bullet base / pressure

jaegermister

do boat tail bullets give a different pressure than flat base bullets?

Tailgunner1954

No
Look at load data for the same manufacture & weight in both styles. If they (BT's) ran at a higher pressure, they would be listed separately.

MG1890

Possibly.

For a given weight, the BT bullet has less bearing length, hence potentially lower pressure.

Published load data can be deceiving.

charliemeyer007

I doubt there is much difference between the two designs pressure wise, but the boat tail bullets fly better.

nononsense

charliemeyer007,

quote:...but the boat tail bullets fly better.

You might not want to suggest this to the point blank benchrest shooting crowd, especially those who hold world records for smallest groups using FLAT-base bullets.

jaegermister,

There are several ways to answer this question and everyone will still yield more discussion until the physicists and photographers get together to perfect their techniques of actually recording the events as they actually happen.

I usually suggest reading a masterly tome:

"How Bullets Fly" to achieve the best understanding of everything you ever wanted to know about bullets in flight.

http://www.nennstiel-ruprecht.de/bullfly/

It can be a little daunting to get through but it will answer nearly every question you might have. Besides, there are some great photographs, graphs and GIFs to help with explanations.

Best.

Cheechako

Never say never, always avoid the use of the word always, the only thing certain is that nothing is certain.

"For a given weight, the BT bullet has less bearing length, hence potentially lower pressure."

Not necessarily. Do you know that the bearing surface of the 150 grain Cal .30 M2 Ball flat base bullet is almost identical to the 147 grain 7.62mm NATO M80 Ball boattail bullet?

"You might not want to suggest this to the point blank benchrest shooting crowd, especially those who hold world records for smallest groups using FLAT-base bullets."

Many point-blank Benchrest shooters have been using BT bullets for years, with success. Many mid-range Benchrest shooters have been using FB bullets for years, with success.

charliemeyer007

Ok so isn't the ballistic coefficient an measure of a bullets ability to maintain velocity - a rating of it's ability to fly. Every high BC bullet I have ever seen was a boat tail.

When you change bullet construction materials you are comparing apples and oranges. Solid copper bullets are longer for a given weight than a lead core copper jacket. Steel and tungsten cores will have their respective place.

Cheechako

Yes, BC is a measure of a bullet's ballistic efficiency. A high BC bullet retains velocity better, resists wind better, and will "fly better". It's also true that BT bullets generally have a higher BC than FB bullets of the same caliber and weight.

But there's a lot more to it than that. Up to mid-range (500-600 yards) there are more important qualities than BC. Accuracy, for example. That's why you will find both BT and FB bullets being used by accuracy shooters such as Benchresters. They shoot the bullet that gives them an accuracy edge and the resultant fake-wood trophies. Beyond mid-range (700 - 1000 yards), environmental factors play a bigger and bigger role and the benefits of high BC bullets overtake the higher accuracy of lower BC bullets.

There's no one bullet best for all yardages and conditions. You have to use what shoots best (but you already knew that).[:)]

charliemeyer007

Fortunately as an offhand shooter almost all bullets and firearms now shoot better than I can hold them or see the target/crosshairs.

jaegermister

thankyou all. From just a point of observation the pressure applied to the bullet base
would be vectored to the out side against the chamber and then the barrel more than applied to the bullet base, by the boat tail design? and taking the same logic would not a cupped base put
more pressure on the bullet than barrel?
I am in the process of loading some very long , ballitically efficient boat tail bullets
in 7mm , and they extend down almost into the powder.
of course I will stay within the recommended loads , but can I
assume 150 gr bt is the same as a 150gr flat base?

charliemeyer007

Yep, a lot of loading manual provide the same data for flat base or boat tail in the same weight. That's why you start at the starting load and work up while watching for signs of pressure.

My favorite bullet in 7mm is the 162 grain Hornady BT Match. The favorite load in my 7mm Rem Mag was a full case of H870 with the charge compressed by the bullet. T870 on the other hand is a case full to the bottom of the neck.

jaegermister

thankyou all for info. in appreciation i will leave you with one of my favorite and useful
reloads. the mouse load: sooner or later a mouse will get into your house, even with a cat (which may actually bring in a live mouse) , you need to take immediate action.
being in unfamiliar territory the mouse will seek cover under furniture or behind a
appliance, unable for you to reach him, but see him.
20 ga is my favorite but any will do. prime the case and insert a plastic soft wad like AA wad, no powder no crimp. it knocks the mouse out cold and does no damage to anything. a side by side with two triggers is best since you never know the mouse may charge!

Cheechako

quote:Originally posted by jaegermister. . .I am in the process of loading some very long , ballitically efficient boat tail bullets in 7mm , and they extend down almost into the powder.. . .

There are not a lot of High BC 7mm bullets to choose from so I am assuming you are talking about one in the 180 + grain neighborhood? If so, those bullets require a very fast rifling twist otherwise you'll just be wasting powder.

Just sayin'.