Gas checks and shank dimensions

[Wm Cook]

I’m confused about gas checks on the molds I'm working with.

I’ve read most every thread about gas checks on the forum and I learned about annealing, flaring the check with a carriage bolt, custom gas check dies, "small" ball peen hammers to start the check, .011 versus .014 thick material, expanding the check so it seats properly, starting the check on the bullet shank prior to sizing (I'm using a Lyman 450), after market hardware to start the gas check and even the super glue idea. But what I have on the bench is not adding up. There's a difference in the shank dimensions that I didn't expect and the checks I have work great on some molds and not at all on others.

I’m working with four different molds that I had hoped to use on two new 7.62 rifles. From small to large the molds are the MP 314-140SH, Lee C-155-2R, NOE 312-165-FN-H3 and the Lyman 311299. The rifles are both 7.62x39 Ruger’s. One is the Ruger Ranch bolt gun and the other is their Mini 30. So far most all the molds look doable with the exception of the 200 grain in the Mini 30. Kissing the lands they all have the gas check in the neck. All of the heavy stuff will be subsonic. The Ruger bolt gun bore is .3098 and the Mini 30 is .3100. Alloy used is 90-5-5.

Initially all will be shot over a chronograph and through a suppressor so the check has to stay with the bullet. The Hornady and Lyman checks work fine on the NOE and the Lyman. The same checks that fit the NOE and the Lyman perfectly will either not seat squarely on the MP and the Lee or if they do they spin.

To make things simple I’ll focus on the Lee 155.

• The NOE 312-165-FN-H3 shank measurement nearest the body of the bullet measures .2857. Furthest from the bullet body (nearest sprue cut) the shank measures .2854. Both the Hornady and the Lyman seat tight and square.
• The Lee C-155-2R shank nearest the body of the bullet measures .2889. Furthest from the body of the bullet (nearest the sprue cut) the shank measures .2887. Both the Hornady and the Lyman look to be not fully seated and about half of the check spin.

The MP mold leans in the same direction with the shank about the same size as the Lee. If I could flare the check I could get it over the base of the MP shank and if the check material was a couple thousands thicker I think it would grip the shank?

Is that why Pat Marlin sells one check maker for the .308 and another for the 7.62?

Unfortunately sending back the Lee is not an option. Lead time on everything is so crazy I would be waiting a long long time to receive a replacement. And if a custom gas check maker solves the issue I'll only have to wait 3 months. Using a thicker material for the check should tighten up the grip on the shank should it not?

So what I’m asking is can I buy myself out of a bind by buying Pat’s check making die using various thickness for the check material and if so should I buy the 7.62 or the .308. To me it almost looks like the inside dimension of the check is too small for the Lee and the MP. Thanks, Bill.

[Winger Ed.]

For subsonic, and somewhat above-- you shouldn't need a gas check, especially if you powder coast.

[danmat]

For subsonic, and somewhat above-- you shouldn't need a gas check, especially if you powder coast.

Did I miss something,What does this have to do with the ops question?

[Bloodman14]

The OP is shooting through a suppressor; that's the problem. The GC's need to stay attached to the base of the boolit. Wm, I would hit your local home improvement store, take a digital caliper with you, and mike some of the rolls of aluminum flashing. Get the thickest you can find. When the GC is formed, the metal will flow around the GC forming mandrel. The 'excess' metal will be contained by the die, and you will end up with a check that has thicker walls. The voice of experience.

[Winger Ed.]

Did I miss something,What does this have to do with the ops question?

On the outside chance he just might be interested in not making extra work, and expense for himself---- maybe a lot.

And that's before we get to the part about others maybe seeing a solution to a issue they may or may not ask about in the future.

[Bad Ass Wallace]

Well, I'm going to throw a spanner in the works. The Hornady gas checks that I use are "oversized" for the boolit.

32 cal (0.323") I am using for 8mm, 303 (0.316") and 7.62x39 (0.314")
7mm (0.284") for 270 winchester (0.277")
25 cal (0.257") for my 243 Winchester (.245")

No this may sound silly, but these Hornadys crimp on and stay put on the powder coated boolits.

[Wm Cook]

With some shanks at .2889 and some at .2885 having a gas check die and various material .011 to .016 should bring the problem under control. I ordered a gas check 30 cal die from Pat yesterday and I’ll give him the dimension I’m working with. Eventually I’ll find out there what the difference is between his 30 cal die and his 7.62x39 die.

