Author Topic: 55 gr. BBT HP (Read 4211 times))

rsterne · « **on:** March 07, 2019, 07:00:58 PM »

I have a hot .25 cal Disco that is a genuine 100+ FPE gun, so I pulled it off the wall today to try some velocity experiments with different size bullets.... I have some 50.4 gr. FN BBTs (NOE 250-51), and also some 58.3 gr. FN (NOE 250-60), plus the HP versions as well.... I tried them as cast (0.250" nose / 0.252" drive band), and they were hard to chamber in my TJ's .25 ACP barrel.... so I sized some of each down to 0.251", 0.250" and 0.249".... I tethered the gun at 2950 psi (it is modified for 3K plus) and both bullets picked up a lot of velocity between as cast and 0.251", gained more at 0.250", and then lost about 10 fps at 0.249", presumably from a small amount of blowby….

The 58.3 gr. FN were well over 900 fps, so I thought I would tune the gun for the 55.0 gr. HP version of that bullet, sized to 0.250".... Mean looking little devil....

I maxed out the preload and hit 993 fps (120 FPE), and then backed it off a turn and got 965 fps.... At that setting, off the tether, I got 2 equal shots and then a 3rd at about 940 fps, so I backed the preload out a bit more and ended up with 3 shots off tether of 956, 963 and 945 fps (111 FPE average) within a 2% ES.... Tethered, of course, it shoots 956, within a few fps.... which will give me a good platform to test these HP bullets.... The gun is loud, and not very efficient.... but at 110 FPE it should really lay a smackdown on a Marmot....

This is a penetration test of the 55 gr. BBT HP in soap at 110 FPE.... The nose came apart.... penetration of the base was 95 mm (3.75")….

Bob

PeterL · « **Reply #1 on:** March 07, 2019, 09:31:14 PM »

Nice looking bullet Bob. What’s your barrel length?

Peter

KnifeMaker · « **Reply #2 on:** March 07, 2019, 09:40:31 PM »

Well, we know now that it is fast, dumps energy well for a varmint bullet. Now is it accurate? This is the most important thing well before the other criteria.

Knife

Nvreloader · « **Reply #3 on:** March 08, 2019, 02:44:25 AM »

OK guys

I am on the fence about a 25 cal AG,
And you guys are driving me nuts, with all the 25 info posted,
so out to the shop thru the cold and got to digging around in the bbl pile,
and guess what I find..................

A 25 caliber bbl, .257 bore (I think, haven't slugged it yet),
24.5" long long, the only possible problem is it's a Marlin Micro lands and groves, and FIRR the twist is 1x14".
Also found a 25/06 bbl, I had forgot about...........

Would this be a better for pellets or slugs, in a repeater action?
Thinking real hard on changing Leakin Lena to a 25 caliber HPA,
or my need to buy another donor AG, to change over, to fit this bbl.

Your thoughts or suggestions...........
I gotta to quit scratchin this itch............I am leakin blood..................

K.O. · « **Reply #4 on:** March 08, 2019, 03:34:42 AM »

Hmmm have never seen a .257 Roberts Marlin microgroove.... But do remember a friend having a Marlin that like your pistol used a necked .357 case... 22 lands 14 twist... so maybe that barrel is a .256 Win, Mag..?

I have a old model 60 22LR barrel (more modern are shorter at 19") very seasond but bet it will be fine... 16 land and twist...

New unused have a model 883n .22 WMR 16 twist also... 20 lands...

Been thinking they belong on a Marauder...

K.O. · « **Reply #5 on:** March 08, 2019, 04:29:24 AM »

I do think with proper sizing to ~.0005 over under groove... should be great subsonic barrels...

http://castboolits.gunloads.com/showthread.php?319002-My-Experience-With-Shooting-Cast-in-a-Microgroove-Barrel

KnifeMaker · « **Reply #6 on:** March 08, 2019, 05:36:13 AM »

The one thing your going to run into with the 1:14 twist is the need to use long heavier bullets, starting in the 70+ grain area such as the Lyman or Arsenal 257400. shorter lighter bullets will start to loose stability at fairly short ranges. 50+ yards.

It takes a fairly stout pcp to sling the heavier, longer bullets.

