Bevel base versus gas check and pressure?

[jaycocreek]

Never claimed to be a cast genius or even close.I am wanting to use(try) RL-10X with a 420/425 cast bullet(instead of RL-7) and found some interesting pressure data today where a 405 grain bevel based Oregon trail gets more velocity with less powder and less pressure than a gas checked 405 grain from Cast Performance.

Why?

Edtited to ad the link to the pressure data I referred to above..

http://www.realguns.com/archives/117.htm

Thanks..Jayco

[Larry Gibson]

The author gives the reason; "COL, crimp type and pressure, case thickness, bullet construction all have a marked effect on pressure."

Pressure drives the train or more precisely the time/pressure curve drives the velocity train. The author does not show the time/pressure curves measured by the M43 Oehler. Having used one fairly extensively this 1 1/2 years I would say the reason for the higher velocity is one of bearing surface, different alloy, sized diameter and of course the one is GC'd. The GC in particular offers a better gas seal which gives more resistance. The non GC'd bullet slips down the bore easier so it takes less pressure to drive it faster. Also the GC'd bullet was a cast Performance bullet which was a couple thousanths larger than the other bullet. Hence the higher peak pressure(?) and lower velocity of the GC'd bullet. Now with that in mind the author also doesn't mention the test conditions; thus we don't really know whether the loads were all tested on the same day under the same conditions. I've found when using a specific "lot" of M118SB 7.62 ammunition when fired out of the same rifle can give several thousand psi variation. That is why ballistic labs go to great lengths (or at least they are thought to) to maintain the same 'conditions" for testing.

Larry Gibson

[jaycocreek]

Damn..:mrgreen:

Thank you for such a detailed explanatory post.

My next dumb question would be that I was under the understanding without a gas check that over around 1600 fps would lead to leading.Is this true and in the case of Oregon Trails fairly hard bullets?

While Cast Performance advertises there bullets are sized to .459 it appears there really not and probably mass produced giving the error in diameter.They shoot fine out of my BFR in 45-70(or the few I have tried) but yet the .460 BTB bullets are semi forced into the chamber with a feel as they slide in.

Somewhat confused but thank you very much..

Jayco

[Bret4207]

Damn..:mrgreen:

Thank you for such a detailed explanatory post.

My next dumb question would be that I was under the understanding without a gas check that over around 1600 fps would lead to leading.Is this true and in the case of Oregon Trails fairly hard bullets?It all depends on gun, load, bore condition, temp, lube, alloy, boolit design and probably 100 other things. In very general terms gas checks make good, accurate, lead free shooting easier, especially at speeds over 14-1600 fps.

While Cast Performance advertises there bullets are sized to .459 it appears there really not and probably mass produced giving the error in diameter.They shoot fine out of my BFR in 45-70(or the few I have tried) but yet the .460 BTB bullets are semi forced into the chamber with a feel as they slide in.

Somewhat confused but thank you very much..


Jayco

Can't speak to the size issue without a mic in hand. Even a sizer die marked .459 may not size that diameter.

[44man]

Can't speak to the size issue without a mic in hand. Even a sizer die marked .459 may not size that diameter.
I found that out with a Lee die for my BFR. I never bothered to check a sized boolit when I bought the die. The gun just shot too good. I found it was making my boolits .458" so I lapped it out but made a turn or two too much and made it .4593.
BFR throats will run about .4592" with a groove to groove of .458".
I have not seen any difference in accuracy but it makes me feel better! :drinks:
Jayco, if you want to make the BFR shine, use SR4759 powder and a Fed 155 LP mag primer. I would say somewhere between 27 and 29 gr with a 405 gr boolit will work. Put a tuft of Dacron over the powder for even more accuracy. You can approach one hole at 50 yards.
The gun will shoot anything from 300 to 420 gr boolits but I have not tried heavier because there is no need to.

[jaycocreek]

44 Man

I have had great luck using the same loads I use in my Guide Gun in the BFR.I use RL-7/Starline and a CCI#34(Mag) primer..No unburnt powder and great velocity per pressure..

The 420 Cast performance(46 grains) shoots 1850 fps in the Guide Gun in 65-70 degree temps and at 39 degree's in the 7.5" BFR it hit 1560 fps while the Beartooth 525 grain(37 grains) is 1515 fps(65-70 degree's) in the Guide Gun hit 1300 fps in the 7.5" BFR again at 39 degree's.

I could not be happier with both these loads.I have not shot jacketed in the BFR yet and don't know if I ever will?

This is at 25-30 yards standing with the BFR and the 420 grain loads standing free hand with know rest.

http://img.photobucket.com/albums/v652/jaycocreek/04-03-08_1545.jpg

I luv's my BFR and am going to go shoot a few in a couple minutes.Thanks for the replies.

Jayco

[44man]

44 Man

I have had great luck using the same loads I use in my Guide Gun in the BFR.I use RL-7/Starline and a CCI#34(Mag) primer..No unburnt powder and great velocity per pressure..

The 420 Cast performance(46 grains) shoots 1850 fps in the Guide Gun in 65-70 degree temps and at 39 degree's in the 7.5" BFR it hit 1560 fps while the Beartooth 525 grain(37 grains) is 1515 fps(65-70 degree's) in the Guide Gun hit 1300 fps in the 7.5" BFR again at 39 degree's.

I could not be happier with both these loads.I have not shot jacketed in the BFR yet and don't know if I ever will?

This is at 25-30 yards standing with the BFR and the 420 grain loads standing free hand with know rest.

http://img.photobucket.com/albums/v652/jaycocreek/04-03-08_1545.jpg

I luv's my BFR and am going to go shoot a few in a couple minutes.Thanks for the replies.

Jayco
GREAT off hand shooting! :Fire:
But I tried that powder and 4759 beats it. As good as you shoot. I don't know if you will see a difference at close range.
I shoot mine no less then 50 yards and all the way to 500 meters. That is when you will really see what a powder change will do.
The BFR is just the best and I wish I could buy more.