None of this effort will go to waste since I’ll be shooting weights from 130 to 200 grain with velocities from 900 to 1,900. And being OCD I have an issue of expecting all bullets to go through the same hole. Ex-Benchrest competition shooter here. I switched to cast because there were more variables to control. To me gas checks is just another course I’m taking. And I know that I’ll come out of this with a broader knowledge of casting than I started with. Thanks for the support, Bill.

[popper]

I use hornady GCs in my 30 cal. Not a problem and I do PC most. it helps. There was a discussion here about GC coming off - non suppressed. A lot depended on alloy. Higher Sb and little tin seemed to be worst. Lino lost them, #2 didn't. I make an assumption - high Sb and HV (pressure) loads weaken/heats the base so it stretches - Cu friction more than Pb. Tin allows some expansion of the base. I've not lost one, best I can tell. A problem most haven't considered is the throat of the rifle/pistol. a sharp step may catch the edge of the GC and loosen it. Don't have a can but also don't GC subs when i do shoot them. Last GC mould I ordered I spec'd the shank smaller and haven't lost one yet (300 BO). If you PC, any residue in the can will dissolve with solvent. I have a linear comp on my BO pistol, shoot plain base and get slight lead buildup in it. I've also shot HV GCd from it and no strikes (KVA comp - kinda looks like a shower head). Standard shank is 284 so yours are large due to alloy and temp. I run 145gc @ 2k fps carbine and guess at 17-1800 from 10" pistol. I don't use tin but do add copper.
Your problem isn't the 1/2 thous difference but the larger shank. Hope the ideas help. My 308W carbine runs 2400 1 68gr PC, GC and ~MOA @ 200.

[Wm Cook]

Sorry popper, that was a typo on the numbers I last gave. The Lee shanks are .2859, NOE .2887. My theory is that the check material can be dialed in to get the checks to form a tight grip on the Lee 155’s and keep the check from spinning. And I agree that PC would move toward the same results.

PC’ing is a course I’ll be taking next semester. I’m still taking the required courses.

Lots of variables in this including bhn, build up on mold face or an assortment of operator error mistakes. .

[charlie b]

https://castbulletassoc.org/default.aspx

Have you joined yet?

Yes, lots more variables. And frustration. Just when I think I have a good, solid <MOA load I get a day where every group has a flier.

I have the .311 version of the NOE mold (XCB) and it works really well in my .308.

[Wm Cook]

Thanks for the direction. I Just joined this morning.

[popper]

Cookie, you can flare the GC with a NOE tool, ball bearing, etc and that does work, but extra work. You can use VHT (exaust manifold paint) on the mould shank to make it smaller - it will eventually wear off. Spray in a puddle on paper, brush on the shank area & cook mould 400F for an hour. Repeat.

[Wm Cook]

I’m thinking that I finished my course on gas checks today. Thanks for everyone’s help. I’d only give myself a “C-” grade but at least I passed. As you all know I’m working on my GED in casting.

Bringing four molds on line at the same time had its positives and negatives. The negative was that I hit a wall and was seeing stars for a couple days. The positive was that I could do a lot of comparison between the four molds and I learned how critical the shank dimensions are if you are using mass produced gas checks.

After the dust settled I finally figured out that two of the molds had shanks that measured about .003 larger than the other two. The Lee and the MP .312, .314 molds were casting about .288 and the two .311 NOE and .311 Lyman molds were dropping at about .285. Neither the Lyman nor Hornady checks cleared the oversize shanks of the MP and LEE. That was causing the crimps to seat crooked and loose.

There are a number of ways to work around that problem so I won’t belabor the point. But PC’ing, painting, expanding the check and a couple other ways could be used. The only word of caution I would offer is not to blindly enlarge the mold shank without measuring. In the case of the Lee the check was clearly spinning and first impression was that the shank was too small. Enlarging the shank would have made it worse not better. It was the damage done to the check going over the oversized Lee shank that was causing it to spin.

In my situation I followed Popper’s suggestion and flared the check ever so slightly. You only need a few thousands so you don’t have to mash it. Once that was done I sized and checked a couple dozen from each of the four molds and I had 100% success with tight square crimps.

I’m still going to go forward with the PatMarlins custom check die as a "just because". Just because reloading supplies are and probably will continue to be hard to come by for the next year or so. And second I think there’s advantages to having material thickness options that will secure the check even tighter onto the shank. Thanks, Bill.

PS. And while I was in a cloud of confusion I ordered an NOE 311-184-PB-J5. That ought to be fun to work as subsonic in the 7.62's. With only a .990 length it should keep the check in the neck and be able to fit both the Ruger Ranch and the Ruger Mini 30's magazine.