Mike

rsterne · « **Reply #7 on:** March 08, 2019, 01:15:25 PM »

I think you will find that this boattail will be great in a 14" twist, as boattails need higher RPM than the same length flat base bullets do.... This bullet is available in three different diameters, 0.250/.252".... 0.253/.255".... and 0.257/.259" (which is actually 0.014" longer).... I did that because I consider this weight range (~ 60 gr.) to be the crossover point between .25 cal and .257 cal.... If you want to go heavier, go .257 cal, IMO.... Plus, you can get TJ's liners in both that are a 14" twist, which should be ideal for this bullet.... although it should also work in the 15.5" twist GM barrel on the MRod….

Bob

Nvreloader · « **Reply #8 on:** March 08, 2019, 03:39:48 PM »

KO
It is a 256 Win Mag bbl, 60 HP @ 2300 fps+, a Marlin 62 bbl. A 257 Roberts case is a lot bigger.......

Have to find some 257 dia slug to check the bore diameter now.

Thanks Guys,
Have some thinking to do now............

Don

rsterne · « **Reply #9 on:** March 08, 2019, 03:57:01 PM »

Sorry, Peter, I missed your question.... The barrel is 24", the gun looks like a stock Disco, right down to the front sight mount with the scooped out bottom to clear the air tube, except it has a TJ's .25 ACP liner that is 7/16" OD and slides right into the Disco receiver.... Inside, though, it has a custom valve with bore sized porting and a rear velocity adjuster on the back of the tube....

Bob

PeterL · « **Reply #10 on:** March 08, 2019, 11:32:59 PM »

Quote from: rsterne on March 08, 2019, 03:57:01 PM

Sorry, Peter, I missed your question.... The barrel is 24", the gun looks like a stock Disco, right down to the front sight mount with the scooped out bottom to clear the air tube, except it has a TJ's .25 ACP liner that is 7/16" OD and slides right into the Disco receiver.... Inside, though, it has a custom valve with bore sized porting and a rear velocity adjuster on the back of the tube....

Bob

Awesome. Looking stock but has a nasty bite when needed. Just the way I like my rifles. I also have the 25ACP barrel in .500” on my Synrod. Very tight barrel but extremely accurate with rebated boattails.

Peter

KnifeMaker · « **Reply #11 on:** March 09, 2019, 02:50:32 AM »

Odd, I had several members send me different sizes of BBT's in .25 and .257 and none would group in my 1:14 twist .25 factory RS or TJ 1:14 .257 barrels. It was simply too fast for the light bullets.

They worked on paper, but not actual shooting. Terrible spirling at anything near 50 yards and beyond. This, trying velocities from 790 all the way to above 1000 fps. Nothing worked. the faster the fps, the worse. Telling The tail that the Twist was simply too fast for the bullets.

A shame, as I had high hopes for them.

Knife

rsterne · « **Reply #12 on:** March 09, 2019, 12:37:40 PM »

Michael, could you please explain this statement?

Quote

the faster the fps, the worse. Telling The tail that the Twist was simply too fast for the bullets.

When Subsonic, you need a faster twist as you go faster, the opposite of what happens Supersonic.... Typical graph of optimum twist:

Or, are you saying that you think that the bullet is Dynamically Unstable, like a pellet in too fast a twist?.... Static Stability, as in the graph, is what we need to avoid tumbling.... Dynamic Instability leads to spiraling (corkscrewing) as the bullet goes downrange and slows, and is impossible to predict or calculate.... It sounds like you were actually able to observe such spiraling?.... There is usually a very large range of twists that will work between these two conditions, as one is at one end of the stability limits, and the other occurs at the other end.... $:-\$

Do I remember reading that you had good success with some of the BBTs when you used a slower twist barrel?.... Which lengths did not work for you in the 14"?.... Did you find any difference between the FN and HP versions?....

Bob

K.O. · « **Reply #13 on:** March 09, 2019, 03:30:49 PM »

seems a bit weird to me that they are spiraling at short range... the 14 twist should be just about right for 60g rounds..?

the .256 Win. Mag was design as a 60g Varmint pistol cartridge for the Ruger Hawkeye single shot pistol (holy grail for Ruger collectors (Blackhawk frame swinging breech block instead of cylinder)).

and the T.C. Contender... was about 2200-2300 fps out of a 8.5" pistol barrel...was a big brother to the .22 jet and a flame thrower as a pistol also...

The Short throw Marlin Levermatic .256 came a few years later... I think the model 62 came out in 62... I only remember cause that was when I came out...

point is it was 14 twist barrels and designed for a 60g .257 round...

