

I put a knob on a 1/4 steel rod to sit in the die as an ejector. It fits through the power-thru expander plug. When I size the bullet, the base of the bullet pushes the rod up. After lowering the ram, I give the knob a smack with my hand, and the bullet drops out.

It's a bit tedious, but the check will fit on there fully by hand. And the rest of the bullet is still unsized, so the checks get crimped on nice and consistently, now.

[gloob]

Top to bottom:
1. bullets as cast after tumble lubing
2. base-sized with mak die
3. checks placed by hand
4. nose-first sized to crimp check in place.
https://i.imgur.com/icmEMse.jpg


Here's the mouth of the mak die. I shortened a spare expander plug to sit on the base of the bullet. The die is set to TDC of the press, but I think a positive base will help to ensure the bullet finishes straight.

https://i.imgur.com/UYNwDXf.jpg

I added a spacer. And the ejector rod. That's pretty much it, beside some polishing. And the little paddle slips into the ram, with that little handle to easily take it back out. You can see a spot of lube in the middle from use.

https://i.imgur.com/ZRy3kkV.jpg

You can see the result of the sizing better in person. The sizing is very minimal, and it is not even visible all the way around. Just where the bullets are larger than 401, which is only some of the not-so-round bullets.


Place bullet nose down
https://i.imgur.com/xzoyOTx.jpg
Ram reaches TDC
https://i.imgur.com/YbopUVZ.jpg
Lower ram. Smack the ejector knob.
https://i.imgur.com/ZVxHnXr.jpg

I also made a base-sizer just by drilling and sanding a hole in a 1/8" thick piece of steel. It works fine, tapping or pressing a bullet in. But when I got round to figuring out how to attach it to the press, I discovered I could just use the mak expander die!

[gloob]

I finally got to test my 401 bullets. I shot some unchecked bullets with just tumble lube. Some "greaseballs" that had the entire lube groove filled in with beeswax and motor oil. And I shot some checked bullets, mostly with just tumbled once, before checking/sizing.

Tumble lube bullets were the worst of them. They left patches of pretty thick fouling in both 40 and 10mm. Not full length layer of lead, but clearly not good. The greaseballs worked obviously better, but still a bit more fouling than MBC. MBC bullets are much harder than my bullets. Mine might be too soft for 40 cal.

My checked bullets with 9 thous roof flashing worked great. They cleaned the fouling out of the bores, just like jacketed bullets. Accuracy was good out to 50 yards, at least. Couple caveats. One of my guns has a groove size that is evidently larger than my sizer. Even my checked bullets left some fouling in the grooves. But even jacketed bullets did not clean out that lead.

After realizing how improper seating left some of the checks barely clinging on, I fixed most of them. But I went ahead and loaded up about 25 of them, just to see what happened. I found 9 detached checks, all from 5 to 15 feet away. They are obviously from the ones that weren't seated flush enough.

https://i.imgur.com/1DMue6y.jpg


I also made a new base-sizing die. My mak die only just touched the bases, leaving them about 401. My new die takes them down to 395 or so. I found the gas checks seat a few thous flusher when using my new die. And you don't have to push to get the check on. Just touch the bullets into the check, and it fits good enough to hold the check as you put it into the sizer.


https://i.imgur.com/JAdeu8t.jpg

place bullet in
[Imgur](https://i.imgur.com/JiCu1rj.jpg)
lift to TDC
[Imgur](https://i.imgur.com/4aXUk3t.jpg)
lower ram, and the bullet autoejects, using the primer arm.
[Imgur](https://i.imgur.com/8Ap4TUn.jpg)
https://i.imgur.com/Wa37CAu.jpg

I screwed up my measurements, and I had to glue a brass slug into the primer cup to get it to eject the bullet.


Edit: I also discovered that the checks were going on consistently nose-first with the hard MBC bullets, but consistently bad, like Larry warned of. There was a large air gap between the bullet and check. These 18 BHN bullets appear to take checks better sizing base-first. Even after base-sizing, I had to push on the nose with a rod, to get them to seat well when going nose first. I bet that could be sorted with yet a smaller base-sizing die.

I also found the checks were going on near flat to slightly concave when crimping nose-first on these hard bullets. Pulling the checks off, there was a rim of lead sticking up around the entire rim of the bullet, contributing to this effect. Base-first, the checks were convexed, but if I pressed hard on the back of the check to "remove the air," they also become slightly concaved, due to that rim of hard lead.

When seated good (for me, so far) the length of the bullet grows by the thickness of my check plus 20 thous. The badly seated ones can grow by the thickness of the check plus maybe 60 thous. This is the same with my super soft bullets and the MBC (the softer ones are just more easy and automatic to seat nose-first to +20). Maybe thinner or better checks can be seated even flusher than +20.

I'm still a noob at this, but my favorite way to do this so far with my fat checks is using soft bullets, base size the bullets, add check, then size nose-first. My checks seat almost as flush as so-far possible this way; they shoot great; and they look the best, with perfectly flat and perpendicular checks.

My die won't make soda can checks. A bigger button would probably help. Or maybe my die is too soft/dull or too loose in the tolerances. I might be shopping for a 6 cavity TL groove mold. My bullets seem way softer than anything for sale. And pouring two bullets at a time just doesn't do it for me, other than in a pinch.

edit:
I tried sizing the bases of these hard MBC bullets down to 390. It works ok, but even if I use my 395 die, first, this leaves a huge flange of lead sticking out the side of the bullet. If I size the bases extra high, that leaves some space for this lead to fold into, when crimping nose first, and the flange adds resistance in the sizing die, even if the bullets were already sized. So it might work ok if I make a new die. The lead flange kinda messes up the looks a little, because the flange breaks off in some spots rather than filling back in. But the checks come out flush and flat, nose-first.

