Boat Tail vs Flat base - same load data

Reloading equipment, methods, load data, powder and projectile information.

Boat Tail vs Flat base - same load data

Post by goldiexxxx » 20 Jun 2017, 5:15 pm

I was wondering if anyone can give some insight into this topic.
I have worked up a great load for my 308 consisting of the following:

40.6gr AR2208
Win Brass
Hornady 150gr BTSP Interlock
COL 2.755"

Now the other day, I purchased a new box of projectiles, but when I got home I realised that they were the Flat Base version, not the boat tails. I know there has to be a difference in how they perform but would be interested to know if anyone knows what the expected difference will be?

I have a hunting trip coming up and don't have time to work the load again before hand.

Thanks for any and all input.
Goldie
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Re: Boat Tail vs Flat base - same load data

Post by bladeracer » 20 Jun 2017, 6:48 pm

goldiexxxx wrote:I was wondering if anyone can give some insight into this topic.
I have worked up a great load for my 308 consisting of the following:

40.6gr AR2208
Win Brass
Hornady 150gr BTSP Interlock
COL 2.755"

Now the other day, I purchased a new box of projectiles, but when I got home I realised that they were the Flat Base version, not the boat tails. I know there has to be a difference in how they perform but would be interested to know if anyone knows what the expected difference will be?

I have a hunting trip coming up and don't have time to work the load again before hand.

Thanks for any and all input.
Goldie


You would have to check your zero regardless.
Assuming the bullets are the same weights, the differences will be in the BC and how it affects the trajectory.
BC of the 150gn Spitzer Interlocks only varies by 0.011 which won't have a huge effect on the curve within hunting ranges. The RN has significantly lower BC though.
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Re: Boat Tail vs Flat base - same load data

Post by Cooper » 20 Jun 2017, 6:57 pm

I did pretty much the same thing with my 7mm-08. Bought the flat bases bullets when I had worked up a load for the BT ones.
I only released when I seated the bullet and the cannelure didn't line up to where it had previsousily. All my BTs bullets were loaded up and I thrown out the box for the BT Projectiles. Had me a bit stumped for awhile.

Anyway I shoot the 139 BTSP, 139 Interlock Sp and 139gr SST in 7mm 08 and use the same charge of Ar2208 and the all pretty much shoot the same. By the same I mean one or two clicks difference at 100metres. So I reckon you'd be pretty right.
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Re: Boat Tail vs Flat base - same load data

Post by Cooper » 20 Jun 2017, 7:06 pm

image.jpeg
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Pretty your not talking about the RN (round nose) 150gr interlock. See picture of Hornady reloading data.

There is a difference between the the 150gr interlock SP and the 150gr interlock BTSP. But I don't think you'll have to change your load. The RN (round nose 150gr) would be a different story
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Re: Boat Tail vs Flat base - same load data

Post by Oldbloke » 20 Jun 2017, 7:39 pm

Very little difference unless it is, close to max pressure. I would load up a box of 20 just for the trip and check the zero. If pressure looks OK and they shoot OK just use them. Perhaps work up a load later.

Edit, I think boat tails generally generate a bit more pressure, but might be wrong.
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Re: Boat Tail vs Flat base - same load data

Post by happyhunter » 20 Jun 2017, 7:59 pm

Don't be suprised if you get higher velocities at the muzzle with the flat base bullets due to the greater bearing surface, I use Sierra Pro hunters in the 308 and they are also a flat base bullet. Unless you are shooting past 500 meters the boat tail is no advantage anyway.
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Re: Boat Tail vs Flat base - same load data

Post by Barrettmr » 21 Jun 2017, 5:33 pm

I went from 150gr rn hotcors to 150gr hornady interlock with no change in charge and the point of impact was so similar that I didn't need to change the rifle.
I am using adi data so am using 46gr 2208. I got some 150gr tbf hollow points the other day cheap and they shoot the best with 47gr of 2208.
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Re: Boat Tail vs Flat base - same load data

Post by bladeracer » 21 Jun 2017, 5:59 pm

Barrettmr wrote:I went from 150gr rn hotcors to 150gr hornady interlock with no change in charge and the point of impact was so similar that I didn't need to change the rifle.
I am using adi data so am using 46gr 2208. I got some 150gr tbf hollow points the other day cheap and they shoot the best with 47gr of 2208.


