How much increase in pressure ?

[Johnch]

I have been playing with a non factory 308 barrel for a Savage rifle
Not sure who made or chambered it
Not even close to any factory conture I have seen
Had to open the barrel channel on the stock for it to fit

It has a super smooth .308 bore
But the neck area is oversized
A .316 boolit just slides into a fired case
So I am loading .314 boolits for it

Current loads are light , mainly for plinking
Are shooting great

But I am thinking of using this rifle for deer this fall
So I am wondering how much will the pressure increase
From shooting a .314 boolit ( 50/50 WW & Pure )
Hope to get 1800 - 2000 FPS and don't realy care if I get some leading

Your thoughts ?

Thanks
John

[Larry Gibson]

John

Not thoughts but measured facts; I conducted an extensive test to determine the answer to your question some time back. I pressure test cast bullets (311466) of .308, .309, .310, .311, .312 and .314 in my .308W Palma rifle using a high psi (42,500 psi) load of AA4350 with a velocity of 2600+ fps.

While there was a slight increase of the rate of pressure rise as the diameter increased there was no measureable increase in peak psi or the MAP.

The cast bullet is sized down to groove/bore dimensions in the 1st length of travel. This occurs early in the time/pressure curve when the psi is still low and rising. After the larger diameter cast bullets are swaged down they offer the same resistence as the smaller diameter cast bullets during the rest of the barrel travel (all but one bearing surface of travel). The psi then levels out and was the same for all the bullets except the .308 diameter as it was .001" under diameter for the .309 groove diameter barrel.

Larry Gibson

[wmitty]

Larry

Was there a significant decrease in accuracy as the initial diameter was increased? If not, it would seem that using the largest diameter the throat will allow would reduce working of the case neck. Was the chamber neck dimension intentionally made oversize or were necks turned thinner to allow the larger diameter slugs?

[mroliver77]

John you could use 30-06 brass to form .308 and they will have thick necks. Did you ,make a slug of the throat?

Wait! Where are you using a .308 for deer?
Jay

[Johnch]

Larry

Was there a significant decrease in accuracy as the initial diameter was If not, it would seem that using the largest diameter the throat will allow would reduce working of the case neck. increased?

In my case accuracy was the reason I went to a larger boolit
And it sure helped




John you could use 30-06 brass to form .308 and they will have thick necks. Did you ,make a slug of the throat?

Wait! Where are you using a .308 for deer?
Jay

No throat slug .....yeat
But with the large base boolits I went from 6-9" at 100 yds
To 2" or less

BTW I have a place I can hunt outside of Manistee Mi



Also THANK YOU Larry for the tested info
As I am not interested in blowing up a rifle

John

[44man]

Larry is correct as usual.
Now another worry is about the boolit choice. Will making them so small at the rifling wipe out lube grooves?

[Larry Gibson]

Larry

Was there a significant decrease in accuracy as the initial diameter was increased? If not, it would seem that using the largest diameter the throat will allow would reduce working of the case neck. Was the chamber neck dimension intentionally made oversize or were necks turned thinner to allow the larger diameter slugs?

Ther was no observable (10 shot groups) difference in accuracy with the .310 & .311 sized bullets. The .308, .309 gave less accuracy to a greater degree than did the .312 & .314 sized bullets. My conjecture with oversized bullets concludes is a "point of no return" to using oversize bullets. I have found this to be the case in rifles and handguns. It obviously takes a bit more psi to size the over sized bullet into the throat/barrel for the 1st bearing length of bullet travel. That added rsistance can cause the back part of the bullet to obturate to an even larger size and then it has to get sized down again. This can created imbalances in the bullet and the base can be off square to the bore axis as it is sized down. Those are probably small imperfections created by the bullet obturating and then sizing down again but those imperfections lead to inaccuracy.

I would suggest a .311 sizing for that barrel even with the larger chamber neck. I have had many .30 cal rifles with that large a chamber neck and .311 sizing of cast bullets almost always proved best for a .308 - .309 groove diameter barrel.

Larry Gibson

[pdawg_shooter]

Larry, I sure wish I had your toys!

[Larry Gibson]

pdawg shooter

Took me a long time to get them. I don't think the equipment I use is for everyone. Shooting, reloading and casting bullets has always been a serious avocation for me and now that I am retired it's what I "do". I think most serious reloaders can get by very well with a good chronograph if they learn how pressures relate to velocities with similar componants. Not exact by any means and one must always watch for the usual pressure signs and always use reliable loading manuals as a source of loads, especially the maximum ones. I, like many, went along using reliable data, the usual signs, CHE and PRE and now Quickload and only managed to get into trouble a few times. Those were all my own fault BTW. The addition of the M43 Oehler has been a long dream of mine and when I got a sizeable bonus the wife said "get that danged machine you always talk about".....so I did, bless her heart.