[gloob]

My apologies to the OP for taking over the thread. I have tweaked my "base-sizing" die a bit with a more progressive taper and a high polish, and I think the results are quite good and consistent, now.

I tapped the die for screws, so I can easily play with the dimensions without worrying too much about going too far. I can also use different inserts for different bullets or check thicknesses, or size down in steps. Here are some of the hard 18 BHN bullets that were run through the base sizer. The rim that pushes out of the base when you squeeze the check on an unsized hard bullet barely occurs when base-sizing with my die. And by setting the press to slightly "oversmush" the bullets, it somewhat flattens out what little rim occurs.

The flange that I was getting out the side of the bullet is pretty much gone, too, just from better tapering and polishing.

The OD of the sized portion is 388-390, well below anything you can do with a normal sizing die without destroying your bullet, but leaving a decent amount of lead left to be displaced/swaged by the check.
https://i.imgur.com/grgiHxB.jpg


As you can see, I am now getting the checks on there more flush. Length of this bullet grew by less than 17 thousandths, including the ~9.5 thou thickness of the check, itself. Sized nose-first with no rod/pressure on the bullet. And the best part is the consistency...

https://i.imgur.com/Mw6jxVW.jpg
https://i.imgur.com/pUKz3VW.jpg


... They all measure that. This entire lot of GC'd bullets varies in OAL by only 2 thousandths of an inch extreme spread, just run through the sizing die nose first. That's the same variation in OAL of the bullets before adding the checks.

https://i.imgur.com/khgWtX6.jpg

[northernlead]

Just what I wanted to here.

[Soundguy]

Neat.

[gloob]

Thanks. I guess I'll add some new data for those interested.

I made another insert for 358 bullets. I'll probably post some pics, soon. But here's what I found.

It took two tries to get it right. My first one only sized the base to 350, because that was the size of my closest drill bit. I got a bit of variation when crimping them on, unless I pressed on the nose with a rod in the sizing die.

Second try, I went down a drill then opened it out. I ended up at 346. Results appear to be just as good, now, as with the 40. At least regarding flush-ness and consistency. The checks end up very slightly concaved, though.

So with the 40 cal, I ended up at 12 thous under bullet size. And on the 358, I am also pretty happy at 12 thous under. Same thickness of checks, about 9.5 thous.

[gloob]

358 bullets with 9.5 thous checks.
https://i.imgur.com/CiE4EQr.jpg

Here's a better angle where you can see the slight concave check base. The two on top are already base-sized. You can maybe see the actual base of the bullet is very slightly concaved by the displaced lead.

https://i.imgur.com/CiOasFq.jpg

These checks add ~18.5 thous to the OAL of these 12 BHN bullets, consistently to a thous or so. About 2 thous more length than the 40 cal checks, maybe due to being taller and displacing more lead.

I needed to use a good fitting top punch to get these fine-pointed bullets into the base-sizer. I converted my Mak seater die into a universal top punch.
https://i.imgur.com/XiRwmtX.jpg

I am posting a new thread on this, in Reloading Equipment.

edit: here are some mixed bullets, 4 before base-sizing, 4 after sizing the base down to 345-346.

https://i.imgur.com/2lPIaUc.jpg

The base-sizing adds a step, but it's pretty easy to execute once the dies are dialed in. Lube builds up and makes the primer arm stick in the die, so after ejecting the bullet the primer arm is sitting up in the die, forming a flat surface. Just place the bullet roughly over the hole in the die, and it will sit straight with the top of the primer arm supporting it there, so no worries about the bullet tilting or falling over while raising the ram. The top punch will easily catch and guide the nose of the bullet, and the bevel on the bullet base will guide it into the mouth of the base sizing die. Everything stays straight. No hiccups or malformed bullets with a decent top punch. This step goes fast and smooth!

[pt4u2nv]

Been awhile since I have been on here but I have many PBGC dies that I bought from Pat Marlin and they have worked flawlessly . Nobody has mentioned him that I saw on this thread . Is he still around ? Nobody buying from him ? Whats up ?

I use his checkmaker for 9mm, 10MM, 40 , 45, 38, 357, 44 Mag ,357 Sig and they have worked great . I also PC all my boolits with no lube and barrels are very clean when i finish

[Larry Gibson]

Guess I should have given Pat credit as it's one of his GC makers I use to make PB 45 cal GC's.......my apologies to Pat. I also have one of his regular GC makers which I make 35 cal GCs with.

[TD1886]

Here's what I do and have been doing it for decades. I make my modified version of what the call a freechecker. I make thick washers that fit inside the nut that retains the H & I died in Lyman and RCBS Luber/Sizers. I make those washers for each caliber I'm going to freecheck. I then cut a small recess in the base of that thick washer to hole the aluminum disc that will become my gascheck. The purpose if this washer is to guede the bullet straight into the sizing die. The only thing I do to the H & I die is to radius it's open more and polish it up with good. This aids in the transition of the aluminum discs and the bullet entering the die. You have to make a discs cutter to the correct diameter. So here is how it works: You take the thick washer, put a discs on that bottem recess cut for it, and it was stay there from the little lube that area gathers, place the washer with the discs in it into the inside of the die nut. Next place the bullet to be sized, lubed, and gaschecked gently into the washer and then lube/sizer as normal and when you eject it you have a sized/lubed gaschecked (in this case "freechecked" bullet) bullet. No having to size the shank area of the bullet down. If the discs are made of soda cans they can withstand up to 2100 fps. Lot simplers making them and using them than explaining them. Like I said l've been using them for 20 years.