How did I get an extra 150fps? 300Wby

[Bart B]

Bart I know your sole purpose in life is to prove others wrong, but last I checked a standard 30 cal barrel was .300 on the lands and .308" on the grooves, since the lands start the engraving how does this occur between .307-.309", do tell oh wise one!

First off, check out the chamber and bullet specs for the .300 Wby Mag at:

http://www.saami.org/PubResources/CC_Drawings/Rifle/300 Weatherby Magnum.pdf

and you'll see the SAAMI specs for the chamber throat diameter is .3084" to .3094". Its leade angle is 1 deg. 2 min. (that'll vary as much as 20% across the chamber reamers) and tapers down to the groove diameter of .3080" to .3090". Finally down to the bore diameter of .3005" to .3015".

Bullet diameter specs range from .3053" to .3083" so I can imagine the low resistance and peak pressure if a .3053" diameter bullets shot through a barrel with a .3015" bore diameter. The opposite's the case with maximum diameter bullets in a minimum diameter bore and groove barrel. And differences in ogive radius also have an effect.

Other variables is the bore cross sectional area where the grooves can vary in width as well as numbers. The bore cross sectional area has a SAMMI spec minimum of .0736" square inches but it can be a lot bigger and that'll mean lower peak pressures for a given load.

Barrels made to SAAMI specs will have these area's dimensions somewhere in the range listed above. But all 30 caliber barrels and .300 Wby Mag chamber reamers are not made to SAAMI specs.

Engraving starts where the leade first contacts the bullet. Get your calculator out then figure out where the leade starts touching the jacket of several bullets with different diameters and ogive dimensions. Or coat a bunch of bullets with machinists layout dye, gently push them into the bore, carefully remove them then measure their diameter where the barrel marks them. Start with Sierra's HPMK bullets some of which are .3084" diameter. You may already be able to figure out where a .3090" diameter inch 30 caliber bullet will first start being engraved in a .3094" diameter throat and a 1 degree leade angle. Then you'll see where first contact between bullet and barrel starts.

It doesn't take but a few ten-thousandths dimensional or a few minutes of angle in the physical properties of chambers and bullets to change the diameter a few thousandths inch on the bullet where the barrel first touches it.

 

[backwoods83]

Get up off your ******* ***, do some real testing instead of your automated computer ********, then you might realize that the peak pressure is going to occur after the bullet is fully engraved anyway. Just like your ******** graph, which almost proves my point, since it shows about a whopping 400psi change for every .025", with a high spike when contact is made. Also I know for fact that when seating a bullet out further, even if its chasing the lands, at some point the charge will have to be raised to maintain velocity. This crap about like the ******** stories of you and your buddies shooting <2" groups a 1k with a 308, those have to be some kind of world records, so where the hell are they at??? As for the new SAAMI 300wby reamer, we just got one about two and a half months ago and the leade is now 1*-30min. And I don't speak out of my ***, I actually shoot 300wbys.

 

[Bart B]

Backwoods, go gulp down some depressants and stop misquoting me. I've made real measurements for decades and seen the realities. You need to do the same. So, you need to stop making assumptions that are far removed from realities.

 

[backwoods83]

Yes Sir Bart, I'll get right on it, just because I am so overwhelmed by your intelligence.

 

[Bart B]

Yes Sir Bart, I'll get right on it, just because I am so overwhelmed by your intelligence.

Whatever lets you sleep at night.....

 

[BountyHunter]

This may be a stupid question, but on the surface it's perplexing for a simpleton like me.
Here's the data, an ideas what may be causing this?

300 Weatherby Accumark, same gun, same brass/primers, same powder load, same OAL:

168 gr Berger Classic Hunter (BC .496) = 3125fps

168 gr Nosler BT (BC .490) = 3278fps

I have a theory but tell me what you think.

Length of bearing surface and variances in bullet diameters.

Minute but those differences can make a huge difference.

 

[TOM H]

Get up off your ******* ***, do some real testing instead of your automated computer ********, then you might realize that the peak pressure is going to occur after the bullet is fully engraved anyway. Just like your ******** graph, which almost proves my point, since it shows about a whopping 400psi change for every .025", with a high spike when contact is made. Also I know for fact that when seating a bullet out further, even if its chasing the lands, at some point the charge will have to be raised to maintain velocity. This crap about like the ******** stories of you and your buddies shooting <2" groups a 1k with a 308, those have to be some kind of world records, so where the hell are they at??? As for the new SAAMI 300wby reamer, we just got one about two and a half months ago and the leade is now 1*-30min. And I don't speak out of my ***, I actually shoot 300wbys.

Didn't you know that Bart B was special ops guy according to his post.

Bart B.
Firearm Aficionado

Join Date: Mar 2009
Location: Loveland, CO
Posts: 608


Quote:
I thought you were on an Army rifle team?I never knew the SEAL,s "came after" anyone from other branches of service and you must be very special for them to have been after you since they had lots of volunteers to choose from.

I was on the USN Rifle Team. The SEAL Team bosses asked the USN Small Arms Marksmanship Program to give them the names of a handful of their top long range competitors and they did just that. Was first sought to go to their training facility at Hawthorne, NV as a sniper. Later sought to go there as an instructor, but my detailer learned most students went "in country" along with their instructor, so he didn't release me.

I was a chief instructor in San Diego at the time managing a group of people training ships crews in large arms marksmanship. That's the skills and knowledge needed to shoot shipboard guns and guided missiles effectively as opposed to small arms marksmanship involving rifles and pistols shooting bullets effectively.

Note that 50 BMG bullets will be deflected less going through (plexi)glass enroute to their targets. They're a better choice when you gotta drive one through frangible obstacles into their designated impact zone.

you have to understand Bart B is an enlisted man. With Bart B being one of the top navy long range competitors you would think with that kind of know reputation(leadership skills)when he retire he would of been much sough after for coach/shooter or team captain for the Palma team.

Something isn't right

 

[Edd]

I thought he was a shooter on a Palma team.

 

[TOM H]

I thought he was a shooter on a Palma team.

Bart B spend 20yr in the Navy shooting that's how he got started. He was just a Palma team member and he had coaches like every other team member after he retired.

Bart B can tell you more about his navy shooting and what he won and score even picture since he was top navy shooter. I'm sure Bart B can post when he was selected for the Palma team as they do write up on each member and he can post that also.

 

[Lefty7mmstw]

This may be a stupid question, but on the surface it's perplexing for a simpleton like me.
Here's the data, an ideas what may be causing this?

300 Weatherby Accumark, same gun, same brass/primers, same powder load, same OAL:

168 gr Berger Classic Hunter (BC .496) = 3125fps

168 gr Nosler BT (BC .490) = 3278fps

I have a theory but tell me what you think.

You are getting more speed because the nosler is creating higher pressure than the Berger.
I highly doubt it is run to the rifling though, but bullet construction. Nosler pills tend to have a pretty stiff base (the old ones before the bt were called "solid base") and often create more pressure than sierra in my 7stw. I suspect it is the same for you with your 30roy.