Pressure Question GC/PB

[TCLouis]

I am addressing this to Larry Gibson since he is the only one here that has pressure measuring equipment (that I know of).

Do you get any difference in pressure between gas checked and plain based boolits in the same loading?

[Larry Gibson]

That's a good question. I've not made that comparison. I could check my records but I hesitate to post any speculation based on comparing the pressure tests of different bullets probably conducted at different time/dates. The variables would be there and I'd get the usual raft of manure from the usual critics here.

However, if someone has a mould with different cavities that casts the same bullet for use with and without a GC I could conduct a test. All that's needed would be a quantity of each cast of the same alloy. I would size, GC the ones for GCs and lube them for the test. Fifty of each would be sufficient for sighters/foulers and 3 ten shot test strings of each. Any takers?

Are we talking rifle or handgun cartridges?

[mattw]

I would love to see that test with 30 cal and maybe a 357 or 41 mag. But, I do not have identical moulds other than the GC cut. I will be watching this thread.

[Gewehr-Guy]

I would be willing to supply some NOE 311299 PB, but the opposing GC bullets would be from a Lyman mould. Would they be close enough to get good data, or would the need to come from a combo mould?

[Larry Gibson]

Ideally they should be from the same mould which was either lathe cut via the same program or with the same cherry with one cavity having the GC shank opened up to full diameter......that perhaps should satisfy the critics. I would suggest the test using your bullets would be valid if the same bullet/different mould bullets were cast of the same alloy from the same pot, had the same bearing length, the same nose diameter and the GC bullet was within 3 gr of the PB bullet?

I can easily test the cast bullets any of these calibers; .224, 6mm, 25, 7mm, 30, 31, 8mm, 35 (35 Rem, 38 SPL or 357 Mag), 375, 44 and 45 (45 ACP, 45 Colt or 45-70).

[JonB_in_Glencoe]

I have a couple 41 cal. Ranch Dog molds (by Lee) CTL411-255-RF and the TL411-255-RF
If it matters? I use a aluminum GC with these, due to not being able to find 41 cal copper GCs that fit this design.

PS, I believe Ranch Dog cut/bored the GC shank to PB, using molds from the same batch from Lee.

[Larry Gibson]

Don't have a 41 caliber test barrel......sorry.

[Old Coot]

Larry,
Why would it not be feasible and simpler to just check the pressure of a bullet with the gas check and without. The bullets would be the same, from the same mold, and of the same weight, within slight variation, and one lacking the gas check. The check itself would not weigh much, and if they are loaded to velocities less than 1500 fps should not lead the barrel. If you use bullets cast with and without a gas check, the base of the plain based bullet would up the weight by 2 to 5gr. (?) . Just my guess on that. ANyway I look forward to the results. Brodie

[popper]

Can't imagine how there would be any difference. Added friction from GC might change the curve a tad. Same load density, same burn efficiency.

[Bazoo]

Tagged with interest.

[Time Killer]

Larry I have one that I believe you are very familiar with the NOE 310-165-FN-H3 (30XCB). Its a 2 banger one gas check one plain base. If it will work how would you like them cast. I can do soft lead + tin for fill out, 50/50 soft lead / wheel weight + tin for fill out, or Wheel weight + tin if needed for fill out. Air cooled or water dropped let me know your preference. It will take me a few days to cast them as I have a busy work week but I would be happy to help out for the test. I also have the NOE TL311-166-RF-AI4 and the NOE 311-137-RF-CA3 if one of them will be better.

[Rcmaveric]

Tagged to follow. Wondered this myself. Maybe try a 35 cal plain based bullet vs a 35 cal plain based with a plain based gas check.

Sent from my SM-G950U using Tapatalk

[Larry Gibson]

Time Killer

The 30 XCB, cast both PB and for a GC will work for me. TCLouis, the OP, didn't say whether he was inquiring about a rifle or handgun cartridge. If you can cast then of COWW + 2% tin alloy and air cool them it would be fine. With 100 of each I can test them over a classic Unique load of 10, 11 or 12 gr and over a bit more powerful load using H4895 and a Dacron filler.