The M43 Oehler is a wonderful machine allowing me to actually measure the pressures of my loads and compare them to factory ammunition pressures (measured myself, not taken out of books, magazines, etc.). I also have SAAMI's data for reference. The use of the M43 requires the loads to be fired to be measured. It is a real PITA to have to set up and take down at the range all the time, although if one is careful and methodical the results are consistent. I am working on setting up a permenant test range in my RV garage. It will have a bench, an external sound suppressor, the velocity screens and a Bullet Bunker trap. That way I can control the conditions and keep them constant just like in a real ballistic lab. Of course the various conditions are entered into the program at the range but having the equipment always set up and ready to go will be much nicer and I'll probably test a lot more that way. Range in the RV garage will be short (10 meters from muzzle to target on the Bullet Bunker) so accuracy testing will still need to be done at the rifle range. I have a 50, 100, 200 and 300 yard range locally for that or I have a lot of square miles of BLM to go set up on just a mile from my house so I can shoot as close or as far as I want. Already knowing the velocity and pressures will then let me just concentrate on accuracy. Life is good......

Larry Gibson

[pdawg_shooter]

Another 4 years till I can retire. Then I can play all I want. Out here in western Kansas calm days are hard to come by. And when them come it always seem like it is on a work day. I have rifles in my safe that haven't been out in over a year now. I have stacks of ammo trays with loads to test. Well, someday, if I last that long!

[44man]

Larry, do you have ideas for a suppressor? I tried all kinds of things in my woods. A huge baffle box filled with fiber glass, barrels end to end with tires and filler.
Some guns I fired through them had a back pressure that blew my hat off! :coffeecom
Noise was still there.

[Larry Gibson]

The tires and filler around the tires works but you also need a second and probably a third barrier boxing in the tires. Also need a smaller hole than the rim diameter to put the muzzle in. It should be just small enough to so the barrel doesn't bang it and you can aim. A verticle oblong hole works best. 3/4 - 1" plywood works works best front and back and also in between the tires for max suppresion. That will encapsillate the muzzle blast but keep in mind it has to vent some where and out the front hole and the back hole arshould be the only place. The smaller the hole in back the less you'll get your hat blown off. Of course eye protenction is always a must. The holes through all should be the same size with the back one as small as practical. A local fellow caster is with a professional back ground in sound suppression is helping my build mine.

A suppressor only suppresses the muzzle balst so there are two things it won't suppress; 1st, a revolver with just the muzzle in the suppressor will not encapsulate the blast from the barrel cylinder gap. Care must be used with revolvers because blast back off the face of the suppressor will happen. 2nd is if the bullets are tran-sonic there will be ballistic crack out the front end. How loud the crack is depends on how big the bullet is and the velocity. Keeping the bullet trap close also minimizes that sound duration. My range will be short enough that I may actually "tunnel" the whole distance from the suppressor to the trap except for smal spaces for the chronograph sceens. None the less ear protection for the shooter at least is still good to use with revolvers and tran-sonic loads.

The suppressor can make shooting more pleasant but it's primary purpose in my use is to suppress the muzzle blast sound so the neighbors don't get excited.

Larry Gibson

[pdawg_shooter]

I use a truck muffler wrapped in carpet scraps. It is 48" long, 10" in diameter with 5" inlet and outlet. Bought it used (barely) for $25. Works for me anyway.

[subsonic]

[smilie=s:[smilie=s:My suppressors just screw on the barrel?

Are those legal in WV, Jim?

Of course they don't work on 99.9% of revolvers because of the gap...

[303Guy]

That added resistance can cause the back part of the bullet to obturate to an even larger size and then it has to get sized down again.This can cause trailing edge damage as well.

[BAGTIC]

Amazing isn't it how rifles come with built in bullet sizers?

[tomme boy]

Look for Federal brass. It is always thicker for the 308. My 308 wants the Federal brass.

[303Guy]

Another 4 years till I can retire.Heck, I have to work till I die! :groner: Mind you, that's still a long way off - I'm only sixty.

And to Larry, :drinks: thanks for all that work.

[pdawg_shooter]

[QUOTE=mroliver77;2249143]John you could use 30-06 brass to form .308 and they will have thick necks. Did you ,make a slug of the throat?

Wait! Where are you using a .308 for deer?

Use on all the time out here, along with a 25-06, 30-30, 30-06 303 Brit, 45-70 and even my .458Win.

[Johnch]

[QUOTE=mroliver77;2249143]John you could use 30-06 brass to form .308 and they will have thick necks. Did you ,make a slug of the throat?

Wait! Where are you using a .308 for deer?

Use on all the time out here, along with a 25-06, 30-30, 30-06 303 Brit, 45-70 and even my .458Win.

The reason he ask
Is I live in Ohio, a State that dosn't allow a centerfire rifle to be used for deer hunting
Handguns , Shotguns with slugs or a Muzzel loader


But I head up to Michigan many years
Errr ...I also use crop damage deer permits most years
With those permits , all firearms are leagal
Even 2 AM spotlighting

John

[pdawg_shooter]

Amazing isn't it how rifles come with built in bullet sizers?

Yep, and some people worry about loading a out of round bullet. Unless you bore is oval shaped I tend to think the bullet will exit round. You kick the bullet in the butt with up to 60,000 psi. (for paper patched bullets) shove them down a 16 to 30" sizing die and expect them to exit still out of round? Don't think so.