PeterL · « **Reply #14 on:** March 09, 2019, 08:08:08 PM »

Quote from: KnifeMaker on March 09, 2019, 02:50:32 AM

Odd, I had several members send me different sizes of BBT's in .25 and .257 and none would group in my 1:14 twist .25 factory RS or TJ 1:14 .257 barrels. It was simply too fast for the light bullets.

They worked on paper, but not actual shooting. Terrible spirling at anything near 50 yards and beyond. This, trying velocities from 790 all the way to above 1000 fps. Nothing worked. the faster the fps, the worse. Telling The tail that the Twist was simply too fast for the bullets.

A shame, as I had high hopes for them.

Knife

Mike I thought you were having great success with your 1:14 twist on your RSII shooting lighter slugs? I’m shooting both 52 & 55gr slugs out of my .25 cal sized to .248 & .249. I get one hole at 60yds but it’s not consistent. That’s why I’m sleeving my barrel because my suspicion is the harmonics is changing during the shot cycle.

Peter

K.O. · « **Reply #15 on:** March 09, 2019, 10:01:29 PM »

The 40g .25 BBT well yeah can see that spiraling about 50 75 yards out... heck thought it would at about 75 yards out of a 15.5 twist barrel... from the begining I have thought of the 40g as a sib to a bevel base SWC... and yep bevel base are just as accurate as plain base IMO... Just do not try to +p them... The Buddy I had reloading for my .357 liked them for ease of loading...

so yeah I can see it with the 40g which I think wants about 1:19 twist...have seen it out of overspun short SWC...

50g .250-257 BBT would be over spun I think at 1:14... but not bad enough to spiral at 50 yards..?

here is the thing tho... over the years have seen stuff that is not s'posed to work actually work very well... also have seen things not work that should work ...

KnifeMaker · « **Reply #16 on:** March 10, 2019, 01:54:36 AM »

My go to bullets are mostly 50.6 gr and lighter. They do fine at 70 yards. At 100, I am seeding spirling. Moreso with the 1-14 than the 1:17.7 barrel.

At night, with a spotlight on the gun and a dark target, I can see a beginning of a tail wag at 76 yards. Yet it is still very accurate. However, I would not expect it to be so at 100 yards +. No room for testing the 100 yards at the moment. Working on it again though.

The heavier bullets I have here, 60 and 70 grain do well in the 1-14 twist.

The length of my favourite bullet is .447inch at 50.6 grains, and the other is .403" At 44.5 inch. I don't remember the length of the BBT's I tested, an they were in the one in 14 twist. But they were short!

I do have one other bullet, a spire point that is .526 at 57 grains and is single loaded. All the others fit a modded RS Evanix Mag.The really suprising bullet is the offering from the MP mold t;hat is a BT/round nose. It is 47 grains at .427 in length, and shoots very well in the 1:17.7 Twist. I have not tried it in the 1 in 14 twist so far.

Mike

KnifeMaker · « **Reply #17 on:** March 10, 2019, 03:06:31 AM »

It must be remembered that what I may consider and what another my consider accurate may very well be two completely different things.

In good air, I am not satisfied if it cannot print under 1/2" at 80 yards. And I consider that marginal. The Talondor .257 with i:14 twist will shot several bullets under 1/4" at the same range. Consistently. I have not achieved this level of accuracy with the Rainstorm Yet. Trigger is a bit issue at the moment, as are the scope mounts.

I did learn today that the quick detach scope mounts are not as secure as I thought they were. Time to change them! And as the old saying goes, "Tonight's the Night!

KnifeMaker · « **Reply #18 on:** March 10, 2019, 03:10:13 AM »

This is the accuracy obtained with the new MP boat tail bullet at 47 grains/80 yards. Also, the second target at 35 yds, is two in the top hole, and 8 in the bottom hole. Excellent accuracy for a sporter I think.

These bullets are not showing the tendency to wag their tails at either range at all.

The top two bullets were at 35 yards, adn the bottom two were at 80 yards.
Left target is 20 shots tethered, on a one inch target dot. As you can see, 17 of the 20 came in under 1/2 inch. Woo-Hoo!!!

Knife

K.O. · « **Reply #19 on:** March 10, 2019, 04:41:02 PM »

Hmm all this .25 talk got me wondering... 4500 psi helium 160g BBT .256 Holland & Holland..

possible with a reasonable barrel length..?

would certainly be the King of the 25 Cal... Falling block would be nice..

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55 gr. BBT HP

Author Topic: 55 gr. BBT HP (Read 4211 times))