With an additional 30 of each I could also test them in in a pistol cartridge using the 32 H&R Contender barrel?

[Larry Gibson]

Old Coot

I don't know if the results would be any different using a GC bullet with and without the GC(?). That remains to be seen. With the 30 XCB bullets from Time Killer I should be able to run at least a 10 shot test string of the GC XCBs w/o the GCs and get an idea?

[Time Killer]

Larry I am draining and cleaning my pot tonight. I may even have time to get them cast depending on what the missis has planned.

[osteodoc08]

My prediction is that the pressures will not show any statistical difference and within the realm of standard variance.

Great test.

Thank you for all involved especially Larry and Time Killer

[Treetop]

Subscribed. Results should be interesting. Semper Fi, Treetop

[Larry Gibson]

Time Killer

PM with address sent. No real hurry as the AC'd bullets need to age 2+ weeks anyway. Also will be out of the net hunting so I probably won't get the test done till next month.

[gwpercle]

My vote is ....little or no difference.

I have been wrong before so we shall see.
Gary

[mr surveyor]

my guess ....

with GC bullets, pressure increase will be 1-2% - velocity increase will be 1-2% - ES and SD will dramatically decrease - also (obviously) chance of leading will decrease.

But, since we're talking more about pressures, I stick by my guess that GC bullets will tend to show a 1-2% increase in pressure compared to similar plain base bullets.

Just my guess ....


jd

[Bazoo]

I think that gas checks would cause an increase in pressure. I expect the percentage of pressure increase to grow with the gas check load when it moves from a reduced load into a full charge load.

A gas check design bullet without check vs a plain base bullet of the same design I expect would be nearly identical, with the plain base bullet having a slight increase in pressure due to larger driving band surface.

Thank you Larry for the testing, and thanks for all those that will contribute bullets, time and knowledge to this. It is a furtherment of the understanding of our craft and hobby.

[mr surveyor]

I think that gas checks would cause an increase in pressure. I expect the percentage of pressure increase to grow with the gas check load when it moves from a reduced load into a full charge load.

A gas check design bullet without check vs a plain base bullet of the same design I expect would be nearly identical, with the plain base bullet having a slight increase in pressure due to larger driving band surface.

Thank you Larry for the testing, and thanks for all those that will contribute bullets, time and knowledge to this. It is a furtherment of the understanding of our craft and hobby.


Yep, that is exactly what it's all about!


jd

[FredBuddy]

Yesterday, I tested boolits from my new NOE 311-127-FN.

4 cavity, 2 PB and 2 GC.

All details of the load identical, except, of course,
one set with GC, other set with PB.

POI for GC was 2 inches higher than PB at
approx 50 yards.

Certainly NOT SCIENTIFIC, but an observation
that seems to fit in this thread.

[TCLouis]

Hopefully we will get some pressure and precision data out of Larry's gracious help.
Unlike others in my one attempt I found leaving the GC off lead to significant increase in group size.
That may well be a boolit to bore diameter issue also.
So many things can be hidden as to the real reason that one gets a certain result.

[Rcmaveric]

I wonder if different gas check materials and designs would change any thing. Like the hornady short copper cups compared to homemade taller aluminum/copper checks.

Sent from my SM-G950U using Tapatalk

[Paul105]

Ross Seyfried wrote an article titled "Ultimate Cast Handgun Bullets" in Oct of 1993. Among other things, he addressed the Pressure/Velocity of two cast bullets, one plain base and one gas checked. He had two identical 44 caliber, 305gr cast bullet molds cut, one plain base and one GC.

He had Hodgdon's laboratory test the loaded ammo which was 21.9gr H110, CCI 350, Fed cases, with the following results.

Gas Check -- 33,300 CUP, 1,383 fps
Plain Base -- 38,200 CUP, 1,346 fps

I double checked the results and yes, the GC load was faster at less pressure.

Would copy the results, but can't figure out how to work with PDF file article.


FWIW,

Paul

[Bazoo]

Paul, that is very interesting, thank you for posting.