At what specific range was the PoI similar though?
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Re: Boat Tail vs Flat base - same load data

Post by Barrettmr » 21 Jun 2017, 7:12 pm

bladeracer wrote:
Barrettmr wrote:I went from 150gr rn hotcors to 150gr hornady interlock with no change in charge and the point of impact was so similar that I didn't need to change the rifle.
I am using adi data so am using 46gr 2208. I got some 150gr tbf hollow points the other day cheap and they shoot the best with 47gr of 2208.


At what specific range was the PoI similar though?


Always sighted in at 100m
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Re: Boat Tail vs Flat base - same load data

Post by bladeracer » 21 Jun 2017, 7:21 pm

Barrettmr wrote:
bladeracer wrote:
Barrettmr wrote:I went from 150gr rn hotcors to 150gr hornady interlock with no change in charge and the point of impact was so similar that I didn't need to change the rifle.
I am using adi data so am using 46gr 2208. I got some 150gr tbf hollow points the other day cheap and they shoot the best with 47gr of 2208.


At what specific range was the PoI similar though?


Always sighted in at 100m


Did you check the PoI at 50m and 200m to confirm the trajectory matches the other load?
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Re: Boat Tail vs Flat base - same load data

Post by Barrettmr » 22 Jun 2017, 6:29 pm

bladeracer wrote:
Barrettmr wrote:
bladeracer wrote:
Barrettmr wrote:I went from 150gr rn hotcors to 150gr hornady interlock with no change in charge and the point of impact was so similar that I didn't need to change the rifle.
I am using adi data so am using 46gr 2208. I got some 150gr tbf hollow points the other day cheap and they shoot the best with 47gr of 2208.


At what specific range was the PoI similar though?


Always sighted in at 100m


Did you check the PoI at 50m and 200m to confirm the trajectory matches the other load?

No
I very rarely shoot past 130/150 and have never missed at 50 so must be close :thumbsup:
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Re: Boat Tail vs Flat base - same load data

Post by goldiexxxx » 23 Jun 2017, 5:53 am

Thanks very much for the info. I didn't buy the round nose, just the flat base of the same spitzers.
So I will just check the zero with a few rounds before I start hunting next week.

Thanks to everyone for your help, my knowledge journey continues.

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Re: Boat Tail vs Flat base - same load data

Post by Lorgar » 02 Aug 2017, 1:33 pm

happyhunter wrote:I use Sierra Pro hunters in the 308 and they are also a flat base bullet. Unless you are shooting past 500 meters the boat tail is no advantage anyway.


When I had my Ruger I used to shoot the flat-base Pro-Hunters too. Excellent bullet for accuracy and effect I found.
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Re: Boat Tail vs Flat base - same load data

Post by goldiexxxx » 05 Aug 2017, 9:02 pm

So the result was two clicks of the scope and not a single pig complained about the change to flat base projectiles.

Thanks to everyone for your help and comments.

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Re: Boat Tail vs Flat base - same load data

Post by Bourt » 15 Aug 2017, 2:22 pm

goldiexxxx wrote:not a single pig complained about the change to flat base projectiles.


Gotta keep the customers satisfied :mrgreen:
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Re: Boat Tail vs Flat base - same load data

Post by SneakyPigeon22 » 17 Mar 2024, 8:12 am

I thought I'd dig this old cow out of the ditch with a recent experience of my own:

I reload 30-06 for my Tikka T3 Battue and started out with 180gr Speer HotKor (flat base) bullets, did my load development and settled on 54.5gr of ADI AR2209. Recently I changed to Speer BTSP bullets and also found that the BTSP bullets seated a fair bit deeper than the HotKor. I loaded them with the same 54.5gr charge and took the chrono to the range, and the difference in average velocity is around 70FPS with otherwise identical metrics (same cases, primers, env conditions). Also ran the data through GRT and saw that with the boat tails seated at 12mm, the projected chamber pressure was over 50k PSI. Still within safe limits, but creeping up from where the HotKor's were.

Below is the target from my range tests. Values in circles is the charge, and opposite 4-digit values are average velocities for the group.

Tikka3006_Chrono - Copy.jpg
Load Test Results for Tikka T3
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