[osteodoc08]

Ross Seyfried wrote an article titled "Ultimate Cast Handgun Bullets" in Oct of 1993. Among other things, he addressed the Pressure/Velocity of two cast bullets, one plain base and one gas checked. He had two identical 44 caliber, 305gr cast bullet molds cut, one plain base and one GC.

He had Hodgdon's laboratory test the loaded ammo which was 21.9gr H110, CCI 350, Fed cases, with the following results.

Gas Check -- 33,300 CUP, 1,383 fps
Plain Base -- 38,200 CUP, 1,346 fps

I double checked the results and yes, the GC load was faster at less pressure.

Would copy the results, but can't figure out how to work with PDF file article.


FWIW,

Paul


I’d love to see if Larry’s results reflect this as well. I guess the question is, why?

[TCLouis]

doc

OBTURATION?

[JonB_in_Glencoe]

Plain Base -- 38,200 CUP, 1,346 fps
That's a lot of pressure on a plain base boolit, I wonder what alloy he used...and what hardness?

[earlmck]

That's a lot of pressure on a plain base boolit, I wonder what alloy he used...and what hardness?

That Seyfried load is very similar (in fact a scosh less powder) to my full-power 44 mag load I use in my Redhawk, though my plain-based is a 280 grainer. Water-dropped ww's and I am not a good enough shot to detect a difference in accuracy between the 280 grain PB and my 300 grain GC boolits, so shoot the PB one in the revolver. A Rossi lever gets the GC boolit. Velocity somewhat north of 1300 fps from the revolver: shot a couple cow elk with the load but quit using it for elk because of failure to make exit except on a pure broad-side shot.

I'll be most interested in seeing Larry's results. Thanks for doing this fellows!

[.22-10-45]

I don't know about pressure but...I had Fred Leeth of Pioneer Products make a couple of nose-pour molds that are identical in shape & weight except for the gas-check shank. These are in .22 for my Hornet rifle. Now concerning pure accuracy..NOT velocity..the only difference between the gas-checked one & the plain-base was .3 of a grain of H4227..the gas checked requiring the "heaver" load.

[ddixie884]

Interesting..............

[Old Coot]

You all realize of course that a plain base bullet of the same design as one with a gas check will weigh more than the gas check bullet. Depending on the caliber it could weigh as much as eight grains more (for the plain base in say 45 or 50 cal. bullet). This could explain the rise in pressure for the same load in both plain base and gas check.

[Dieselhorses]

doc

OBTURATION?

I think that is the key element.

[Larry Gibson]

Got the 30 XCB bullets, GC and PB, in from Time Killer....they look real good. Will be 3+ weeks before I can test as a mule deer hunt with old friends is calling me away.......

I'll test them in the 30-30 cartridge at probably 1200 - 1400 fps with a faster powder such as Unique and at 1700 - 1800 fps with probably 2400.

Not sure what I'll use in the 32 H&R yet, still cogitating......

[GregLaROCHE]

While you’re at it, why not add a plain base powder coated to see how it compares ?

[osteodoc08]

Was reading through an old article written by Keith himself. He was discussing his favorite loads in a G&A article. His claim was GC were useless in Pistol bullets and raise pressures 3-5K and don’t allow the bullet tonobturate and fit.

[Larry Gibson]

Got the bullets sized and lubed and the GC put on the GC'd bullets. Going to test 8 shot strings (18 test strings) in 3 rifles; 30-30, 308W and 30-06. Will test 3 different powders in each rifle with each style of bullet; Unique, 2400 and RL7. That is 144 bullets of each; GC'd and PB'd with just enough bullets left over for sighters/foulers. Maybe that won't give a definitive answer (to some anyway) but it should give a very strong indication.

[osteodoc08]

Strong work Larry!

[Shuz]

I anxiously await your results! By the way, are you using Alliant 2400 or the Hercules 2400(hee hee)--Shuz

[Larry Gibson]

Test results posted in new thread.

[ulav8r]

http://castboolits.gunloads.com/showthread.php?369858-Pressure-Question-GC-vs-PB-(original-thread-by-TCLewis)-test-results&p=4482456#post4482456

Larry changed forums to post the results.